Allow "./configure --with-protect-args" to make -s the default.

[rsync/rsync.git] / io.c

/*
 * Socket and pipe I/O utilities used in rsync.
 *
 * Copyright (C) 1996-2001 Andrew Tridgell
 * Copyright (C) 1996 Paul Mackerras
 * Copyright (C) 2001, 2002 Martin Pool <mbp@samba.org>
 * Copyright (C) 2003-2009 Wayne Davison
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, visit the http://fsf.org website.
 */

/* Rsync provides its own multiplexing system, which is used to send
 * stderr and stdout over a single socket.
 *
 * For historical reasons this is off during the start of the
 * connection, but it's switched on quite early using
 * io_start_multiplex_out() and io_start_multiplex_in(). */

#include "rsync.h"
#include "ifuncs.h"
#include "inums.h"

/** If no timeout is specified then use a 60 second select timeout */
#define SELECT_TIMEOUT 60

extern int bwlimit;
extern size_t bwlimit_writemax;
extern int io_timeout;
extern int am_server;
extern int am_sender;
extern int am_receiver;
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;
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
extern int filesfrom_convert;
extern iconv_t ic_send, ic_recv;
#endif

int csum_length = SHORT_SUM_LENGTH; /* initial value */
int allowed_lull = 0;
int batch_fd = -1;
int msgdone_cnt = 0;
int forward_flist_data = 0;
BOOL flist_receiving_enabled = False;
BOOL we_send_keepalive_messages = False;

/* Ignore an EOF error if non-zero. See whine_about_eof(). */
int kluge_around_eof = 0;

int sock_f_in = -1;
int sock_f_out = -1;

int64 total_data_read = 0;
int64 total_data_written = 0;

static struct {
        xbuf in, out, msg;
        int in_fd;
        int out_fd; /* Both "out" and "msg" go to this fd. */
        int 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 };

static time_t last_io_in;
static time_t last_io_out;

static int write_batch_monitor_in = -1;
static int write_batch_monitor_out = -1;

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 select_timeout = SELECT_TIMEOUT;
static int active_filecnt = 0;
static OFF_T active_bytecnt = 0;
static int first_message = 1;

static char int_byte_extra[64] = {
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* (00 - 3F)/4 */
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* (40 - 7F)/4 */
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, /* (80 - BF)/4 */
        2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 5, 6, /* (C0 - FF)/4 */
};

/* Our I/O buffers are sized with no bits on in the lowest byte of the "size"
 * (indeed, our rounding of sizes in 1024-byte units assures more than this).
 * This allows the code that is storing bytes near the physical end of a
 * circular buffer to temporarily reduce the buffer's size (in order to make
 * some storing idioms easier), while also making it simple to restore the
 * buffer's actual size when the buffer's "pos" wraps around to the start (we
 * just round the buffer's size up again). */

#define IOBUF_WAS_REDUCED(siz) ((siz) & 0xFF)
#define IOBUF_RESTORE_SIZE(siz) (((siz) | 0xFF) + 1)

#define IN_MULTIPLEXED (iobuf.in_multiplexed != 0)
#define IN_MULTIPLEXED_AND_READY (iobuf.in_multiplexed > 0)
#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 read_a_msg(void);
static void drain_multiplex_messages(void);
static void sleep_for_bwlimit(int bytes_written);

static void check_timeout(BOOL allow_keepalive)
{
        time_t t, chk;

        /* On the receiving side, the generator is now handling timeouts, so
         * the receiver ignores them.  Note that the am_receiver flag is not
         * set until the receiver forks from the generator, so timeouts will be
         * based on receiving data on the receiving side until that event. */
        if (!io_timeout || am_receiver)
                return;

        t = time(NULL);

        if (allow_keepalive && we_send_keepalive_messages) {
                /* This may put data into iobuf.msg w/o flushing. */
                maybe_send_keepalive(t, False);
        }

        if (!last_io_in)
                last_io_in = t;

        chk = MAX(last_io_out, last_io_in);
        if (t - chk >= io_timeout) {
                if (am_server)
                        msgs2stderr = 1;
                rprintf(FERROR, "[%s] io timeout after %d seconds -- exiting\n",
                        who_am_i(), (int)(t-chk));
                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);
                        }
                        if (we_send_keepalive_messages)
                                maybe_send_keepalive(time(NULL), True);
                        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);
                        }
                        if (we_send_keepalive_messages)
                                maybe_send_keepalive(time(NULL), True);
                        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);
                }
        }
}

void reduce_iobuf_size(xbuf *out, size_t new_size)
{
        if (new_size < out->size) {
                if (DEBUG_GTE(IO, 4)) {
                        const char *name = out == &iobuf.out ? "iobuf.out"
                                         : out == &iobuf.msg ? "iobuf.msg"
                                         : NULL;
                        if (name) {
                                rprintf(FINFO, "[%s] reduced size of %s (-%d)\n",
                                        who_am_i(), name, (int)(out->size - new_size));
                        }
                }
                out->size = new_size;
        }
}

void restore_iobuf_size(xbuf *out)
{
        if (IOBUF_WAS_REDUCED(out->size)) {
                size_t new_size = IOBUF_RESTORE_SIZE(out->size);
                if (DEBUG_GTE(IO, 4)) {
                        const char *name = out == &iobuf.out ? "iobuf.out"
                                         : out == &iobuf.msg ? "iobuf.msg"
                                         : NULL;
                        if (name) {
                                rprintf(FINFO, "[%s] restored size of %s (+%d)\n",
                                        who_am_i(), name, (int)(new_size - out->size));
                        }
                }
                out->size = new_size;
        }
}

