guess default branch from HEAD

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@cis.fu-berlin.de>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>

2 files changed, 38 insertions, 1 deletions

diff --git a/cgitrc.5.txt b/cgitrc.5.txt
index 4721c1e..c2c5680 100644
--- a/cgitrc.5.txt
+++ b/cgitrc.5.txt
@@ -377,7 +377,8 @@ 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 378d795..a429a9f 100644
--- a/scan-tree.c
+++ b/scan-tree.c
@@ -68,6 +68,39 @@ static char *xstrrchr(char *s, char *from, int c)
         return from < s ? NULL : from;
 }
 
+static char *guess_defbranch(const char *repo_path)
+{
+        int fd, len;
+        char buffer[256];
+        char *ref_start;
+        char *head;
+
+        head = fmt("%s/HEAD", repo_path);
+        fd = open(head, O_RDONLY);
+        if (fd == -1)
+                return xstrdup("master");
+
+        memset(buffer, 0, sizeof(buffer));
+        len = read_in_full(fd, buffer, sizeof(buffer)-1);
+        close(fd);
+
+        if(!memcmp(buffer, "ref: refs/heads/", 16))
+                return xstrndup(buffer+16, len-17);
+
+        if(strlen(buffer) == 41) {
+                /* probably contains a SHA1 sum */
+                memset(buffer, 0, sizeof(buffer));
+                if(readlink(head, buffer, sizeof(buffer)-1)) {
+                        ref_start = memmem(buffer, sizeof(buffer)-1, "refs/heads/", 11);
+                        if(ref_start)
+                                return xstrdup(ref_start+11);
+                }
+        }
+
+        return xstrdup("master");
+}
+
+
 static void add_repo(const char *base, const char *path, repo_config_fn fn)
 {
         struct stat st;
@@ -105,6 +138,9 @@ static void add_repo(const char *base, const char *path, repo_config_fn fn)
                         *p = '\0';
         repo->name = repo->url;
         repo->path = xstrdup(path);
+
+        repo->defbranch = guess_defbranch(repo->path);
+
         while (!owner) {
                 if ((pwd = getpwuid(st.st_uid)) == NULL) {
                         fprintf(stderr, "Error reading owner-info for %s: %s (%d)\n",