[PATCH 1/2] upload-pack: support subtree packing

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

This patch adds a new capability "subtree", which supports two new
requests "subtree" and "commit-subtree".

"subtree" asks upload-pack to create a pack that contains only blobs
from the given tree prefix (and necessary commits/trees to reach
those blobs).

"commit-tree" asks upload-pack to create a pack that contains trees of
the given prefix (and necessary commits/trees to reach those trees)

With "subtree" request, Git client may then rewrite commits to create
a valid commit tree again, so that users can work on it independently.
When users want to push from such a tree, "commit-tree" may then be
used to re-match what users have and what is in upstream, recreate
proper push commits.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 upload-pack.c |   31 ++++++++++++++++++++++++++++++-
 1 files changed, 30 insertions(+), 1 deletions(-)

diff --git a/upload-pack.c b/upload-pack.c
index dc464d7..f97296a 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -41,6 +41,8 @@ static int use_sideband;
 static int debug_fd;
 static int advertise_refs;
 static int stateless_rpc;
+static char *subtree;
+static int commit_subtree;
 
 static void reset_timeout(void)
 {
@@ -89,6 +91,17 @@ static void show_object(struct object *obj, const struct name_path *path, const
 	 */
 	const char *name = path_name(path, component);
 	const char *ep = strchr(name, '\n');
+	if (subtree) {
+		int len = strlen(name);
+		/* parent trees should always be kept */
+		if (obj->type == OBJ_TREE && !prefixcmp(subtree, name) && subtree[len] == '/')
+			; /* in */
+		else if (commit_subtree)
+			goto out;
+		else if (prefixcmp(name, subtree))
+			goto out;
+	}
+
 	if (ep) {
 		fprintf(pack_pipe, "%s %.*s\n", sha1_to_hex(obj->sha1),
 		       (int) (ep - name),
@@ -97,6 +110,7 @@ static void show_object(struct object *obj, const struct name_path *path, const
 	else
 		fprintf(pack_pipe, "%s %s\n",
 				sha1_to_hex(obj->sha1), name);
+out:
 	free((char *)name);
 }
 
@@ -504,6 +518,21 @@ static void receive_needs(void)
 		if (debug_fd)
 			write_in_full(debug_fd, line, len);
 
+		if (!prefixcmp(line, "subtree ")) {
+			int len = strlen(line+8);
+			subtree = malloc(len+1);
+			memcpy(subtree, line+8, len-1);
+			subtree[len-1] = '\0'; /* \n */
+			continue;
+		}
+		if (!prefixcmp(line, "commit-subtree ")) {
+			int len = strlen(line+15);
+			subtree = malloc(len+1);
+			memcpy(subtree, line+15, len-1);
+			subtree[len-1] = '\0'; /* \n */
+			commit_subtree = 1;
+			continue;
+		}
 		if (!prefixcmp(line, "shallow ")) {
 			unsigned char sha1[20];
 			struct object *object;
@@ -623,7 +652,7 @@ static int send_ref(const char *refname, const unsigned char *sha1, int flag, vo
 {
 	static const char *capabilities = "multi_ack thin-pack side-band"
 		" side-band-64k ofs-delta shallow no-progress"
-		" include-tag multi_ack_detailed";
+		" include-tag multi_ack_detailed subtree";
 	struct object *o = parse_object(sha1);
 
 	if (!o)
-- 
1.7.1.rc1.69.g24c2f7