Merge branch 'jk/upload-pack-keepalive'

When running "fetch -q", a long silence while the sender side
computes the set of objects to send can be mistaken by proxies as
dropped connection.  The server side has been taught to send a small
empty messages to keep the connection alive.

* jk/upload-pack-keepalive:
  upload-pack: bump keepalive default to 5 seconds
  upload-pack: send keepalive packets during pack computation

Documentation/config.txt

@@ -2288,6 +2288,17 @@ uploadpack.allowtipsha1inwant::
 	of a hidden ref (by default, such a request is rejected).
 	see also `uploadpack.hiderefs`.
 
+uploadpack.keepalive::
+	When `upload-pack` has started `pack-objects`, there may be a
+	quiet period while `pack-objects` prepares the pack. Normally
+	it would output progress information, but if `--quiet` was used
+	for the fetch, `pack-objects` will output nothing at all until
+	the pack data begins. Some clients and networks may consider
+	the server to be hung and give up. Setting this option instructs
+	`upload-pack` to send an empty keepalive packet every
+	`uploadpack.keepalive` seconds. Setting this option to 0
+	disables keepalive packets entirely. The default is 5 seconds.
+
 url.<base>.insteadOf::
 	Any URL that starts with this value will be rewritten to
 	start, instead, with <base>. In cases where some site serves a

upload-pack.c

@@ -41,6 +41,7 @@ static struct object_array have_obj;
 static struct object_array want_obj;
 static struct object_array extra_edge_obj;
 static unsigned int timeout;
+static int keepalive = 5;
 /* 0 for no sideband,
  * otherwise maximum packet size (up to 65520 bytes).
  */
@@ -134,6 +135,7 @@ static void create_pack_file(void)
 	while (1) {
 		struct pollfd pfd[2];
 		int pe, pu, pollsize;
+		int ret;
 
 		reset_timeout();
 
@@ -156,7 +158,8 @@ static void create_pack_file(void)
 		if (!pollsize)
 			break;
 
-		if (poll(pfd, pollsize, -1) < 0) {
+		ret = poll(pfd, pollsize, 1000 * keepalive);
+		if (ret < 0) {
 			if (errno != EINTR) {
 				error("poll failed, resuming: %s",
 				      strerror(errno));
@@ -218,6 +221,21 @@ static void create_pack_file(void)
 			if (sz < 0)
 				goto fail;
 		}
+
+		/*
+		 * We hit the keepalive timeout without saying anything; send
+		 * an empty message on the data sideband just to let the other
+		 * side know we're still working on it, but don't have any data
+		 * yet.
+		 *
+		 * If we don't have a sideband channel, there's no room in the
+		 * protocol to say anything, so those clients are just out of
+		 * luck.
+		 */
+		if (!ret && use_sideband) {
+			static const char buf[] = "0005\1";
+			write_or_die(1, buf, 5);
+		}
 	}
 
 	if (finish_command(&pack_objects)) {
@@ -722,6 +740,11 @@ static int upload_pack_config(const char *var, const char *value, void *unused)
 {
 	if (!strcmp("uploadpack.allowtipsha1inwant", var))
 		allow_tip_sha1_in_want = git_config_bool(var, value);
+	else if (!strcmp("uploadpack.keepalive", var)) {
+		keepalive = git_config_int(var, value);
+		if (!keepalive)
+			keepalive = -1;
+	}
 	return parse_hide_refs_config(var, value, "uploadpack");
 }