Make some RERR_* choices better, and another noop_io_until_death() tweak.
[rsync/rsync.git] / io.c
diff --git a/io.c b/io.c
index 5f70e81..4a6b95f 100644 (file)
--- a/io.c
+++ b/io.c
@@ -41,10 +41,13 @@ extern int am_server;
 extern int am_daemon;
 extern int am_sender;
 extern int am_generator;
+extern int msgs2stderr;
 extern int inc_recurse;
 extern int io_error;
 extern int eol_nulls;
 extern int flist_eof;
+extern int file_total;
+extern int file_old_total;
 extern int list_only;
 extern int read_batch;
 extern int protect_args;
@@ -52,6 +55,7 @@ extern int checksum_seed;
 extern int protocol_version;
 extern int remove_source_files;
 extern int preserve_hard_links;
+extern BOOL extra_flist_sending_enabled;
 extern struct stats stats;
 extern struct file_list *cur_flist;
 #ifdef ICONV_OPTION
@@ -64,44 +68,41 @@ int allowed_lull = 0;
 int ignore_timeout = 0;
 int batch_fd = -1;
 int msgdone_cnt = 0;
+int forward_flist_data = 0;
 
 /* Ignore an EOF error if non-zero. See whine_about_eof(). */
 int kluge_around_eof = 0;
 
-int msg_fd_in = -1;
-int msg_fd_out = -1;
 int sock_f_in = -1;
 int sock_f_out = -1;
 
-static int iobuf_f_in = -1;
-static char *iobuf_in;
-static size_t iobuf_in_siz;
-static size_t iobuf_in_ndx;
-static size_t iobuf_in_remaining;
+int64 total_data_read = 0;
+int64 total_data_written = 0;
 
-static int iobuf_f_out = -1;
-static char *iobuf_out;
-static int iobuf_out_cnt;
+static struct {
+       xbuf in, out, msg;
+       int in_fd;
+       int out_fd; /* Both "out" and "msg" go to this fd. */
+       BOOL in_multiplexed;
+       unsigned out_empty_len;
+       size_t raw_data_header_pos;      /* in the out xbuf */
+       size_t raw_flushing_ends_before; /* in the out xbuf */
+       size_t raw_input_ends_before;    /* in the in xbuf */
+} iobuf = { .in_fd = -1, .out_fd = -1 };
 
-int flist_forward_from = -1;
-
-static int io_multiplexing_out;
-static int io_multiplexing_in;
 static time_t last_io_in;
 static time_t last_io_out;
-static int no_flush;
 
 static int write_batch_monitor_in = -1;
 static int write_batch_monitor_out = -1;
 
-static int io_filesfrom_f_in = -1;
-static int io_filesfrom_f_out = -1;
-static xbuf ff_buf = EMPTY_XBUF;
-static char ff_lastchar;
+static int ff_forward_fd = -1;
+static int ff_reenable_multiplex = -1;
+static char ff_lastchar = '\0';
+static xbuf ff_xb = EMPTY_XBUF;
 #ifdef ICONV_OPTION
 static xbuf iconv_buf = EMPTY_XBUF;
 #endif
-static int defer_forwarding_messages = 0, keep_defer_forwarding = 0;
 static int select_timeout = SELECT_TIMEOUT;
 static int active_filecnt = 0;
 static OFF_T active_bytecnt = 0;
@@ -114,33 +115,811 @@ static char int_byte_extra[64] = {
        2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 5, 6, /* (C0 - FF)/4 */
 };
 
