+This adds a --usermap and a --groupmap option.
+
+TODO: make this work when --numeric-ids was specified.
+
+--- old/flist.c
++++ new/flist.c
+@@ -61,6 +61,8 @@ extern int copy_links;
+ extern int copy_unsafe_links;
+ extern int protocol_version;
+ extern int sanitize_paths;
++extern char *usermap;
++extern char *groupmap;
+ extern struct stats stats;
+
+ extern char curr_dir[MAXPATHLEN];
+@@ -1882,8 +1884,13 @@ struct file_list *recv_file_list(int f)
+ int dstart, flags;
+ int64 start_read;
+
+- if (!first_flist)
++ if (!first_flist) {
+ rprintf(FLOG, "receiving file list\n");
++ if (usermap)
++ parse_name_map(usermap, 1);
++ if (groupmap)
++ parse_name_map(groupmap, 0);
++ }
+ if (show_filelist_p())
+ start_filelist_progress("receiving file list");
+ else if (inc_recurse && verbose && !am_server && !first_flist)
+--- old/options.c
++++ new/options.c
+@@ -156,6 +156,8 @@ char *rsync_path = RSYNC_PATH;
+ char *backup_dir = NULL;
+ char backup_dir_buf[MAXPATHLEN];
+ char *sockopts = NULL;
++char *usermap = NULL;
++char *groupmap = NULL;
+ int rsync_port = 0;
+ int compare_dest = 0;
+ int copy_dest = 0;
+@@ -367,6 +369,8 @@ void usage(enum logcode F)
+ rprintf(F," --delay-updates put all updated files into place at transfer's end\n");
+ rprintf(F," -m, --prune-empty-dirs prune empty directory chains from the file-list\n");
+ rprintf(F," --numeric-ids don't map uid/gid values by user/group name\n");
++ rprintf(F," --usermap=STRING custom username mapping\n");
++ rprintf(F," --groupmap=STRING custom groupname mapping\n");
+ rprintf(F," --timeout=TIME set I/O timeout in seconds\n");
+ rprintf(F," -I, --ignore-times don't skip files that match in size and mod-time\n");
+ rprintf(F," --size-only skip files that match in size\n");
+@@ -568,6 +572,8 @@ static struct poptOption long_options[]
+ {"files-from", 0, POPT_ARG_STRING, &files_from, 0, 0, 0 },
+ {"from0", '0', POPT_ARG_NONE, &eol_nulls, 0, 0, 0},
+ {"numeric-ids", 0, POPT_ARG_NONE, &numeric_ids, 0, 0, 0 },
++ {"usermap", 0, POPT_ARG_STRING, &usermap, 0, 0, 0 },
++ {"groupmap", 0, POPT_ARG_STRING, &groupmap, 0, 0, 0 },
+ {"timeout", 0, POPT_ARG_INT, &io_timeout, 0, 0, 0 },
+ {"rsh", 'e', POPT_ARG_STRING, &shell_cmd, 0, 0, 0 },
+ {"rsync-path", 0, POPT_ARG_STRING, &rsync_path, 0, 0, 0 },
+@@ -1857,6 +1863,22 @@ void server_options(char **args,int *arg
+ args[ac++] = "--numeric-ids";
+
+ if (am_sender) {
++ if (usermap) {
++ if (strchr(usermap, '\'') != NULL)
++ usermap = "INVALID";
++ if (asprintf(&arg, "--usermap='%s'", usermap) < 0)
++ goto oom;
++ args[ac++] = arg;
++ }
++
++ if (groupmap) {
++ if (strchr(groupmap, '\'') != NULL)
++ groupmap = "INVALID";
++ if (asprintf(&arg, "--groupmap='%s'", groupmap) < 0)
++ goto oom;
++ args[ac++] = arg;
++ }
++
+ if (ignore_existing)
+ args[ac++] = "--ignore-existing";
+
+--- old/rsync.yo
++++ new/rsync.yo
+@@ -361,6 +361,8 @@ to the detailed description below for a
+ --delay-updates put all updated files into place at end
+ -m, --prune-empty-dirs prune empty directory chains from file-list
+ --numeric-ids don't map uid/gid values by user/group name
++ --usermap=STRING custom username mapping
++ --groupmap=STRING custom groupname mapping
+ --timeout=TIME set I/O timeout in seconds
+ -I, --ignore-times don't skip files that match size and time
+ --size-only skip files that match in size
+@@ -1445,6 +1447,25 @@ from the source system is used instead.
