pkt-line: introduce struct packet_writer

A future patch will allow the client to request multiplexing of the
entire fetch response (and not only during packfile transmission), which
in turn allows the server to send progress and keepalive messages at any
time during the response.

It will be convenient for a future patch if writing options
(specifically, whether the written data is to be multiplexed) could be
controlled from a single place, so create struct packet_writer to serve
as that place, and modify upload-pack to use it.

Currently, it only stores the output fd, but a subsequent patch will (as
described above) introduce an option to determine if the written data is
to be multiplexed.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

3 files changed, 115 insertions, 58 deletions

diff --git a/pkt-line.c b/pkt-line.c
index e70ea6d88f..9d3e402d41 100644
--- a/pkt-line.c
+++ b/pkt-line.c
@@ -129,12 +129,14 @@ static void set_packet_header(char *buf, const int size)
 	#undef hex
 }
 
-static void format_packet(struct strbuf *out, const char *fmt, va_list args)
+static void format_packet(struct strbuf *out, const char *prefix,
+			  const char *fmt, va_list args)
 {
 	size_t orig_len, n;
 
 	orig_len = out->len;
 	strbuf_addstr(out, "0000");
+	strbuf_addstr(out, prefix);
 	strbuf_vaddf(out, fmt, args);
 	n = out->len - orig_len;
 
@@ -145,13 +147,13 @@ static void format_packet(struct strbuf *out, const char *fmt, va_list args)
 	packet_trace(out->buf + orig_len + 4, n - 4, 1);
 }
 
-static int packet_write_fmt_1(int fd, int gently,
+static int packet_write_fmt_1(int fd, int gently, const char *prefix,
 			      const char *fmt, va_list args)
 {
 	static struct strbuf buf = STRBUF_INIT;
 
 	strbuf_reset(&buf);
-	format_packet(&buf, fmt, args);
+	format_packet(&buf, prefix, fmt, args);
 	if (write_in_full(fd, buf.buf, buf.len) < 0) {
 		if (!gently) {
 			check_pipe(errno);
@@ -168,7 +170,7 @@ void packet_write_fmt(int fd, const char *fmt, ...)
 	va_list args;
 
 	va_start(args, fmt);
-	packet_write_fmt_1(fd, 0, fmt, args);
+	packet_write_fmt_1(fd, 0, "", fmt, args);
 	va_end(args);
 }
 
@@ -178,7 +180,7 @@ int packet_write_fmt_gently(int fd, const char *fmt, ...)
 	va_list args;
 
 	va_start(args, fmt);
-	status = packet_write_fmt_1(fd, 1, fmt, args);
+	status = packet_write_fmt_1(fd, 1, "", fmt, args);
 	va_end(args);
 	return status;
 }
@@ -211,7 +213,7 @@ void packet_buf_write(struct strbuf *buf, const char *fmt, ...)
 	va_list args;
 
 	va_start(args, fmt);
-	format_packet(buf, fmt, args);
+	format_packet(buf, "", fmt, args);
 	va_end(args);
 }
 
@@ -486,3 +488,36 @@ enum packet_read_status packet_reader_peek(struct packet_reader *reader)
 	reader->line_peeked = 1;
 	return reader->status;
 }
+
+void packet_writer_init(struct packet_writer *writer, int dest_fd)
+{
+	writer->dest_fd = dest_fd;
+}
+
+void packet_writer_write(struct packet_writer *writer, const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	packet_write_fmt_1(writer->dest_fd, 0, "", fmt, args);
+	va_end(args);
+}
+
+void packet_writer_error(struct packet_writer *writer, const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	packet_write_fmt_1(writer->dest_fd, 0, "ERR ", fmt, args);
+	va_end(args);
+}
+
+void packet_writer_delim(struct packet_writer *writer)
+{
+	packet_delim(writer->dest_fd);
+}
+
+void packet_writer_flush(struct packet_writer *writer)
+{
+	packet_flush(writer->dest_fd);
+}
diff --git a/pkt-line.h b/pkt-line.h
index d7e1dbc047..023ad2951d 100644
--- a/pkt-line.h
+++ b/pkt-line.h
@@ -183,4 +183,18 @@ extern enum packet_read_status packet_reader_peek(struct packet_reader *reader);
 #define LARGE_PACKET_DATA_MAX (LARGE_PACKET_MAX - 4)
 extern char packet_buffer[LARGE_PACKET_MAX];
 
