On Fri, May 17, 2019 at 12:39:39AM -0400, Jeff King wrote: > > I think to trigger it you'd have to manually assemble an evil pack as I > > described (e.g., using the routines in t/lib-pack.sh). I'm going offline > > for a bit, but I may have a go at it later tonight or tomorrow. > > OK, doing so wasn't _too_ bad, though I did have to resurrect the > horrible generator patch from [1]. My results are below. But more > importantly, there is good news.
Oh, I forgot my [1]. It was this message: https://public-inbox.org/git/20130823182409.ga30...@sigill.intra.peff.net/ which explained how I hacked up pack-objects to generate the binary goo in lib-pack.sh. Here's my forward-ported version of it, in case we need it again. I do think it would be useful for debugging and experimenting to have a mode for pack-objects that takes in a list of instructions (add object X, make it a delta against object Y) that skips its usual ordering and delta constraints. This isn't it, but it's enough to hackily get what you need. ;) --- diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c index 9f424aabab..87955d9404 100644 --- a/builtin/pack-objects.c +++ b/builtin/pack-objects.c @@ -3234,6 +3234,7 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix) struct argv_array rp = ARGV_ARRAY_INIT; int rev_list_unpacked = 0, rev_list_all = 0, rev_list_reflog = 0; int rev_list_index = 0; + int magic = 0; struct string_list keep_pack_list = STRING_LIST_INIT_NODUP; struct option pack_objects_options[] = { OPT_SET_INT('q', "quiet", &progress, @@ -3321,6 +3322,7 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix) N_("do not pack objects in promisor packfiles")), OPT_BOOL(0, "delta-islands", &use_delta_islands, N_("respect islands during delta compression")), + OPT_BOOL(0, "magic", &magic, "make deltas"), OPT_END(), }; @@ -3337,6 +3339,34 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix) argc = parse_options(argc, argv, prefix, pack_objects_options, pack_usage, 0); + if (magic) { + struct object_id oid; + struct delta_index *index; + void *src, *trg, *delta; + enum object_type src_type, trg_type; + unsigned long src_size, trg_size, delta_size, z_delta_size; + unsigned char header[10]; + unsigned long header_len; + + get_oid(argv[0], &oid); + trg = read_object_file(&oid, &trg_type, &trg_size); + + get_oid(argv[1], &oid); + src = read_object_file(&oid, &src_type, &src_size); + + index = create_delta_index(src, src_size); + delta = create_delta(index, trg, trg_size, &delta_size, 8192); + + z_delta_size = do_compress(&delta, delta_size); + header_len = encode_in_pack_object_header(header, sizeof(header), + OBJ_REF_DELTA, + delta_size); + fwrite(header, 1, header_len, stdout); + fwrite(oid.hash, 1, the_hash_algo->rawsz, stdout); + fwrite(delta, 1, z_delta_size, stdout); + return 0; + } + if (argc) { base_name = argv[0]; argc--;
