add internal git ReadAPI/WriteAPI impl scaffolding + refactor GitBlobstore reads

go/store/blobstore/git_blobstore.go

@@ -34,6 +34,7 @@ type GitBlobstore struct {
 	gitDir string
 	ref    string
 	runner *git.Runner
+	api    git.GitAPI
 }
 
 var _ Blobstore = (*GitBlobstore)(nil)
@@ -45,7 +46,7 @@ func NewGitBlobstore(gitDir, ref string) (*GitBlobstore, error) {
 	if err != nil {
 		return nil, err
 	}
-	return &GitBlobstore{gitDir: gitDir, ref: ref, runner: r}, nil
+	return &GitBlobstore{gitDir: gitDir, ref: ref, runner: r, api: git.NewGitAPIImpl(r)}, nil
 }
 
 func (gbs *GitBlobstore) Path() string {
@@ -57,14 +58,14 @@ func (gbs *GitBlobstore) Exists(ctx context.Context, key string) (bool, error) {
 	if err != nil {
 		return false, err
 	}
-	commit, ok, err := git.TryResolveRefCommit(ctx, gbs.runner, gbs.ref)
+	commit, ok, err := gbs.api.TryResolveRefCommit(ctx, gbs.ref)
 	if err != nil {
 		return false, err
 	}
 	if !ok {
 		return false, nil
 	}
-	_, err = git.ResolvePathBlob(ctx, gbs.runner, commit, key)
+	_, err = gbs.api.ResolvePathBlob(ctx, commit, key)
 	if err != nil {
 		if git.IsPathNotFound(err) {
 			return false, nil
@@ -79,7 +80,7 @@ func (gbs *GitBlobstore) Get(ctx context.Context, key string, br BlobRange) (io.
 	if err != nil {
 		return nil, 0, "", err
 	}
-	commit, ok, err := git.TryResolveRefCommit(ctx, gbs.runner, gbs.ref)
+	commit, ok, err := gbs.api.TryResolveRefCommit(ctx, gbs.ref)
 	if err != nil {
 		return nil, 0, "", err
 	}
@@ -92,23 +93,23 @@ func (gbs *GitBlobstore) Get(ctx context.Context, key string, br BlobRange) (io.
 		return nil, 0, "", &git.RefNotFoundError{Ref: gbs.ref}
 	}
 
-	blobOID, err := git.ResolvePathBlob(ctx, gbs.runner, commit, key)
+	blobOID, err := gbs.api.ResolvePathBlob(ctx, commit, key)
 	if err != nil {
 		if git.IsPathNotFound(err) {
 			return nil, 0, commit.String(), NotFound{Key: key}
 		}
 		return nil, 0, commit.String(), err
 	}
 
-	sz, err := git.BlobSize(ctx, gbs.runner, blobOID)
+	sz, err := gbs.api.BlobSize(ctx, blobOID)
 	if err != nil {
 		return nil, 0, commit.String(), err
 	}
 
 	// TODO(gitblobstore): This streaming implementation is correct but may be slow for workloads
 	// that do many small ranged reads (e.g. table index/footer reads). Consider caching/materializing
 	// blobs to a local file (or using a batched git cat-file mode) to serve ranges efficiently.
-	rc, err := git.BlobReader(ctx, gbs.runner, blobOID)
+	rc, err := gbs.api.BlobReader(ctx, blobOID)
 	if err != nil {
 		return nil, 0, commit.String(), err
 	}

go/store/blobstore/internal/git/write.go → go/store/blobstore/internal/git/api.go

@@ -16,16 +16,33 @@ package git
 
 import (
 	"context"
-	"fmt"
+	"io"
 )
 