+struct packet_writer {
+	int dest_fd;
+};
+
+void packet_writer_init(struct packet_writer *writer, int dest_fd);
+
+/* These functions die upon failure. */
+__attribute__((format (printf, 2, 3)))
+void packet_writer_write(struct packet_writer *writer, const char *fmt, ...);
+__attribute__((format (printf, 2, 3)))
+void packet_writer_error(struct packet_writer *writer, const char *fmt, ...);
+void packet_writer_delim(struct packet_writer *writer);
+void packet_writer_flush(struct packet_writer *writer);
+
 #endif
diff --git a/upload-pack.c b/upload-pack.c
index 08b547cf01..60a26bbbfd 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -613,13 +613,14 @@ error:
 	}
 }
 
-static void send_shallow(struct commit_list *result)
+static void send_shallow(struct packet_writer *writer,
+			 struct commit_list *result)
 {
 	while (result) {
 		struct object *object = &result->item->object;
 		if (!(object->flags & (CLIENT_SHALLOW|NOT_SHALLOW))) {
-			packet_write_fmt(1, "shallow %s",
-					 oid_to_hex(&object->oid));
+			packet_writer_write(writer, "shallow %s",
+					    oid_to_hex(&object->oid));
 			register_shallow(the_repository, &object->oid);
 			shallow_nr++;
 		}
@@ -627,7 +628,8 @@ static void send_shallow(struct commit_list *result)
 	}
 }
 
-static void send_unshallow(const struct object_array *shallows,
+static void send_unshallow(struct packet_writer *writer,
+			   const struct object_array *shallows,
 			   struct object_array *want_obj)
 {
 	int i;
@@ -636,8 +638,8 @@ static void send_unshallow(const struct object_array *shallows,
 		struct object *object = shallows->objects[i].item;
 		if (object->flags & NOT_SHALLOW) {
 			struct commit_list *parents;
-			packet_write_fmt(1, "unshallow %s",
-					 oid_to_hex(&object->oid));
+			packet_writer_write(writer, "unshallow %s",
+					    oid_to_hex(&object->oid));
 			object->flags &= ~CLIENT_SHALLOW;
 			/*
 			 * We want to _register_ "object" as shallow, but we
@@ -662,7 +664,7 @@ static void send_unshallow(const struct object_array *shallows,
 	}
 }
 
-static void deepen(int depth, int deepen_relative,
+static void deepen(struct packet_writer *writer, int depth, int deepen_relative,
 		   struct object_array *shallows, struct object_array *want_obj)
 {
 	if (depth == INFINITE_DEPTH && !is_repository_shallow(the_repository)) {
@@ -680,7 +682,7 @@ static void deepen(int depth, int deepen_relative,
 		result = get_shallow_commits(&reachable_shallows,
 					     depth + 1,
 					     SHALLOW, NOT_SHALLOW);
-		send_shallow(result);
+		send_shallow(writer, result);
 		free_commit_list(result);
 		object_array_clear(&reachable_shallows);
 	} else {
@@ -688,14 +690,15 @@ static void deepen(int depth, int deepen_relative,
 
 		result = get_shallow_commits(want_obj, depth,
 					     SHALLOW, NOT_SHALLOW);
-		send_shallow(result);
+		send_shallow(writer, result);
 		free_commit_list(result);
 	}
 
-	send_unshallow(shallows, want_obj);
+	send_unshallow(writer, shallows, want_obj);
 }
 
-static void deepen_by_rev_list(int ac, const char **av,
+static void deepen_by_rev_list(struct packet_writer *writer, int ac,
+			       const char **av,
 			       struct object_array *shallows,
 			       struct object_array *want_obj)
 {
@@ -703,13 +706,14 @@ static void deepen_by_rev_list(int ac, const char **av,
 
 	close_commit_graph(the_repository);
 	result = get_shallow_commits_by_rev_list(ac, av, SHALLOW, NOT_SHALLOW);
-	send_shallow(result);
+	send_shallow(writer, result);
 	free_commit_list(result);
-	send_unshallow(shallows, want_obj);
+	send_unshallow(writer, shallows, want_obj);
 }
 
