fetch: pass refspec to http server

When fetching over http, send the requested refspec to the server.
The server will then only send refs matching that refspec.  It is
permitted for old servers to ignore that parameter, and the client
will automatically handle this.

When the server has many refs, and the client only wants a few, this
can save bandwidth and reduce fetch latency.

Signed-off-by: David Turner <dturner@twopensource.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

5 files changed, 98 insertions, 2 deletions

diff --git a/Documentation/technical/protocol-capabilities.txt b/Documentation/technical/protocol-capabilities.txt
index eaab6b4ac7..8c4a0b90ca 100644
--- a/Documentation/technical/protocol-capabilities.txt
+++ b/Documentation/technical/protocol-capabilities.txt
@@ -275,3 +275,26 @@ to accept a signed push certificate, and asks the <nonce> to be
 included in the push certificate.  A send-pack client MUST NOT
 send a push-cert packet unless the receive-pack server advertises
 this capability.
+
+interesting-refs
+----------------
+
+For HTTP(S) servers only:
+
+Whether or not the upload-pack server advertises this capability,
+fetch-pack may send a "refspec" parameter in the query string of a
+fetch request.  This capability indicates that such a parameter will
+be respected, in case the client cares.
+
+Whenever the receive-pack server gets that parameter, it will not
+advertise all refs and will instead only advertise refs that match
+those listed in the header. The parameter is a space-separated list of
+refs.  A ref may optionally contain up to one wildcard.
+Advertisements will still respect hideRefs.
+
+The presence or absence of the "refspec" parameter does not affect
+what refs a client is permitted to fetch; this is still controlled in
+the normal fashion.
+
+This saves time in the presence of a large number of refs, because the
+client need not wait for the server to send the complete list of refs.
diff --git a/builtin/fetch.c b/builtin/fetch.c
index de095551f0..f2492c5463 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -302,9 +302,27 @@ static struct ref *get_ref_map(struct transport *transport,
 
 	/* opportunistically-updated references: */
 	struct ref *orefs = NULL, **oref_tail = &orefs;
+	struct refspec *qualified_refspecs;
 	const struct ref *remote_refs;
 
-	remote_refs = transport_get_remote_refs(transport, NULL, 0);
+	qualified_refspecs = xcalloc(refspec_count, sizeof(*qualified_refspecs));
+	for (i = 0; i < refspec_count; i++) {
+		if (starts_with(refspecs[i].src, "refs/")) {
+			qualified_refspecs[i].src = xstrdup(refspecs[i].src);
+		} else {
+			struct strbuf buf = STRBUF_INIT;
+			strbuf_addf(&buf, "refs/heads/%s", refspecs[i].src);
+			qualified_refspecs[i].src = strbuf_detach(&buf, NULL);
+		}
+	}
+
+	remote_refs = transport_get_remote_refs(transport, qualified_refspecs,
+						refspec_count);
+
+	for (i = 0; i < refspec_count; i++) {
+		free(qualified_refspecs[i].src);
+	}
+	free(qualified_refspecs);
 
 	if (refspec_count) {
 		struct refspec *fetch_refspec;
diff --git a/remote-curl.c b/remote-curl.c
index b9b6a90aa3..e914d3f65b 100644
--- a/remote-curl.c
+++ b/remote-curl.c
@@ -20,6 +20,7 @@ static struct strbuf url = STRBUF_INIT;
 struct options {
 	int verbosity;
 	unsigned long depth;
+	char *refspec;
 	unsigned progress : 1,
 		check_self_contained_and_connected : 1,
 		cloning : 1,
@@ -43,6 +44,10 @@ static int set_option(const char *name, const char *value)
 		options.verbosity = v;
 		return 0;
 	}
+	else if (!strcmp(name, "refspec")) {
+		options.refspec = xstrdup(value);
+		return 0;
+	}
 	else if (!strcmp(name, "progress")) {
 		if (!strcmp(value, "true"))
 			options.progress = 1;
@@ -269,6 +274,8 @@ static struct discovery *discover_refs(const char *service, int for_push)
 		else
 			strbuf_addch(&refs_url, '&');
 		strbuf_addf(&refs_url, "service=%s", service);
+		if (options.refspec)
+			strbuf_addf(&refs_url, "&refspec=%s", options.refspec);
 	}
 
 	memset(&get_options, 0, sizeof(get_options));
diff --git a/t/t5552-http-fetch-branch.sh b/t/t5552-http-fetch-branch.sh
new file mode 100755
index 0000000000..0e905d90b7
--- /dev/null
+++ b/t/t5552-http-fetch-branch.sh
@@ -0,0 +1,42 @@
+#!/bin/sh
+
+test_description='fetch just one branch'
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-httpd.sh
+start_httpd
+
+test_expect_success 'setup repo' '
+	git init "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" &&
+	(
+		cd "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" &&
+		test_commit 1
+	)
+'
+
+test_expect_success 'clone http repository' '
+	git clone $HTTPD_URL/smart/repo.git clone
+'
+
+test_expect_success 'make some more commits' '
+	(
+		cd "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" &&
+		test_commit 2 &&
+		git checkout -b another_branch &&
+		test_commit 3
+		git checkout -b a_third_branch &&
+		test_commit 4
+	)
+'
+
+test_expect_success 'fetch with refspec only fetches requested branch' '
+	test_when_finished "rm trace" &&
+	(
+		cd clone &&
+		GIT_TRACE_PACKET="$TRASH_DIRECTORY/trace" git fetch origin another_branch &&
+		! grep "refs/heads/master" ../trace
+	)
+'
+
+stop_httpd
+test_done
diff --git a/transport-helper.c b/transport-helper.c
index b5c91d2cc4..7d75d64744 100644
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -40,6 +40,9 @@ struct helper_data {
 	struct git_transport_options transport_options;
 };
 
+static int set_helper_option(struct transport *transport,
+			     const char *name, const char *value);
+
 static void sendline(struct helper_data *helper, struct strbuf *buffer)
 {
 	if (debug)
@@ -109,6 +112,7 @@ static struct child_process *get_helper(struct transport *transport, const struc
 	int refspec_alloc = 0;
 	int duped;
 	int code;
+	int i;
 
 	if (data->helper)
 		return data->helper;
@@ -202,7 +206,6 @@ static struct child_process *get_helper(struct transport *transport, const struc
 		}
 	}
 	if (refspecs) {
-		int i;
 		data->refspec_nr = refspec_nr;
 		data->refspecs = parse_fetch_refspec(refspec_nr, refspecs);
 		for (i = 0; i < refspec_nr; i++)
@@ -214,6 +217,9 @@ static struct child_process *get_helper(struct transport *transport, const struc
 	strbuf_release(&buf);
 	if (debug)
 		fprintf(stderr, "Debug: Capabilities complete.\n");
+
+	for (i = 0; i < req_refspec_nr; i++)
+		set_helper_option(transport, "refspec", req_refspecs[i].src);
 	standard_options(transport);
 	return data->helper;
 }