/* Perform buffered input and/or output until specified conditions are met.
 * When given a "needed" read or write request, this returns without doing any
 * I/O if the needed input bytes or write space is already available.  Once I/O
 * is needed, this will try to do whatever reading and/or writing is currently
 * possible, up to the maximum buffer allowances, no matter if this is a read
 * or write request.  However, the I/O stops as soon as the required input
 * bytes or output space is available.  If this is not a read request, the
 * routine may also do some advantageous reading of messages from a multiplexed
 * input source (which ensures that we don't jam up with everyone in their
 * "need to write" code and nobody reading the accumulated data that would make
 * writing possible).
 *
 * The iobuf.in, .out and .msg buffers are all circular.  Callers need to be
 * aware that some data copies will need to be split when the bytes wrap around
 * from the end to the start.  In order to help make writing into the output
 * buffers easier for some operations (such as the use of SIVAL() into the
 * buffer) a buffer may be temporarily shortened by a small amount, but the
 * original size will be automatically restored when the .pos wraps to the
 * start.  See also the 3 raw_* iobuf vars that are used in the handling of
 * MSG_DATA bytes as they are read-from/written-into the buffers.
 *
 * 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?
 *
 * 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:
                /* We never resize the circular input buffer. */
                if (iobuf.in.size < needed) {
                        rprintf(FERROR, "need to read %ld bytes, iobuf.in.buf is only %ld bytes.\n",
                                (long)needed, (long)iobuf.in.size);
                        exit_cleanup(RERR_PROTOCOL);
                }

                if (DEBUG_GTE(IO, 3)) {
                        rprintf(FINFO, "[%s] perform_io(%ld, %sinput)\n",
                                who_am_i(), (long)needed, flags & PIO_CONSUME_INPUT ? "consume&" : "");
                }
                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.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 (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;
                                        else if (iobuf.raw_data_header_pos + 4 > iobuf.out.size) {
                                                /* The 4-byte header won't fit at the end of the buffer,
                                                 * so we'll temporarily reduce the output buffer's size
                                                 * and put the header at the start of the buffer. */
                                                reduce_iobuf_size(&iobuf.out, iobuf.raw_data_header_pos);
                                                iobuf.raw_data_header_pos = 0;
                                        }
                                        /* 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((flags & PIO_NEED_INPUT) != 0);
                        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 len, pos = iobuf.in.pos + iobuf.in.len;
                        int n;
                        if (pos >= iobuf.in.size) {
                                pos -= iobuf.in.size;
                                len = iobuf.in.size - iobuf.in.len;
                        } else
                                len = iobuf.in.size - pos;
                        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 (out && 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;
                                restore_iobuf_size(out);
                        } 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;
                                restore_iobuf_size(out);
                                if (empty_buf_len)
                                        iobuf.raw_data_header_pos = 0;
                        }
                }

                /* We need to help prevent deadlock by doing what reading
                 * we can whenever we are here trying to write. */
                if (IN_MULTIPLEXED_AND_READY && !(flags & PIO_NEED_INPUT)) {
                        while (!iobuf.raw_input_ends_before && iobuf.in.len > 512)
                                read_a_msg();
                        if (flist_receiving_enabled && iobuf.in.len > 512)
                                wait_for_receiver(); /* generator only */
                }

                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;
                if (iobuf.in.pos == iobuf.raw_input_ends_before)
                        iobuf.raw_input_ends_before = 0;
                if (iobuf.in.pos >= iobuf.in.size) {
                        iobuf.in.pos -= iobuf.in.size;
                        if (iobuf.raw_input_ends_before)
                                iobuf.raw_input_ends_before -= iobuf.in.size;
                }
        }

        return data;
}

static void raw_read_buf(char *buf, size_t len)
{
        size_t pos = iobuf.in.pos;
        char *data = perform_io(len, PIO_INPUT_AND_CONSUME);
        if (iobuf.in.pos <= pos && len) {
                size_t siz = len - iobuf.in.pos;
                memcpy(buf, data, siz);
                memcpy(buf + siz, iobuf.in.buf, iobuf.in.pos);
        } else
                memcpy(buf, data, len);
}

static int32 raw_read_int(void)
{
        char *data, buf[4];
        if (iobuf.in.size - iobuf.in.pos >= 4)
                data = perform_io(4, PIO_INPUT_AND_CONSUME);
        else
                raw_read_buf(data = buf, 4);
        return IVAL(data, 0);
}

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 not used for (normal) MSG_DATA. */
int send_msg(enum msgcode code, const char *buf, size_t len, int convert)
{
        char *hdr;
        size_t needed, 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);