+ the chroot setting affects rsync's ability to look up the names of the
+ users and groups and what you can do about it.
+
++dit(bf(--usermap=STRING, --groupmap=STRING)) These options allow you to
++specify user/group names and IDs that should be mapped to other values by
++the receiving side. The bf(STRING) is one or more FROM:TO pairs of values
++separated by commas. Any matching FROM value from the sender is replaced
++with a TO value from the receiver. You may specify usernames or user IDs
++for the FROM and TO values, and the FROM value may also be a wild-card
++string, which will be matched against the sender's names (it will not match
++IDs). For example:
++
++ --usermap=0:foo,bar:baz,*:nobody --groupmap=root:1,1:root
++
++The first match in the list is the one that is used.
++
++For the bf(--usermap) option to be effective you will need to have specified
++the bf(-o) (bf(--owner)) option and the receiver will need to be running as
++root (see also the bf(--fake-root) option). For the bf(--groupmap) option
++to be effective you will need to have specified the bf(-g) (bf(--groups))
++option, and the receiver will need to have permissions to set that group.
++
+ dit(bf(--timeout=TIMEOUT)) This option allows you to set a maximum I/O
+ timeout in seconds. If no data is transferred for the specified time
+ then rsync will exit. The default is 0, which means no timeout.
+--- old/uidlist.c
++++ new/uidlist.c
+@@ -38,6 +38,7 @@ extern int preserve_uid;
+ extern int preserve_gid;
+ extern int preserve_acls;
+ extern int numeric_ids;
++extern int protocol_version;
+
+ struct idlist {
+ struct idlist *next;
+@@ -45,8 +46,8 @@ struct idlist {
+ char *name;
+ };
+
+-static struct idlist *uidlist;
+-static struct idlist *gidlist;
++static struct idlist *uidlist, *uidmap;
++static struct idlist *gidlist, *gidmap;
+
+ static struct idlist *add_to_list(struct idlist **root, int id, char *name,
+ int id2)
+@@ -158,8 +159,33 @@ static int is_in_group(gid_t gid)
+ /* Add a uid to the list of uids. Only called on receiving side. */
+ static uid_t recv_add_uid(uid_t id, char *name)
+ {
+- uid_t id2 = name ? map_uid(id, name) : id;
+ struct idlist *node;
++ uid_t id2;
++
++ if (name) {
++ struct idlist *list;
++ for (list = uidmap; list; list = list->next) {
++ switch (list->id) {
++ case -2:
++ if (!wildmatch(list->name, name))
++ continue;
++ break;
++ case -1:
++ if (strcmp(list->name, name) != 0)
++ continue;
++ break;
++ default:
++ if (list->id != (int)id)
++ continue;
++ break;
++ }
++ id2 = list->id2;
++ break;
++ }
++ if (!list)
++ id2 = id ? map_uid(id, name) : 0; /* don't map root */
++ } else
++ id2 = id;
+
+ node = add_to_list(&uidlist, (int)id, name, (int)id2);
+
+@@ -174,8 +200,33 @@ static uid_t recv_add_uid(uid_t id, char
+ /* Add a gid to the list of gids. Only called on receiving side. */
+ static gid_t recv_add_gid(gid_t id, char *name)
