add head support for local repos

4 files changed, 65 insertions, 2 deletions

diff --git a/repository.go b/repository.go
index 0cda947..866f9ff 100644
--- a/repository.go
+++ b/repository.go
@@ -226,6 +226,10 @@ func (r *Repository) Head(remote string) (core.Hash, error) {
 		return r.localHead()
 	}
 
+	return r.remoteHead(remote)
+}
+
+func (r *Repository) remoteHead(remote string) (core.Hash, error) {
 	rem, ok := r.Remotes[remote]
 	if !ok {
 		return core.ZeroHash, fmt.Errorf("unable to find remote %q", remote)
@@ -235,5 +239,11 @@ func (r *Repository) Head(remote string) (core.Hash, error) {
 }
 
 func (r *Repository) localHead() (core.Hash, error) {
-	return core.ZeroHash, nil
+	storage, ok := r.Storage.(*seekable.ObjectStorage)
+	if !ok {
+		return core.ZeroHash,
+			fmt.Errorf("cannot retrieve local head: no local data found")
+	}
+
+	return storage.Head()
 }
diff --git a/repository_test.go b/repository_test.go
index da02a4d..eafbdf7 100644
--- a/repository_test.go
+++ b/repository_test.go
@@ -260,4 +260,8 @@ func (s *SuiteRepository) TestHeadFromRemoteError(c *C) {
 	remote := "not found"
 	_, err = r.Head(remote)
 	c.Assert(err, ErrorMatches, fmt.Sprintf("unable to find remote %q", remote))
+
+	remote = ""
+	_, err = r.Head(remote)
+	c.Assert(err, ErrorMatches, "cannot retrieve local head: no local data found")
 }
diff --git a/storage/seekable/internal/gitdir/gitdir.go b/storage/seekable/internal/gitdir/gitdir.go
index bfdf030..eea980b 100644
--- a/storage/seekable/internal/gitdir/gitdir.go
+++ b/storage/seekable/internal/gitdir/gitdir.go
@@ -25,6 +25,9 @@ var (
 	// ErrPackfileNotFound is returned by Packfile when the packfile is not found
 	// on the repository.
 	ErrPackfileNotFound = errors.New("packfile not found")
+	// ErrHeadfileNotFound is returned by Headfile when the HEAD file is not found
+	// on the repository.
+	ErrHeadfileNotFound = errors.New("headfile not found")
 )
 
 // The GitDir type represents a local git repository on disk. This
@@ -126,7 +129,7 @@ func (d *GitDir) Packfile() (fs.FS, string, error) {
 	return nil, "", ErrPackfileNotFound
 }
 
-// Packfile returns the path of the idx file (really, it returns the
+// Idxfile returns the path of the idx file (really, it returns the
 // path of the first file in the "objects/pack/" directory with an
 // ".idx" extension.
 func (d *GitDir) Idxfile() (fs.FS, string, error) {
diff --git a/storage/seekable/storage.go b/storage/seekable/storage.go
index 8d75700..db436c8 100644
--- a/storage/seekable/storage.go
+++ b/storage/seekable/storage.go
@@ -3,6 +3,7 @@ package seekable
 import (
 	"fmt"
 	"os"
+	"strings"
 
 	"gopkg.in/src-d/go-git.v3/core"
 	"gopkg.in/src-d/go-git.v3/formats/packfile"
@@ -150,3 +151,48 @@ func (s *ObjectStorage) Iter(t core.ObjectType) (core.ObjectIter, error) {
 
 	return core.NewObjectSliceIter(objects), nil
 }
+
+const (
+	headErrPrefix    = "cannot get HEAD reference:"
+	symrefCapability = "symref"
+	headRefPrefix    = "HEAD:"
+)
+
+// Head returns the hash of the HEAD reference
+func (s *ObjectStorage) Head() (core.Hash, error) {
+	cap, err := s.dir.Capabilities()
+	if err != nil {
+		return core.ZeroHash, fmt.Errorf("%s %s", headErrPrefix, err)
+	}
+
+	ok := cap.Supports(symrefCapability)
+	if !ok {
+		return core.ZeroHash,
+			fmt.Errorf("%s symref capability not supported", headErrPrefix)
+	}
+
+	symrefs := cap.Get(symrefCapability)
+	var headRef string
+	for _, ref := range symrefs.Values {
+		if strings.HasPrefix(ref, headRefPrefix) {
+			headRef = strings.TrimPrefix(ref, headRefPrefix)
+		}
+	}
+	if headRef == "" {
+		return core.ZeroHash, fmt.Errorf("%s HEAD reference not found",
+			headErrPrefix)
+	}
+
+	refs, err := s.dir.Refs()
+	if err != nil {
+		return core.ZeroHash, fmt.Errorf("%s %s", headErrPrefix, err)
+	}
+
+	head, ok := refs[headRef]
+	if !ok {
+		return core.ZeroHash, fmt.Errorf("%s reference %q not found",
+			headErrPrefix, headRef)
+	}
+
+	return head, nil
+}