transport-helper: skip ls-refs if unnecessary

Commit e70a3030e7 ("fetch: do not list refs if fetching only hashes",
2018-10-07) and its ancestors taught Git, as an optimization, to skip
the ls-refs step when it is not necessary during a protocol v2 fetch
(for example, when lazy fetching a missing object in a partial clone, or
when running "git fetch --no-tags <remote> <SHA-1>"). But that was only
done for natively supported protocols; in particular, HTTP was not
supported.

Teach Git to skip ls-refs when using remote helpers that support connect
or stateless-connect. To do this, fetch() is made an acceptable entry
point. Because fetch() can now be the first function in the vtable
called, "get_helper(transport);" has to be added to the beginning of
that function to set the transport up (if not yet set up) before
process_connect() is invoked.

When fetch() is called, the transport could be taken over (this happens
if "connect" or "stateless-connect" is successfully run without any
"fallback" response), or not. If the transport is taken over, execution
continues like execution for natively supported protocols
(fetch_refs_via_pack() is executed, which will fetch refs using ls-refs
if needed). If not, the remote helper interface will invoke
get_refs_list() if it hasn't been invoked yet, preserving existing
behavior.

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

1 files changed, 13 insertions, 0 deletions

diff --git a/t/t5702-protocol-v2.sh b/t/t5702-protocol-v2.sh
index fbddd0aea9..ae9175cedf 100755
--- a/t/t5702-protocol-v2.sh
+++ b/t/t5702-protocol-v2.sh
@@ -631,6 +631,19 @@ test_expect_success 'fetch with http:// using protocol v2' '
 	grep "git< version 2" log
 '
 
+test_expect_success 'fetch with http:// by hash without tag following with protocol v2 does not list refs' '
+	test_when_finished "rm -f log" &&
+
+	test_commit -C "$HTTPD_DOCUMENT_ROOT_PATH/http_parent" two_a &&
+	git -C "$HTTPD_DOCUMENT_ROOT_PATH/http_parent" rev-parse two_a >two_a_hash &&
+
+	GIT_TRACE_PACKET="$(pwd)/log" git -C http_child -c protocol.version=2 \
+		fetch --no-tags origin $(cat two_a_hash) &&
+
+	grep "fetch< version 2" log &&
+	! grep "fetch> command=ls-refs" log
+'
+
 test_expect_success 'fetch from namespaced repo respects namespaces' '
 	test_when_finished "rm -f log" &&