+ {
+- gid_t id2 = name ? map_gid(id, name) : id;
+ struct idlist *node;
++ gid_t id2;
++
++ if (name) {
++ struct idlist *list;
++ for (list = gidmap; list; list = list->next) {
++ switch (list->id) {
++ case -2:
++ if (!wildmatch(list->name, name))
++ continue;
++ break;
++ case -1:
++ if (strcmp(list->name, name) != 0)
++ continue;
++ break;
++ default:
++ if (list->id != (int)id)
++ continue;
++ break;
++ }
++ id2 = list->id2;
++ break;
++ }
++ if (!list)
++ id2 = id ? map_gid(id, name) : 0; /* don't map root */
++ } else
++ id2 = id;
+
+ if (!am_root && !is_in_group(id2))
+ id2 = GID_NONE;
+@@ -195,9 +246,6 @@ uid_t match_uid(uid_t uid)
+ static uid_t last_in, last_out;
+ struct idlist *list;
+
+- if (uid == 0)
+- return 0;
+-
+ if (uid == last_in)
+ return last_out;
+
+@@ -238,7 +286,7 @@ char *add_uid(uid_t uid)
+ struct idlist *list;
+ struct idlist *node;
+
+- if (uid == 0) /* don't map root */
++ if (uid == 0 && protocol_version < 30)
+ return NULL;
+
+ for (list = uidlist; list; list = list->next) {
+@@ -256,7 +304,7 @@ char *add_gid(gid_t gid)
+ struct idlist *list;
+ struct idlist *node;
+
+- if (gid == 0) /* don't map root */
++ if (gid == 0 && protocol_version < 30)
+ return NULL;
+
+ for (list = gidlist; list; list = list->next) {
+@@ -356,3 +404,70 @@ void recv_uid_list(int f, struct file_li
+ F_GROUP(flist->files[i]) = match_gid(F_GID(flist->files[i]));
+ }
+ }
++
++void parse_name_map(char *map, int usernames)
++{
++ char *colon, *end, *cp = map + strlen(map);
++ int id1, id2;
++
++ while (1) {
++ end = cp;
++ while (cp > map && cp[-1] != ',') cp--;
++ if (!(colon = strchr(cp, ':'))) {
++ rprintf(FERROR, "No colon found in --%smap: %s\n",
++ usernames ? "user" : "group", cp);
++ exit_cleanup(RERR_SYNTAX);
++ }
++ *colon = '\0';
++
++ if (isDigit(cp)) {
++ if (strspn(cp, "0123456789") != (size_t)(colon - cp)) {
++ bad_number:
++ rprintf(FERROR, "Invalid number in --%smap: %s\n",
++ usernames ? "user" : "group", cp);
++ exit_cleanup(RERR_SYNTAX);
++ }
++ id1 = atoi(cp);
++ } else if (strpbrk(cp, "*[?"))
++ id1 = -2;
++ else
++ id1 = -1;
++
++ if (isDigit(colon+1)) {
++ if (strspn(colon+1, "0123456789") != (size_t)(end - colon - 1)) {
++ cp = colon+1;
++ goto bad_number;
++ }
++ id2 = atoi(colon+1);
++ } else {
++ if (usernames) {
++ uid_t uid;
++ if (name_to_uid(colon+1, &uid))
++ id2 = (int)uid;
++ else
++ id2 = -1;
++ } else {
++ gid_t gid;
++ if (name_to_gid(colon+1, &gid))
++ id2 = (int)gid;
++ else
++ id2 = -1;
++ }
++ if (id2 < 0) {
++ rprintf(FERROR, "Invalid name in --%smap: %s\n",
++ usernames ? "user" : "group", colon+1);
++ exit_cleanup(RERR_SYNTAX);
++ }
++ }
++
++ if (usernames)
++ add_to_list(&uidmap, id1, id1 < 0 ? cp : NULL, id2);
++ else
++ add_to_list(&gidmap, id1, id1 < 0 ? cp : NULL, id2);
++
++ if (cp == map)
++ break;
++
++ *--cp = '\0'; /* replace comma */
++ }
++}