Attempt to find the correct default git branch (#1217)

Signed-off-by: Dave Henderson <dhenderson@gmail.com>

1 files changed, 52 insertions, 0 deletions

diff --git a/data/datasource_git.go b/data/datasource_git.go
index 6c2491de..bd1811b4 100644
--- a/data/datasource_git.go
+++ b/data/datasource_git.go
@@ -14,12 +14,14 @@ import (
 
 	"github.com/hairyhenderson/gomplate/v3/base64"
 	"github.com/hairyhenderson/gomplate/v3/env"
+	"github.com/rs/zerolog"
 
 	"github.com/go-git/go-billy/v5"
 	"github.com/go-git/go-billy/v5/memfs"
 	"github.com/go-git/go-git/v5"
 	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/plumbing/transport"
+	"github.com/go-git/go-git/v5/plumbing/transport/client"
 	"github.com/go-git/go-git/v5/plumbing/transport/http"
 	"github.com/go-git/go-git/v5/plumbing/transport/ssh"
 	"github.com/go-git/go-git/v5/storage/memory"
@@ -141,6 +143,7 @@ func cloneURL(u *url.URL) *url.URL {
 	return out
 }
 
+// refFromURL - extract the ref from the URL fragment if present
 func (g gitsource) refFromURL(u *url.URL) plumbing.ReferenceName {
 	switch {
 	case strings.HasPrefix(u.Fragment, "refs/"):
@@ -152,6 +155,44 @@ func (g gitsource) refFromURL(u *url.URL) plumbing.ReferenceName {
 	}
 }
 
+// refFromRemoteHead - extract the ref from the remote HEAD, to work around
+// hard-coded 'master' default branch in go-git.
+// Should be unnecessary once https://github.com/go-git/go-git/issues/249 is
+// fixed.
+func (g gitsource) refFromRemoteHead(ctx context.Context, u *url.URL, auth transport.AuthMethod) (plumbing.ReferenceName, error) {
+	e, err := transport.NewEndpoint(u.String())
+	if err != nil {
+		return "", err
+	}
+
+	cli, err := client.NewClient(e)
+	if err != nil {
+		return "", err
+	}
+
+	s, err := cli.NewUploadPackSession(e, auth)
+	if err != nil {
+		return "", err
+	}
+
+	info, err := s.AdvertisedReferencesContext(ctx)
+	if err != nil {
+		return "", err
+	}
+
+	refs, err := info.AllReferences()
+	if err != nil {
+		return "", err
+	}
+
+	headRef, ok := refs["HEAD"]
+	if !ok {
+		return "", fmt.Errorf("no HEAD ref found")
+	}
+
+	return headRef.Target(), nil
+}
+
 // clone a repo for later reading through http(s), git, or ssh. u must be the URL to the repo
 // itself, and must have any file path stripped
 func (g gitsource) clone(ctx context.Context, repoURL *url.URL, depth int) (billy.Filesystem, *git.Repository, error) {
@@ -175,6 +216,17 @@ func (g gitsource) clone(ctx context.Context, repoURL *url.URL, depth int) (bill
 	u.Fragment = ""
 	u.RawQuery = ""
 
+	// attempt to get the ref from the remote so we don't default to master
+	if ref == "" {
+		ref, err = g.refFromRemoteHead(ctx, u, auth)
+		if err != nil {
+			zerolog.Ctx(ctx).Warn().
+				Stringer("repoURL", u).
+				Err(err).
+				Msg("failed to get ref from remote, using default")
+		}
+	}
+
 	opts := &git.CloneOptions{
 		URL:           u.String(),
 		Auth:          auth,