Merge branch 'jk/pkt-log-pack'

Enhance packet tracing machinery to allow capturing an incoming
pack data to a file for debugging.

* jk/pkt-log-pack:
  pkt-line: support tracing verbatim pack contents
  pkt-line: tighten sideband PACK check when tracing
  pkt-line: simplify starts_with checks in packet tracing

Documentation/git.txt

@@ -1009,9 +1009,20 @@ Unsetting the variable, or setting it to empty, "0" or
 	Enables trace messages for all packets coming in or out of a
 	given program. This can help with debugging object negotiation
 	or other protocol issues. Tracing is turned off at a packet
-	starting with "PACK".
+	starting with "PACK" (but see 'GIT_TRACE_PACKFILE' below).
 	See 'GIT_TRACE' for available trace output options.
 
+'GIT_TRACE_PACKFILE'::
+	Enables tracing of packfiles sent or received by a
+	given program. Unlike other trace output, this trace is
+	verbatim: no headers, and no quoting of binary data. You almost
+	certainly want to direct into a file (e.g.,
+	`GIT_TRACE_PACKFILE=/tmp/my.pack`) rather than displaying it on
+	the terminal or mixing it with other trace output.
++
+Note that this is currently only implemented for the client side
+of clones and fetches.
+
 'GIT_TRACE_PERFORMANCE'::
 	Enables performance related trace messages, e.g. total execution
 	time of each Git command.

pkt-line.c

@@ -4,16 +4,51 @@
 char packet_buffer[LARGE_PACKET_MAX];
 static const char *packet_trace_prefix = "git";
 static struct trace_key trace_packet = TRACE_KEY_INIT(PACKET);
+static struct trace_key trace_pack = TRACE_KEY_INIT(PACKFILE);
 
 void packet_trace_identity(const char *prog)
 {
 	packet_trace_prefix = xstrdup(prog);
 }
 
+static int packet_trace_pack(const char *buf, unsigned int len, int sideband)
+{
+	if (!sideband) {
+		trace_verbatim(&trace_pack, buf, len);
+		return 1;
+	} else if (len && *buf == '\1') {
+		trace_verbatim(&trace_pack, buf + 1, len - 1);
+		return 1;
+	} else {
+		/* it's another non-pack sideband */
+		return 0;
+	}
+}
+
 static void packet_trace(const char *buf, unsigned int len, int write)
 {
 	int i;
 	struct strbuf out;
+	static int in_pack, sideband;
+
+	if (!trace_want(&trace_packet) && !trace_want(&trace_pack))
+		return;
+
+	if (in_pack) {
+		if (packet_trace_pack(buf, len, sideband))
+			return;
+	} else if (starts_with(buf, "PACK") || starts_with(buf, "\1PACK")) {
+		in_pack = 1;
+		sideband = *buf == '\1';
+		packet_trace_pack(buf, len, sideband);
+
+		/*
+		 * Make a note in the human-readable trace that the pack data
+		 * started.
+		 */
+		buf = "PACK ...";
+		len = strlen(buf);
+	}
 
 	if (!trace_want(&trace_packet))
 		return;
@@ -24,22 +59,15 @@ static void packet_trace(const char *buf, unsigned int len, int write)
 	strbuf_addf(&out, "packet: %12s%c ",
 		    packet_trace_prefix, write ? '>' : '<');
 
-	if ((len >= 4 && starts_with(buf, "PACK")) ||
-	    (len >= 5 && starts_with(buf+1, "PACK"))) {
-		strbuf_addstr(&out, "PACK ...");
-		trace_disable(&trace_packet);
-	}
-	else {
-		/* XXX we should really handle printable utf8 */
-		for (i = 0; i < len; i++) {
-			/* suppress newlines */
-			if (buf[i] == '\n')
-				continue;
-			if (buf[i] >= 0x20 && buf[i] <= 0x7e)
-				strbuf_addch(&out, buf[i]);
-			else
-				strbuf_addf(&out, "\\%o", buf[i]);
-		}
+	/* XXX we should really handle printable utf8 */
+	for (i = 0; i < len; i++) {
+		/* suppress newlines */
+		if (buf[i] == '\n')
+			continue;
+		if (buf[i] >= 0x20 && buf[i] <= 0x7e)
+			strbuf_addch(&out, buf[i]);
+		else
+			strbuf_addf(&out, "\\%o", buf[i]);
 	}
 
 	strbuf_addch(&out, '\n');

t/t5601-clone.sh

@@ -496,4 +496,11 @@ test_expect_success 'shallow clone locally' '
 	( cd ddsstt && git fsck )
 '
 
+test_expect_success 'GIT_TRACE_PACKFILE produces a usable pack' '
+	rm -rf dst.git &&
+	GIT_TRACE_PACKFILE=$PWD/tmp.pack git clone --no-local --bare src dst.git &&
+	git init --bare replay.git &&
+	git -C replay.git index-pack -v --stdin <tmp.pack
+'
+
 test_done

trace.c

@@ -120,6 +120,13 @@ static int prepare_trace_line(const char *file, int line,
 	return 1;
 }
 
+void trace_verbatim(struct trace_key *key, const void *buf, unsigned len)
+{
+	if (!trace_want(key))
+		return;
+	write_or_whine_pipe(get_trace_fd(key), buf, len, err_msg);
+}
+
 static void print_trace_line(struct trace_key *key, struct strbuf *buf)
 {
 	strbuf_complete_line(buf);

trace.h

@@ -18,6 +18,7 @@ extern int trace_want(struct trace_key *key);
 extern void trace_disable(struct trace_key *key);
 extern uint64_t getnanotime(void);
 extern void trace_command_performance(const char **argv);
+extern void trace_verbatim(struct trace_key *key, const void *buf, unsigned len);
 
 #ifndef HAVE_VARIADIC_MACROS