Merge branch 'jt/push-negotiation'

"git push" learns to discover common ancestor with the receiving
end over protocol v2.

* jt/push-negotiation:
  send-pack: support push negotiation
  fetch: teach independent negotiation (no packfile)
  fetch-pack: refactor command and capability write
  fetch-pack: refactor add_haves()
  fetch-pack: refactor process_acks()

Author: gitster

Documentation/config/push.txt

@@ -120,3 +120,10 @@ push.useForceIfIncludes::
 	`--force-if-includes` as an option to linkgit:git-push[1]
 	in the command line. Adding `--no-force-if-includes` at the
 	time of push overrides this configuration setting.
+
+push.negotiate::
+	If set to "true", attempt to reduce the size of the packfile
+	sent by rounds of negotiation in which the client and the
+	server attempt to find commits in common. If "false", Git will
+	rely solely on the server's ref advertisement to find commits
+	in common.

Documentation/technical/protocol-v2.txt

@@ -346,6 +346,14 @@ explained below.
 	client should download from all given URIs. Currently, the
 	protocols supported are "http" and "https".
 
+If the 'wait-for-done' feature is advertised, the following argument
+can be included in the client's request.
+
+    wait-for-done
+	Indicates to the server that it should never send "ready", but
+	should wait for the client to say "done" before sending the
+	packfile.
+
 The response of `fetch` is broken into a number of sections separated by
 delimiter packets (0001), with each section beginning with its section
 header. Most sections are sent only when the packfile is sent.

builtin/fetch.c

@@ -83,6 +83,7 @@ static struct string_list server_options = STRING_LIST_INIT_DUP;
 static struct string_list negotiation_tip = STRING_LIST_INIT_NODUP;
 static int fetch_write_commit_graph = -1;
 static int stdin_refspecs = 0;
+static int negotiate_only;
 
 static int git_fetch_config(const char *k, const char *v, void *cb)
 {
@@ -205,6 +206,8 @@ static struct option builtin_fetch_options[] = {
 			TRANSPORT_FAMILY_IPV6),
 	OPT_STRING_LIST(0, "negotiation-tip", &negotiation_tip, N_("revision"),
 			N_("report that we have only objects reachable from this object")),
+	OPT_BOOL(0, "negotiate-only", &negotiate_only,
+		 N_("do not fetch a packfile; instead, print ancestors of negotiation tips")),
 	OPT_PARSE_LIST_OBJECTS_FILTER(&filter_options),
 	OPT_BOOL(0, "auto-maintenance", &enable_auto_gc,
 		 N_("run 'maintenance --auto' after fetching")),
@@ -2043,7 +2046,29 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 		}
 	}
 
-	if (remote) {
+	if (negotiate_only) {
+		struct oidset acked_commits = OIDSET_INIT;
+		struct oidset_iter iter;
+		const struct object_id *oid;
+
+		if (!remote)
+			die(_("must supply remote when using --negotiate-only"));
+		gtransport = prepare_transport(remote, 1);
+		if (gtransport->smart_options) {
+			gtransport->smart_options->acked_commits = &acked_commits;
+		} else {
+			warning(_("Protocol does not support --negotiate-only, exiting."));
+			return 1;
+		}
+		if (server_options.nr)
+			gtransport->server_options = &server_options;
+		result = transport_fetch_refs(gtransport, NULL);
+
+		oidset_iter_init(&acked_commits, &iter);
+		while ((oid = oidset_iter_next(&iter)))
+			printf("%s\n", oid_to_hex(oid));
+		oidset_clear(&acked_commits);
+	} else if (remote) {
 		if (filter_options.choice || has_promisor_remote())
 			fetch_one_setup_partial(remote);
 		result = fetch_one(remote, argc, argv, prune_tags_ok, stdin_refspecs);