Re: [PATCH v3] Document pack v4 format

From

Nicolas Pitre <nico@fluxnic.net>

Date

Sep 7, 2013, 04:52 UTC

Message-ID

<alpine.LFD.2.03.1309070043420.20709@syhkavp.arg>

In-Reply-To

<1378433643-15638-1-git-send-email-pclouds@gmail.com>

On Fri, 6 Sep 2013, Nguyễn Thái Ngọc Duy wrote:

> 
> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
> ---
>  Should be up to date with Nico's latest implementation and also cover
>  additions to the format that everybody seems to agree on:
> 
>   - new types for canonical trees and commits
>   - sha-1 table covering missing objects in thin packs

commit 98d4b75aff266015b5dff0a324a2984c2a8f7fa2
Author: Nicolas Pitre <nico@fluxnic.net>
Date:   Fri Sep 6 23:45:49 2013 -0400

    pack v4: allow canonical commit and tree objects
    
    If for some reason we can't transcode a commit or tree object (lossy
    encoding such as the zero-padded file mode for example) then we can still
    store the canonical object like in pack v2.
    
    This is also useful for completing a thin pack without having to add
    missing entries to the dictionary tables.
    
    To simplify things, the canonical commit and tree types retain their type
    number 1 and 2 respectively, and the transcoded types are now 9 and 10
    i.e. with bit 3 added.
    
    Signed-off-by: Nicolas Pitre <nico@fluxnic.net>

diff --git a/cache.h b/cache.h
index a6d016b..b68ad5a 100644
--- a/cache.h
+++ b/cache.h
@@ -330,6 +330,8 @@ enum object_type {
 	/* 5 for future expansion */
 	OBJ_OFS_DELTA = 6,
 	OBJ_REF_DELTA = 7,
+	OBJ_PV4_COMMIT = (8 + 1),
+	OBJ_PV4_TREE = (8 + 2),
 	OBJ_ANY,
 	OBJ_MAX
 };
diff --git a/packv4-create.c b/packv4-create.c
index 11cfe6f..38fa594 100644
--- a/packv4-create.c
+++ b/packv4-create.c
@@ -981,10 +981,15 @@ static off_t packv4_write_object(struct sha1file *f, struct packed_git *p,
 		die("unexpected object type %d", type);
 	}
 	free(src);
-	if (!result)
-		die("can't convert %s object %s",
-		    typename(type), sha1_to_hex(obj->sha1));
+	if (!result) {
+		warning("can't convert %s object %s",
+			typename(type), sha1_to_hex(obj->sha1));
+		/* fall back to copy the object in its original form */
+		return copy_object_data(f, p, obj->offset);
+	}
 
+	/* Use bit 3 to indicate a special type encoding */
+	type += 8;
 	hdrlen = write_object_header(f, type, obj_size);
 	sha1write(f, result, buf_size);
 	free(result);
diff --git a/packv4-parse.c b/packv4-parse.c
index 86ec535..63bba03 100644
--- a/packv4-parse.c
+++ b/packv4-parse.c
@@ -266,7 +266,7 @@ static int decode_entries(struct packed_git *p, struct pack_window **w_curs,
 			if (++scp - src >= avail - 20)
 				return -1;
 		/* let's still make sure this is actually a tree */
-		if ((*scp++ & 0xf) != OBJ_TREE)
+		if ((*scp++ & 0xf) != OBJ_PV4_TREE)
 			return -1;
 	}
 
diff --git a/sha1_file.c b/sha1_file.c
index 79e1293..c7bf677 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1806,6 +1806,11 @@ static enum object_type packed_to_object_type(struct packed_git *p,
 	}
 
 	switch (type) {
+	case OBJ_PV4_COMMIT:
+	case OBJ_PV4_TREE:
+		/* hide pack v4 special object types */
+		type -= 8;
+		break;
 	case OBJ_BAD:
 	case OBJ_COMMIT:
 	case OBJ_TREE:
@@ -2171,17 +2176,16 @@ void *unpack_entry(struct packed_git *p, off_t obj_offset,
 		if (data)
 			die("BUG in unpack_entry: left loop at a valid delta");
 		break;
+	case OBJ_PV4_COMMIT:
+		data = pv4_get_commit(p, &w_curs, curpos, size);
+		type -= 8;
+		break;
+	case OBJ_PV4_TREE:
+		data = pv4_get_tree(p, &w_curs, curpos, size);
+		type -= 8;
+		break;
 	case OBJ_COMMIT:
 	case OBJ_TREE:
-		if (p->version >= 4 && !base_from_cache) {
-			if (type == OBJ_COMMIT) {
-				data = pv4_get_commit(p, &w_curs, curpos, size);
-			} else {
-				data = pv4_get_tree(p, &w_curs, curpos, size);
-			}
-			break;
-		}
-		/* fall through */
 	case OBJ_BLOB:
 	case OBJ_TAG:
 		if (!base_from_cache)