-// WriteAPI defines the git plumbing operations needed for Approach A (temporary index
-// via GIT_INDEX_FILE) to perform updates without a working tree checkout.
-//
-// This file intentionally does not implement these operations yet; the current
-// GitBlobstore milestone is read-only. All methods on the default implementation
-// return ErrUnimplemented.
-type WriteAPI interface {
+// GitAPI defines the git plumbing operations needed by GitBlobstore. It includes both
+// read and write operations to allow swapping implementations (e.g. git CLI vs a Go git
+// library) while keeping callers stable.
+type GitAPI interface {
+	// TryResolveRefCommit resolves |ref| to a commit OID. Returns ok=false if the ref does not exist.
+	TryResolveRefCommit(ctx context.Context, ref string) (oid OID, ok bool, err error)
+
+	// ResolveRefCommit resolves |ref| to a commit OID, returning RefNotFoundError if missing.
+	ResolveRefCommit(ctx context.Context, ref string) (OID, error)
+
+	// ResolvePathBlob resolves |path| within |commit| to a blob OID.
+	// It returns PathNotFoundError if the path does not exist, and NotBlobError if it
+	// resolves to a non-blob object.
+	ResolvePathBlob(ctx context.Context, commit OID, path string) (OID, error)
+
+	// CatFileType returns the git object type for |oid| (e.g. "blob", "tree", "commit").
+	CatFileType(ctx context.Context, oid OID) (string, error)
+
+	// BlobSize returns the size in bytes of the blob object |oid|.
+	BlobSize(ctx context.Context, oid OID) (int64, error)
+
+	// BlobReader returns a reader for blob contents.
+	BlobReader(ctx context.Context, oid OID) (io.ReadCloser, error)
+
 	// ReadTree populates |indexFile| with the entries from |commit|'s root tree.
 	// Equivalent plumbing:
 	//   GIT_DIR=... GIT_INDEX_FILE=<indexFile> git read-tree <commit>^{tree}
@@ -62,43 +79,9 @@ type WriteAPI interface {
 	UpdateRef(ctx context.Context, ref string, newOID OID, msg string) error
 }
 
-// Identity represents git author/committer metadata. A future implementation
-// may set this via environment variables (GIT_AUTHOR_NAME, etc.).
+// Identity represents git author/committer metadata. A future implementation may set
+// this via environment variables (GIT_AUTHOR_NAME, etc.).
 type Identity struct {
 	Name  string
 	Email string
 }
-
-// UnimplementedWriteAPI is the default write API for the read-only milestone.
-// It can be embedded or returned by constructors to make write paths fail fast.
-type UnimplementedWriteAPI struct{}
-
-var _ WriteAPI = UnimplementedWriteAPI{}
-
-func (UnimplementedWriteAPI) ReadTree(ctx context.Context, commit OID, indexFile string) error {
-	return fmt.Errorf("%w: ReadTree", ErrUnimplemented)
-}
-
-func (UnimplementedWriteAPI) ReadTreeEmpty(ctx context.Context, indexFile string) error {
-	return fmt.Errorf("%w: ReadTreeEmpty", ErrUnimplemented)
-}
-
-func (UnimplementedWriteAPI) UpdateIndexCacheInfo(ctx context.Context, indexFile string, mode string, oid OID, path string) error {
-	return fmt.Errorf("%w: UpdateIndexCacheInfo", ErrUnimplemented)
-}
-
-func (UnimplementedWriteAPI) WriteTree(ctx context.Context, indexFile string) (OID, error) {
-	return "", fmt.Errorf("%w: WriteTree", ErrUnimplemented)
-}
-
-func (UnimplementedWriteAPI) CommitTree(ctx context.Context, tree OID, parent *OID, message string, author *Identity) (OID, error) {
-	return "", fmt.Errorf("%w: CommitTree", ErrUnimplemented)
-}
-
-func (UnimplementedWriteAPI) UpdateRefCAS(ctx context.Context, ref string, newOID OID, oldOID OID, msg string) error {
-	return fmt.Errorf("%w: UpdateRefCAS", ErrUnimplemented)
-}
-
-func (UnimplementedWriteAPI) UpdateRef(ctx context.Context, ref string, newOID OID, msg string) error {
-	return fmt.Errorf("%w: UpdateRef", ErrUnimplemented)
-}

go/store/blobstore/internal/git/errors.go

@@ -56,11 +56,6 @@ func (e *NotBlobError) Error() string {
 	return fmt.Sprintf("git path is not a blob (%s): %s:%s", e.Type, e.Commit, e.Path)
 }
 
-func IsRefNotFound(err error) bool {
-	var e *RefNotFoundError
-	return errors.As(err, &e)
-}
-
 func IsPathNotFound(err error) bool {
 	var e *PathNotFoundError
 	return errors.As(err, &e)