[PATCH/RFC 6/6] clone: send refspec for single-branch clones

[David Turner <dturner@twopensource.com>]

For single-branch clones (when we know in advance what the remote
branch name will be), send a refspec so that the server doesn't
tell us about any other refs.

Signed-off-by: David Turner <dturner@twopensource.com>
---
 builtin/clone.c              | 16 +++++++++++++++-
 t/t5552-http-fetch-branch.sh |  5 +++++
 transport-helper.c           | 12 +++++++++++-
 3 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/builtin/clone.c b/builtin/clone.c
index 91f668c..9a0291d 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -1010,7 +1010,21 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	if (transport->smart_options && !option_depth)
 		transport->smart_options->check_self_contained_and_connected = 1;
 
-	refs = transport_get_remote_refs(transport, NULL, 0);
+	if (option_single_branch && option_branch) {
+		struct refspec branch_refspec = {0};
+
+		if (starts_with(option_branch, "refs/")) {
+			branch_refspec.src = xstrdup(option_branch);
+		} else {
+			struct strbuf buf = STRBUF_INIT;
+			strbuf_addf(&buf, "refs/heads/%s", option_branch);
+			branch_refspec.src = strbuf_detach(&buf, NULL);
+		}
+		refs = transport_get_remote_refs(transport, &branch_refspec, 1);
+		free(branch_refspec.src);
+	} else {
+		refs = transport_get_remote_refs(transport, NULL, 0);
+	}
 
 	if (refs) {
 		mapped_refs = wanted_peer_refs(refs, refspec);
diff --git a/t/t5552-http-fetch-branch.sh b/t/t5552-http-fetch-branch.sh
index 0e905d9..8a8e218 100755
--- a/t/t5552-http-fetch-branch.sh
+++ b/t/t5552-http-fetch-branch.sh
@@ -38,5 +38,10 @@ test_expect_success 'fetch with refspec only fetches requested branch' '
 	)
 '
 
+test_expect_success 'single-branch clone only fetches requested branch' '
+	GIT_TRACE_PACKET="$TRASH_DIRECTORY/trace" git clone --single-branch -b master $HTTPD_URL/smart/repo.git sbc &&
+	! grep "refs/heads/another_branch" trace
+'
+
 stop_httpd
 test_done
diff --git a/transport-helper.c b/transport-helper.c
index 7d75d64..3775d63 100644
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -28,6 +28,7 @@ struct helper_data {
 		signed_tags : 1,
 		check_connectivity : 1,
 		no_disconnect_req : 1,
+		refspec : 1,
 		no_private_update : 1;
 	char *export_marks;
 	char *import_marks;
@@ -114,8 +115,15 @@ static struct child_process *get_helper(struct transport *transport, const struc
 	int code;
 	int i;
 
-	if (data->helper)
+	if (data->helper) {
+		if (!data->refspec && req_refspec_nr) {
+			for (i = 0; i < req_refspec_nr; i++)
+				set_helper_option(transport, "refspec",
+						  req_refspecs[i].src);
+			data->refspec = 1;
+		}
 		return data->helper;
+	}
 
 	helper = xmalloc(sizeof(*helper));
 	child_process_init(helper);
@@ -220,6 +228,8 @@ static struct child_process *get_helper(struct transport *transport, const struc
 
 	for (i = 0; i < req_refspec_nr; i++)
 		set_helper_option(transport, "refspec", req_refspecs[i].src);
+	if (req_refspec_nr)
+		data->refspec = 1;
 	standard_options(transport);
 	return data->helper;
 }
-- 
2.4.2.767.g62658d5-twtrsrc