Re: How to replace a single corrupt, packed object?

[Nicolas Pitre <nico@cam.org>]

On Fri, 8 Aug 2008, Johannes Schindelin wrote:

> In any case, the pack is too large for me to let my computer repack 
> everything, when only one object needs repacking.

By that you mean you cannot/don't want to use repack -f, right?

There _could_ be a way to hack pack-objects so not to reuse bad objects.  
However I don't want that to impact the code too much for an 
event that hopefully should almost never happens, especially if using -f 
does work around it already.

Well, let's see.

[...]

OK, here's what the patch to allow repacking without -f and still using 
redundant objects in presence of pack corruption might look like.  
Please tell me if that works for you.

diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
index 2dadec1..88e73f3 100644
--- a/builtin-pack-objects.c
+++ b/builtin-pack-objects.c
@@ -277,6 +277,7 @@ static unsigned long write_object(struct sha1file *f,
 				 */
 
 	if (!to_reuse) {
+		no_reuse:
 		if (!usable_delta) {
 			buf = read_sha1_file(entry->idx.sha1, &type, &size);
 			if (!buf)
@@ -364,14 +365,28 @@ static unsigned long write_object(struct sha1file *f,
 			reused_delta++;
 		}
 		hdrlen = encode_header(type, entry->size, header);
+
 		offset = entry->in_pack_offset;
 		revidx = find_pack_revindex(p, offset);
 		datalen = revidx[1].offset - offset;
 		if (!pack_to_stdout && p->index_version > 1 &&
-		    check_pack_crc(p, &w_curs, offset, datalen, revidx->nr))
-			die("bad packed object CRC for %s", sha1_to_hex(entry->idx.sha1));
+		    check_pack_crc(p, &w_curs, offset, datalen, revidx->nr)) {
+			error("bad packed object CRC for %s", sha1_to_hex(entry->idx.sha1));
+			if (entry->delta)
+				reused_delta--;
+			goto no_reuse;
+		}
+
 		offset += entry->in_pack_header_size;
 		datalen -= entry->in_pack_header_size;
+		if (!pack_to_stdout && p->index_version == 1 &&
+		    check_pack_inflate(p, &w_curs, offset, datalen, entry->size)) {
+			die("corrupt packed object for %s", sha1_to_hex(entry->idx.sha1));
+			if (entry->delta)
+				reused_delta--;
+			goto no_reuse;
+		}
+
 		if (type == OBJ_OFS_DELTA) {
 			off_t ofs = entry->idx.offset - entry->delta->idx.offset;
 			unsigned pos = sizeof(dheader) - 1;
@@ -394,10 +409,6 @@ static unsigned long write_object(struct sha1file *f,
 				return 0;
 			sha1write(f, header, hdrlen);
 		}
-
-		if (!pack_to_stdout && p->index_version == 1 &&
-		    check_pack_inflate(p, &w_curs, offset, datalen, entry->size))
-			die("corrupt packed object for %s", sha1_to_hex(entry->idx.sha1));
 		copy_pack_data(f, p, &w_curs, offset, datalen);
 		unuse_pack(&w_curs);
 		reused++;


Nicolas