-#define REMOTE_OPTION_ERROR "rsync: on remote machine: -"
-#define REMOTE_OPTION_ERROR2 ": unknown option"
+#define IN_MULTIPLEXED (iobuf.in_multiplexed)
+#define OUT_MULTIPLEXED (iobuf.out_empty_len != 0)
+
+#define PIO_NEED_INPUT (1<<0) /* The *_NEED_* flags are mutually exclusive. */
+#define PIO_NEED_OUTROOM (1<<1)
+#define PIO_NEED_MSGROOM (1<<2)
+
+#define PIO_CONSUME_INPUT (1<<4) /* Must becombined with PIO_NEED_INPUT. */
+
+#define PIO_INPUT_AND_CONSUME (PIO_NEED_INPUT | PIO_CONSUME_INPUT)
+#define PIO_NEED_FLAGS (PIO_NEED_INPUT | PIO_NEED_OUTROOM | PIO_NEED_MSGROOM)
+
+#define REMOTE_OPTION_ERROR "rsync: on remote machine: -"
+#define REMOTE_OPTION_ERROR2 ": unknown option"
+
+#define FILESFROM_BUFLEN 2048
+
+enum festatus { FES_SUCCESS, FES_REDO, FES_NO_SEND };
+
+static flist_ndx_list redo_list, hlink_list;
+
+static void drain_multiplex_messages(void);
+static void sleep_for_bwlimit(int bytes_written);
+
+static void check_timeout(void)
+{
+       time_t t;
+
+       if (!io_timeout || ignore_timeout)
+               return;
+
+       if (!last_io_in) {
+               last_io_in = time(NULL);
+               return;
+       }
+
+       t = time(NULL);
+
+       if (t - last_io_in >= io_timeout) {
+               if (!am_server && !am_daemon) {
+                       rprintf(FERROR, "io timeout after %d seconds -- exiting\n",
+                               (int)(t-last_io_in));
+               }
+               exit_cleanup(RERR_TIMEOUT);
+       }
+}
+
+/* It's almost always an error to get an EOF when we're trying to read from the
+ * network, because the protocol is (for the most part) self-terminating.
+ *
+ * There is one case for the receiver when it is at the end of the transfer
+ * (hanging around reading any keep-alive packets that might come its way): if
+ * the sender dies before the generator's kill-signal comes through, we can end
+ * up here needing to loop until the kill-signal arrives.  In this situation,
+ * kluge_around_eof will be < 0.
+ *
+ * There is another case for older protocol versions (< 24) where the module
+ * listing was not terminated, so we must ignore an EOF error in that case and
+ * exit.  In this situation, kluge_around_eof will be > 0. */
+static NORETURN void whine_about_eof(BOOL allow_kluge)
+{
+       if (kluge_around_eof && allow_kluge) {
+               int i;
+               if (kluge_around_eof > 0)
+                       exit_cleanup(0);
+               /* If we're still here after 10 seconds, exit with an error. */
+               for (i = 10*1000/20; i--; )
+                       msleep(20);
+       }
+
+       rprintf(FERROR, RSYNC_NAME ": connection unexpectedly closed "
+               "(%s bytes received so far) [%s]\n",
+               big_num(stats.total_read), who_am_i());
+
+       exit_cleanup(RERR_STREAMIO);
+}
+
+/* Do a safe read, handling any needed looping and error handling.
+ * Returns the count of the bytes read, which will only be different
+ * from "len" if we encountered an EOF.  This routine is not used on
+ * the socket except very early in the transfer. */
+static size_t safe_read(int fd, char *buf, size_t len)
+{
+       size_t got;
+       int n;
+
+       assert(fd != iobuf.in_fd);
+
+       n = read(fd, buf, len);
+       if ((size_t)n == len || n == 0) {
+               if (DEBUG_GTE(IO, 2))
+                       rprintf(FINFO, "[%s] safe_read(%d)=%ld\n", who_am_i(), fd, (long)n);
+               return n;
+       }
+       if (n < 0) {
+               if (errno != EINTR && errno != EWOULDBLOCK && errno != EAGAIN) {
+                 read_failed:
+                       rsyserr(FERROR, errno, "safe_read failed to read %ld bytes [%s]",
+                               (long)len, who_am_i());
+                       exit_cleanup(RERR_STREAMIO);
+               }
+               got = 0;
+       } else
+               got = n;
+
+       while (1) {
+               struct timeval tv;
+               fd_set r_fds, e_fds;
+               int cnt;
+
+               FD_ZERO(&r_fds);
+               FD_SET(fd, &r_fds);
+               FD_ZERO(&e_fds);
+               FD_SET(fd, &e_fds);
+               tv.tv_sec = select_timeout;
+               tv.tv_usec = 0;
+
+               cnt = select(fd+1, &r_fds, NULL, &e_fds, &tv);
+               if (cnt <= 0) {
+                       if (cnt < 0 && errno == EBADF) {
+                               rsyserr(FERROR, errno, "safe_read select failed [%s]",
+                                       who_am_i());
+                               exit_cleanup(RERR_FILEIO);
+                       }
+                       check_timeout();
+                       continue;
+               }
+
+               /*if (FD_ISSET(fd, &e_fds))
+                       rprintf(FINFO, "select exception on fd %d\n", fd); */
+
+               if (FD_ISSET(fd, &r_fds)) {
+                       n = read(fd, buf + got, len - got);
+                       if (DEBUG_GTE(IO, 2))
+                               rprintf(FINFO, "[%s] safe_read(%d)=%ld\n", who_am_i(), fd, (long)n);
+                       if (n == 0)
+                               break;
+                       if (n < 0) {
+                               if (errno == EINTR)
+                                       continue;
+                               goto read_failed;
+                       }
+                       if ((got += (size_t)n) == len)
+                               break;
+               }
+       }
+
+       return got;
+}
+
+static const char *what_fd_is(int fd)
+{
+       static char buf[20];
+
+       if (fd == sock_f_out)
+               return "socket";
+       else if (fd == iobuf.out_fd)
+               return "message fd";
+       else if (fd == batch_fd)
+               return "batch file";
+       else {
+               snprintf(buf, sizeof buf, "fd %d", fd);
+               return buf;
+       }
+}
+
+/* Do a safe write, handling any needed looping and error handling.
+ * Returns only if everything was successfully written.  This routine
+ * is not used on the socket except very early in the transfer. */
+static void safe_write(int fd, const char *buf, size_t len)
+{
+       int n;
+
+       assert(fd != iobuf.out_fd);
+
+       n = write(fd, buf, len);
+       if ((size_t)n == len)
+               return;
+       if (n < 0) {
+               if (errno != EINTR && errno != EWOULDBLOCK && errno != EAGAIN) {
+                 write_failed:
+                       rsyserr(FERROR, errno,
+                               "safe_write failed to write %ld bytes to %s [%s]",
+                               (long)len, what_fd_is(fd), who_am_i());
+                       exit_cleanup(RERR_STREAMIO);
+               }
+       } else {
+               buf += n;
+               len -= n;
+       }
+
+       while (len) {
+               struct timeval tv;
+               fd_set w_fds;
+               int cnt;
+
+               FD_ZERO(&w_fds);
+               FD_SET(fd, &w_fds);
+               tv.tv_sec = select_timeout;
+               tv.tv_usec = 0;
+
+               cnt = select(fd + 1, NULL, &w_fds, NULL, &tv);
+               if (cnt <= 0) {
+                       if (cnt < 0 && errno == EBADF) {
+                               rsyserr(FERROR, errno, "safe_write select failed on %s [%s]",
+                                       what_fd_is(fd), who_am_i());
+                               exit_cleanup(RERR_FILEIO);
+                       }
+                       check_timeout();
+                       continue;
+               }
+
+               if (FD_ISSET(fd, &w_fds)) {
+                       n = write(fd, buf, len);
+                       if (n < 0) {
+                               if (errno == EINTR)
+                                       continue;
+                               goto write_failed;
+                       }
+                       buf += n;
+                       len -= n;
+               }
+       }
+}
+
+/* This is only called when files-from data is known to be available.  We read
+ * a chunk of data and put it into the output buffer. */
+static void forward_filesfrom_data(void)
+{
+       int len;
+
+       len = read(ff_forward_fd, ff_xb.buf + ff_xb.len, ff_xb.size - ff_xb.len);
+       if (len <= 0) {
+               if (len == 0 || errno != EINTR) {
+                       /* Send end-of-file marker */
+                       ff_forward_fd = -1;
+                       write_buf(iobuf.out_fd, "\0\0", ff_lastchar ? 2 : 1);
+                       free_xbuf(&ff_xb);
+                       if (ff_reenable_multiplex >= 0)
+                               io_start_multiplex_out(ff_reenable_multiplex);
+               }
+               return;
+       }
+
+       if (DEBUG_GTE(IO, 2))
+               rprintf(FINFO, "[%s] files-from read=%ld\n", who_am_i(), (long)len);
+
+#ifdef ICONV_OPTION
+       len += ff_xb.len;
+#endif
+
+       if (!eol_nulls) {
+               char *s = ff_xb.buf + len;
+               /* Transform CR and/or LF into '\0' */
+               while (s-- > ff_xb.buf) {
+                       if (*s == '\n' || *s == '\r')
+                               *s = '\0';
+               }
+       }
+
+       if (ff_lastchar)
+               ff_xb.pos = 0;
+       else {
+               char *s = ff_xb.buf;
+               /* Last buf ended with a '\0', so don't let this buf start with one. */
+               while (len && *s == '\0')
+                       s++, len--;
+               ff_xb.pos = s - ff_xb.buf;
+       }
+
+#ifdef ICONV_OPTION
+       if (filesfrom_convert && len) {
+               char *sob = ff_xb.buf + ff_xb.pos, *s = sob;
+               char *eob = sob + len;
+               int flags = ICB_INCLUDE_BAD | ICB_INCLUDE_INCOMPLETE | ICB_CIRCULAR_OUT;
+               if (ff_lastchar == '\0')
+                       flags |= ICB_INIT;
+               /* Convert/send each null-terminated string separately, skipping empties. */
+               while (s != eob) {
+                       if (*s++ == '\0') {
+                               ff_xb.len = s - sob - 1;
+                               if (iconvbufs(ic_send, &ff_xb, &iobuf.out, flags) < 0)
+                                       exit_cleanup(RERR_PROTOCOL); /* impossible? */
+                               write_buf(iobuf.out_fd, s-1, 1); /* Send the '\0'. */
+                               while (s != eob && *s == '\0')
+                                       s++;
+                               sob = s;
+                               ff_xb.pos = sob - ff_xb.buf;
+                               flags |= ICB_INIT;
+                       }
+               }
+
+               if ((ff_xb.len = s - sob) == 0)
+                       ff_lastchar = '\0';
+               else {
+                       /* Handle a partial string specially, saving any incomplete chars. */
+                       flags &= ~ICB_INCLUDE_INCOMPLETE;
+                       if (iconvbufs(ic_send, &ff_xb, &iobuf.out, flags) < 0) {
+                               if (errno == E2BIG)
+                                       exit_cleanup(RERR_PROTOCOL); /* impossible? */
+                               if (ff_xb.pos)
+                                       memmove(ff_xb.buf, ff_xb.buf + ff_xb.pos, ff_xb.len);
+                       }
+                       ff_lastchar = 'x'; /* Anything non-zero. */
+               }
+       } else
+#endif
+
+       if (len) {
+               char *f = ff_xb.buf + ff_xb.pos;
+               char *t = ff_xb.buf;
+               char *eob = f + len;
+               /* Eliminate any multi-'\0' runs. */
+               while (f != eob) {
+                       if (!(*t++ = *f++)) {
+                               while (f != eob && *f == '\0')
+                                       f++;
+                       }
+               }
+               ff_lastchar = f[-1];
+               if ((len = t - ff_xb.buf) != 0) {
+                       /* This will not circle back to perform_io() because we only get
+                        * called when there is plenty of room in the output buffer. */
+                       write_buf(iobuf.out_fd, ff_xb.buf, len);
+               }
+       }
+}
+
+/* Perform buffered input and output until specified conditions are met.  When
+ * given a "needed" read requirement, we'll return without doing any I/O if the
+ * iobuf.in bytes are already available.  When reading, we'll read as many
+ * bytes as we can into the buffer, and return as soon as we meet the minimum
+ * read requirement.  When given a "needed" write requirement, we'll return
+ * without doing any I/O if that many bytes will fit in the output buffer (we
+ * check either iobuf.out or iobuf.msg, depending on the flags).  When writing,
+ * we write out as much as we can, and return as soon as the given free-space
+ * requirement is available.
+ *
+ * The iobuf.out and iobuf.msg buffers are circular, so some writes into them
+ * will need to be split when the data needs to wrap around to the start.  In
+ * order to help make this easier for some operations (such as the use of
+ * SIVAL() into the buffer) the buffers MUST have 4 bytes of overflow space at
+ * the end that is not not counted in the "size".  The iobuf.in buffer is not
+ * (currently) circular.  To facilitate the handling of MSG_DATA bytes as they
+ * are read-from/written-into the buffers, see the three raw_* iobuf vars.
+ *
+ * When writing, we flush data in the following priority order:
+ *
+ * 1. Finish writing any in-progress MSG_DATA sequence from iobuf.out.
+ *
+ * 2. Write out all the messages from the message buf (if iobuf.msg is active).
+ *    Yes, this means that a PIO_NEED_OUTROOM call will completely flush any
+ *    messages before getting to the iobuf.out flushing (except for rule 1).
+ *
+ * 3. Write out the raw data from iobuf.out, possibly filling in the multiplexed
+ *    MSG_DATA header that was pre-allocated (when output is multiplexed).
+ *
+ * TODO:  items for possible future work:
+ *
+ *    - Make this routine able to read the generator-to-receiver batch flow?
+ *
+ *    - Make the input buffer circular?
+ *
+ * Unlike the old routines that this replaces, it is OK to read ahead as far as
+ * we can because the read_a_msg() routine now reads its bytes out of the input
+ * buffer.  In the old days, only raw data was in the input buffer, and any
+ * unused raw data in the buf would prevent the reading of socket data. */
+static char *perform_io(size_t needed, int flags)
+{
+       fd_set r_fds, e_fds, w_fds;
+       struct timeval tv;
+       int cnt, max_fd;
+       size_t empty_buf_len = 0;
+       xbuf *out;
+       char *data;
+
+       if (iobuf.in.len == 0 && iobuf.in.pos != 0) {
+               if (iobuf.raw_input_ends_before)
+                       iobuf.raw_input_ends_before -= iobuf.in.pos;
+               iobuf.in.pos = 0;
+       }
+
+       switch (flags & PIO_NEED_FLAGS) {
+       case PIO_NEED_INPUT:
+               if (DEBUG_GTE(IO, 3)) {
+                       rprintf(FINFO, "[%s] perform_io(%ld, %sinput)\n",
+                               who_am_i(), (long)needed, flags & PIO_CONSUME_INPUT ? "consume&" : "");
+               }
+
+               /* Make sure the input buffer is big enough to hold "needed" bytes.
+                * Also make sure it will fit in the free space at the end, or
+                * else we need to shift some bytes. */
+               if (needed && iobuf.in.size < needed) {
+                       if (!(iobuf.in.buf = realloc_array(iobuf.in.buf, char, needed)))
+                               out_of_memory("perform_io");
+                       if (DEBUG_GTE(IO, 4)) {
+                               rprintf(FINFO, "[%s] resized input buffer from %ld to %ld bytes.\n",
+                                       who_am_i(), (long)iobuf.in.size, (long)needed);
+                       }
+                       iobuf.in.size = needed;
+               }
+               if (iobuf.in.size - iobuf.in.pos < needed
+                || (iobuf.in.len < needed && iobuf.in.len < 1024
+                 && iobuf.in.size - (iobuf.in.pos + iobuf.in.len) < 1024)) {
+                       memmove(iobuf.in.buf, iobuf.in.buf + iobuf.in.pos, iobuf.in.len);
+                       if (DEBUG_GTE(IO, 4)) {
+                               rprintf(FINFO,
+                                       "[%s] moved %ld bytes from %ld to 0 in the input buffer (size=%ld, needed=%ld).\n",
+                                       who_am_i(), (long)iobuf.in.len, (long)iobuf.in.pos, (long)iobuf.in.size, (long)needed);
+                       }
+                       if (iobuf.raw_input_ends_before)
+                               iobuf.raw_input_ends_before -= iobuf.in.pos;
+                       iobuf.in.pos = 0;
+               }
+               break;
+
+       case PIO_NEED_OUTROOM:
+               /* We never resize the circular output buffer. */
+               if (iobuf.out.size - iobuf.out_empty_len < needed) {
+                       fprintf(stderr, "need to write %ld bytes, iobuf.out.buf is only %ld bytes.\n",
+                               (long)needed, (long)(iobuf.out.size - iobuf.out_empty_len));
+                       exit_cleanup(RERR_PROTOCOL);
+               }
+
+               if (DEBUG_GTE(IO, 3)) {
+                       rprintf(FINFO, "[%s] perform_io(%ld, outroom) needs to flush %ld\n",
+                               who_am_i(), (long)needed,
+                               iobuf.out.len + needed > iobuf.out.size
+                               ? (long)(iobuf.out.len + needed - iobuf.out.size) : 0L);
+               }
+               break;
+
+       case PIO_NEED_MSGROOM:
+               /* We never resize the circular message buffer. */
+               if (iobuf.msg.size < needed) {
+                       fprintf(stderr, "need to write %ld bytes, iobuf.msg.buf is only %ld bytes.\n",
+                               (long)needed, (long)iobuf.msg.size);
+                       exit_cleanup(RERR_PROTOCOL);
+               }
+
+               if (DEBUG_GTE(IO, 3)) {
+                       rprintf(FINFO, "[%s] perform_io(%ld, msgroom) needs to flush %ld\n",
+                               who_am_i(), (long)needed,
+                               iobuf.msg.len + needed > iobuf.msg.size
+                               ? (long)(iobuf.msg.len + needed - iobuf.msg.size) : 0L);
+               }
+               break;
+
+       case 0:
+               if (DEBUG_GTE(IO, 3))
+                       rprintf(FINFO, "[%s] perform_io(%ld, %d)\n", who_am_i(), (long)needed, flags);
+               break;
+
+       default:
+               exit_cleanup(RERR_UNSUPPORTED);
+       }
+
+       while (1) {
+               switch (flags & PIO_NEED_FLAGS) {
+               case PIO_NEED_INPUT:
+                       if (iobuf.in.len >= needed)
+                               goto double_break;
+                       break;
+               case PIO_NEED_OUTROOM:
+                       /* Note that iobuf.out_empty_len doesn't factor into this check
+                        * because iobuf.out.len already holds any needed header len. */
+                       if (iobuf.out.len + needed <= iobuf.out.size)
+                               goto double_break;
+                       break;
+               case PIO_NEED_MSGROOM:
+                       if (iobuf.msg.len + needed <= iobuf.msg.size)
+                               goto double_break;
+                       break;
+               }
+
+               max_fd = -1;
+
+               FD_ZERO(&r_fds);
+               FD_ZERO(&e_fds);
+               if (iobuf.in_fd >= 0 && iobuf.in.size - (iobuf.in.pos + iobuf.in.len)) {
+                       if (!read_batch || batch_fd >= 0) {
+                               FD_SET(iobuf.in_fd, &r_fds);
+                               FD_SET(iobuf.in_fd, &e_fds);
+                       }
+                       if (iobuf.in_fd > max_fd)
+                               max_fd = iobuf.in_fd;
+               }
+
+               /* Only do more filesfrom processing if there is enough room in the out buffer. */
+               if (ff_forward_fd >= 0 && iobuf.out.size - iobuf.out.len > FILESFROM_BUFLEN*2) {
+                       FD_SET(ff_forward_fd, &r_fds);
+                       if (ff_forward_fd > max_fd)
+                               max_fd = ff_forward_fd;
+               }
+
+               FD_ZERO(&w_fds);
+               if (iobuf.out_fd >= 0) {
+                       if (iobuf.raw_flushing_ends_before
+                        || (!iobuf.msg.len && iobuf.out.len > iobuf.out_empty_len && !(flags & PIO_NEED_MSGROOM))) {
+                               if (OUT_MULTIPLEXED && !iobuf.raw_flushing_ends_before) {
+                                       /* The iobuf.raw_flushing_ends_before value can point off the end
+                                        * of the iobuf.out buffer for a while, for easier subtracting. */
+                                       iobuf.raw_flushing_ends_before = iobuf.out.pos + iobuf.out.len;
+
+                                       SIVAL(iobuf.out.buf + iobuf.raw_data_header_pos, 0,
+                                             ((MPLEX_BASE + (int)MSG_DATA)<<24) + iobuf.out.len - 4);
+                                       if (iobuf.raw_data_header_pos + 4 > iobuf.out.size) {
+                                               int siz = (int)(iobuf.raw_data_header_pos + 4 - iobuf.out.size);
+                                               /* We used some of the overflow bytes, so move them. */
+                                               if (DEBUG_GTE(IO, 4)) {
+                                                       rprintf(FINFO, "[%s] wrap-bytes moved: %d (perform_io)\n",
+                                                               who_am_i(), siz);
+                                               }
+                                               memcpy(iobuf.out.buf, iobuf.out.buf + iobuf.out.size, siz);
+                                       }
+
+                                       if (DEBUG_GTE(IO, 1)) {
+                                               rprintf(FINFO, "[%s] send_msg(%d, %ld)\n",
+                                                       who_am_i(), (int)MSG_DATA, (long)iobuf.out.len - 4);
+                                       }
+
+                                       /* reserve room for the next MSG_DATA header */
+                                       iobuf.raw_data_header_pos = iobuf.raw_flushing_ends_before;
+                                       if (iobuf.raw_data_header_pos >= iobuf.out.size)
+                                               iobuf.raw_data_header_pos -= iobuf.out.size;
+                                       /* Yes, it is possible for this to make len > size for a while. */
+                                       iobuf.out.len += 4;
+                               }
+
+                               empty_buf_len = iobuf.out_empty_len;
+                               out = &iobuf.out;
+                       } else if (iobuf.msg.len) {
+                               empty_buf_len = 0;
+                               out = &iobuf.msg;
+                       } else
+                               out = NULL;
+                       if (out) {
+                               FD_SET(iobuf.out_fd, &w_fds);
+                               if (iobuf.out_fd > max_fd)
+                                       max_fd = iobuf.out_fd;
+                       }
+               } else
+                       out = NULL;
+
+               if (max_fd < 0) {
+                       switch (flags & PIO_NEED_FLAGS) {
+                       case PIO_NEED_INPUT:
+                               iobuf.in.len = 0;
+                               if (kluge_around_eof == 2)
+                                       exit_cleanup(0);
+                               if (iobuf.in_fd == -2)
+                                       whine_about_eof(True);
+                               rprintf(FERROR, "error in perform_io: no fd for input.\n");
+                               exit_cleanup(RERR_PROTOCOL);
+                       case PIO_NEED_OUTROOM:
+                       case PIO_NEED_MSGROOM:
+                               msgs2stderr = 1;
+                               drain_multiplex_messages();
+                               if (iobuf.out_fd == -2)
+                                       whine_about_eof(True);
+                               rprintf(FERROR, "error in perform_io: no fd for output.\n");
+                               exit_cleanup(RERR_PROTOCOL);
+                       default:
+                               /* No stated needs, so I guess this is OK. */
+                               break;
+                       }
+                       break;
+               }
+
+               if (extra_flist_sending_enabled) {
+                       if (file_total - file_old_total < MAX_FILECNT_LOOKAHEAD)
+                               tv.tv_sec = 0;
+                       else {
+                               extra_flist_sending_enabled = False;
+                               tv.tv_sec = select_timeout;
+                       }
+               } else
+                       tv.tv_sec = select_timeout;
+               tv.tv_usec = 0;
+
+               cnt = select(max_fd + 1, &r_fds, &w_fds, &e_fds, &tv);
+
+               if (cnt <= 0) {
+                       if (cnt < 0 && errno == EBADF) {
+                               msgs2stderr = 1;
+                               exit_cleanup(RERR_SOCKETIO);
+                       }
+                       if (extra_flist_sending_enabled) {
+                               extra_flist_sending_enabled = False;
+                               send_extra_file_list(sock_f_out, -1);
+                               extra_flist_sending_enabled = !flist_eof;
+                       } else
+                               check_timeout();
+                       FD_ZERO(&r_fds); /* Just in case... */
+                       FD_ZERO(&w_fds);
+               }
+
+               if (iobuf.in_fd >= 0 && FD_ISSET(iobuf.in_fd, &r_fds)) {
+                       size_t pos = iobuf.in.pos + iobuf.in.len;
+                       size_t len = iobuf.in.size - pos;
+                       int n;
+                       if ((n = read(iobuf.in_fd, iobuf.in.buf + pos, len)) <= 0) {
+                               if (n == 0) {
+                                       /* Signal that input has become invalid. */
+                                       if (!read_batch || batch_fd < 0 || am_generator)
+                                               iobuf.in_fd = -2;
+                                       batch_fd = -1;
+                                       continue;
+                               }
+                               if (errno == EINTR || errno == EWOULDBLOCK || errno == EAGAIN)
+                                       n = 0;
+                               else {
+                                       /* Don't write errors on a dead socket. */
+                                       if (iobuf.in_fd == sock_f_in) {
+                                               if (am_sender)
+                                                       msgs2stderr = 1;
+                                               rsyserr(FERROR_SOCKET, errno, "read error");
+                                       } else
+                                               rsyserr(FERROR, errno, "read error");
+                                       exit_cleanup(RERR_SOCKETIO);
+                               }
+                       }
+                       if (msgs2stderr && DEBUG_GTE(IO, 2))
+                               rprintf(FINFO, "[%s] recv=%ld\n", who_am_i(), (long)n);
+
+                       if (io_timeout)
+                               last_io_in = time(NULL);
+                       stats.total_read += n;
+
+                       iobuf.in.len += n;
+               }
+
+               if (iobuf.out_fd >= 0 && FD_ISSET(iobuf.out_fd, &w_fds)) {
+                       size_t len = iobuf.raw_flushing_ends_before ? iobuf.raw_flushing_ends_before - out->pos : out->len;
+                       int n;
+
+                       if (bwlimit_writemax && len > bwlimit_writemax)
+                               len = bwlimit_writemax;
+
+                       if (out->pos + len > out->size)
+                               len = out->size - out->pos;
+                       if ((n = write(iobuf.out_fd, out->buf + out->pos, len)) <= 0) {
+                               if (errno == EINTR || errno == EWOULDBLOCK || errno == EAGAIN)
+                                       n = 0;
+                               else {
+                                       /* Don't write errors on a dead socket. */
+                                       msgs2stderr = 1;
+                                       iobuf.out_fd = -2;
+                                       iobuf.out.len = iobuf.msg.len = iobuf.raw_flushing_ends_before = 0;
+                                       rsyserr(FERROR_SOCKET, errno, "[%s] write error", who_am_i());
+                                       drain_multiplex_messages();
+                                       exit_cleanup(RERR_SOCKETIO);
+                               }
+                       }
+                       if (msgs2stderr && DEBUG_GTE(IO, 2)) {
+                               rprintf(FINFO, "[%s] %s sent=%ld\n",
+                                       who_am_i(), out == &iobuf.out ? "out" : "msg", (long)n);
+                       }
+
+                       if (io_timeout)
+                               last_io_out = time(NULL);
+                       stats.total_written += n;
+
+                       if (bwlimit_writemax)
+                               sleep_for_bwlimit(n);
+
+                       if ((out->pos += n) == out->size) {
+                               if (iobuf.raw_flushing_ends_before)
+                                       iobuf.raw_flushing_ends_before -= out->size;
+                               out->pos = 0;
+                       } else if (out->pos == iobuf.raw_flushing_ends_before)
+                               iobuf.raw_flushing_ends_before = 0;
+                       if ((out->len -= n) == empty_buf_len) {
+                               out->pos = 0;
+                               if (empty_buf_len)
+                                       iobuf.raw_data_header_pos = 0;
+                       }
+               }
+
+               if (ff_forward_fd >= 0 && FD_ISSET(ff_forward_fd, &r_fds)) {
+                       /* This can potentially flush all output and enable
+                        * multiplexed output, so keep this last in the loop
+                        * and be sure to not cache anything that would break
+                        * such a change. */
+                       forward_filesfrom_data();
+               }
+       }
+  double_break:
+
+       data = iobuf.in.buf + iobuf.in.pos;
+
+       if (flags & PIO_CONSUME_INPUT) {
+               iobuf.in.len -= needed;
+               iobuf.in.pos += needed;
+       }
+
+       return data;
+}
+
+void noop_io_until_death(void)
+{
+       char buf[1024];
+
+       kluge_around_eof = 2;
+       /* Setting an I/O timeout ensures that if something inexplicably weird
+        * happens, we won't hang around forever. */
+       if (!io_timeout)
+               set_io_timeout(60);
+
+       while (1)
+               read_buf(iobuf.in_fd, buf, sizeof buf);
+}
+
+/* Buffer a message for the multiplexed output stream.  Is never used for MSG_DATA. */
+int send_msg(enum msgcode code, const char *buf, size_t len, int convert)
+{
+       char *hdr;
+       size_t pos;
+       BOOL want_debug = DEBUG_GTE(IO, 1) && convert >= 0 && (msgs2stderr || code != MSG_INFO);
+
+       if (!OUT_MULTIPLEXED)
+               return 0;
+
+       if (want_debug)
+               rprintf(FINFO, "[%s] send_msg(%d, %ld)\n", who_am_i(), (int)code, (long)len);
+
+#ifdef ICONV_OPTION
+       if (convert > 0 && ic_send == (iconv_t)-1)
+               convert = 0;
+       if (convert > 0) {
+               /* Ensuring double-size room leaves space for maximal conversion expansion. */
+               if (iobuf.msg.len + len*2 + 4 > iobuf.msg.size)
+                       perform_io(len*2 + 4, PIO_NEED_MSGROOM);
+       } else
+#endif
+       if (iobuf.msg.len + len + 4 > iobuf.msg.size)
+               perform_io(len + 4, PIO_NEED_MSGROOM);
+
+       pos = iobuf.msg.pos + iobuf.msg.len; /* Must be set after any flushing. */
+       if (pos >= iobuf.msg.size)
+               pos -= iobuf.msg.size;
+       hdr = iobuf.msg.buf + pos;
+
+       iobuf.msg.len += 4; /* Allocate room for the coming header bytes. */
+
+#ifdef ICONV_OPTION
+       if (convert > 0) {
+               xbuf inbuf;
+
+               INIT_XBUF(inbuf, (char*)buf, len, (size_t)-1);
+
+               len = iobuf.msg.len;
+               iconvbufs(ic_send, &inbuf, &iobuf.msg,
+                         ICB_INCLUDE_BAD | ICB_INCLUDE_INCOMPLETE | ICB_CIRCULAR_OUT | ICB_INIT);
+               if (inbuf.len > 0) {
+                       rprintf(FERROR, "overflowed iobuf.msg buffer in send_msg");
+                       exit_cleanup(RERR_UNSUPPORTED);
+               }
+               len = iobuf.msg.len - len;
+       } else
+#endif
+       {
+               size_t siz;
+
+               if ((pos += 4) >= iobuf.msg.size)
+                       pos -= iobuf.msg.size;
 
