[PATCH] Allow reading "symbolic refs" that point to other refs

This extends the ref reading to understand a "symbolic ref": a ref file
that starts with "ref: " and points to another ref file, and thus
introduces the notion of ref aliases.

This is in preparation of allowing HEAD to eventually not be a symlink,
but one of these symbolic refs instead.

[jc: Linus originally required the prefix to be "ref: " five bytes
 and nothing else, but I changed it to allow and strip any number of
 leading whitespaces to match what update-ref.c does.]

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/cache.h b/cache.h
index b8e3d9b..958c96e 100644 (file)
--- a/cache.h
+++ b/cache.h
@@ -229,6 +229,7 @@ extern int has_pack_index(const unsigned char *sha1);
 extern int get_sha1(const char *str, unsigned char *sha1);
 extern int get_sha1_hex(const char *hex, unsigned char *sha1);
 extern char *sha1_to_hex(const unsigned char *sha1);   /* static buffer result! */
+extern int read_ref(const char *filename, unsigned char *sha1);
 
 /* General helper functions */
 extern void usage(const char *err) NORETURN;

diff --git a/refs.c b/refs.c
index 1610180..d4f3612 100644 (file)
--- a/refs.c
+++ b/refs.c
@@ -2,17 +2,43 @@
 #include "cache.h"
 
 #include <errno.h>
+#include <ctype.h>
 
-static int read_ref(const char *refname, unsigned char *sha1)
+/* We allow "recursive" symbolic refs. Only within reason, though */
+#define MAXDEPTH 5
+
+int read_ref(const char *filename, unsigned char *sha1)
 {
-       int ret = -1;
-       int fd = open(git_path("%s", refname), O_RDONLY);
+       int depth = 0;
+       int ret = -1, fd;
+
+       while ((fd = open(filename, O_RDONLY)) >= 0) {
+               char buffer[256];
+               int len = read(fd, buffer, sizeof(buffer)-1);
 
-       if (fd >= 0) {
-               char buffer[60];
-               if (read(fd, buffer, sizeof(buffer)) >= 40)
-                       ret = get_sha1_hex(buffer, sha1);
                close(fd);
+               if (len < 0)
+                       break;
+
+               buffer[len] = 0;
+               while (len && isspace(buffer[len-1]))
+                       buffer[--len] = 0;
+
+               if (!strncmp(buffer, "ref:", 4)) {
+                       char *buf;
+                       if (depth > MAXDEPTH)
+                               break;
+                       depth++;
+                       buf = buffer + 4;
+                       len -= 4;
+                       while (len && isspace(*buf))
+                               buf++, len--;
+                       filename = git_path("%.*s", len, buf);
+                       continue;
+               }
+               if (len >= 40)
+                       ret = get_sha1_hex(buffer, sha1);
+               break;
        }
        return ret;
 }
@@ -54,7 +80,7 @@ static int do_for_each_ref(const char *base, int (*fn)(const char *path, const u
                                        break;
                                continue;
                        }
-                       if (read_ref(path, sha1) < 0)
+                       if (read_ref(git_path("%s", path), sha1) < 0)
                                continue;
                        if (!has_sha1_file(sha1))
                                continue;
@@ -71,7 +97,7 @@ static int do_for_each_ref(const char *base, int (*fn)(const char *path, const u
 int head_ref(int (*fn)(const char *path, const unsigned char *sha1))
 {
        unsigned char sha1[20];
-       if (!read_ref("HEAD", sha1))
+       if (!read_ref(git_path("HEAD"), sha1))
                return fn("HEAD", sha1);
        return 0;
 }
@@ -101,33 +127,14 @@ static char *ref_lock_file_name(const char *ref)
        return ret;
 }
 
-static int read_ref_file(const char *filename, unsigned char *sha1) {
-       int fd = open(filename, O_RDONLY);
-       char hex[41];
-       if (fd < 0) {
-               return error("Couldn't open %s\n", filename);
-       }
-       if ((read(fd, hex, 41) < 41) ||
-           (hex[40] != '\n') ||
-           get_sha1_hex(hex, sha1)) {
-               error("Couldn't read a hash from %s\n", filename);
-               close(fd);
-               return -1;
-       }
-       close(fd);
-       return 0;
-}
-
 int get_ref_sha1(const char *ref, unsigned char *sha1)
 {
-       char *filename;
-       int retval;
+       const char *filename;
+
        if (check_ref_format(ref))
                return -1;
-       filename = ref_file_name(ref);
-       retval = read_ref_file(filename, sha1);
-       free(filename);
-       return retval;
+       filename = git_path("refs/%s", ref);
+       return read_ref(filename, sha1);
 }
 
 static int lock_ref_file(const char *filename, const char *lock_filename,
@@ -140,7 +147,7 @@ static int lock_ref_file(const char *filename, const char *lock_filename,
                return error("Couldn't open lock file for %s: %s",
                             filename, strerror(errno));
        }
-       retval = read_ref_file(filename, current_sha1);
+       retval = read_ref(filename, current_sha1);
        if (old_sha1) {
                if (retval) {
                        close(fd);

diff --git a/sha1_name.c b/sha1_name.c
index b4fed92..57e6cd3 100644 (file)
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -119,21 +119,6 @@ static int get_short_sha1(const char *name, int len, unsigned char *sha1)
        return -1;
 }
 
-static int get_sha1_file(const char *path, unsigned char *result)
-{
-       char buffer[60];
-       int fd = open(path, O_RDONLY);
-       int len;
-
-       if (fd < 0)
-               return -1;
-       len = read(fd, buffer, sizeof(buffer));
-       close(fd);
-       if (len < 40)
-               return -1;
-       return get_sha1_hex(buffer, result);
-}
-
 static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 {
        static const char *prefix[] = {
@@ -150,7 +135,7 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 
        for (p = prefix; *p; p++) {
                char *pathname = git_path("%s/%.*s", *p, len, str);
-               if (!get_sha1_file(pathname, sha1))
+               if (!read_ref(pathname, sha1))
                        return 0;
        }