        /* When checking for enough free space for this message, we need to
         * make sure that there is space for the 4-byte header, plus we'll
         * assume that we may waste up to 3 bytes (if the header doesn't fit
         * at the physical end of the buffer). */
#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. */
                needed = len*2 + 4 + 3;
        } else
#endif
                needed = len + 4 + 3;
        if (iobuf.msg.len + needed > iobuf.msg.size)
                perform_io(needed, 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;
        else if (pos + 4 > iobuf.msg.size) {
                /* The 4-byte header won't fit at the end of the buffer,
                 * so we'll temporarily reduce the message buffer's size
                 * and put the header at the start of the buffer. */
                reduce_iobuf_size(&iobuf.msg, pos);
                pos = 0;
        }
        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 = 0;

                /* 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;
        }

        SIVAL(hdr, 0, ((MPLEX_BASE + (int)code)<<24) + len);

        if (want_debug && convert > 0)
                rprintf(FINFO, "[%s] converted msg len=%ld\n", who_am_i(), (long)len);

        return 1;
}

void send_msg_int(enum msgcode code, int num)
{
        char numbuf[4];

        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, int ndx)
{
        struct file_list *flist = flist_for_ndx(ndx, "got_flist_entry_status");

        if (remove_source_files) {
                active_filecnt--;
                active_bytecnt -= F_LENGTH(flist->files[ndx - flist->ndx_start]);
        }

        if (inc_recurse)
                flist->in_progress--;

        switch (status) {
        case FES_SUCCESS:
                if (remove_source_files)
                        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)) {
                                flist_ndx_push(&hlink_list, ndx);
                                flist->in_progress++;
                        }
                }
                break;
        case FES_REDO:
                if (read_batch) {
                        if (inc_recurse)
                                flist->in_progress++;
                        break;
                }
                if (inc_recurse)
                        flist->to_redo++;
                flist_ndx_push(&redo_list, ndx);
                break;
        case FES_NO_SEND:
                break;
        }
}

/* 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)
{
        sock_f_in = f_in;
        sock_f_out = f_out;
}

void set_io_timeout(int secs)
{
        io_timeout = secs;

        if (!io_timeout || io_timeout > SELECT_TIMEOUT)
                select_timeout = SELECT_TIMEOUT;
        else
                select_timeout = io_timeout;

        allowed_lull = read_batch ? 0 : (io_timeout + 1) / 2;
}

static void check_for_d_option_error(const char *msg)
{
        static char rsync263_opts[] = "BCDHIKLPRSTWabceghlnopqrtuvxz";
        char *colon;
        int saw_d = 0;

        if (*msg != 'r'
         || strncmp(msg, REMOTE_OPTION_ERROR, sizeof REMOTE_OPTION_ERROR - 1) != 0)
                return;

        msg += sizeof REMOTE_OPTION_ERROR - 1;
        if (*msg == '-' || (colon = strchr(msg, ':')) == NULL
         || strncmp(colon, REMOTE_OPTION_ERROR2, sizeof REMOTE_OPTION_ERROR2 - 1) != 0)
                return;

        for ( ; *msg != ':'; msg++) {
                if (*msg == 'd')
                        saw_d = 1;
                else if (*msg == 'e')
                        break;
                else if (strchr(rsync263_opts, *msg) == NULL)
                        return;
        }

        if (saw_d) {
                rprintf(FWARNING,
                    "*** Try using \"--old-d\" if remote rsync is <= 2.6.3 ***\n");
        }
}

/* 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. */
void increment_active_files(int ndx, int itemizing, enum logcode code)
{
        while (1) {
                /* TODO: tune these limits? */
                int limit = active_bytecnt >= 128*1024 ? 10 : 50;
                if (active_filecnt < limit)
                        break;
                check_for_finished_files(itemizing, code, 0);
                if (active_filecnt < limit)
                        break;
                wait_for_receiver();
        }

        active_filecnt++;
        active_bytecnt += F_LENGTH(cur_flist->files[ndx - cur_flist->ndx_start]);
}

int get_redo_num(void)
{
        return flist_ndx_pop(&redo_list);
}

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
 * 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 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;

        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;

#ifdef ICONV_OPTION
        if (flags & RL_CONVERT && iconv_buf.size < bufsiz)
                realloc_xbuf(&iconv_buf, bufsiz + 1024);
#endif

  start:
#ifdef ICONV_OPTION
        s = flags & RL_CONVERT ? iconv_buf.buf : buf;
#else
        s = buf;
#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. */
                        if (flags & RL_DUMP_COMMENTS && s == buf)
                                continue;
                        break;
                }
                if (s < eob)
                        *s++ = ch;
        }
        *s = '\0';

        if (flags & RL_DUMP_COMMENTS && (*buf == '#' || *buf == ';'))
                goto start;

#ifdef ICONV_OPTION
        if (flags & RL_CONVERT) {
                xbuf outbuf;
                INIT_XBUF(outbuf, buf, 0, bufsiz);
                iconv_buf.pos = 0;
                iconv_buf.len = s - iconv_buf.buf;
                iconvbufs(ic_recv, &iconv_buf, &outbuf,
                          ICB_INCLUDE_BAD | ICB_INCLUDE_INCOMPLETE | ICB_INIT);
                outbuf.buf[outbuf.len] = '\0';
                return outbuf.len;
        }
#endif

        return s - buf;
}

void read_args(int f_in, char *mod_name, char *buf, size_t bufsiz, int rl_nulls,
               char ***argv_p, int *argc_p, char **request_p)
{
        int maxargs = MAX_ARGS;
        int dot_pos = 0;
        int argc = 0;
        char **argv, *p;
        int rl_flags = (rl_nulls ? RL_EOL_NULLS : 0);