-enum festatus { FES_SUCCESS, FES_REDO, FES_NO_SEND };
+               /* Handle a split copy if we wrap around the end of the circular buffer. */
+               if (pos >= iobuf.msg.pos && (siz = iobuf.msg.size - pos) < len) {
+                       memcpy(iobuf.msg.buf + pos, buf, siz);
+                       memcpy(iobuf.msg.buf, buf + siz, len - siz);
+               } else
+                       memcpy(iobuf.msg.buf + pos, buf, len);
+
+               iobuf.msg.len += len;
+       }
 
-static void readfd(int fd, char *buffer, size_t N);
-static void writefd(int fd, const char *buf, size_t len);
-static void writefd_unbuffered(int fd, const char *buf, size_t len);
-static void mplex_write(int fd, enum msgcode code, const char *buf, size_t len, int convert);
+       SIVAL(hdr, 0, ((MPLEX_BASE + (int)code)<<24) + len);
+       /* If the header used any overflow bytes, move them to the start. */
+       if ((pos = hdr+4 - iobuf.msg.buf) > iobuf.msg.size) {
+               int siz = (int)(pos - iobuf.msg.size);
+               if (DEBUG_GTE(IO, 4))
+                       rprintf(FINFO, "[%s] wrap-bytes moved: %d (send_msg)\n", who_am_i(), siz);
+               memcpy(iobuf.msg.buf, iobuf.msg.buf + iobuf.msg.size, siz);
+       }
 
-static flist_ndx_list redo_list, hlink_list;
+       if (want_debug && convert > 0)
+               rprintf(FINFO, "[%s] converted msg len=%ld\n", who_am_i(), (long)len);
 
-struct msg_list_item {
-       struct msg_list_item *next;
-       char convert;
-       char buf[1];
-};
+       return 1;
+}
 
-struct msg_list {
-       struct msg_list_item *head, *tail;
-};
+void send_msg_int(enum msgcode code, int num)
+{
+       char numbuf[4];
 
-static struct msg_list msg_queue;
+       if (DEBUG_GTE(IO, 1))
+               rprintf(FINFO, "[%s] send_msg_int(%d, %d)\n", who_am_i(), (int)code, num);
+
+       SIVAL(numbuf, 0, num);
+       send_msg(code, numbuf, 4, -1);
+}
 
-static void got_flist_entry_status(enum festatus status, const char *buf)
+static void got_flist_entry_status(enum festatus status, int ndx)
 {
-       int ndx = IVAL(buf, 0);
        struct file_list *flist = flist_for_ndx(ndx, "got_flist_entry_status");
 
        if (remove_source_files) {
@@ -154,7 +933,7 @@ static void got_flist_entry_status(enum festatus status, const char *buf)
        switch (status) {
        case FES_SUCCESS:
                if (remove_source_files)
-                       send_msg(MSG_SUCCESS, buf, 4, 0);
+                       send_msg_int(MSG_SUCCESS, ndx);
                if (preserve_hard_links) {
                        struct file_struct *file = flist->files[ndx - flist->ndx_start];
                        if (F_IS_HLINKED(file)) {
@@ -178,29 +957,6 @@ static void got_flist_entry_status(enum festatus status, const char *buf)
        }
 }
 
-static void check_timeout(void)
-{
-       time_t t;
-
-       if (!io_timeout || ignore_timeout)
-               return;
-
-       if (!last_io_in) {
-               last_io_in = time(NULL);
-               return;
-       }
-
-       t = time(NULL);
-
-       if (t - last_io_in >= io_timeout) {
-               if (!am_server && !am_daemon) {
-                       rprintf(FERROR, "io timeout after %d seconds -- exiting\n",
-                               (int)(t-last_io_in));
-               }
-               exit_cleanup(RERR_TIMEOUT);
-       }
-}
-
 /* Note the fds used for the main socket (which might really be a pipe
  * for a local transfer, but we can ignore that). */
 void io_set_sock_fds(int f_in, int f_out)
@@ -221,71 +977,6 @@ void set_io_timeout(int secs)
        allowed_lull = read_batch ? 0 : (io_timeout + 1) / 2;
 }
 
