daemon: extend user-relative path notation.

Earlier, we made --base-path to automatically forbid
user-relative paths, which was probably a mistake.  This
introduces --user-path (or --user-path=path) option to control
the use of user-relative paths independently.  The latter form
of the option can be used to restrict accesses to a part of each
user's home directory, similar to "public_html" some webservers
supports.

If we're invoked with --user-path=FOO option, then a URL of the
form git://~USER/PATH/... resolves to the path HOME/FOO/PATH/...,
where HOME is USER's home directory.

[jc: This is much reworked by me so bugs are mine, but the
 original patch was done by Mark Wooding.]

Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-daemon.txt

@@ -10,7 +10,8 @@ SYNOPSIS
 [verse]
 'git-daemon' [--verbose] [--syslog] [--inetd | --port=n] [--export-all]
              [--timeout=n] [--init-timeout=n] [--strict-paths]
-             [--base-path=path] [directory...]
+             [--base-path=path] [--user-path | --user-path=path]
+	     [directory...]
 
 DESCRIPTION
 -----------
@@ -42,8 +43,7 @@ OPTIONS
 	This is sort of "GIT root" - if you run git-daemon with
 	'--base-path=/srv/git' on example.com, then if you later try to pull
 	'git://example.com/hello.git', `git-daemon` will interpret the path
-	as '/srv/git/hello.git'. Home directories (the '~login' notation)
-	access is disabled.
+	as '/srv/git/hello.git'.
 
 --export-all::
 	Allow pulling from all directories that look like GIT repositories
@@ -70,6 +70,15 @@ OPTIONS
 	Log to syslog instead of stderr. Note that this option does not imply
 	--verbose, thus by default only error conditions will be logged.
 
+--user-path, --user-path=path::
+	Allow ~user notation to be used in requests.  When
+	specified with no parameter, requests to
+	git://host/~alice/foo is taken as a request to access
+	'foo' repository in the home directory of user `alice`.
+	If `--user-path=path` is specified, the same request is
+	taken as a request to access `path/foo` repository in
+	the home directory of user `alice`.
+
 --verbose::
 	Log details about the incoming connections and requested files.
 

daemon.c

@@ -18,7 +18,8 @@ static int reuseaddr;
 static const char daemon_usage[] =
 "git-daemon [--verbose] [--syslog] [--inetd | --port=n] [--export-all]\n"
 "           [--timeout=n] [--init-timeout=n] [--strict-paths]\n"
-"           [--base-path=path] [--reuseaddr] [directory...]";
+"           [--base-path=path] [--user-path | --user-path=path]\n"
+"           [--reuseaddr] [directory...]";
 
 /* List of acceptable pathname prefixes */
 static char **ok_paths = NULL;
@@ -30,6 +31,12 @@ static int export_all_trees = 0;
 /* Take all paths relative to this one if non-NULL */
 static char *base_path = NULL;
 
+/* If defined, ~user notation is allowed and the string is inserted
+ * after ~user/.  E.g. a request to git://host/~alice/frotz would
+ * go to /home/alice/pub_git/frotz with --user-path=pub_git.
+ */
+static char *user_path = NULL;
+
 /* Timeout, and initial timeout */
 static unsigned int timeout = 0;
 static unsigned int init_timeout = 0;
@@ -137,6 +144,7 @@ static int avoid_alias(char *p)
 
 static char *path_ok(char *dir)
 {
+	static char rpath[PATH_MAX];
 	char *path;
 
 	if (avoid_alias(dir)) {
@@ -144,12 +152,31 @@ static char *path_ok(char *dir)
 		return NULL;
 	}
 
-	if (base_path) {
-		static char rpath[PATH_MAX];
-		if (!strict_paths && *dir == '~')
-			; /* allow user relative paths */
-		else if (*dir != '/') {
-			/* otherwise allow only absolute */
+	if (*dir == '~') {
+		if (!user_path) {
+			logerror("'%s': User-path not allowed", dir);
+			return NULL;
+		}
+		if (*user_path) {
+			/* Got either "~alice" or "~alice/foo";
+			 * rewrite them to "~alice/%s" or
+			 * "~alice/%s/foo".
+			 */
+			int namlen, restlen = strlen(dir);
+			char *slash = strchr(dir, '/');
+			if (!slash)
+				slash = dir + restlen;
+			namlen = slash - dir;
+			restlen -= namlen;
+			loginfo("userpath <%s>, request <%s>, namlen %d, restlen %d, slash <%s>", user_path, dir, namlen, restlen, slash);
+			snprintf(rpath, PATH_MAX, "%.*s/%s%.*s",
+				 namlen, dir, user_path, restlen, slash);
+			dir = rpath;
+		}
+	}
+	else if (base_path) {
+		if (*dir != '/') {
+			/* Allow only absolute */
 			logerror("'%s': Non-absolute path denied (base-path active)", dir);
 			return NULL;
 		}
@@ -688,6 +715,14 @@ int main(int argc, char **argv)
 			reuseaddr = 1;
 			continue;
 		}
+		if (!strcmp(arg, "--user-path")) {
+			user_path = "";
+			continue;
+		}
+		if (!strncmp(arg, "--user-path=", 12)) {
+			user_path = arg + 12;
+			continue;
+		}
 		if (!strcmp(arg, "--")) {
 			ok_paths = &argv[i+1];
 			break;