#ifdef ICONV_OPTION
        rl_flags |= (protect_args && ic_recv != (iconv_t)-1 ? RL_CONVERT : 0);
#endif

        if (!(argv = new_array(char *, maxargs)))
                out_of_memory("read_args");
        if (mod_name && !protect_args)
                argv[argc++] = "rsyncd";

        while (1) {
                if (read_line(f_in, buf, bufsiz, rl_flags) == 0)
                        break;

                if (argc == maxargs-1) {
                        maxargs += MAX_ARGS;
                        if (!(argv = realloc_array(argv, char *, maxargs)))
                                out_of_memory("read_args");
                }

                if (dot_pos) {
                        if (request_p) {
                                *request_p = strdup(buf);
                                request_p = NULL;
                        }
                        if (mod_name)
                                glob_expand_module(mod_name, buf, &argv, &argc, &maxargs);
                        else
                                glob_expand(buf, &argv, &argc, &maxargs);
                } else {
                        if (!(p = strdup(buf)))
                                out_of_memory("read_args");
                        argv[argc++] = p;
                        if (*p == '.' && p[1] == '\0')
                                dot_pos = argc;
                }
        }
        argv[argc] = NULL;

        glob_expand(NULL, NULL, NULL, NULL);

        *argc_p = argc;
        *argv_p = argv;
}

BOOL io_start_buffering_out(int f_out)
{
        if (msgs2stderr && DEBUG_GTE(IO, 2))
                rprintf(FINFO, "[%s] io_start_buffering_out(%d)\n", who_am_i(), f_out);

        if (iobuf.out.buf) {
                if (iobuf.out_fd == -1)
                        iobuf.out_fd = f_out;
                else
                        assert(f_out == iobuf.out_fd);
                return False;
        }

        alloc_xbuf(&iobuf.out, ROUND_UP_1024(IO_BUFFER_SIZE * 2));
        iobuf.out_fd = f_out;

        return True;
}

BOOL io_start_buffering_in(int f_in)
{
        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;
        }

        alloc_xbuf(&iobuf.in, ROUND_UP_1024(IO_BUFFER_SIZE));
        iobuf.in_fd = f_in;

        return True;
}

void io_end_buffering_in(BOOL free_buffers)
{
        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(BOOL free_buffers)
{
        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);

        if (free_buffers) {
                free_xbuf(&iobuf.out);
                free_xbuf(&iobuf.msg);
        }

        iobuf.out_fd = -1;
}

void maybe_flush_socket(int important)
{
        if (flist_eof && iobuf.out.buf && iobuf.out.len > iobuf.out_empty_len
         && (important || time(NULL) - last_io_out >= 5))
                io_flush(NORMAL_FLUSH);
}

/* Older rsync versions used to send either a MSG_NOOP (protocol 30) or a
 * raw-data-based keep-alive (protocol 29), both of which implied forwarding of
 * the message through the sender.  Since the new timeout method does not need
 * any forwarding, we just send an empty MSG_DATA message, which works with all
 * rsync versions.  This avoids any message forwarding, and leaves the raw-data
 * stream alone (since we can never be quite sure if that stream is in the
 * right state for a keep-alive message). */
void maybe_send_keepalive(time_t now, BOOL allow_flush)
{
        if (now - last_io_out >= allowed_lull) {
                if (!iobuf.msg.len && iobuf.out.len == iobuf.out_empty_len)
                        send_msg(MSG_DATA, "", 0, 0);
                if (!allow_flush) {
                        /* Let the caller worry about writing out the data. */
                } else 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 ndx)
{
        write_int(iobuf.out_fd, ndx);
        forward_flist_data = 1;
}

void stop_flist_forward(void)
{
        forward_flist_data = 0;
}

/* Read a message from a multiplexed source. */
static void read_a_msg(void)
{
        char data[BIGPATHBUFLEN];
        int tag, val;
        size_t msg_bytes;

        /* This ensures that perform_io() does not try to do any message reading
         * until we've read all of the data for this message.  We should also
         * try to avoid calling things that will cause data to be written via
         * perform_io() prior to this being reset to 1. */
        iobuf.in_multiplexed = -1;

        tag = raw_read_int();

        msg_bytes = tag & 0xFFFFFF;
        tag = (tag >> 24) - MPLEX_BASE;

        if (DEBUG_GTE(IO, 1) && msgs2stderr)
                rprintf(FINFO, "[%s] got msg=%d, len=%ld\n", who_am_i(), (int)tag, (long)msg_bytes);

