use io reader for GetFormatPatch (#105)

repo_pull.go

@@ -5,8 +5,10 @@
 package git
 
 import (
+	"bytes"
 	"container/list"
 	"fmt"
+	"io"
 	"strconv"
 	"strings"
 	"time"
@@ -75,6 +77,13 @@ func (repo *Repository) GetPatch(base, head string) ([]byte, error) {
 }
 
 // GetFormatPatch generates and returns format-patch data between given revisions.
-func (repo *Repository) GetFormatPatch(base, head string) ([]byte, error) {
-	return NewCommand("format-patch", "--binary", "--stdout", base + "..." + head).RunInDirBytes(repo.Path)
+func (repo *Repository) GetFormatPatch(base, head string) (io.Reader, error) {
+	stdout := new(bytes.Buffer)
+	stderr := new(bytes.Buffer)
+
+	if err := NewCommand("format-patch", "--binary", "--stdout", base+"..."+head).
+		RunInDirPipeline(repo.Path, stdout, stderr); err != nil {
+		return nil, concatenateError(err, stderr.String())
+	}
+	return stdout, nil
 }

repo_pull_test.go

@@ -5,15 +5,18 @@
 package git
 
 import (
+	"io/ioutil"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 )
 
 func TestGetFormatPatch(t *testing.T) {
-	repo, err := OpenRepository(".");
+	repo, err := OpenRepository(".")
 	assert.NoError(t, err)
-	patchb, err := repo.GetFormatPatch("cdb43f0e^", "cdb43f0e")
+	rd, err := repo.GetFormatPatch("cdb43f0e^", "cdb43f0e")
+	assert.NoError(t, err)
+	patchb, err := ioutil.ReadAll(rd)
 	assert.NoError(t, err)
 	patch := string(patchb)
 	assert.Regexp(t, "^From cdb43f0e", patch)