Add basic functionality for commit lookup/parsing

The external API function "git_commit_parse" has been renamed
to "git_commit_lookup" and has been partially implemented with
support for loading commits straight from the ODB. It still lacks
the functionality to lookup cached commits in the revpool and to
resolve tags to commits.

The following internal functions have been partially implemented:

int git_commit__parse_buffer(...);
int git_commit__parse_time(...);
int git_commit__parse_oid(...);

Commits are now fully parsed but the generated parent and tree
references are not handled yet.

Signed-off-by: Vicent Marti <tanoku@gmail.com>
Signed-off-by: Andreas Ericsson <ae@op5.se>

src/commit.c

@@ -23,10 +23,128 @@
  * Boston, MA 02110-1301, USA.
  */
 
+#include <time.h>
+
 #include "common.h"
 #include "commit.h"
+#include "revwalk.h"
+#include "git/odb.h"
 
 const git_oid *git_commit_id(git_commit *c)
 {
 	return &c->id;
 }
+
+git_commit *git_commit_lookup(git_revpool *pool, const git_oid *id)
+{
+    git_obj commit_obj;
+    git_commit *commit = NULL;
+
+    /*
+     * TODO: check if the commit is already cached in the
+     * revpool instead of loading it from the odb
+     */
+
+    if (git_odb_read(&commit_obj, pool->db, id) < 0)
+        return NULL;
+
+    if (commit_obj.type != GIT_OBJ_COMMIT)
+        goto error_cleanup;
+
+    commit = git__malloc(sizeof(git_commit));
+    memset(commit, 0x0, sizeof(git_commit));
+
+    git_oid_cpy(&commit->id, id);
+    commit->pool = pool;
+
+    if (git_commit__parse_buffer(commit, commit_obj.data, commit_obj.len) < 0)
+        goto error_cleanup;
+
+    return commit;
+
+error_cleanup:
+    git_obj_close(&commit_obj);
+    free(commit);
+
+    return NULL;
+}
+
+int git_commit__parse_time(time_t *commit_time, char *buffer, const char *buffer_end)
+{
+	if (memcmp(buffer, "author ", 7) != 0)
+		return -1;
+
+    buffer = memchr(buffer, '\n', buffer_end - buffer);
+    if (buffer == 0 || buffer >= buffer_end)
+        return -1;
+
+	if (memcmp(buffer, "committer ", 10) != 0)
+		return -1;
+
+    buffer = memchr(buffer, '\n', buffer_end - buffer);
+    if (buffer == 0 || buffer >= buffer_end)
+        return -1;
+
+	*commit_time = strtol(buffer, &buffer, 10);
+
+    return (buffer < buffer_end) ? 0 : -1;
+}
+
+int git_commit__parse_oid(git_oid *oid, char **buffer_out, const char *buffer_end, const char *header)
+{
+    size_t sha_len = GIT_OID_HEXSZ;
+    size_t header_len = strlen(header);
+
+    char *buffer = *buffer_out;
+
+    if (buffer + (header_len + sha_len + 1) > buffer_end)
+        return -1;
+
+    if (memcmp(buffer, header, header_len) != 0)
+        return -1;
+
+    if (buffer[header_len + sha_len] != '\n')
+        return -1;
+
+    if (git_oid_mkstr(oid, buffer + header_len) < 0)
+        return -1;
+
+    *buffer_out = buffer + (header_len + sha_len + 1);
+
+    return 0;
+}
+
+int git_commit__parse_buffer(git_commit *commit, void *data, size_t len)
+{
+	char *buffer = (char *)data;
+	const char *buffer_end = (char *)data + len;
+
+    git_oid oid;
+
+    if (commit->parsed)
+		return 0;
+
+    if (git_commit__parse_oid(&oid, &buffer, buffer_end, "tree ") < 0)
+        return -1;
+
+    /*
+     * TODO: load tree into commit object
+     * TODO: commit grafts!
+     */
+
+    while (git_commit__parse_oid(&oid, &buffer, buffer_end, "parent ") == 0) {
+        git_commit *parent;
+
+        if ((parent = git_commit_lookup(commit->pool, &oid)) == NULL)
+            return -1;
+
+        // TODO: push the new commit into the revpool
+    }
+
+    if (git_commit__parse_time(&commit->commit_time, buffer, buffer_end) < 0)
+        return -1;
+
+    commit->parsed = 1;
+
+	return 0;
+}

src/commit.h

@@ -5,11 +5,20 @@
 
 #include <time.h>
 
+#define GIT_COMMIT_SEEN     (1 << 0)
+#define GIT_COMMIT_HIDE     (1 << 1)
+#define GIT_COMMIT_DELAY    (1 << 2)
+
 struct git_commit {
 	git_oid id;
 	time_t commit_time;
+    git_revpool *pool;
 	unsigned parsed:1,
 		 flags:26;
 };
 
+int git_commit__parse_oid(git_oid *oid, char **buffer_out, const char *buffer_end, const char *header);
+int git_commit__parse_buffer(git_commit *commit, void *data, size_t len);
+int git_commit__parse_time(time_t *commit_time, char *buffer, const char *buffer_end);
+
 #endif

src/git/commit.h

@@ -17,7 +17,7 @@ GIT_BEGIN_DECL
 typedef struct git_commit git_commit;
 
 /**
- * Parse (or lookup) a commit from a revision pool.
+ * Lookup a commit from a revision pool, and parse it if needed.
  * @param pool the pool to use when parsing/caching the commit.
  * @param id identity of the commit to locate.  If the object is
  *        an annotated tag it will be peeled back to the commit.
@@ -25,7 +25,7 @@ typedef struct git_commit git_commit;
  *         pool's git_odb, or if the commit is present but is
  *         too malformed to be parsed successfully.
  */
-GIT_EXTERN(git_commit *) git_commit_parse(git_revpool *pool, const git_oid *id);
+GIT_EXTERN(git_commit *) git_commit_lookup(git_revpool *pool, const git_oid *id);
 
 /**
  * Get the id of a commit.