        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 wrap around and eventually become real. */
                if (msg_bytes)
                        iobuf.raw_input_ends_before = iobuf.in.pos + msg_bytes;
                iobuf.in_multiplexed = 1;
                break;
        case MSG_STATS:
                if (msg_bytes != sizeof stats.total_read || !am_generator)
                        goto invalid_msg;
                raw_read_buf((char*)&stats.total_read, sizeof stats.total_read);
                iobuf.in_multiplexed = 1;
                break;
        case MSG_REDO:
                if (msg_bytes != 4 || !am_generator)
                        goto invalid_msg;
                val = raw_read_int();
                iobuf.in_multiplexed = 1;
                got_flist_entry_status(FES_REDO, val);
                break;
        case MSG_IO_ERROR:
                if (msg_bytes != 4)
                        goto invalid_msg;
                val = raw_read_int();
                iobuf.in_multiplexed = 1;
                io_error |= val;
                if (am_receiver)
                        send_msg_int(MSG_IO_ERROR, val);
                break;
        case MSG_IO_TIMEOUT:
                if (msg_bytes != 4 || am_server || am_generator)
                        goto invalid_msg;
                val = raw_read_int();
                iobuf.in_multiplexed = 1;
                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:
                /* Support protocol-30 keep-alive method. */
                if (msg_bytes != 0)
                        goto invalid_msg;
                iobuf.in_multiplexed = 1;
                if (am_sender)
                        maybe_send_keepalive(time(NULL), True);
                break;
        case MSG_DELETED:
                if (msg_bytes >= sizeof data)
                        goto overflow;
                if (am_generator) {
                        raw_read_buf(data, msg_bytes);
                        iobuf.in_multiplexed = 1;
                        send_msg(MSG_DELETED, data, msg_bytes, 1);
                        break;
                }
#ifdef ICONV_OPTION
                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, data);
                        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;
                                raw_read_buf(ibuf + inbuf.len, 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);
                                }
                                flags &= ~ICB_INIT;
                        }
                        if (add_null) {
                                if (outbuf.len == outbuf.size)
                                        goto overflow;
                                outbuf.buf[outbuf.len++] = '\0';
                        }
                        msg_bytes = outbuf.len;
                } else
#endif
                        raw_read_buf(data, msg_bytes);
                iobuf.in_multiplexed = 1;
                /* A directory name was sent with the trailing null */
                if (msg_bytes > 0 && !data[msg_bytes-1])
                        log_delete(data, S_IFDIR);
                else {
                        data[msg_bytes] = '\0';
                        log_delete(data, 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);
                }
                val = raw_read_int();
                iobuf.in_multiplexed = 1;
                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;
                val = raw_read_int();
                iobuf.in_multiplexed = 1;
                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 data) {
                    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);
                }
                raw_read_buf(data, msg_bytes);
                iobuf.in_multiplexed = 1;
                rwrite((enum logcode)tag, data, msg_bytes, !am_generator);
                if (first_message) {
                        if (list_only && !am_sender && tag == 1 && msg_bytes < sizeof data) {
                                data[msg_bytes] = '\0';
                                check_for_d_option_error(data);
                        }
                        first_message = 0;
                }
                break;
        case MSG_ERROR_EXIT:
                if (msg_bytes == 4)
                        val = raw_read_int();
                else if (msg_bytes == 0)
                        val = 0;
                else
                        goto invalid_msg;
                iobuf.in_multiplexed = 1;
                if (DEBUG_GTE(EXIT, 3))
                        rprintf(FINFO, "[%s] got MSG_ERROR_EXIT with %ld bytes\n", who_am_i(), (long)msg_bytes);
                if (msg_bytes == 0) {
                        if (!am_sender && !am_generator) {
                                if (DEBUG_GTE(EXIT, 3)) {
                                        rprintf(FINFO, "[%s] sending MSG_ERROR_EXIT (len 0)\n",
                                                who_am_i());
                                }
                                send_msg(MSG_ERROR_EXIT, "", 0, 0);
                                io_flush(FULL_FLUSH);
                        }
                } else if (protocol_version >= 31) {
                        if (am_generator) {
                                if (DEBUG_GTE(EXIT, 3)) {
                                        rprintf(FINFO, "[%s] sending MSG_ERROR_EXIT with exit_code %d\n",
                                                who_am_i(), val);
                                }
                                send_msg_int(MSG_ERROR_EXIT, val);
                        } else {
                                if (DEBUG_GTE(EXIT, 3)) {
                                        rprintf(FINFO, "[%s] sending MSG_ERROR_EXIT (len 0)\n",
                                                who_am_i());
                                }
                                send_msg(MSG_ERROR_EXIT, "", 0, 0);
                        }
                }
                /* 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);
        }

        assert(iobuf.in_multiplexed > 0);
}

static void drain_multiplex_messages(void)
{
        while (IN_MULTIPLEXED_AND_READY && 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.len -= raw_len;
                        if ((iobuf.in.pos += raw_len) >= iobuf.in.size)
                                iobuf.in.pos -= iobuf.in.size;
                }
                read_a_msg();
        }
}

