[RFC PATCH v2 2/4] transport: do not list refs if possible

[Jonathan Tan]

When all refs to be fetched are exact OIDs, it is possible to perform a
fetch without requiring the remote to list refs if protocol v2 is used.
Teach Git to do this.

This currently has an effect only for lazy fetches done from partial
clones. The change necessary to likewise optimize "git fetch <remote>
<sha-1>" will be done in a subsequent patch.

Signed-off-by: Jonathan Tan <jonathanta...@google.com>
---
 fetch-pack.c           |  2 +-
 t/t5702-protocol-v2.sh |  5 +++++
 transport.c            | 13 +++++++++++--
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/fetch-pack.c b/fetch-pack.c
index 75047a4b2a..15652b4776 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -1598,7 +1598,7 @@ struct ref *fetch_pack(struct fetch_pack_args *args,
        if (nr_sought)
                nr_sought = remove_duplicates_in_refs(sought, nr_sought);
 
-       if (!ref) {
+       if (version != protocol_v2 && !ref) {
                packet_flush(fd[1]);
                die(_("no matching remote head"));
        }
diff --git a/t/t5702-protocol-v2.sh b/t/t5702-protocol-v2.sh
index 3beeed4546..a316bb9bf4 100755
--- a/t/t5702-protocol-v2.sh
+++ b/t/t5702-protocol-v2.sh
@@ -286,6 +286,11 @@ test_expect_success 'dynamically fetch missing object' '
        grep "version 2" trace
 '
 
+test_expect_success 'when dynamically fetching missing object, do not list 
refs' '
+       cat trace &&
+       ! grep "git> command=ls-refs" trace
+'
+
 test_expect_success 'partial fetch' '
        rm -rf client "$(pwd)/trace" &&
        git init client &&
diff --git a/transport.c b/transport.c
index 5fb9ff6b56..4329cca8e5 100644
--- a/transport.c
+++ b/transport.c
@@ -341,8 +341,17 @@ static int fetch_refs_via_pack(struct transport *transport,
        args.server_options = transport->server_options;
        args.negotiation_tips = data->options.negotiation_tips;
 
-       if (!data->got_remote_heads)
-               refs_tmp = get_refs_via_connect(transport, 0, NULL);
+       if (!data->got_remote_heads) {
+               int i;
+               int must_list_refs = 0;
+               for (i = 0; i < nr_heads; i++) {
+                       if (!to_fetch[i]->exact_oid) {
+                               must_list_refs = 1;
+                               break;
+                       }
+               }
+               refs_tmp = handshake(transport, 0, NULL, must_list_refs);
+       }
 
        switch (data->version) {
        case protocol_v2:
-- 
2.19.0.605.g01d371f741-goog