[WIP RFC 4/5] upload-pack: refactor writing of "packfile" line

[Jonathan Tan <jonathantanmy@google.com>]

A subsequent patch allows pack-objects to output additional information
(in addition to the packfile that it currently outputs). This means that
we must hold off on writing the "packfile" section header to the client
before we process the output of pack-objects, so move the writing of
the "packfile" section header to read_pack_objects_stdout().

Unfortunately, this also means that we cannot send keepalive packets
until pack-objects starts sending out the packfile, since the sideband
is only established when the "packfile" section header is sent.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
---
 upload-pack.c | 47 ++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 36 insertions(+), 11 deletions(-)

diff --git a/upload-pack.c b/upload-pack.c
index cec43e0a46..aa2589b858 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -104,9 +104,12 @@ static int write_one_shallow(const struct commit_graft *graft, void *cb_data)
 struct output_state {
 	char buffer[8193];
 	int used;
+	unsigned packfile_started : 1;
+	struct strbuf progress_buf;
 };
 
-static int read_pack_objects_stdout(int outfd, struct output_state *os)
+static int read_pack_objects_stdout(int outfd, struct output_state *os,
+				    int use_protocol_v2)
 {
 	/* Data ready; we keep the last byte to ourselves
 	 * in case we detect broken rev-list, so that we
@@ -126,6 +129,12 @@ static int read_pack_objects_stdout(int outfd, struct output_state *os)
 	}
 	os->used += readsz;
 
+	if (!os->packfile_started) {
+		os->packfile_started = 1;
+		if (use_protocol_v2)
+			packet_write_fmt(1, "packfile\n");
+	}
+
 	if (os->used > 1) {
 		send_client_data(1, os->buffer, os->used - 1);
 		os->buffer[0] = os->buffer[os->used - 1];
@@ -138,8 +147,17 @@ static int read_pack_objects_stdout(int outfd, struct output_state *os)
 	return readsz;
 }
 
+static void flush_progress_buf(struct strbuf *progress_buf)
+{
+	if (!progress_buf->len)
+		return;
+	send_client_data(2, progress_buf->buf, progress_buf->len);
+	strbuf_reset(progress_buf);
+}
+
 static void create_pack_file(const struct object_array *have_obj,
-			     const struct object_array *want_obj)
+			     const struct object_array *want_obj,
+			     int use_protocol_v2)
 {
 	struct child_process pack_objects = CHILD_PROCESS_INIT;
 	struct output_state output_state = {0};
@@ -260,9 +278,13 @@ static void create_pack_file(const struct object_array *have_obj,
 			 */
 			sz = xread(pack_objects.err, progress,
 				  sizeof(progress));
-			if (0 < sz)
-				send_client_data(2, progress, sz);
-			else if (sz == 0) {
+			if (0 < sz) {
+				if (output_state.packfile_started)
+					send_client_data(2, progress, sz);
+				else
+					strbuf_add(&output_state.progress_buf,
+						   progress, sz);
+			} else if (sz == 0) {
 				close(pack_objects.err);
 				pack_objects.err = -1;
 			}
@@ -273,8 +295,10 @@ static void create_pack_file(const struct object_array *have_obj,
 		}
 		if (0 <= pu && (pfd[pu].revents & (POLLIN|POLLHUP))) {
 			int result = read_pack_objects_stdout(pack_objects.out,
-							      &output_state);
-
+							      &output_state,
+							      use_protocol_v2);
+			if (output_state.packfile_started)
+				flush_progress_buf(&output_state.progress_buf);
 			if (result == 0) {
 				close(pack_objects.out);
 				pack_objects.out = -1;
@@ -293,12 +317,14 @@ static void create_pack_file(const struct object_array *have_obj,
 		 * protocol to say anything, so those clients are just out of
 		 * luck.
 		 */
-		if (!ret && use_sideband) {
+		if (!ret && use_sideband && output_state.packfile_started) {
 			static const char buf[] = "0005\1";
 			write_or_die(1, buf, 5);
 		}
 	}
 
+	flush_progress_buf(&output_state.progress_buf);
+
 	if (finish_command(&pack_objects)) {
 		error("git upload-pack: git-pack-objects died with error.");
 		goto fail;
@@ -1094,7 +1120,7 @@ void upload_pack(struct upload_pack_options *options)
 	if (want_obj.nr) {
 		struct object_array have_obj = OBJECT_ARRAY_INIT;
 		get_common_commits(&have_obj, &want_obj);
-		create_pack_file(&have_obj, &want_obj);
+		create_pack_file(&have_obj, &want_obj, 0);
 	}
 }
 
@@ -1475,8 +1501,7 @@ int upload_pack_v2(struct repository *r, struct argv_array *keys,
 			send_wanted_ref_info(&data);
 			send_shallow_info(&data, &want_obj);
 
-			packet_write_fmt(1, "packfile\n");
-			create_pack_file(&have_obj, &want_obj);
+			create_pack_file(&have_obj, &want_obj, 1);
 			state = FETCH_DONE;
 			break;
 		case FETCH_DONE:
-- 
2.19.0.271.gfe8321ec05.dirty