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;
                        flist_receiving_enabled = False;
                        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
                        flist_receiving_enabled = True;
                }
        }
}

unsigned short read_shortint(int f)
{
        char b[2];
        read_buf(f, b, 2);
        return (UVAL(b, 1) << 8) + UVAL(b, 0);
}

int32 read_int(int f)
{
        char b[4];
        int32 num;

        read_buf(f, b, 4);
        num = IVAL(b, 0);
#if SIZEOF_INT32 > 4
        if (num & (int32)0x80000000)
                num |= ~(int32)0xffffffff;
#endif
        return num;
}

int32 read_varint(int f)
{
        union {
                char b[5];
                int32 x;
        } u;
        uchar ch;
        int extra;

        u.x = 0;
        ch = read_byte(f);
        extra = int_byte_extra[ch / 4];
        if (extra) {
                uchar bit = ((uchar)1<<(8-extra));
                if (extra >= (int)sizeof u.b) {
                        rprintf(FERROR, "Overflow in read_varint()\n");
                        exit_cleanup(RERR_STREAMIO);
                }
                read_buf(f, u.b, extra);
                u.b[extra] = ch & (bit-1);
        } else
                u.b[0] = ch;
#if CAREFUL_ALIGNMENT
        u.x = IVAL(u.b,0);
#endif
#if SIZEOF_INT32 > 4
        if (u.x & (int32)0x80000000)
                u.x |= ~(int32)0xffffffff;
#endif
        return u.x;
}

int64 read_varlong(int f, uchar min_bytes)
{
        union {
                char b[9];
                int64 x;
        } u;
        char b2[8];
        int extra;

#if SIZEOF_INT64 < 8
        memset(u.b, 0, 8);
#else
        u.x = 0;
#endif
        read_buf(f, b2, min_bytes);
        memcpy(u.b, b2+1, min_bytes-1);
        extra = int_byte_extra[CVAL(b2, 0) / 4];
        if (extra) {
                uchar bit = ((uchar)1<<(8-extra));
                if (min_bytes + extra > (int)sizeof u.b) {
                        rprintf(FERROR, "Overflow in read_varlong()\n");
                        exit_cleanup(RERR_STREAMIO);
                }
                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) {
                        rprintf(FERROR, "Integer overflow: attempted 64-bit offset\n");
                        exit_cleanup(RERR_UNSUPPORTED);
                }
#endif
        } else
                u.b[min_bytes + extra - 1] = CVAL(b2, 0);
#if SIZEOF_INT64 < 8
        u.x = IVAL(u.b,0);
#elif CAREFUL_ALIGNMENT
        u.x = IVAL(u.b,0) | (((int64)IVAL(u.b,4))<<32);
#endif
        return u.x;
}

int64 read_longint(int f)
{
#if SIZEOF_INT64 >= 8
        char b[9];
#endif
        int32 num = read_int(f);

        if (num != (int32)0xffffffff)
                return num;

#if SIZEOF_INT64 < 8
        rprintf(FERROR, "Integer overflow: attempted 64-bit offset\n");
        exit_cleanup(RERR_UNSUPPORTED);
#else
        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)
{
        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) {
                raw_read_buf(buf, 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) {
                size_t siz;

                while (!iobuf.raw_input_ends_before)
                        read_a_msg();

                siz = MIN(len, iobuf.raw_input_ends_before - iobuf.in.pos);
                if (siz >= iobuf.in.size)
                        siz = iobuf.in.size;
                raw_read_buf(buf, 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)
{
        read_buf(f, buf, len);
        buf[len] = '\0';
}

uchar read_byte(int f)
{
        uchar c;
        read_buf(f, (char*)&c, 1);
        return c;
}

int read_vstring(int f, char *buf, int bufsize)
{
        int len = read_byte(f);

        if (len & 0x80)
                len = (len & ~0x80) * 0x100 + read_byte(f);

        if (len >= bufsize) {
                rprintf(FERROR, "over-long vstring received (%d > %d)\n",
                        len, bufsize - 1);
                return -1;
        }

        if (len)
                read_buf(f, buf, len);
        buf[len] = '\0';
        return len;
}

/* Populate a sum_struct with values from the socket.  This is
 * called by both the sender and the receiver. */
void read_sum_head(int f, struct sum_struct *sum)
{
        int32 max_blength = protocol_version < 30 ? OLD_MAX_BLOCK_SIZE : MAX_BLOCK_SIZE;
        sum->count = read_int(f);
        if (sum->count < 0) {
                rprintf(FERROR, "Invalid checksum count %ld [%s]\n",
                        (long)sum->count, who_am_i());
                exit_cleanup(RERR_PROTOCOL);
        }
        sum->blength = read_int(f);
        if (sum->blength < 0 || sum->blength > max_blength) {
                rprintf(FERROR, "Invalid block length %ld [%s]\n",
                        (long)sum->blength, who_am_i());
                exit_cleanup(RERR_PROTOCOL);
        }
        sum->s2length = protocol_version < 27 ? csum_length : (int)read_int(f);
        if (sum->s2length < 0 || sum->s2length > MAX_DIGEST_LEN) {
                rprintf(FERROR, "Invalid checksum length %d [%s]\n",
                        sum->s2length, who_am_i());
                exit_cleanup(RERR_PROTOCOL);
        }
        sum->remainder = read_int(f);
        if (sum->remainder < 0 || sum->remainder > sum->blength) {
                rprintf(FERROR, "Invalid remainder length %ld [%s]\n",
                        (long)sum->remainder, who_am_i());
                exit_cleanup(RERR_PROTOCOL);
        }
}

/* Send the values from a sum_struct over the socket.  Set sum to
 * NULL if there are no checksums to send.  This is called by both
 * the generator and the sender. */
void write_sum_head(int f, struct sum_struct *sum)
{
        static struct sum_struct null_sum;

        if (sum == NULL)
                sum = &null_sum;

        write_int(f, sum->count);
        write_int(f, sum->blength);
        if (protocol_version >= 27)
                write_int(f, sum->s2length);
        write_int(f, sum->remainder);
}

