fetch-pack: support negotiation tip whitelist

During negotiation, fetch-pack eventually reports as "have" lines all
commits reachable from all refs. Allow the user to restrict the commits
sent in this way by providing a whitelist of tips; only the tips
themselves and their ancestors will be sent.

Both globs and single objects are supported.

This feature is only supported for protocols that support connect or
stateless-connect (such as HTTP with protocol v2).

This will speed up negotiation when the repository has multiple
relatively independent branches (for example, when a repository
interacts with multiple repositories, such as with linux-next [1] and
torvalds/linux [2]), and the user knows which local branch is likely to
have commits in common with the upstream branch they are fetching.

[1] https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next/
[2] https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux/

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

1 files changed, 43 insertions, 0 deletions

diff --git a/builtin/fetch.c b/builtin/fetch.c
index ea5b966..49ab6ac 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -63,6 +63,7 @@ static int shown_url = 0;
 static struct refspec refmap = REFSPEC_INIT_FETCH;
 static struct list_objects_filter_options filter_options;
 static struct string_list server_options = STRING_LIST_INIT_DUP;
+static struct string_list negotiation_tip = STRING_LIST_INIT_NODUP;
 
 static int git_fetch_config(const char *k, const char *v, void *cb)
 {
@@ -174,6 +175,8 @@ static struct option builtin_fetch_options[] = {
 			TRANSPORT_FAMILY_IPV4),
 	OPT_SET_INT('6', "ipv6", &family, N_("use IPv6 addresses only"),
 			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_PARSE_LIST_OBJECTS_FILTER(&filter_options),
 	OPT_END()
 };
@@ -1049,6 +1052,40 @@ static void set_option(struct transport *transport, const char *name, const char
 			name, transport->url);
 }
 
+
+static int add_oid(const char *refname, const struct object_id *oid, int flags,
+		   void *cb_data)
+{
+	struct oid_array *oids = cb_data;
+
+	oid_array_append(oids, oid);
+	return 0;
+}
+
+static void add_negotiation_tips(struct git_transport_options *smart_options)
+{
+	struct oid_array *oids = xcalloc(1, sizeof(*oids));
+	int i;
+
+	for (i = 0; i < negotiation_tip.nr; i++) {
+		const char *s = negotiation_tip.items[i].string;
+		int old_nr;
+		if (!has_glob_specials(s)) {
+			struct object_id oid;
+			if (get_oid(s, &oid))
+				die("%s is not a valid object", s);
+			oid_array_append(oids, &oid);
+			continue;
+		}
+		old_nr = oids->nr;
+		for_each_glob_ref(add_oid, s, oids);
+		if (old_nr == oids->nr)
+			warning("Ignoring --negotiation-tip=%s because it does not match any refs",
+				s);
+	}
+	smart_options->negotiation_tips = oids;
+}
+
 static struct transport *prepare_transport(struct remote *remote, int deepen)
 {
 	struct transport *transport;
@@ -1075,6 +1112,12 @@ static struct transport *prepare_transport(struct remote *remote, int deepen)
 			   filter_options.filter_spec);
 		set_option(transport, TRANS_OPT_FROM_PROMISOR, "1");
 	}
+	if (negotiation_tip.nr) {
+		if (transport->smart_options)
+			add_negotiation_tips(transport->smart_options);
+		else
+			warning("Ignoring --negotiation-tip because the protocol does not support it.");
+	}
 	return transport;
 }