add packet tracing debug code

This shows a trace of all packets coming in or out of a given
program. This can help with debugging object negotiation or
other protocol issues.

To keep the code changes simple, we operate at the lowest
level, meaning we don't necessarily understand what's in the
packets. The one exception is a packet starting with "PACK",
which causes us to skip that packet and turn off tracing
(since the gigantic pack data will not be interesting to
read, at least not in the trace format).

We show both written and read packets. In the local case,
this may mean you will see packets twice (written by the
sender and read by the receiver). However, for cases where
the other end is remote, this allows you to see the full
conversation.

Packet tracing can be enabled with GIT_TRACE_PACKET=<foo>,
where <foo> takes the same arguments as GIT_TRACE.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

5 files changed, 8 insertions, 0 deletions

diff --git a/builtin/clone.c b/builtin/clone.c
index 60d9a64280..38b4b71cd2 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -383,6 +383,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 
 	junk_pid = getpid();
 
+	packet_trace_identity("clone");
 	argc = parse_options(argc, argv, prefix, builtin_clone_options,
 			     builtin_clone_usage, 0);
 
diff --git a/builtin/fetch-pack.c b/builtin/fetch-pack.c
index b999413934..272bc383d6 100644
--- a/builtin/fetch-pack.c
+++ b/builtin/fetch-pack.c
@@ -804,6 +804,8 @@ int cmd_fetch_pack(int argc, const char **argv, const char *prefix)
 	char **pack_lockfile_ptr = NULL;
 	struct child_process *conn;
 
+	packet_trace_identity("fetch-pack");
+
 	nr_heads = 0;
 	heads = NULL;
 	for (i = 1; i < argc; i++) {
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 357f3cdbbf..e94e0015c9 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -906,6 +906,8 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 	struct remote *remote;
 	int result = 0;
 
+	packet_trace_identity("fetch");
+
 	/* Record the command line for the reflog */
 	strbuf_addstr(&default_rla, "fetch");
 	for (i = 1; i < argc; i++)
diff --git a/builtin/push.c b/builtin/push.c
index e655eb7695..26171ff50f 100644
--- a/builtin/push.c
+++ b/builtin/push.c
@@ -228,6 +228,7 @@ int cmd_push(int argc, const char **argv, const char *prefix)
 		OPT_END()
 	};
 
+	packet_trace_identity("push");
 	git_config(git_default_config, NULL);
 	argc = parse_options(argc, argv, prefix, options, push_usage, 0);
 
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 760817dbd7..5fa4be8fb4 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -778,6 +778,8 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix)
 	char *dir = NULL;
 	struct command *commands;
 
+	packet_trace_identity("receive-pack");
+
 	argv++;
 	for (i = 1; i < argc; i++) {
 		const char *arg = *argv++;