fix(pkg/git/git.go): write the pre-receive hook script directly to the file descriptor

Fixes #321

Author: arschles

.gitignore

@@ -3,3 +3,4 @@ vendor/
 rootfs/usr/bin/
 ./builder
 coverage.txt
+testdata/hooks/pre-receive

pkg/git/git.go

@@ -7,7 +7,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -158,16 +157,20 @@ func createRepo(repoPath string) (bool, error) {
 
 // createPreReceiveHook renders preReceiveHookTpl to repoPath/hooks/pre-receive
 func createPreReceiveHook(gitHome, repoPath string) error {
-	// parse & generate the template anew each receive for each new git home
-	var hookByteBuf bytes.Buffer
-	if err := preReceiveHookTpl.Execute(&hookByteBuf, map[string]string{"GitHome": gitHome}); err != nil {
-		return err
+	writePath := filepath.Join(repoPath, "hooks", "pre-receive")
+	fd, err := os.Create(writePath)
+	if err != nil {
+		return fmt.Errorf("Cannot create pre-receive hook file at %s (%s)", writePath, err)
 	}
+	defer fd.Close()
 
-	writePath := filepath.Join(repoPath, "hooks", "pre-receive")
-	log.Info("Writing pre-receive hook to %s", writePath)
-	if err := ioutil.WriteFile(writePath, hookByteBuf.Bytes(), 0755); err != nil {
+	// parse & generate the template anew each receive for each new git home
+	if err := preReceiveHookTpl.Execute(fd, map[string]string{"GitHome": gitHome}); err != nil {
 		return fmt.Errorf("Cannot write pre-receive hook to %s (%s)", writePath, err)
 	}
+	if err := os.Chmod(writePath, 0755); err != nil {
+		return fmt.Errorf("Cannot change pre-receive hook script permissions (%s)", err)
+	}
+
 	return nil
 }

pkg/git/git_test.go

@@ -0,0 +1,24 @@
+package git
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/arschles/assert"
+)
+
+func TestCreatePreReceiveHook(t *testing.T) {
+	const gitHome = "TestGitHome"
+	gopath := os.Getenv("GOPATH")
+	repoPath := filepath.Join(gopath, "src", "github.com", "deis", "builder", "testdata")
+	assert.NoErr(t, createPreReceiveHook(gitHome, repoPath))
+	hookBytes, err := ioutil.ReadFile(filepath.Join(repoPath, "hooks", "pre-receive"))
+	assert.NoErr(t, err)
+	hookStr := string(hookBytes)
+	gitHomeIdx := strings.Index(hookStr, fmt.Sprintf("GIT_HOME=%s", gitHome))
+	assert.False(t, gitHomeIdx == -1, "GIT_HOME was not found")
+}