Improve memory usage for Blob.Data() by ~50% (go-gitea#96)

Signed-off-by: Duncan Ogilvie <mr.exodia.tpodt@gmail.com>

Author: mrexodia

blob.go

@@ -22,11 +22,16 @@ type Blob struct {
 // Data gets content of blob all at once and wrap it as io.Reader.
 // This can be very slow and memory consuming for huge content.
 func (b *Blob) Data() (io.Reader, error) {
-	stdout, err := NewCommand("show", b.ID.String()).RunInDirBytes(b.repo.Path)
-	if err != nil {
-		return nil, err
+	stdout := new(bytes.Buffer)
+	stderr := new(bytes.Buffer)
+
+	// Preallocate memory to save ~50% memory usage on big files.
+	stdout.Grow(int(b.Size() + 2048))
+
+	if err := b.DataPipeline(stdout, stderr); err != nil {
+		return nil, concatenateError(err, stderr.String())
 	}
-	return bytes.NewBuffer(stdout), nil
+	return stdout, nil
 }
 
 // DataPipeline gets content of blob and write the result or error to stdout or stderr

blob_test.go

@@ -17,6 +17,9 @@ var testBlob = &Blob{
 	repo: &Repository{},
 	TreeEntry: &TreeEntry{
 		ID: MustIDFromString("176d8dfe018c850d01851b05fb8a430096247353"),
+		ptree: &Tree{
+			repo: &Repository{},
+		},
 	},
 }