[PATCH v2] guess default branch from HEAD

[Julius Plenz]

This is a saner alternative than hardcoding the default branch to be
"master". The add_repo() function will now check for a symbolic ref in
repo_path/HEAD. If there is a suitable one, overwrite repo->defbranch
with it. Note that you'll need to strip the newline from the file (->
len-17).

If HEAD is a symbolic link pointing directly to a branch below
refs/heads/, do a readlink() instead to find the ref name.

Signed-off-by: Julius Plenz <plenz at cis.fu-berlin.de>
---
 cgitrc.5.txt |    3 ++-
 scan-tree.c  |   21 +++++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletions(-)

diff --git a/cgitrc.5.txt b/cgitrc.5.txt
index c3698a6..f0ef6a7 100644
--- a/cgitrc.5.txt
+++ b/cgitrc.5.txt
@@ -362,7 +362,8 @@ repo.commit-filter::
 repo.defbranch::
 	The name of the default branch for this repository. If no such branch
 	exists in the repository, the first branch name (when sorted) is used
-	as default instead. Default value: "master".
+	as default instead. Default value: branch pointed to by HEAD, or
+	"master" if there is no suitable HEAD.
 
 repo.desc::
 	The value to show as repository description. Default value: none.
diff --git a/scan-tree.c b/scan-tree.c
index 627af1b..bec747f 100644
--- a/scan-tree.c
+++ b/scan-tree.c
@@ -75,6 +75,8 @@ static void add_repo(const char *base, const char *path, repo_config_fn fn)
 	char *rel, *p, *slash;
 	int n;
 	size_t size;
+	char buffer[256];
+	int fd;
 
 	if (stat(path, &st)) {
 		fprintf(stderr, "Error accessing %s: %s (%d)\n",
@@ -105,6 +107,25 @@ static void add_repo(const char *base, const char *path, repo_config_fn fn)
 			*p = '\0';
 	repo->name = repo->url;
 	repo->path = xstrdup(path);
+
+	fd = open(fmt("%s/HEAD", repo->path), O_RDONLY);
+	if (fd != -1) {
+		int len;
+		memset(buffer, 0, sizeof(buffer)-1);
+		len = read_in_full(fd, buffer, sizeof(buffer)-1);
+		if(!memcmp(buffer, "ref: refs/heads/", 16)) {
+			repo->defbranch = xstrndup(buffer+16, len-17);
+		} else if(strlen(buffer) == 41) { /* probably contains a SHA1 sum */
+			memset(buffer, 0, sizeof(buffer)-1);
+			readlink(fmt("%s/HEAD", repo->path), buffer, sizeof(buffer)-1);
+			char *ref_start;
+			ref_start = memmem(buffer, sizeof(buffer)-1, "refs/heads/", 11);
+			if(ref_start)
+				repo->defbranch = xstrdup(ref_start+11);
+		}
+		close(fd);
+	}
+
 	while (!owner) {
 		if ((pwd = getpwuid(st.st_uid)) == NULL) {
 			fprintf(stderr, "Error reading owner-info for %s: %s (%d)\n",
-- 
1.7.3.1