-/* Setup the fd used to receive MSG_* messages.  Only needed during the
- * early stages of being a local sender (up through the sending of the
- * file list) or when we're the generator (to fetch the messages from
- * the receiver). */
-void set_msg_fd_in(int fd)
-{
-       msg_fd_in = fd;
-}
-
-/* Setup the fd used to send our MSG_* messages.  Only needed when
- * we're the receiver (to send our messages to the generator). */
-void set_msg_fd_out(int fd)
-{
-       msg_fd_out = fd;
-       set_nonblocking(msg_fd_out);
-}
-
-/* Add a message to the pending MSG_* list. */
-static void msg_list_add(struct msg_list *lst, int code, const char *buf, int len, int convert)
-{
-       struct msg_list_item *m;
-       int sz = len + 4 + sizeof m[0] - 1;
-
-       if (!(m = (struct msg_list_item *)new_array(char, sz)))
-               out_of_memory("msg_list_add");
-       m->next = NULL;
-       m->convert = convert;
-       SIVAL(m->buf, 0, ((code+MPLEX_BASE)<<24) | len);
-       memcpy(m->buf + 4, buf, len);
-       if (lst->tail)
-               lst->tail->next = m;
-       else
-               lst->head = m;
-       lst->tail = m;
-}
-
-static inline int flush_a_msg(int fd)
-{
-       struct msg_list_item *m = msg_queue.head;
-       int len = IVAL(m->buf, 0) & 0xFFFFFF;
-       int tag = *((uchar*)m->buf+3) - MPLEX_BASE;
-
-       if (!(msg_queue.head = m->next))
-               msg_queue.tail = NULL;
-
-       defer_forwarding_messages++;
-       mplex_write(fd, tag, m->buf + 4, len, m->convert);
-       defer_forwarding_messages--;
-
-       free(m);
-
-       return len;
-}
-
-static void msg_flush(void)
-{
-       if (am_generator) {
-               while (msg_queue.head && io_multiplexing_out)
-                       stats.total_written += flush_a_msg(sock_f_out) + 4;
-       } else {
-               while (msg_queue.head)
-                       (void)flush_a_msg(msg_fd_out);
-       }
-}
-
 static void check_for_d_option_error(const char *msg)
 {
        static char rsync263_opts[] = "BCDHIKLPRSTWabceghlnopqrtuvxz";
@@ -316,132 +1007,6 @@ static void check_for_d_option_error(const char *msg)
        }
 }
 
-/* Read a message from the MSG_* fd and handle it.  This is called either
- * during the early stages of being a local sender (up through the sending
- * of the file list) or when we're the generator (to fetch the messages
- * from the receiver). */
-static void read_msg_fd(void)
-{
-       char buf[2048];
-       size_t n;
-       struct file_list *flist;
-       int fd = msg_fd_in;
-       int tag, len;
-
-       /* Temporarily disable msg_fd_in.  This is needed to avoid looping back
-        * to this routine from writefd_unbuffered(). */
-       no_flush++;
-       msg_fd_in = -1;
-       defer_forwarding_messages++;
-
-       readfd(fd, buf, 4);
-       tag = IVAL(buf, 0);
-
-       len = tag & 0xFFFFFF;
-       tag = (tag >> 24) - MPLEX_BASE;
-
-       switch (tag) {
-       case MSG_DONE:
-               if (len < 0 || len > 1 || !am_generator) {
-                 invalid_msg:
-                       rprintf(FERROR, "invalid message %d:%d [%s%s]\n",
-                               tag, len, who_am_i(),
-                               inc_recurse ? "/inc" : "");
-                       exit_cleanup(RERR_STREAMIO);
-               }
-               if (len) {
-                       readfd(fd, buf, len);
-                       stats.total_read = read_varlong(fd, 3);
-               }
-               msgdone_cnt++;
-               break;
-       case MSG_REDO:
-               if (len != 4 || !am_generator)
-                       goto invalid_msg;
-               readfd(fd, buf, 4);
-               got_flist_entry_status(FES_REDO, buf);
-               break;
-       case MSG_FLIST:
-               if (len != 4 || !am_generator || !inc_recurse)
-                       goto invalid_msg;
-               readfd(fd, buf, 4);
-               /* Read extra file list from receiver. */
-               assert(iobuf_in != NULL);
-               assert(iobuf_f_in == fd);
-               if (DEBUG_GTE(FLIST, 2)) {
-                       rprintf(FINFO, "[%s] receiving flist for dir %d\n",
-                               who_am_i(), IVAL(buf,0));
-               }
-               flist = recv_file_list(fd);
-               flist->parent_ndx = IVAL(buf,0);
-#ifdef SUPPORT_HARD_LINKS
-               if (preserve_hard_links)
-                       match_hard_links(flist);
-#endif
-               break;
-       case MSG_FLIST_EOF:
-               if (len != 0 || !am_generator || !inc_recurse)
-                       goto invalid_msg;
-               flist_eof = 1;
-               break;
-       case MSG_IO_ERROR:
-               if (len != 4)
-                       goto invalid_msg;
-               readfd(fd, buf, len);
-               io_error |= IVAL(buf, 0);
-               break;
-       case MSG_DELETED:
-               if (len >= (int)sizeof buf || !am_generator)
-                       goto invalid_msg;
-               readfd(fd, buf, len);
-               send_msg(MSG_DELETED, buf, len, 1);
-               break;
-       case MSG_SUCCESS:
-               if (len != 4 || !am_generator)
-                       goto invalid_msg;
-               readfd(fd, buf, 4);
-               got_flist_entry_status(FES_SUCCESS, buf);
-               break;
-       case MSG_NO_SEND:
-               if (len != 4 || !am_generator)
-                       goto invalid_msg;
-               readfd(fd, buf, 4);
-               got_flist_entry_status(FES_NO_SEND, buf);
-               break;
-       case MSG_ERROR_SOCKET:
-       case MSG_ERROR_UTF8:
-       case MSG_CLIENT:
-               if (!am_generator)
-                       goto invalid_msg;
-               if (tag == MSG_ERROR_SOCKET)
-                       io_end_multiplex_out();
-               /* FALL THROUGH */
-       case MSG_INFO:
-       case MSG_ERROR:
-       case MSG_ERROR_XFER:
-       case MSG_WARNING:
-       case MSG_LOG:
-               while (len) {
-                       n = len;
-                       if (n >= sizeof buf)
-                               n = sizeof buf - 1;
-                       readfd(fd, buf, n);
-                       rwrite((enum logcode)tag, buf, n, !am_generator);
-                       len -= n;
-               }
-               break;
-       default:
-               rprintf(FERROR, "unknown message %d:%d [%s]\n",
-                       tag, len, who_am_i());
-               exit_cleanup(RERR_STREAMIO);
-       }
-
-       no_flush--;
-       msg_fd_in = fd;
-       if (!--defer_forwarding_messages && !no_flush)
-               msg_flush();
-}
-
 /* This is used by the generator to limit how many file transfers can
  * be active at once when --remove-source-files is specified.  Without
  * this, sender-side deletions were mostly happening at the end. */
@@ -455,90 +1020,13 @@ void increment_active_files(int ndx, int itemizing, enum logcode code)
                check_for_finished_files(itemizing, code, 0);
                if (active_filecnt < limit)
                        break;
-               if (iobuf_out_cnt)
-                       io_flush(NORMAL_FLUSH);
-               else
-                       read_msg_fd();
+               wait_for_receiver();
        }
 
        active_filecnt++;
        active_bytecnt += F_LENGTH(cur_flist->files[ndx - cur_flist->ndx_start]);
 }
 
-/* Write an message to a multiplexed stream. If this fails, rsync exits. */
-static void mplex_write(int fd, enum msgcode code, const char *buf, size_t len, int convert)
-{
-       char buffer[BIGPATHBUFLEN]; /* Oversized for use by iconv code. */
-       size_t n = len;
-
-#ifdef ICONV_OPTION
-       /* We need to convert buf before doing anything else so that we
-        * can include the (converted) byte length in the message header. */
-       if (convert && ic_send != (iconv_t)-1) {
-               xbuf outbuf, inbuf;
-
-               INIT_XBUF(outbuf, buffer + 4, 0, sizeof buffer - 4);
-               INIT_XBUF(inbuf, (char*)buf, len, (size_t)-1);
-
-               iconvbufs(ic_send, &inbuf, &outbuf,
-                         ICB_INCLUDE_BAD | ICB_INCLUDE_INCOMPLETE);
-               if (inbuf.len > 0) {
-                       rprintf(FERROR, "overflowed conversion buffer in mplex_write");
-                       exit_cleanup(RERR_UNSUPPORTED);
-               }
-
-               n = len = outbuf.len;
-       } else
-#endif
-       if (n > 1024 - 4) /* BIGPATHBUFLEN can handle 1024 bytes */
-               n = 0;    /* We'd rather do 2 writes than too much memcpy(). */
-       else
-               memcpy(buffer + 4, buf, n);
-
-       SIVAL(buffer, 0, ((MPLEX_BASE + (int)code)<<24) + len);
-
-       keep_defer_forwarding++; /* defer_forwarding_messages++ on return */
-       writefd_unbuffered(fd, buffer, n+4);
-       keep_defer_forwarding--;
-
-       if (len > n)
-               writefd_unbuffered(fd, buf+n, len-n);
-
-       if (!--defer_forwarding_messages && !no_flush)
-               msg_flush();
-}
-
-int send_msg(enum msgcode code, const char *buf, int len, int convert)
-{
-       if (msg_fd_out < 0) {
-               if (!defer_forwarding_messages)
-                       return io_multiplex_write(code, buf, len, convert);
-               if (!io_multiplexing_out)
-                       return 0;
-               msg_list_add(&msg_queue, code, buf, len, convert);
-               return 1;
-       }
-       if (flist_forward_from >= 0)
-               msg_list_add(&msg_queue, code, buf, len, convert);
-       else
-               mplex_write(msg_fd_out, code, buf, len, convert);
-       return 1;
-}
-
-void send_msg_int(enum msgcode code, int num)
-{
-       char numbuf[4];
-       SIVAL(numbuf, 0, num);
-       send_msg(code, numbuf, 4, 0);
-}
-
-void wait_for_receiver(void)
-{
-       if (io_flush(FULL_FLUSH))
-               return;
-       read_msg_fd();
-}
-
 int get_redo_num(void)
 {
        return flist_ndx_pop(&redo_list);
@@ -549,232 +1037,31 @@ int get_hlink_num(void)
        return flist_ndx_pop(&hlink_list);
 }
 