 /* Returns 1 if a shallow list is sent or 0 otherwise */
-static int send_shallow_list(int depth, int deepen_rev_list,
+static int send_shallow_list(struct packet_writer *writer,
+			     int depth, int deepen_rev_list,
 			     timestamp_t deepen_since,
 			     struct string_list *deepen_not,
 			     struct object_array *shallows,
@@ -720,7 +724,7 @@ static int send_shallow_list(int depth, int deepen_rev_list,
 	if (depth > 0 && deepen_rev_list)
 		die("git upload-pack: deepen and deepen-since (or deepen-not) cannot be used together");
 	if (depth > 0) {
-		deepen(depth, deepen_relative, shallows, want_obj);
+		deepen(writer, depth, deepen_relative, shallows, want_obj);
 		ret = 1;
 	} else if (deepen_rev_list) {
 		struct argv_array av = ARGV_ARRAY_INIT;
@@ -741,7 +745,7 @@ static int send_shallow_list(int depth, int deepen_rev_list,
 			struct object *o = want_obj->objects[i].item;
 			argv_array_push(&av, oid_to_hex(&o->oid));
 		}
-		deepen_by_rev_list(av.argc, av.argv, shallows, want_obj);
+		deepen_by_rev_list(writer, av.argc, av.argv, shallows, want_obj);
 		argv_array_clear(&av);
 		ret = 1;
 	} else {
@@ -834,8 +838,10 @@ static void receive_needs(struct packet_reader *reader, struct object_array *wan
 	int has_non_tip = 0;
 	timestamp_t deepen_since = 0;
 	int deepen_rev_list = 0;
+	struct packet_writer writer;
 
 	shallow_nr = 0;
+	packet_writer_init(&writer, 1);
 	for (;;) {
 		struct object *o;
 		const char *features;
@@ -892,9 +898,9 @@ static void receive_needs(struct packet_reader *reader, struct object_array *wan
 
 		o = parse_object(the_repository, &oid_buf);
 		if (!o) {
-			packet_write_fmt(1,
-					 "ERR upload-pack: not our ref %s",
-					 oid_to_hex(&oid_buf));
+			packet_writer_error(&writer,
+					    "upload-pack: not our ref %s",
+					    oid_to_hex(&oid_buf));
 			die("git upload-pack: not our ref %s",
 			    oid_to_hex(&oid_buf));
 		}
@@ -923,7 +929,7 @@ static void receive_needs(struct packet_reader *reader, struct object_array *wan
 	if (depth == 0 && !deepen_rev_list && shallows.nr == 0)
 		return;
 
-	if (send_shallow_list(depth, deepen_rev_list, deepen_since,
+	if (send_shallow_list(&writer, depth, deepen_rev_list, deepen_since,
 			      &deepen_not, &shallows, want_obj))
 		packet_flush(1);
 	object_array_clear(&shallows);
@@ -1102,6 +1108,8 @@ struct upload_pack_data {
 	int deepen_rev_list;
 	int deepen_relative;
 
+	struct packet_writer writer;
+
 	unsigned stateless_rpc : 1;
 
 	unsigned use_thin_pack : 1;
@@ -1125,6 +1133,7 @@ static void upload_pack_data_init(struct upload_pack_data *data)
 	data->haves = haves;
 	data->shallows = shallows;
 	data->deepen_not = deepen_not;
+	packet_writer_init(&data->writer, 1);
 }
 
 static void upload_pack_data_clear(struct upload_pack_data *data)
@@ -1136,7 +1145,8 @@ static void upload_pack_data_clear(struct upload_pack_data *data)
 	string_list_clear(&data->deepen_not, 0);
 }
 
-static int parse_want(const char *line, struct object_array *want_obj)
+static int parse_want(struct packet_writer *writer, const char *line,
+		      struct object_array *want_obj)
 {
 	const char *arg;
 	if (skip_prefix(line, "want ", &arg)) {
@@ -1149,9 +1159,9 @@ static int parse_want(const char *line, struct object_array *want_obj)
 
 		o = parse_object(the_repository, &oid);
 		if (!o) {
-			packet_write_fmt(1,
-					 "ERR upload-pack: not our ref %s",
-					 oid_to_hex(&oid));
+			packet_writer_error(writer,
+					    "upload-pack: not our ref %s",
+					    oid_to_hex(&oid));
 			die("git upload-pack: not our ref %s",
 			    oid_to_hex(&oid));
 		}
@@ -1167,7 +1177,8 @@ static int parse_want(const char *line, struct object_array *want_obj)
 	return 0;
 }
 
-static int parse_want_ref(const char *line, struct string_list *wanted_refs,
+static int parse_want_ref(struct packet_writer *writer, const char *line,
+			  struct string_list *wanted_refs,
 			  struct object_array *want_obj)
 {
 	const char *arg;
@@ -1177,7 +1188,7 @@ static int parse_want_ref(const char *line, struct string_list *wanted_refs,
 		struct object *o;
 
 		if (read_ref(arg, &oid)) {
-			packet_write_fmt(1, "ERR unknown ref %s", arg);
+			packet_writer_error(writer, "unknown ref %s", arg);
 			die("unknown ref %s", arg);
 		}
 
@@ -1220,10 +1231,11 @@ static void process_args(struct packet_reader *request,
 		const char *p;
 
