Teach update-ref about a symbolic ref stored in a textfile.

A symbolic ref is a regular file whose contents is "ref:", followed by
optional leading whitespaces, followed by a GIT_DIR relative pathname,
followed by optional trailing whitespaces (the optional whitespaces
are unconditionally removed, so you cannot have leading nor trailing
whitespaces).  This can be used in place of a traditional symbolic
link .git/HEAD that usually points at "refs/heads/master".  You can
instead have a regular file .git/HEAD whose contents is
"ref: refs/heads/master".

[jc: currently the code does not enforce the symbolic ref to begin with
 refs/, unlike the symbolic link case.  It may be worthwhile to require
 either case to begin with refs/ and not have any /./ nor /../ in them.]

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

diff --git a/update-ref.c b/update-ref.c
index 1863b82..6919cea 100644 (file)
--- a/update-ref.c
+++ b/update-ref.c
@@ -13,6 +13,7 @@ static const char *resolve_ref(const char *path, unsigned char *sha1)
 
        for (;;) {
                struct stat st;
+               char *buf;
                int fd;
 
                if (--depth < 0)
@@ -44,7 +45,19 @@ static const char *resolve_ref(const char *path, unsigned char *sha1)
                        return NULL;
                len = read(fd, buffer, sizeof(buffer)-1);
                close(fd);
-               break;
+
+               /*
+                * Is it a symbolic ref?
+                */
+               if (len < 4 || memcmp("ref:", buffer, 4))
+                       break;
+               buf = buffer + 4;
+               len -= 4;
+               while (len && isspace(*buf))
+                       buf++, len--;
+               while (len && isspace(buf[len-1]))
+                       buf[--len] = 0;
+               path = git_path("%.*s", len, buf);
        }
        if (len < 40 || get_sha1_hex(buffer, sha1))
                return NULL;