/* 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
 * use a bit less bandwidth than specified, because it doesn't make up
 * for slow periods.  But arguably this is a feature.  In addition, we
 * ought to take the time used to write the data into account.
 *
 * During some phases of big transfers (file FOO is uptodate) this is
 * called with a small bytes_written every time.  As the kernel has to
 * 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. */
static void sleep_for_bwlimit(int bytes_written)
{
        static struct timeval prior_tv;
        static long total_written = 0;
        struct timeval tv, start_tv;
        long elapsed_usec, sleep_usec;

#define ONE_SEC 1000000L /* # of microseconds in a second */

        total_written += bytes_written;

        gettimeofday(&start_tv, NULL);
        if (prior_tv.tv_sec) {
                elapsed_usec = (start_tv.tv_sec - prior_tv.tv_sec) * ONE_SEC
                             + (start_tv.tv_usec - prior_tv.tv_usec);
                total_written -= elapsed_usec * bwlimit / (ONE_SEC/1024);
                if (total_written < 0)
                        total_written = 0;
        }

        sleep_usec = total_written * (ONE_SEC/1024) / bwlimit;
        if (sleep_usec < ONE_SEC / 10) {
                prior_tv = start_tv;
                return;
        }

        tv.tv_sec  = sleep_usec / ONE_SEC;
        tv.tv_usec = sleep_usec % ONE_SEC;
        select(0, NULL, NULL, NULL, &tv);

        gettimeofday(&prior_tv, NULL);
        elapsed_usec = (prior_tv.tv_sec - start_tv.tv_sec) * ONE_SEC
                     + (prior_tv.tv_usec - start_tv.tv_usec);
        total_written = (sleep_usec - elapsed_usec) * bwlimit / (ONE_SEC/1024);
}

void io_flush(int flush_it_all)
{
        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)
{
        char b[2];
        b[0] = (char)x;
        b[1] = (char)(x >> 8);
        write_buf(f, b, 2);
}

void write_int(int f, int32 x)
{
        char b[4];
        SIVAL(b, 0, x);
        write_buf(f, b, 4);
}

void write_varint(int f, int32 x)
{
        char b[5];
        uchar bit;
        int cnt = 4;

        SIVAL(b, 1, x);

        while (cnt > 1 && b[cnt] == 0)
                cnt--;
        bit = ((uchar)1<<(7-cnt+1));
        if (CVAL(b, cnt) >= bit) {
                cnt++;
                *b = ~(bit-1);
        } else if (cnt > 1)
                *b = b[cnt] | ~(bit*2-1);
        else
                *b = b[cnt];

        write_buf(f, b, cnt);
}

void write_varlong(int f, int64 x, uchar min_bytes)
{
        char b[9];
        uchar bit;
        int cnt = 8;

        SIVAL(b, 1, x);
#if SIZEOF_INT64 >= 8
        SIVAL(b, 5, x >> 32);
#else
        if (x <= 0x7FFFFFFF && x >= 0)
                memset(b + 5, 0, 4);
        else {
                rprintf(FERROR, "Integer overflow: attempted 64-bit offset\n");
                exit_cleanup(RERR_UNSUPPORTED);
        }
#endif

        while (cnt > min_bytes && b[cnt] == 0)
                cnt--;
        bit = ((uchar)1<<(7-cnt+min_bytes));
        if (CVAL(b, cnt) >= bit) {
                cnt++;
                *b = ~(bit-1);
        } else if (cnt > min_bytes)
                *b = b[cnt] | ~(bit*2-1);
        else
                *b = b[cnt];

        write_buf(f, b, cnt);
}

/*
 * Note: int64 may actually be a 32-bit type if ./configure couldn't find any
 * 64-bit types on this platform.
 */
void write_longint(int f, int64 x)
{
        char b[12], * const s = b+4;

        SIVAL(s, 0, x);
        if (x <= 0x7FFFFFFF && x >= 0) {
                write_buf(f, s, 4);
                return;
        }

#if SIZEOF_INT64 < 8
        rprintf(FERROR, "Integer overflow: attempted 64-bit offset\n");
        exit_cleanup(RERR_UNSUPPORTED);
#else
        memset(b, 0xFF, 4);
        SIVAL(s, 4, x >> 32);
        write_buf(f, b, 12);
#endif
}

void write_buf(int f, const char *buf, size_t 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 */
void write_sbuf(int f, const char *buf)
{
        write_buf(f, buf, strlen(buf));
}

void write_byte(int f, uchar c)
{
        write_buf(f, (char *)&c, 1);
}

void write_vstring(int f, const char *str, int len)
{
        uchar lenbuf[3], *lb = lenbuf;

        if (len > 0x7F) {
                if (len > 0x7FFF) {
                        rprintf(FERROR,
                                "attempting to send over-long vstring (%d > %d)\n",
                                len, 0x7FFF);
                        exit_cleanup(RERR_PROTOCOL);
                }
                *lb++ = len / 0x100 + 0x80;
        }
        *lb = len;

        write_buf(f, (char*)lenbuf, lb - lenbuf + 1);
        if (len)
                write_buf(f, str, len);
}

