Re: [PATCH 0/4] jk/version-string and google code

Jeff King [off-list ref] writes:

On Fri, Aug 10, 2012 at 11:13:30AM -0700, Dave Borowitz wrote:

quoted

quoted

Thanks for the data point. I knew you guys ran some custom code, so I
wasn't sure how widespread this is. The fact that other dulwich-based
servers would see the same issue makes me doubly sure that my fix is the
right direction.

You may also notice in that code a set of innocuous_capabilities,
which IIRC is the complete set of capabilities, at the time of
writing, that the C git client may send without the server advertising
them. Such a set (painstakingly assembled, I assure you :) may be
useful as we move further in this direction.

Oh, hmm. When initially writing my message I thought that might be the
case, but I checked to see that the features were sent only when the
server had first advertised them. However, I didn't notice that is true
only in _some_ of these lines from fetch-pack.c:

    if (multi_ack == 2)     strbuf_addstr(&c, " multi_ack_detailed");
    if (multi_ack == 1)     strbuf_addstr(&c, " multi_ack");
    if (no_done)            strbuf_addstr(&c, " no-done");
    if (use_sideband == 2)  strbuf_addstr(&c, " side-band-64k");
    if (use_sideband == 1)  strbuf_addstr(&c, " side-band");
    if (args.use_thin_pack) strbuf_addstr(&c, " thin-pack");
    if (args.no_progress)   strbuf_addstr(&c, " no-progress");
    if (args.include_tag)   strbuf_addstr(&c, " include-tag");

The early ones are checking that the server claimed support, but all of
the args.* ones are influenced directly by the arguments, whether the
server supports it or not.

I don't think there's any bug here. They are all of a class of features
where the client can handle the case where the server simply ignores the
request. However it is certainly food for thought if we are considering
tightening git's server side (even if we fix these, we have to support
the innocuous capabilities list forever for older clients).

I doubt the "innocuous" approach is really viable, unless we have an
autoritative documentation that tells which ones are and which ones
are not innocuous, and everybody follows it, so that everybody's
server and client understands the same set of capabilities as such.

Which is not likely to happen.  So in that sense, the above have
three bugs.  A new person that starts writing his server without
knowing the workaround Dulwich used that has been hidden from the
Git community until today will have to rediscover the "innocuous"
workaround on his server, unless such buggy clients die out.

I'd rather make sure that 10 years on, the maintainer does not have
to worry about interoperating with a new server written by some
third-party.

Something like this, perhaps.

 builtin/fetch-pack.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/builtin/fetch-pack.c b/builtin/fetch-pack.c
index bc7a0f9..fdec7f6 100644
--- a/builtin/fetch-pack.c
+++ b/builtin/fetch-pack.c

@@ -818,6 +818,12 @@ static struct ref *do_fetch_pack(int fd[2],
 			fprintf(stderr, "Server supports side-band\n");
 		use_sideband = 1;
 	}
+	if (!server_supports("thin-pack"))
+		args.use_thin_pack = 0;
+	if (!server_supports("no-progress"))
+		args.no_progress = 0;
+	if (!server_supports("include-tag"))
+		args.include_tag = 0;
 	if (server_supports("ofs-delta")) {
 		if (args.verbose)
 			fprintf(stderr, "Server supports ofs-delta\n");