-/**
- * When we're the receiver and we have a local --files-from list of names
+/* When we're the receiver and we have a local --files-from list of names
  * that needs to be sent over the socket to the sender, we have to do two
  * things at the same time: send the sender a list of what files we're
  * processing and read the incoming file+info list from the sender.  We do
- * this by augmenting the read_timeout() function to copy this data.  It
- * uses ff_buf to read a block of data from f_in (when it is ready, since
- * it might be a pipe) and then blast it out f_out (when it is ready to
- * receive more data).
- */
-void io_set_filesfrom_fds(int f_in, int f_out)
-{
-       io_filesfrom_f_in = f_in;
-       io_filesfrom_f_out = f_out;
-       alloc_xbuf(&ff_buf, 2048);
-#ifdef ICONV_OPTION
-       if (protect_args)
-               alloc_xbuf(&iconv_buf, 1024);
-#endif
-}
-
-/* It's almost always an error to get an EOF when we're trying to read from the
- * network, because the protocol is (for the most part) self-terminating.
- *
- * There is one case for the receiver when it is at the end of the transfer
- * (hanging around reading any keep-alive packets that might come its way): if
- * the sender dies before the generator's kill-signal comes through, we can end
- * up here needing to loop until the kill-signal arrives.  In this situation,
- * kluge_around_eof will be < 0.
- *
- * There is another case for older protocol versions (< 24) where the module
- * listing was not terminated, so we must ignore an EOF error in that case and
- * exit.  In this situation, kluge_around_eof will be > 0. */
-static void whine_about_eof(int fd)
-{
-       if (kluge_around_eof && fd == sock_f_in) {
-               int i;
-               if (kluge_around_eof > 0)
-                       exit_cleanup(0);
-               /* If we're still here after 10 seconds, exit with an error. */
-               for (i = 10*1000/20; i--; )
-                       msleep(20);
-       }
-
-       rprintf(FERROR, RSYNC_NAME ": connection unexpectedly closed "
-               "(%s bytes received so far) [%s]\n",
-               big_num(stats.total_read), who_am_i());
-
-       exit_cleanup(RERR_STREAMIO);
-}
-
-/**
- * Read from a socket with I/O timeout. return the number of bytes
- * read. If no bytes can be read then exit, never return a number <= 0.
- *
- * TODO: If the remote shell connection fails, then current versions
- * actually report an "unexpected EOF" error here.  Since it's a
- * fairly common mistake to try to use rsh when ssh is required, we
- * should trap that: if we fail to read any data at all, we should
- * give a better explanation.  We can tell whether the connection has
- * started by looking e.g. at whether the remote version is known yet.
- */
-static int read_timeout(int fd, char *buf, size_t len)
-{
-       int n, cnt = 0;
-
-       io_flush(FULL_FLUSH);
-
-       while (cnt == 0) {
-               /* until we manage to read *something* */
-               fd_set r_fds, w_fds;
-               struct timeval tv;
-               int maxfd = fd;
-               int count;
-
-               FD_ZERO(&r_fds);
-               FD_ZERO(&w_fds);
-               FD_SET(fd, &r_fds);
-               if (io_filesfrom_f_out >= 0) {
-                       int new_fd;
-                       if (ff_buf.len == 0) {
-                               if (io_filesfrom_f_in >= 0) {
-                                       FD_SET(io_filesfrom_f_in, &r_fds);
-                                       new_fd = io_filesfrom_f_in;
-                               } else {
-                                       io_filesfrom_f_out = -1;
-                                       new_fd = -1;
-                               }
-                       } else {
-                               FD_SET(io_filesfrom_f_out, &w_fds);
-                               new_fd = io_filesfrom_f_out;
-                       }
-                       if (new_fd > maxfd)
-                               maxfd = new_fd;
-               }
-
-               tv.tv_sec = select_timeout;
-               tv.tv_usec = 0;
-
-               errno = 0;
-
-               count = select(maxfd + 1, &r_fds, &w_fds, NULL, &tv);
-
-               if (count <= 0) {
-                       if (errno == EBADF) {
-                               defer_forwarding_messages = 0;
-                               exit_cleanup(RERR_SOCKETIO);
-                       }
-                       check_timeout();
-                       continue;
-               }
-
-               if (io_filesfrom_f_out >= 0) {
-                       if (ff_buf.len) {
-                               if (FD_ISSET(io_filesfrom_f_out, &w_fds)) {
-                                       int l = write(io_filesfrom_f_out,
-                                                     ff_buf.buf + ff_buf.pos,
-                                                     ff_buf.len);
-                                       if (l > 0) {
-                                               if (!(ff_buf.len -= l))
-                                                       ff_buf.pos = 0;
-                                               else
-                                                       ff_buf.pos += l;
-                                       } else if (errno != EINTR) {
-                                               /* XXX should we complain? */
-                                               io_filesfrom_f_out = -1;
-                                       }
-                               }
-                       } else if (io_filesfrom_f_in >= 0) {
-                               if (FD_ISSET(io_filesfrom_f_in, &r_fds)) {
-#ifdef ICONV_OPTION
-                                       xbuf *ibuf = filesfrom_convert ? &iconv_buf : &ff_buf;
-#else
-                                       xbuf *ibuf = &ff_buf;
-#endif
-                                       int l = read(io_filesfrom_f_in, ibuf->buf, ibuf->size);
-                                       if (l <= 0) {
-                                               if (l == 0 || errno != EINTR) {
-                                                       /* Send end-of-file marker */
-                                                       memcpy(ff_buf.buf, "\0\0", 2);
-                                                       ff_buf.len = ff_lastchar? 2 : 1;
-                                                       ff_buf.pos = 0;
-                                                       io_filesfrom_f_in = -1;
-                                               }
-                                       } else {
-#ifdef ICONV_OPTION
-                                               if (filesfrom_convert) {
-                                                       iconv_buf.pos = 0;
-                                                       iconv_buf.len = l;
-                                                       iconvbufs(ic_send, &iconv_buf, &ff_buf,
-                                                           ICB_EXPAND_OUT|ICB_INCLUDE_BAD|ICB_INCLUDE_INCOMPLETE);
-                                                       l = ff_buf.len;
-                                               }
-#endif
-                                               if (!eol_nulls) {
-                                                       char *s = ff_buf.buf + l;
-                                                       /* Transform CR and/or LF into '\0' */
-                                                       while (s-- > ff_buf.buf) {
-                                                               if (*s == '\n' || *s == '\r')
-                                                                       *s = '\0';
-                                                       }
-                                               }
-                                               if (!ff_lastchar) {
-                                                       /* Last buf ended with a '\0', so don't
-                                                        * let this buf start with one. */
-                                                       while (l && ff_buf.buf[ff_buf.pos] == '\0')
-                                                               ff_buf.pos++, l--;
-                                               }
-                                               if (!l)
-                                                       ff_buf.pos = 0;
-                                               else {
-                                                       char *f = ff_buf.buf + ff_buf.pos;
-                                                       char *t = f;
-                                                       char *eob = f + l;
-                                                       /* Eliminate any multi-'\0' runs. */
-                                                       while (f != eob) {
-                                                               if (!(*t++ = *f++)) {
-                                                                       while (f != eob && !*f)
-                                                                               f++, l--;
-                                                               }
-                                                       }
-                                                       ff_lastchar = f[-1];
-                                               }
-                                               ff_buf.len = l;
-                                       }
-                               }
-                       }
-               }
-
-               if (!FD_ISSET(fd, &r_fds))
-                       continue;
-
-               n = read(fd, buf, len);
-
-               if (n <= 0) {
-                       if (n == 0)
-                               whine_about_eof(fd); /* Doesn't return. */
-                       if (errno == EINTR || errno == EWOULDBLOCK
-                           || errno == EAGAIN)
-                               continue;
-
-                       /* Don't write errors on a dead socket. */
-                       if (fd == sock_f_in) {
-                               io_end_multiplex_out();
-                               rsyserr(FERROR_SOCKET, errno, "read error");
-                       } else
-                               rsyserr(FERROR, errno, "read error");
-                       exit_cleanup(RERR_STREAMIO);
-               }
-
-               buf += n;
-               len -= n;
-               cnt += n;
-
-               if (fd == sock_f_in && io_timeout)
-                       last_io_in = time(NULL);
+ * this by making recv_file_list() call forward_filesfrom_data(), which
+ * will ensure that we forward data to the sender until we get some data
+ * for recv_file_list() to use. */
+void start_filesfrom_forwarding(int fd)
+{
+       if (protocol_version < 31 && OUT_MULTIPLEXED) {
+               /* Older protocols send the files-from data w/o packaging
+                * it in multiplexed I/O packets, so temporarily switch
+                * to buffered I/O to match this behavior. */
+               iobuf.msg.pos = iobuf.msg.len = 0; /* Be extra sure no messages go out. */
+               ff_reenable_multiplex = io_end_multiplex_out(MPLX_TO_BUFFERED);
        }
+       ff_forward_fd = fd;
 
-       return cnt;
+       alloc_xbuf(&ff_xb, FILESFROM_BUFLEN);
 }
 
 /* Read a line into the "buf" buffer. */
 int read_line(int fd, char *buf, size_t bufsiz, int flags)
 {
        char ch, *s, *eob;
-       int cnt;
 
 #ifdef ICONV_OPTION
        if (flags & RL_CONVERT && iconv_buf.size < bufsiz)
@@ -786,27 +1073,13 @@ int read_line(int fd, char *buf, size_t bufsiz, int flags)
        s = flags & RL_CONVERT ? iconv_buf.buf : buf;
 #else
        s = buf;
-#endif
-       eob = s + bufsiz - 1;
-       while (1) {
-               cnt = read(fd, &ch, 1);
-               if (cnt < 0 && (errno == EWOULDBLOCK
-                 || errno == EINTR || errno == EAGAIN)) {
-                       struct timeval tv;
-                       fd_set r_fds, e_fds;
-                       FD_ZERO(&r_fds);
-                       FD_SET(fd, &r_fds);
-                       FD_ZERO(&e_fds);
-                       FD_SET(fd, &e_fds);
-                       tv.tv_sec = select_timeout;
-                       tv.tv_usec = 0;
-                       if (!select(fd+1, &r_fds, NULL, &e_fds, &tv))
-                               check_timeout();
-                       /*if (FD_ISSET(fd, &e_fds))
-                               rprintf(FINFO, "select exception on fd %d\n", fd); */
-                       continue;
-               }
-               if (cnt != 1)
+#endif
+       eob = s + bufsiz - 1;
+       while (1) {
+               /* We avoid read_byte() for files because files can return an EOF. */
+               if (fd == iobuf.in_fd)
+                       ch = read_byte(fd);
+               else if (safe_read(fd, &ch, 1) == 0)
                        break;
                if (flags & RL_EOL_NULLS ? ch == '\0' : (ch == '\r' || ch == '\n')) {
                        /* Skip empty lines if dumping comments. */
@@ -829,7 +1102,7 @@ int read_line(int fd, char *buf, size_t bufsiz, int flags)
                iconv_buf.pos = 0;
                iconv_buf.len = s - iconv_buf.buf;
                iconvbufs(ic_recv, &iconv_buf, &outbuf,
-                         ICB_INCLUDE_BAD | ICB_INCLUDE_INCOMPLETE);
+                         ICB_INCLUDE_BAD | ICB_INCLUDE_INCOMPLETE | ICB_INIT);
                outbuf.buf[outbuf.len] = '\0';
                return outbuf.len;
        }
@@ -891,56 +1164,95 @@ void read_args(int f_in, char *mod_name, char *buf, size_t bufsiz, int rl_nulls,
        *argv_p = argv;
 }
 
-int io_start_buffering_out(int f_out)
+BOOL io_start_buffering_out(int f_out)
 {
-       if (iobuf_out) {
-               assert(f_out == iobuf_f_out);
-               return 0;
+       if (msgs2stderr && DEBUG_GTE(IO, 2))
+               rprintf(FINFO, "[%s] io_start_buffering_out(%d)\n", who_am_i(), f_out);
+
+       if (OUT_MULTIPLEXED && !iobuf.msg.buf) {
+               iobuf.msg.size = IO_BUFFER_SIZE - 4;
+               if (!(iobuf.msg.buf = new_array(char, iobuf.msg.size + 4)))
+                       out_of_memory("io_start_buffering_out");
+               iobuf.msg.pos = iobuf.msg.len = 0;
+       }
+
+       if (iobuf.out.buf) {
+               if (iobuf.out_fd == -1)
+                       iobuf.out_fd = f_out;
+               else
+                       assert(f_out == iobuf.out_fd);
+               return False;
        }
-       if (!(iobuf_out = new_array(char, IO_BUFFER_SIZE)))
+
+       iobuf.out.size = IO_BUFFER_SIZE * 2 - 4;
+       /* The 4 overflow bytes makes some circular-buffer wrapping operations easier. */
+       if (!(iobuf.out.buf = new_array(char, iobuf.out.size + 4)))
                out_of_memory("io_start_buffering_out");
-       iobuf_out_cnt = 0;
-       iobuf_f_out = f_out;
-       return 1;
+       iobuf.out.pos = iobuf.out.len = 0;
+       iobuf.out_fd = f_out;
+
+       return True;
 }
 
-int io_start_buffering_in(int f_in)
+BOOL io_start_buffering_in(int f_in)
 {
-       if (iobuf_in) {
-               assert(f_in == iobuf_f_in);
-               return 0;
+       if (msgs2stderr && DEBUG_GTE(IO, 2))
+               rprintf(FINFO, "[%s] io_start_buffering_in(%d)\n", who_am_i(), f_in);
+
+       if (iobuf.in.buf) {
+               if (iobuf.in_fd == -1)
+                       iobuf.in_fd = f_in;
+               else
+                       assert(f_in == iobuf.in_fd);
+               return False;
        }
-       iobuf_in_siz = 2 * IO_BUFFER_SIZE;
-       if (!(iobuf_in = new_array(char, iobuf_in_siz)))
+
+       iobuf.in.size = IO_BUFFER_SIZE;
+       if (!(iobuf.in.buf = new_array(char, iobuf.in.size)))
                out_of_memory("io_start_buffering_in");
-       iobuf_f_in = f_in;
-       return 1;
+
+       iobuf.in.pos = iobuf.in.len = 0;
+
+       iobuf.in_fd = f_in;
+
+       return True;
 }
 
-void io_end_buffering_in(void)
+void io_end_buffering_in(BOOL free_buffers)
 {
-       if (!iobuf_in)
-               return;
-       free(iobuf_in);
-       iobuf_in = NULL;
-       iobuf_in_ndx = 0;
-       iobuf_in_remaining = 0;
-       iobuf_f_in = -1;
+       if (msgs2stderr && DEBUG_GTE(IO, 2)) {
+               rprintf(FINFO, "[%s] io_end_buffering_in(IOBUF_%s_BUFS)\n",
+                       who_am_i(), free_buffers ? "FREE" : "KEEP");
+       }
+
+       if (free_buffers)
+               free_xbuf(&iobuf.in);
+       else
+               iobuf.in.pos = iobuf.in.len = 0;
+
+       iobuf.in_fd = -1;
 }
 
-void io_end_buffering_out(void)
+void io_end_buffering_out(BOOL free_buffers)
 {
-       if (!iobuf_out)
-               return;
+       if (msgs2stderr && DEBUG_GTE(IO, 2)) {
+               rprintf(FINFO, "[%s] io_end_buffering_out(IOBUF_%s_BUFS)\n",
+                       who_am_i(), free_buffers ? "FREE" : "KEEP");
+       }
+
        io_flush(FULL_FLUSH);
-       free(iobuf_out);
-       iobuf_out = NULL;
-       iobuf_f_out = -1;
+
+       if (free_buffers) {
+               free_xbuf(&iobuf.out);
+               free_xbuf(&iobuf.msg);
+       }
+
+       iobuf.out_fd = -1;
 }
 
 void maybe_flush_socket(int important)
 {
-       if (iobuf_out && iobuf_out_cnt
+       if (flist_eof && iobuf.out.buf && iobuf.out.len > iobuf.out_empty_len
         && (important || time(NULL) - last_io_out >= 5))
                io_flush(NORMAL_FLUSH);
 }
@@ -948,232 +1260,288 @@ void maybe_flush_socket(int important)
 void maybe_send_keepalive(void)
 {
        if (time(NULL) - last_io_out >= allowed_lull) {
-               if (!iobuf_out || !iobuf_out_cnt) {
+               if (!iobuf.msg.len && iobuf.out.len == iobuf.out_empty_len) {
                        if (protocol_version < 29)
                                return; /* there's nothing we can do */
                        if (protocol_version >= 30)
                                send_msg(MSG_NOOP, "", 0, 0);
                        else {
-                               write_int(sock_f_out, cur_flist->used);
-                               write_shortint(sock_f_out, ITEM_IS_NEW);
+                               write_int(iobuf.out_fd, cur_flist->used);
+                               write_shortint(iobuf.out_fd, ITEM_IS_NEW);
                        }
                }
-               if (iobuf_out)
+               if (iobuf.msg.len)
+                       perform_io(iobuf.msg.size - iobuf.msg.len + 1, PIO_NEED_MSGROOM);
+               else if (iobuf.out.len > iobuf.out_empty_len)
                        io_flush(NORMAL_FLUSH);
        }
 }
 
