1 files changed, 142 insertions, 0 deletions
diff --git a/cmd/gitaly-git2go/rebase.go b/cmd/gitaly-git2go/rebase.go
new file mode 100644
index 000000000..9bb13f2a6
--- /dev/null
+++ b/cmd/gitaly-git2go/rebase.go
@@ -0,0 +1,142 @@
+// +build static,system_libgit2
+
+package main
+
+import (
+	"context"
+	"encoding/gob"
+	"errors"
+	"flag"
+	"fmt"
+	"io"
+
+	git "github.com/libgit2/git2go/v31"
+	"gitlab.com/gitlab-org/gitaly/internal/git2go"
+)
+
+type rebaseSubcommand struct{}
+
+func (cmd *rebaseSubcommand) Flags() *flag.FlagSet {
+	return flag.NewFlagSet("rebase", flag.ExitOnError)
+}
+
+func (cmd *rebaseSubcommand) Run(ctx context.Context, r io.Reader, w io.Writer) error {
+	var request git2go.RebaseCommand
+	if err := gob.NewDecoder(r).Decode(&request); err != nil {
+		return err
+	}
+
+	commitID, err := cmd.rebase(ctx, &request)
+	return gob.NewEncoder(w).Encode(git2go.Result{
+		CommitID: commitID,
+		Error:    git2go.SerializableError(err),
+	})
+}
+
+func (cmd *rebaseSubcommand) verify(ctx context.Context, r *git2go.RebaseCommand) error {
+	if r.Repository == "" {
+		return errors.New("missing repository")
+	}
+	if r.Committer.Name == "" {
+		return errors.New("missing committer name")
+	}
+	if r.Committer.Email == "" {
+		return errors.New("missing committer email")
+	}
+	if r.BranchName == "" {
+		return errors.New("missing branch name")
+	}
+	if r.UpstreamRevision == "" {
+		return errors.New("missing upstream revision")
+	}
+	return nil
+}
+
+func (cmd *rebaseSubcommand) rebase(ctx context.Context, request *git2go.RebaseCommand) (string, error) {
+	if err := cmd.verify(ctx, request); err != nil {
+		return "", err
+	}
+
+	repo, err := git.OpenRepository(request.Repository)
+	if err != nil {
+		return "", fmt.Errorf("open repository: %w", err)
+	}
+
+	opts, err := git.DefaultRebaseOptions()
+	if err != nil {
+		return "", fmt.Errorf("get rebase options: %w", err)
+	}
+	opts.InMemory = 1
+
+	branch, err := repo.AnnotatedCommitFromRevspec(fmt.Sprintf("refs/heads/%s", request.BranchName))
+	if err != nil {
+		return "", fmt.Errorf("look up branch %q: %w", request.BranchName, err)
+	}
+
+	ontoOid, err := git.NewOid(request.UpstreamRevision)
+	if err != nil {
+		return "", fmt.Errorf("parse upstream revision %q: %w", request.UpstreamRevision, err)
+	}
+
+	onto, err := repo.LookupAnnotatedCommit(ontoOid)
+	if err != nil {
+		return "", fmt.Errorf("look up upstream revision %q: %w", request.UpstreamRevision, err)
+	}
+
+	mergeBase, err := repo.MergeBase(onto.Id(), branch.Id())
+	if err != nil {
+		return "", fmt.Errorf("find merge base: %w", err)
+	}
+
+	if mergeBase.Equal(onto.Id()) {
+		// Branch is zero commits behind, so do not rebase
+		return branch.Id().String(), nil
+	}
+
+	if mergeBase.Equal(branch.Id()) {
+		// Branch is merged, so fast-forward to upstream
+		return onto.Id().String(), nil
+	}
+
+	mergeCommit, err := repo.LookupAnnotatedCommit(mergeBase)
+	if err != nil {
+		return "", fmt.Errorf("look up merge base: %w", err)
+	}
+
+	rebase, err := repo.InitRebase(branch, mergeCommit, onto, &opts)
+	if err != nil {
+		return "", fmt.Errorf("initiate rebase: %w", err)
+	}
+
+	committer := git.Signature(request.Committer)
+	var oid *git.Oid
+	for {
+		op, err := rebase.Next()
+		if git.IsErrorCode(err, git.ErrIterOver) {
+			break
+		} else if err != nil {
+			return "", fmt.Errorf("rebase iterate: %w", err)
+		}
+
+		commit, err := repo.LookupCommit(op.Id)
+		if err != nil {
+			return "", fmt.Errorf("lookup commit: %w", err)
+		}
+
+		oid = op.Id.Copy()
+		err = rebase.Commit(oid, nil, &committer, commit.Message())
+		if err != nil {
+			return "", fmt.Errorf("commit %q: %w", op.Id.String(), err)
+		}
+	}
+
+	if oid == nil {
+		return branch.Id().String(), nil
+	}
+
+	if err = rebase.Finish(); err != nil {
+		return "", fmt.Errorf("finish rebase: %w", err)
+	}
+
+	return oid.String(), nil
+}