remote: add the last 100 commits for each ref in haves list

If the local ref is not an ancestor of the remote ref being fetched,
then when we send an UploadPack request with that local ref as one of
the Haves, the remote will not recognize it, and will think we are
asking for the entire history of the repo, even if there's a common
ancestor.

To do this right, we need to support the multi-ack protocol so we can
negotiate a common commit.  That's hard though; this is a quick fix
just to include the previous 100 commits for each local ref in the
Haves list, and hope that one of them is the common commit.

Author: strib

remote.go

@@ -284,7 +284,7 @@ func (r *Remote) fetch(ctx context.Context, o *FetchOptions) (storer.ReferenceSt
 
 	req.Wants, err = getWants(r.s, refs)
 	if len(req.Wants) > 0 {
-		req.Haves, err = getHaves(localRefs)
+		req.Haves, err = getHaves(localRefs, remoteRefs, r.s)
 		if err != nil {
 			return nil, err
 		}
@@ -490,8 +490,29 @@ func (r *Remote) references() ([]*plumbing.Reference, error) {
 	return localRefs, nil
 }
 
-func getHaves(localRefs []*plumbing.Reference) ([]plumbing.Hash, error) {
+func getHaves(
+	localRefs []*plumbing.Reference,
+	remoteRefs storer.ReferenceStorer,
+	s storage.Storer,
+) ([]plumbing.Hash, error) {
 	haves := map[plumbing.Hash]bool{}
+
+	// Build a map of all the remote references, to avoid loading too
+	// many parent commits for references we know don't need to be
+	// transferred.
+	stopEarlyRefs := map[plumbing.Hash]bool{}
+	iter, err := remoteRefs.IterReferences()
+	if err != nil {
+		return nil, err
+	}
+	err = iter.ForEach(func(ref *plumbing.Reference) error {
+		stopEarlyRefs[ref.Hash()] = true
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+
 	for _, ref := range localRefs {
 		if haves[ref.Hash()] == true {
 			continue
@@ -501,7 +522,36 @@ func getHaves(localRefs []*plumbing.Reference) ([]plumbing.Hash, error) {
 			continue
 		}
 
-		haves[ref.Hash()] = true
+		// No need to load the commit if we know the remote already
+		// has this hash.
+		if stopEarlyRefs[ref.Hash()] {
+			haves[ref.Hash()] = true
+			continue
+		}
+
+		commit, err := object.GetCommit(s, ref.Hash())
+		if err != nil {
+			haves[ref.Hash()] = true
+			continue
+		}
+
+		// Until go-git supports proper commit negotiation during an
+		// upload pack request, include up to 100 commits from the
+		// history of each ref.
+		walker := object.NewCommitPreorderIter(commit, haves, nil)
+		const maxToVisit = 100
+		toVisit := maxToVisit
+		err = walker.ForEach(func(c *object.Commit) error {
+			haves[c.Hash] = true
+			toVisit--
+			if toVisit == 0 || stopEarlyRefs[c.Hash] {
+				return storer.ErrStop
+			}
+			return nil
+		})
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	var result []plumbing.Hash

remote_test.go

@@ -625,6 +625,10 @@ func (s *RemoteSuite) TestPushWrongRemoteName(c *C) {
 }
 
 func (s *RemoteSuite) TestGetHaves(c *C) {
+	f := fixtures.Basic().One()
+	sto, err := filesystem.NewStorage(f.DotGit())
+	c.Assert(err, IsNil)
+
 	var localRefs = []*plumbing.Reference{
 		plumbing.NewReferenceFromStrings(
 			"foo",
@@ -640,7 +644,7 @@ func (s *RemoteSuite) TestGetHaves(c *C) {
 		),
 	}
 
-	l, err := getHaves(localRefs)
+	l, err := getHaves(localRefs, memory.NewStorage(), sto)
 	c.Assert(err, IsNil)
 	c.Assert(l, HasLen, 2)
 }