-void start_flist_forward(int f_in)
-{
-       assert(iobuf_out != NULL);
-       assert(iobuf_f_out == msg_fd_out);
-       flist_forward_from = f_in;
-}
-
-void stop_flist_forward()
+void start_flist_forward(int ndx)
 {
-       flist_forward_from = -1;
-       io_flush(FULL_FLUSH);
+       write_int(iobuf.out_fd, ndx);
+       forward_flist_data = 1;
 }
 
-/**
- * Continue trying to read len bytes - don't return until len has been
- * read.
- **/
-static void read_loop(int fd, char *buf, size_t len)
+void stop_flist_forward(void)
 {
-       while (len) {
-               int n = read_timeout(fd, buf, len);
-
-               buf += n;
-               len -= n;
-       }
+       forward_flist_data = 0;
 }
 
-/**
- * Read from the file descriptor handling multiplexing - return number
- * of bytes read.
- *
- * Never returns <= 0.
- */
-static int readfd_unbuffered(int fd, char *buf, size_t len)
+/* Read a message from a multiplexed source. */
+static void read_a_msg(void)
 {
+       char *data, line[BIGPATHBUFLEN];
+       int tag, val;
        size_t msg_bytes;
-       int tag, cnt = 0;
-       char line[BIGPATHBUFLEN];
-
-       if (!iobuf_in || fd != iobuf_f_in)
-               return read_timeout(fd, buf, len);
-
-       if (!io_multiplexing_in && iobuf_in_remaining == 0) {
-               iobuf_in_remaining = read_timeout(fd, iobuf_in, iobuf_in_siz);
-               iobuf_in_ndx = 0;
-       }
 
-       while (cnt == 0) {
-               if (iobuf_in_remaining) {
-                       len = MIN(len, iobuf_in_remaining);
-                       memcpy(buf, iobuf_in + iobuf_in_ndx, len);
-                       iobuf_in_ndx += len;
-                       iobuf_in_remaining -= len;
-                       cnt = len;
-                       break;
-               }
+       data = perform_io(4, PIO_INPUT_AND_CONSUME);
+       tag = IVAL(data, 0);
 
-               read_loop(fd, line, 4);
-               tag = IVAL(line, 0);
+       msg_bytes = tag & 0xFFFFFF;
+       tag = (tag >> 24) - MPLEX_BASE;
 
-               msg_bytes = tag & 0xFFFFFF;
-               tag = (tag >> 24) - MPLEX_BASE;
+       if (DEBUG_GTE(IO, 1) && (msgs2stderr || tag != MSG_INFO))
+               rprintf(FINFO, "[%s] got msg=%d, len=%ld\n", who_am_i(), (int)tag, (long)msg_bytes);
 
-               switch (tag) {
-               case MSG_DATA:
-                       if (msg_bytes > iobuf_in_siz) {
-                               if (!(iobuf_in = realloc_array(iobuf_in, char,
-                                                              msg_bytes)))
-                                       out_of_memory("readfd_unbuffered");
-                               iobuf_in_siz = msg_bytes;
-                       }
-                       read_loop(fd, iobuf_in, msg_bytes);
-                       iobuf_in_remaining = msg_bytes;
-                       iobuf_in_ndx = 0;
-                       break;
-               case MSG_NOOP:
-                       if (am_sender)
-                               maybe_send_keepalive();
-                       break;
-               case MSG_IO_ERROR:
-                       if (msg_bytes != 4)
-                               goto invalid_msg;
-                       read_loop(fd, line, msg_bytes);
-                       send_msg_int(MSG_IO_ERROR, IVAL(line, 0));
-                       io_error |= IVAL(line, 0);
-                       break;
-               case MSG_DEL_STATS:
-                       if (msg_bytes)
-                               goto invalid_msg;
-                       read_del_stats(fd);
-                       if (am_sender && am_server)
-                               write_del_stats(sock_f_out);
+       switch (tag) {
+       case MSG_DATA:
+               assert(iobuf.raw_input_ends_before == 0);
+               /* Though this does not yet read the data, we do mark where in
+                * the buffer the msg data will end once it is read.  It is
+                * possible that this points off the end of the buffer, in
+                * which case the gradual reading of the input stream will
+                * cause this value to decrease and eventually become real. */
+               iobuf.raw_input_ends_before = iobuf.in.pos + msg_bytes;
+               break;
+       case MSG_STATS:
+               if (msg_bytes != sizeof stats.total_read || !am_generator)
+                       goto invalid_msg;
+               data = perform_io(sizeof stats.total_read, PIO_INPUT_AND_CONSUME);
+               memcpy((char*)&stats.total_read, data, sizeof stats.total_read);
+               break;
+       case MSG_REDO:
+               if (msg_bytes != 4 || !am_generator)
+                       goto invalid_msg;
+               data = perform_io(4, PIO_INPUT_AND_CONSUME);
+               got_flist_entry_status(FES_REDO, IVAL(data, 0));
+               break;
+       case MSG_IO_ERROR:
+               if (msg_bytes != 4 || am_sender)
+                       goto invalid_msg;
+               data = perform_io(4, PIO_INPUT_AND_CONSUME);
+               val = IVAL(data, 0);
+               io_error |= val;
+               if (!am_generator)
+                       send_msg_int(MSG_IO_ERROR, val);
+               break;
+       case MSG_IO_TIMEOUT:
+               if (msg_bytes != 4 || am_server || am_generator)
+                       goto invalid_msg;
+               data = perform_io(4, PIO_INPUT_AND_CONSUME);
+               val = IVAL(data, 0);
+               if (!io_timeout || io_timeout > val) {
+                       if (INFO_GTE(MISC, 2))
+                               rprintf(FINFO, "Setting --timeout=%d to match server\n", val);
+                       set_io_timeout(val);
+               }
+               break;
+       case MSG_NOOP:
+               if (am_sender)
+                       maybe_send_keepalive();
+               break;
+       case MSG_DELETED:
+               if (msg_bytes >= sizeof line)
+                       goto overflow;
+               if (am_generator) {
+                       memcpy(line, perform_io(msg_bytes, PIO_INPUT_AND_CONSUME), msg_bytes);
+                       send_msg(MSG_DELETED, line, msg_bytes, 1);
                        break;
-               case MSG_DELETED:
-                       if (msg_bytes >= sizeof line)
-                               goto overflow;
+               }
 #ifdef ICONV_OPTION
-                       if (ic_recv != (iconv_t)-1) {
-                               xbuf outbuf, inbuf;
-                               char ibuf[512];
-                               int add_null = 0;
-
-                               INIT_CONST_XBUF(outbuf, line);
-                               INIT_XBUF(inbuf, ibuf, 0, (size_t)-1);
-
-                               while (msg_bytes) {
-                                       inbuf.len = msg_bytes > sizeof ibuf
-                                                 ? sizeof ibuf : msg_bytes;
-                                       read_loop(fd, inbuf.buf, inbuf.len);
-                                       if (!(msg_bytes -= inbuf.len)
-                                        && !ibuf[inbuf.len-1])
-                                               inbuf.len--, add_null = 1;
-                                       if (iconvbufs(ic_send, &inbuf, &outbuf,
-                                           ICB_INCLUDE_BAD | ICB_INCLUDE_INCOMPLETE) < 0)
+               if (ic_recv != (iconv_t)-1) {
+                       xbuf outbuf, inbuf;
+                       char ibuf[512];
+                       int add_null = 0;
+                       int flags = ICB_INCLUDE_BAD | ICB_INIT;
+
+                       INIT_CONST_XBUF(outbuf, line);
+                       INIT_XBUF(inbuf, ibuf, 0, (size_t)-1);
+
+                       while (msg_bytes) {
+                               size_t len = msg_bytes > sizeof ibuf - inbuf.len ? sizeof ibuf - inbuf.len : msg_bytes;
+                               memcpy(ibuf + inbuf.len, perform_io(len, PIO_INPUT_AND_CONSUME), len);
+                               inbuf.pos = 0;
+                               inbuf.len += len;
+                               if (!(msg_bytes -= len) && !ibuf[inbuf.len-1])
+                                       inbuf.len--, add_null = 1;
+                               if (iconvbufs(ic_send, &inbuf, &outbuf, flags) < 0) {
+                                       if (errno == E2BIG)
                                                goto overflow;
+                                       /* Buffer ended with an incomplete char, so move the
+                                        * bytes to the start of the buffer and continue. */
+                                       memmove(ibuf, ibuf + inbuf.pos, inbuf.len);
                                }
-                               if (add_null) {
-                                       if (outbuf.len == outbuf.size)
-                                               goto overflow;
-                                       outbuf.buf[outbuf.len++] = '\0';
-                               }
-                               msg_bytes = outbuf.len;
-                       } else
+                               flags &= ~ICB_INIT;
+                       }
+                       if (add_null) {
+                               if (outbuf.len == outbuf.size)
+                                       goto overflow;
+                               outbuf.buf[outbuf.len++] = '\0';
+                       }
+                       msg_bytes = outbuf.len;
+               } else
 #endif
-                               read_loop(fd, line, msg_bytes);
-                       /* A directory name was sent with the trailing null */
-                       if (msg_bytes > 0 && !line[msg_bytes-1])
-                               log_delete(line, S_IFDIR);
-                       else {
+                       memcpy(line, perform_io(msg_bytes, PIO_INPUT_AND_CONSUME), msg_bytes);
+               /* A directory name was sent with the trailing null */
+               if (msg_bytes > 0 && !line[msg_bytes-1])
+                       log_delete(line, S_IFDIR);
+               else {
+                       line[msg_bytes] = '\0';
+                       log_delete(line, S_IFREG);
+               }
+               break;
+       case MSG_SUCCESS:
+               if (msg_bytes != 4) {
+                 invalid_msg:
+                       rprintf(FERROR, "invalid multi-message %d:%lu [%s%s]\n",
+                               tag, (unsigned long)msg_bytes, who_am_i(),
+                               inc_recurse ? "/inc" : "");
+                       exit_cleanup(RERR_STREAMIO);
+               }
+               data = perform_io(4, PIO_INPUT_AND_CONSUME);
+               val = IVAL(data, 0);
+               if (am_generator)
+                       got_flist_entry_status(FES_SUCCESS, val);
+               else
+                       successful_send(val);
+               break;
+       case MSG_NO_SEND:
+               if (msg_bytes != 4)
+                       goto invalid_msg;
+               data = perform_io(4, PIO_INPUT_AND_CONSUME);
+               val = IVAL(data, 0);
+               if (am_generator)
+                       got_flist_entry_status(FES_NO_SEND, val);
+               else
+                       send_msg_int(MSG_NO_SEND, val);
+               break;
+       case MSG_ERROR_SOCKET:
+       case MSG_ERROR_UTF8:
+       case MSG_CLIENT:
+       case MSG_LOG:
+               if (!am_generator)
+                       goto invalid_msg;
+               if (tag == MSG_ERROR_SOCKET)
+                       msgs2stderr = 1;
+               /* FALL THROUGH */
+       case MSG_INFO:
+       case MSG_ERROR:
+       case MSG_ERROR_XFER:
+       case MSG_WARNING:
+               if (msg_bytes >= sizeof line) {
+                   overflow:
+                       rprintf(FERROR,
+                               "multiplexing overflow %d:%lu [%s%s]\n",
+                               tag, (unsigned long)msg_bytes, who_am_i(),
+                               inc_recurse ? "/inc" : "");
+                       exit_cleanup(RERR_STREAMIO);
+               }
+               memcpy(line, perform_io(msg_bytes, PIO_INPUT_AND_CONSUME), msg_bytes);
+               rwrite((enum logcode)tag, line, msg_bytes, !am_generator);
+               if (first_message) {
+                       if (list_only && !am_sender && tag == 1 && msg_bytes < sizeof line) {
                                line[msg_bytes] = '\0';
-                               log_delete(line, S_IFREG);
+                               check_for_d_option_error(line);
                        }
-                       break;
-               case MSG_SUCCESS:
-                       if (msg_bytes != 4) {
-                         invalid_msg:
-                               rprintf(FERROR, "invalid multi-message %d:%ld [%s]\n",
-                                       tag, (long)msg_bytes, who_am_i());
-                               exit_cleanup(RERR_STREAMIO);
-                       }
-                       read_loop(fd, line, msg_bytes);
-                       successful_send(IVAL(line, 0));
-                       break;
-               case MSG_NO_SEND:
-                       if (msg_bytes != 4)
-                               goto invalid_msg;
-                       read_loop(fd, line, msg_bytes);
-                       send_msg_int(MSG_NO_SEND, IVAL(line, 0));
-                       break;
-               case MSG_INFO:
-               case MSG_ERROR:
-               case MSG_ERROR_XFER:
-               case MSG_WARNING:
-                       if (msg_bytes >= sizeof line) {
-                           overflow:
-                               rprintf(FERROR,
-                                       "multiplexing overflow %d:%ld [%s]\n",
-                                       tag, (long)msg_bytes, who_am_i());
-                               exit_cleanup(RERR_STREAMIO);
+                       first_message = 0;
+               }
+               break;
+       case MSG_ERROR_EXIT:
+               if (msg_bytes == 0) {
+                       if (!am_sender && !am_generator) {
+                               send_msg(MSG_ERROR_EXIT, "", 0, 0);
+                               io_flush(FULL_FLUSH);
                        }
-                       read_loop(fd, line, msg_bytes);
-                       rwrite((enum logcode)tag, line, msg_bytes, 1);
-                       if (first_message) {
-                               if (list_only && !am_sender && tag == 1) {
-                                       line[msg_bytes] = '\0';
-                                       check_for_d_option_error(line);
-                               }
-                               first_message = 0;
+                       val = 0;
+               } else if (msg_bytes == 4) {
+                       data = perform_io(4, PIO_INPUT_AND_CONSUME);
+                       val = IVAL(data, 0);
+                       if (protocol_version >= 31) {
+                               if (am_generator)
+                                       send_msg_int(MSG_ERROR_EXIT, val);
+                               else
+                                       send_msg(MSG_ERROR_EXIT, "", 0, 0);
                        }
-                       break;
-               default:
-                       rprintf(FERROR, "unexpected tag %d [%s]\n",
-                               tag, who_am_i());
-                       exit_cleanup(RERR_STREAMIO);
-               }
+               } else
+                       goto invalid_msg;
+               /* Send a negative linenum so that we don't end up
+                * with a duplicate exit message. */
+               _exit_cleanup(val, __FILE__, 0 - __LINE__);
+       default:
+               rprintf(FERROR, "unexpected tag %d [%s%s]\n",
+                       tag, who_am_i(), inc_recurse ? "/inc" : "");
+               exit_cleanup(RERR_STREAMIO);
        }
-
-       if (iobuf_in_remaining == 0)
-               io_flush(NORMAL_FLUSH);
-
-       return cnt;
 }
 