 		/* process want */
-		if (parse_want(arg, want_obj))
+		if (parse_want(&data->writer, arg, want_obj))
 			continue;
 		if (allow_ref_in_want &&
-		    parse_want_ref(arg, &data->wanted_refs, want_obj))
+		    parse_want_ref(&data->writer, arg, &data->wanted_refs,
+				   want_obj))
 			continue;
 		/* process have line */
 		if (parse_have(arg, &data->haves))
@@ -1317,26 +1329,26 @@ static int process_haves(struct oid_array *haves, struct oid_array *common,
 	return 0;
 }
 
-static int send_acks(struct oid_array *acks, struct strbuf *response,
+static int send_acks(struct packet_writer *writer, struct oid_array *acks,
 		     const struct object_array *have_obj,
 		     struct object_array *want_obj)
 {
 	int i;
 
-	packet_buf_write(response, "acknowledgments\n");
+	packet_writer_write(writer, "acknowledgments\n");
 
 	/* Send Acks */
 	if (!acks->nr)
-		packet_buf_write(response, "NAK\n");
+		packet_writer_write(writer, "NAK\n");
 
 	for (i = 0; i < acks->nr; i++) {
-		packet_buf_write(response, "ACK %s\n",
-				 oid_to_hex(&acks->oid[i]));
+		packet_writer_write(writer, "ACK %s\n",
+				    oid_to_hex(&acks->oid[i]));
 	}
 
 	if (ok_to_give_up(have_obj, want_obj)) {
 		/* Send Ready */
-		packet_buf_write(response, "ready\n");
+		packet_writer_write(writer, "ready\n");
 		return 1;
 	}
 
@@ -1348,25 +1360,20 @@ static int process_haves_and_send_acks(struct upload_pack_data *data,
 				       struct object_array *want_obj)
 {
 	struct oid_array common = OID_ARRAY_INIT;
-	struct strbuf response = STRBUF_INIT;
 	int ret = 0;
 
 	process_haves(&data->haves, &common, have_obj);
 	if (data->done) {
 		ret = 1;
-	} else if (send_acks(&common, &response, have_obj, want_obj)) {
-		packet_buf_delim(&response);
+	} else if (send_acks(&data->writer, &common, have_obj, want_obj)) {
+		packet_writer_delim(&data->writer);
 		ret = 1;
 	} else {
 		/* Add Flush */
-		packet_buf_flush(&response);
+		packet_writer_flush(&data->writer);
 		ret = 0;
 	}
 
-	/* Send response */
-	write_or_die(1, response.buf, response.len);
-	strbuf_release(&response);
-
 	oid_array_clear(&data->haves);
 	oid_array_clear(&common);
 	return ret;
@@ -1379,15 +1386,15 @@ static void send_wanted_ref_info(struct upload_pack_data *data)
 	if (!data->wanted_refs.nr)
 		return;
 
-	packet_write_fmt(1, "wanted-refs\n");
+	packet_writer_write(&data->writer, "wanted-refs\n");
 
 	for_each_string_list_item(item, &data->wanted_refs) {
-		packet_write_fmt(1, "%s %s\n",
-				 oid_to_hex(item->util),
-				 item->string);
+		packet_writer_write(&data->writer, "%s %s\n",
+				    oid_to_hex(item->util),
+				    item->string);
 	}
 
-	packet_delim(1);
+	packet_writer_delim(&data->writer);
 }
 
 static void send_shallow_info(struct upload_pack_data *data,
@@ -1398,14 +1405,15 @@ static void send_shallow_info(struct upload_pack_data *data,
 	    !is_repository_shallow(the_repository))
 		return;
 
-	packet_write_fmt(1, "shallow-info\n");
+	packet_writer_write(&data->writer, "shallow-info\n");
 
-	if (!send_shallow_list(data->depth, data->deepen_rev_list,
+	if (!send_shallow_list(&data->writer, data->depth,
+			       data->deepen_rev_list,
 			       data->deepen_since, &data->deepen_not,
 			       &data->shallows, want_obj) &&
 	    is_repository_shallow(the_repository))
-		deepen(INFINITE_DEPTH, data->deepen_relative, &data->shallows,
-		       want_obj);
+		deepen(&data->writer, INFINITE_DEPTH, data->deepen_relative,
+		       &data->shallows, want_obj);
 
 	packet_delim(1);
 }
@@ -1467,7 +1475,7 @@ 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");
+			packet_writer_write(&data.writer, "packfile\n");
 			create_pack_file(&have_obj, &want_obj);
 			state = FETCH_DONE;
 			break;