/* Send a file-list index using a byte-reduction method. */
void write_ndx(int f, int32 ndx)
{
        static int32 prev_positive = -1, prev_negative = 1;
        int32 diff, cnt = 0;
        char b[6];

        if (protocol_version < 30 || read_batch) {
                write_int(f, ndx);
                return;
        }

        /* Send NDX_DONE as a single-byte 0 with no side effects.  Send
         * negative nums as a positive after sending a leading 0xFF. */
        if (ndx >= 0) {
                diff = ndx - prev_positive;
                prev_positive = ndx;
        } else if (ndx == NDX_DONE) {
                *b = 0;
                write_buf(f, b, 1);
                return;
        } else {
                b[cnt++] = (char)0xFF;
                ndx = -ndx;
                diff = ndx - prev_negative;
                prev_negative = ndx;
        }

        /* A diff of 1 - 253 is sent as a one-byte diff; a diff of 254 - 32767
         * or 0 is sent as a 0xFE + a two-byte diff; otherwise we send 0xFE
         * & all 4 bytes of the (non-negative) num with the high-bit set. */
        if (diff < 0xFE && diff > 0)
                b[cnt++] = (char)diff;
        else if (diff < 0 || diff > 0x7FFF) {
                b[cnt++] = (char)0xFE;
                b[cnt++] = (char)((ndx >> 24) | 0x80);
                b[cnt++] = (char)ndx;
                b[cnt++] = (char)(ndx >> 8);
                b[cnt++] = (char)(ndx >> 16);
        } else {
                b[cnt++] = (char)0xFE;
                b[cnt++] = (char)(diff >> 8);
                b[cnt++] = (char)diff;
        }
        write_buf(f, b, cnt);
}

/* Receive a file-list index using a byte-reduction method. */
int32 read_ndx(int f)
{
        static int32 prev_positive = -1, prev_negative = 1;
        int32 *prev_ptr, num;
        char b[4];

        if (protocol_version < 30)
                return read_int(f);

        read_buf(f, b, 1);
        if (CVAL(b, 0) == 0xFF) {
                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) {
                read_buf(f, b, 2);
                if (CVAL(b, 0) & 0x80) {
                        b[3] = CVAL(b, 0) & ~0x80;
                        b[0] = b[1];
                        read_buf(f, b+1, 2);
                        num = IVAL(b, 0);
                } else
                        num = (UVAL(b,0)<<8) + UVAL(b,1) + *prev_ptr;
        } else
                num = UVAL(b, 0) + *prev_ptr;
        *prev_ptr = num;
        if (prev_ptr == &prev_negative)
                num = -num;
        return num;
}

/* 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 fd, char *buf, size_t bufsiz)
{
        bufsiz--; /* leave room for the null */
        while (bufsiz > 0) {
                assert(fd != iobuf.in_fd);
                if (safe_read(fd, buf, 1) == 0)
                        return 0;
                if (*buf == '\0')
                        return 0;
                if (*buf == '\n')
                        break;
                if (*buf != '\r') {
                        buf++;
                        bufsiz--;
                }
        }
        *buf = '\0';
        return bufsiz > 0;
}

void io_printf(int fd, const char *format, ...)
{
        va_list ap;
        char buf[BIGPATHBUFLEN];
        int len;

        va_start(ap, format);
        len = vsnprintf(buf, sizeof buf, format, ap);
        va_end(ap);

        if (len < 0)
                exit_cleanup(RERR_PROTOCOL);

        if (len > (int)sizeof buf) {
                rprintf(FERROR, "io_printf() was too long for the buffer.\n");
                exit_cleanup(RERR_PROTOCOL);
        }

        write_sbuf(fd, buf);
}

/* Setup for multiplexing a MSG_* stream with the data stream. */
void io_start_multiplex_out(int fd)
{
        io_flush(FULL_FLUSH);

        if (msgs2stderr && DEBUG_GTE(IO, 2))
                rprintf(FINFO, "[%s] io_start_multiplex_out(%d)\n", who_am_i(), fd);

        if (!iobuf.msg.buf)
                alloc_xbuf(&iobuf.msg, ROUND_UP_1024(IO_BUFFER_SIZE));

        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;
}

/* Setup for multiplexing a MSG_* stream with the data stream. */
void io_start_multiplex_in(int fd)
{
        if (msgs2stderr && DEBUG_GTE(IO, 2))
                rprintf(FINFO, "[%s] io_start_multiplex_in(%d)\n", who_am_i(), fd);

        iobuf.in_multiplexed = 1; /* See also IN_MULTIPLEXED */
        io_start_buffering_in(fd);
}

int io_end_multiplex_in(int mode)
{
        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 = 0;
        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;
}

int io_end_multiplex_out(int mode)
{
        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)
{
        /* Some communication has already taken place, but we don't
         * enable batch writing until here so that we can write a
         * canonical record of the communication even though the
         * actual communication so far depends on whether a daemon
         * is involved. */
        write_int(batch_fd, protocol_version);
        if (protocol_version >= 30)
                write_byte(batch_fd, inc_recurse);
        write_int(batch_fd, checksum_seed);

        if (am_sender)
                write_batch_monitor_out = fd;
        else
                write_batch_monitor_in = fd;
}

void stop_write_batch(void)
{
        write_batch_monitor_out = -1;
        write_batch_monitor_in = -1;
}