-/* Do a buffered read from fd.  Don't return until all N bytes have
- * been read.  If all N can't be read then exit with an error. */
-static void readfd(int fd, char *buffer, size_t N)
+static void drain_multiplex_messages(void)
 {
-       int  cnt;
-       size_t total = 0;
-
-       while (total < N) {
-               cnt = readfd_unbuffered(fd, buffer + total, N-total);
-               total += cnt;
+       while (IN_MULTIPLEXED && iobuf.in.len) {
+               if (iobuf.raw_input_ends_before) {
+                       size_t raw_len = iobuf.raw_input_ends_before - iobuf.in.pos;
+                       iobuf.raw_input_ends_before = 0;
+                       if (raw_len >= iobuf.in.len) {
+                               iobuf.in.len = 0;
+                               break;
+                       }
+                       iobuf.in.pos += raw_len;
+                       iobuf.in.len -= raw_len;
+               }
+               read_a_msg();
        }
+}
 
-       if (fd == write_batch_monitor_in) {
-               if ((size_t)write(batch_fd, buffer, total) != total)
-                       exit_cleanup(RERR_FILEIO);
+void wait_for_receiver(void)
+{
+       if (!iobuf.raw_input_ends_before)
+               read_a_msg();
+
+       if (iobuf.raw_input_ends_before) {
+               int ndx = read_int(iobuf.in_fd);
+               if (ndx < 0) {
+                       switch (ndx) {
+                       case NDX_FLIST_EOF:
+                               flist_eof = 1;
+                               if (DEBUG_GTE(FLIST, 3))
+                                       rprintf(FINFO, "[%s] flist_eof=1\n", who_am_i());
+                               break;
+                       case NDX_DONE:
+                               msgdone_cnt++;
+                               break;
+                       default:
+                               exit_cleanup(RERR_STREAMIO);
+                       }
+               } else {
+                       struct file_list *flist;
+                       if (DEBUG_GTE(FLIST, 2)) {
+                               rprintf(FINFO, "[%s] receiving flist for dir %d\n",
+                                       who_am_i(), ndx);
+                       }
+                       flist = recv_file_list(iobuf.in_fd);
+                       flist->parent_ndx = ndx;
+#ifdef SUPPORT_HARD_LINKS
+                       if (preserve_hard_links)
+                               match_hard_links(flist);
+#endif
+               }
        }
-
-       if (fd == flist_forward_from)
-               writefd(iobuf_f_out, buffer, total);
-
-       if (fd == sock_f_in)
-               stats.total_read += total;
 }
 
 unsigned short read_shortint(int f)
 {
        char b[2];
-       readfd(f, b, 2);
+       read_buf(f, b, 2);
        return (UVAL(b, 1) << 8) + UVAL(b, 0);
 }
 
@@ -1182,7 +1550,7 @@ int32 read_int(int f)
        char b[4];
        int32 num;
 
-       readfd(f, b, 4);
+       read_buf(f, b, 4);
        num = IVAL(b, 0);
 #if SIZEOF_INT32 > 4
        if (num & (int32)0x80000000)
@@ -1194,14 +1562,14 @@ int32 read_int(int f)
 int32 read_varint(int f)
 {
        union {
-           char b[5];
-           int32 x;
+               char b[5];
+               int32 x;
        } u;
        uchar ch;
        int extra;
 
        u.x = 0;
-       readfd(f, (char*)&ch, 1);
+       ch = read_byte(f);
        extra = int_byte_extra[ch / 4];
        if (extra) {
                uchar bit = ((uchar)1<<(8-extra));
@@ -1209,7 +1577,7 @@ int32 read_varint(int f)
                        rprintf(FERROR, "Overflow in read_varint()\n");
                        exit_cleanup(RERR_STREAMIO);
                }
-               readfd(f, u.b, extra);
+               read_buf(f, u.b, extra);
                u.b[extra] = ch & (bit-1);
        } else
                u.b[0] = ch;
@@ -1226,8 +1594,8 @@ int32 read_varint(int f)
 int64 read_varlong(int f, uchar min_bytes)
 {
        union {
-           char b[9];
-           int64 x;
+               char b[9];
+               int64 x;
        } u;
        char b2[8];
        int extra;
@@ -1237,7 +1605,7 @@ int64 read_varlong(int f, uchar min_bytes)
 #else
        u.x = 0;
 #endif
-       readfd(f, b2, min_bytes);
+       read_buf(f, b2, min_bytes);
        memcpy(u.b, b2+1, min_bytes-1);
        extra = int_byte_extra[CVAL(b2, 0) / 4];
        if (extra) {
@@ -1246,7 +1614,7 @@ int64 read_varlong(int f, uchar min_bytes)
                        rprintf(FERROR, "Overflow in read_varlong()\n");
                        exit_cleanup(RERR_STREAMIO);
                }
-               readfd(f, u.b + min_bytes - 1, extra);
+               read_buf(f, u.b + min_bytes - 1, extra);
                u.b[min_bytes + extra - 1] = CVAL(b2, 0) & (bit-1);
 #if SIZEOF_INT64 < 8
                if (min_bytes + extra > 5 || u.b[4] || CVAL(u.b,3) & 0x80) {
@@ -1278,26 +1646,69 @@ int64 read_longint(int f)
        rprintf(FERROR, "Integer overflow: attempted 64-bit offset\n");
        exit_cleanup(RERR_UNSUPPORTED);
 #else
-       readfd(f, b, 8);
+       read_buf(f, b, 8);
        return IVAL(b,0) | (((int64)IVAL(b,4))<<32);
 #endif
 }
 
 void read_buf(int f, char *buf, size_t len)
 {
-       readfd(f,buf,len);
+       if (f != iobuf.in_fd) {
+               if (safe_read(f, buf, len) != len)
+                       whine_about_eof(False); /* Doesn't return. */
+               goto batch_copy;
+       }
+
+       if (!IN_MULTIPLEXED) {
+               memcpy(buf, perform_io(len, PIO_INPUT_AND_CONSUME), len);
+               total_data_read += len;
+               if (forward_flist_data)
+                       write_buf(iobuf.out_fd, buf, len);
+         batch_copy:
+               if (f == write_batch_monitor_in)
+                       safe_write(batch_fd, buf, len);
+               return;
+       }
+
+       while (1) {
+               char *data;
+               size_t siz;
+
+               while (!iobuf.raw_input_ends_before)
+                       read_a_msg();
+
+               siz = MIN(len, iobuf.raw_input_ends_before - iobuf.in.pos);
+               data = perform_io(siz, PIO_INPUT_AND_CONSUME);
+               if (iobuf.in.pos == iobuf.raw_input_ends_before)
+                       iobuf.raw_input_ends_before = 0;
+
+               /* The bytes at the "data" pointer will survive long
+                * enough to make a copy, but not past future I/O. */
+               memcpy(buf, data, siz);
+               total_data_read += siz;
+
+               if (forward_flist_data)
+                       write_buf(iobuf.out_fd, buf, siz);
+
+               if (f == write_batch_monitor_in)
+                       safe_write(batch_fd, buf, siz);
+
+               if ((len -= siz) == 0)
+                       break;
+               buf += siz;
+       }
 }
 
 void read_sbuf(int f, char *buf, size_t len)
 {
-       readfd(f, buf, len);
+       read_buf(f, buf, len);
        buf[len] = '\0';
 }
 
 uchar read_byte(int f)
 {
        uchar c;
-       readfd(f, (char *)&c, 1);
+       read_buf(f, (char*)&c, 1);
        return c;
 }
 
@@ -1315,7 +1726,7 @@ int read_vstring(int f, char *buf, int bufsize)
        }
 
        if (len)
-               readfd(f, buf, len);
+               read_buf(f, buf, len);
        buf[len] = '\0';
        return len;
 }
@@ -1368,8 +1779,7 @@ void write_sum_head(int f, struct sum_struct *sum)
        write_int(f, sum->remainder);
 }
 
-/**
- * Sleep after writing to limit I/O bandwidth usage.
+/* Sleep after writing to limit I/O bandwidth usage.
  *
  * @todo Rather than sleeping after each write, it might be better to
  * use some kind of averaging.  The current algorithm seems to always
@@ -1382,8 +1792,7 @@ void write_sum_head(int f, struct sum_struct *sum)
  * round small waits up to guarantee that we actually wait at least the
  * requested number of microseconds, this can become grossly inaccurate.
  * We therefore keep track of the bytes we've written over time and only
- * sleep when the accumulated delay is at least 1 tenth of a second.
- **/
+ * sleep when the accumulated delay is at least 1 tenth of a second. */
 static void sleep_for_bwlimit(int bytes_written)
 {
        static struct timeval prior_tv;
@@ -1393,9 +1802,6 @@ static void sleep_for_bwlimit(int bytes_written)
 
 #define ONE_SEC        1000000L /* # of microseconds in a second */
 
-       if (!bwlimit_writemax)
-               return;
-
        total_written += bytes_written;
 
        gettimeofday(&start_tv, NULL);
@@ -1423,165 +1829,16 @@ static void sleep_for_bwlimit(int bytes_written)
        total_written = (sleep_usec - elapsed_usec) * bwlimit / (ONE_SEC/1024);
 }
 
