remote: use reference deltas on push when the remote server does not

support offset deltas

Signed-off-by: Benjamin Ash <bash@intelerad.com>

Author: Benjamin Ash

remote.go

@@ -155,7 +155,7 @@ func (r *Remote) PushContext(ctx context.Context, o *PushOptions) (err error) {
 		}
 	}
 
-	rs, err := pushHashes(ctx, s, r.s, req, hashesToPush)
+	rs, err := pushHashes(ctx, s, r.s, req, hashesToPush, r.useRefDeltas(ar))
 	if err != nil {
 		return err
 	}
@@ -167,6 +167,10 @@ func (r *Remote) PushContext(ctx context.Context, o *PushOptions) (err error) {
 	return r.updateRemoteReferenceStorage(req, rs)
 }
 
+func (r *Remote) useRefDeltas(ar *packp.AdvRefs) bool {
+	return !ar.Capabilities.Supports(capability.OFSDelta)
+}
+
 func (r *Remote) newReferenceUpdateRequest(
 	o *PushOptions,
 	localRefs []*plumbing.Reference,
@@ -994,6 +998,7 @@ func pushHashes(
 	s storage.Storer,
 	req *packp.ReferenceUpdateRequest,
 	hs []plumbing.Hash,
+	useRefDeltas bool,
 ) (*packp.ReportStatus, error) {
 
 	rd, wr := io.Pipe()
@@ -1004,7 +1009,7 @@ func pushHashes(
 	}
 	done := make(chan error)
 	go func() {
-		e := packfile.NewEncoder(wr, s, false)
+		e := packfile.NewEncoder(wr, s, useRefDeltas)
 		if _, err := e.Encode(hs, config.Pack.Window); err != nil {
 			done <- wr.CloseWithError(err)
 			return

remote_test.go

@@ -11,6 +11,7 @@ import (
 	"gopkg.in/src-d/go-git.v4/plumbing"
 	"gopkg.in/src-d/go-git.v4/plumbing/cache"
 	"gopkg.in/src-d/go-git.v4/plumbing/protocol/packp"
+	"gopkg.in/src-d/go-git.v4/plumbing/protocol/packp/capability"
 	"gopkg.in/src-d/go-git.v4/plumbing/storer"
 	"gopkg.in/src-d/go-git.v4/storage"
 	"gopkg.in/src-d/go-git.v4/storage/filesystem"
@@ -798,3 +799,25 @@ func (s *RemoteSuite) TestUpdateShallows(c *C) {
 		c.Assert(shallow, DeepEquals, t.result)
 	}
 }
+
+func (s *RemoteSuite) TestUseRefDeltas(c *C) {
+	url := c.MkDir()
+	_, err := PlainInit(url, true)
+	c.Assert(err, IsNil)
+
+	fs := fixtures.ByURL("https://github.com/git-fixtures/tags.git").One().DotGit()
+	sto := filesystem.NewStorage(fs, cache.NewObjectLRUDefault())
+
+	r := newRemote(sto, &config.RemoteConfig{
+		Name: DefaultRemoteName,
+		URLs: []string{url},
+	})
+
+	ar := packp.NewAdvRefs()
+
+	ar.Capabilities.Add(capability.OFSDelta)
+	c.Assert(r.useRefDeltas(ar), Equals, false)
+
+	ar.Capabilities.Delete(capability.OFSDelta)
+	c.Assert(r.useRefDeltas(ar), Equals, true)
+}