-/* Write len bytes to the file descriptor fd, looping as necessary to get
- * the job done and also (in certain circumstances) reading any data on
- * msg_fd_in to avoid deadlock.
- *
- * This function underlies the multiplexing system.  The body of the
- * application never calls this function directly. */
-static void writefd_unbuffered(int fd, const char *buf, size_t len)
-{
-       size_t n, total = 0;
-       fd_set w_fds, r_fds, e_fds;
-       int maxfd, count, cnt, using_r_fds;
-       int defer_inc = 0;
-       struct timeval tv;
-
-       if (no_flush++)
-               defer_forwarding_messages++, defer_inc++;
-
-       while (total < len) {
-               FD_ZERO(&w_fds);
-               FD_SET(fd, &w_fds);
-               FD_ZERO(&e_fds);
-               FD_SET(fd, &e_fds);
-               maxfd = fd;
-
-               if (msg_fd_in >= 0) {
-                       FD_ZERO(&r_fds);
-                       FD_SET(msg_fd_in, &r_fds);
-                       if (msg_fd_in > maxfd)
-                               maxfd = msg_fd_in;
-                       using_r_fds = 1;
-               } else
-                       using_r_fds = 0;
-
-               tv.tv_sec = select_timeout;
-               tv.tv_usec = 0;
-
-               errno = 0;
-               count = select(maxfd + 1, using_r_fds ? &r_fds : NULL,
-                              &w_fds, &e_fds, &tv);
-
-               if (count <= 0) {
-                       if (count < 0 && errno == EBADF)
-                               exit_cleanup(RERR_SOCKETIO);
-                       check_timeout();
-                       continue;
-               }
-
-               /*if (FD_ISSET(fd, &e_fds))
-                       rprintf(FINFO, "select exception on fd %d\n", fd); */
-
-               if (using_r_fds && FD_ISSET(msg_fd_in, &r_fds))
-                       read_msg_fd();
-
-               if (!FD_ISSET(fd, &w_fds))
-                       continue;
-
-               n = len - total;
-               if (bwlimit_writemax && n > bwlimit_writemax)
-                       n = bwlimit_writemax;
-               cnt = write(fd, buf + total, n);
-
-               if (cnt <= 0) {
-                       if (cnt < 0) {
-                               if (errno == EINTR)
-                                       continue;
-                               if (errno == EWOULDBLOCK || errno == EAGAIN) {
-                                       msleep(1);
-                                       continue;
-                               }
-                       }
-
-                       /* Don't try to write errors back across the stream. */
-                       if (fd == sock_f_out)
-                               io_end_multiplex_out();
-                       /* Don't try to write errors down a failing msg pipe. */
-                       if (am_server && fd == msg_fd_out)
-                               exit_cleanup(RERR_STREAMIO);
-                       rsyserr(FERROR, errno,
-                               "writefd_unbuffered failed to write %ld bytes [%s]",
-                               (long)len, who_am_i());
-                       /* If the other side is sending us error messages, try
-                        * to grab any messages they sent before they died. */
-                       while (!am_server && fd == sock_f_out && io_multiplexing_in) {
-                               char buf[1024];
-                               set_io_timeout(30);
-                               ignore_timeout = 0;
-                               readfd_unbuffered(sock_f_in, buf, sizeof buf);
-                       }
-                       exit_cleanup(RERR_STREAMIO);
-               }
-
-               total += cnt;
-               defer_forwarding_messages++, defer_inc++;
-
-               if (fd == sock_f_out) {
-                       if (io_timeout || am_generator)
-                               last_io_out = time(NULL);
-                       sleep_for_bwlimit(cnt);
-               }
-       }
-
-       no_flush--;
-       if (keep_defer_forwarding)
-               defer_inc--;
-       if (!(defer_forwarding_messages -= defer_inc) && !no_flush)
-               msg_flush();
-}
-
-int io_flush(int flush_it_all)
-{
-       int flushed_something = 0;
-
-       if (no_flush)
-               return 0;
-
-       if (iobuf_out_cnt) {
-               if (io_multiplexing_out)
-                       mplex_write(sock_f_out, MSG_DATA, iobuf_out, iobuf_out_cnt, 0);
-               else
-                       writefd_unbuffered(iobuf_f_out, iobuf_out, iobuf_out_cnt);
-               iobuf_out_cnt = 0;
-               flushed_something = 1;
-       }
-
-       if (flush_it_all && !defer_forwarding_messages && msg_queue.head) {
-               msg_flush();
-               flushed_something = 1;
-       }
-
-       return flushed_something;
-}
-
-static void writefd(int fd, const char *buf, size_t len)
+void io_flush(int flush_it_all)
 {
-       if (fd == sock_f_out)
-               stats.total_written += len;
-
-       if (fd == write_batch_monitor_out) {
-               if ((size_t)write(batch_fd, buf, len) != len)
-                       exit_cleanup(RERR_FILEIO);
-       }
-
-       if (!iobuf_out || fd != iobuf_f_out) {
-               writefd_unbuffered(fd, buf, len);
-               return;
-       }
-
-       while (len) {
-               int n = MIN((int)len, IO_BUFFER_SIZE - iobuf_out_cnt);
-               if (n > 0) {
-                       memcpy(iobuf_out+iobuf_out_cnt, buf, n);
-                       buf += n;
-                       len -= n;
-                       iobuf_out_cnt += n;
-               }
-
-               if (iobuf_out_cnt == IO_BUFFER_SIZE)
-                       io_flush(NORMAL_FLUSH);
+       if (iobuf.out.len > iobuf.out_empty_len) {
+               if (flush_it_all) /* FULL_FLUSH: flush everything in the output buffers */
+                       perform_io(iobuf.out.size - iobuf.out_empty_len, PIO_NEED_OUTROOM);
+               else /* NORMAL_FLUSH: flush at least 1 byte */
+                       perform_io(iobuf.out.size - iobuf.out.len + 1, PIO_NEED_OUTROOM);
        }
+       if (iobuf.msg.len)
+               perform_io(iobuf.msg.size, PIO_NEED_MSGROOM);
 }
 
 void write_shortint(int f, unsigned short x)
@@ -1589,14 +1846,14 @@ void write_shortint(int f, unsigned short x)
        char b[2];
        b[0] = (char)x;
        b[1] = (char)(x >> 8);
-       writefd(f, b, 2);
+       write_buf(f, b, 2);
 }
 
 void write_int(int f, int32 x)
 {
        char b[4];
        SIVAL(b, 0, x);
-       writefd(f, b, 4);
+       write_buf(f, b, 4);
 }
 
 void write_varint(int f, int32 x)
@@ -1618,7 +1875,7 @@ void write_varint(int f, int32 x)
        else
                *b = b[cnt];
 
-       writefd(f, b, cnt);
+       write_buf(f, b, cnt);
 }
 
 void write_varlong(int f, int64 x, uchar min_bytes)
@@ -1650,7 +1907,7 @@ void write_varlong(int f, int64 x, uchar min_bytes)
        else
                *b = b[cnt];
 
-       writefd(f, b, cnt);
+       write_buf(f, b, cnt);
 }
 
 /*
@@ -1663,7 +1920,7 @@ void write_longint(int f, int64 x)
 
        SIVAL(s, 0, x);
        if (x <= 0x7FFFFFFF && x >= 0) {
-               writefd(f, s, 4);
+               write_buf(f, s, 4);
                return;
        }
 
@@ -1673,24 +1930,50 @@ void write_longint(int f, int64 x)
 #else
        memset(b, 0xFF, 4);
        SIVAL(s, 4, x >> 32);
-       writefd(f, b, 12);
+       write_buf(f, b, 12);
 #endif
 }
 
 void write_buf(int f, const char *buf, size_t len)
 {
-       writefd(f,buf,len);
+       size_t pos, siz;
+
+       if (f != iobuf.out_fd) {
+               safe_write(f, buf, len);
+               goto batch_copy;
+       }
+
+       if (iobuf.out.len + len > iobuf.out.size)
+               perform_io(len, PIO_NEED_OUTROOM);
+
+       pos = iobuf.out.pos + iobuf.out.len; /* Must be set after any flushing. */
+       if (pos >= iobuf.out.size)
+               pos -= iobuf.out.size;
+
+       /* Handle a split copy if we wrap around the end of the circular buffer. */
+       if (pos >= iobuf.out.pos && (siz = iobuf.out.size - pos) < len) {
+               memcpy(iobuf.out.buf + pos, buf, siz);
+               memcpy(iobuf.out.buf, buf + siz, len - siz);
+       } else
+               memcpy(iobuf.out.buf + pos, buf, len);
+
+       iobuf.out.len += len;
+       total_data_written += len;
+
+  batch_copy:
+       if (f == write_batch_monitor_out)
+               safe_write(batch_fd, buf, len);
 }
 
-/** Write a string to the connection */
+/* Write a string to the connection */
 void write_sbuf(int f, const char *buf)
 {
-       writefd(f, buf, strlen(buf));
+       write_buf(f, buf, strlen(buf));
 }
 
 void write_byte(int f, uchar c)
 {
-       writefd(f, (char *)&c, 1);
+       write_buf(f, (char *)&c, 1);
 }
 
 void write_vstring(int f, const char *str, int len)
@@ -1708,9 +1991,9 @@ void write_vstring(int f, const char *str, int len)
        }
        *lb = len;
 
-       writefd(f, (char*)lenbuf, lb - lenbuf + 1);
+       write_buf(f, (char*)lenbuf, lb - lenbuf + 1);
        if (len)
-               writefd(f, str, len);
+               write_buf(f, str, len);
 }
 
 /* Send a file-list index using a byte-reduction method. */
@@ -1732,7 +2015,7 @@ void write_ndx(int f, int32 ndx)
                prev_positive = ndx;
        } else if (ndx == NDX_DONE) {
                *b = 0;
-               writefd(f, b, 1);
+               write_buf(f, b, 1);
                return;
        } else {
                b[cnt++] = (char)0xFF;
@@ -1757,7 +2040,7 @@ void write_ndx(int f, int32 ndx)
                b[cnt++] = (char)(diff >> 8);
                b[cnt++] = (char)diff;
        }
-       writefd(f, b, cnt);
+       write_buf(f, b, cnt);
 }
 
 /* Receive a file-list index using a byte-reduction method. */
@@ -1770,20 +2053,20 @@ int32 read_ndx(int f)
        if (protocol_version < 30)
                return read_int(f);
 
-       readfd(f, b, 1);
+       read_buf(f, b, 1);
        if (CVAL(b, 0) == 0xFF) {
-               readfd(f, b, 1);
+               read_buf(f, b, 1);
                prev_ptr = &prev_negative;
        } else if (CVAL(b, 0) == 0)
                return NDX_DONE;
        else
                prev_ptr = &prev_positive;
        if (CVAL(b, 0) == 0xFE) {
-               readfd(f, b, 2);
+               read_buf(f, b, 2);
                if (CVAL(b, 0) & 0x80) {
                        b[3] = CVAL(b, 0) & ~0x80;
                        b[0] = b[1];
-                       readfd(f, b+1, 2);
+                       read_buf(f, b+1, 2);
                        num = IVAL(b, 0);
                } else
                        num = (UVAL(b,0)<<8) + UVAL(b,1) + *prev_ptr;
@@ -1798,17 +2081,18 @@ int32 read_ndx(int f)
 /* Read a line of up to bufsiz-1 characters into buf.  Strips
  * the (required) trailing newline and all carriage returns.
  * Returns 1 for success; 0 for I/O error or truncation. */
-int read_line_old(int f, char *buf, size_t bufsiz)
+int read_line_old(int fd, char *buf, size_t bufsiz)
 {
        bufsiz--; /* leave room for the null */
        while (bufsiz > 0) {
-               buf[0] = 0;
-               read_buf(f, buf, 1);
-               if (buf[0] == 0)
+               assert(fd != iobuf.in_fd);
+               if (safe_read(fd, buf, 1) == 0)
                        return 0;
-               if (buf[0] == '\n')
+               if (*buf == '\0')
+                       return 0;
+               if (*buf == '\n')
                        break;
-               if (buf[0] != '\r') {
+               if (*buf != '\r') {
                        buf++;
                        bufsiz--;
                }
@@ -1828,54 +2112,75 @@ void io_printf(int fd, const char *format, ...)
        va_end(ap);
 
        if (len < 0)
-               exit_cleanup(RERR_STREAMIO);
+               exit_cleanup(RERR_PROTOCOL);
 
        if (len > (int)sizeof buf) {
                rprintf(FERROR, "io_printf() was too long for the buffer.\n");
-               exit_cleanup(RERR_STREAMIO);
+               exit_cleanup(RERR_PROTOCOL);
        }
 
        write_sbuf(fd, buf);
 }
 
-/** Setup for multiplexing a MSG_* stream with the data stream. */
-void io_start_multiplex_out(void)
+/* Setup for multiplexing a MSG_* stream with the data stream. */
+void io_start_multiplex_out(int fd)
 {
-       io_flush(NORMAL_FLUSH);
-       io_start_buffering_out(sock_f_out);
-       io_multiplexing_out = 1;
-}
+       io_flush(FULL_FLUSH);
 
-/** Setup for multiplexing a MSG_* stream with the data stream. */
-void io_start_multiplex_in(void)
-{
-       io_flush(NORMAL_FLUSH);
-       io_start_buffering_in(sock_f_in);
-       io_multiplexing_in = 1;
+       if (msgs2stderr && DEBUG_GTE(IO, 2))
+               rprintf(FINFO, "[%s] io_start_multiplex_out(%d)\n", who_am_i(), fd);
+
+       iobuf.out_empty_len = 4; /* See also OUT_MULTIPLEXED */
+       io_start_buffering_out(fd);
+
+       iobuf.raw_data_header_pos = iobuf.out.pos + iobuf.out.len;
+       iobuf.out.len += 4;
 }
 
-/** Write an message to the multiplexed data stream. */
-int io_multiplex_write(enum msgcode code, const char *buf, size_t len, int convert)
+/* Setup for multiplexing a MSG_* stream with the data stream. */
+void io_start_multiplex_in(int fd)
 {
-       if (!io_multiplexing_out)
-               return 0;
-       io_flush(NORMAL_FLUSH);
-       stats.total_written += (len+4);
-       mplex_write(sock_f_out, code, buf, len, convert);
-       return 1;
+       if (msgs2stderr && DEBUG_GTE(IO, 2))
+               rprintf(FINFO, "[%s] io_start_multiplex_in(%d)\n", who_am_i(), fd);
+
+       iobuf.in_multiplexed = True; /* See also IN_MULTIPLEXED */
+       io_start_buffering_in(fd);
 }
 
-void io_end_multiplex_in(void)
+int io_end_multiplex_in(int mode)
 {
-       io_multiplexing_in = 0;
-       io_end_buffering_in();
+       int ret = iobuf.in_multiplexed ? iobuf.in_fd : -1;
+
+       if (msgs2stderr && DEBUG_GTE(IO, 2))
+               rprintf(FINFO, "[%s] io_end_multiplex_in(mode=%d)\n", who_am_i(), mode);
+
+       iobuf.in_multiplexed = False;
+       if (mode == MPLX_SWITCHING)
+               iobuf.raw_input_ends_before = 0;
+       else
+               assert(iobuf.raw_input_ends_before == 0);
+       if (mode != MPLX_TO_BUFFERED)
+               io_end_buffering_in(mode);
+
+       return ret;
 }
 
-/** Stop output multiplexing. */
-void io_end_multiplex_out(void)
+int io_end_multiplex_out(int mode)
 {
-       io_multiplexing_out = 0;
-       io_end_buffering_out();
+       int ret = iobuf.out_empty_len ? iobuf.out_fd : -1;
+
+       if (msgs2stderr && DEBUG_GTE(IO, 2))
+               rprintf(FINFO, "[%s] io_end_multiplex_out(mode=%d)\n", who_am_i(), mode);
+
+       if (mode != MPLX_TO_BUFFERED)
+               io_end_buffering_out(mode);
+       else
+               io_flush(FULL_FLUSH);
+
+       iobuf.out.len = 0;
+       iobuf.out_empty_len = 0;
+
+       return ret;
 }
 
 void start_write_batch(int fd)