Handle EEXIST when finalizing git archive

Closes https://gitlab.com/gitlab-org/gitlab-workhorse/issues/63

internal/git/archive.go

@@ -173,7 +173,11 @@ func finalizeCachedArchive(tempFile *os.File, archivePath string) error {
 	if err := tempFile.Close(); err != nil {
 		return err
 	}
-	return os.Link(tempFile.Name(), archivePath)
+	if err := os.Link(tempFile.Name(), archivePath); err != nil && !os.IsExist(err) {
+		return err
+	}
+
+	return nil
 }
 
 func parseBasename(basename string) (string, bool) {

internal/git/archive_test.go

 package git
 
 import (
+	"io/ioutil"
 	"testing"
 )
 
@@ -27,3 +28,17 @@ func TestParseBasename(t *testing.T) {
 		}
 	}
 }
+
+func TestFinalizeArchive(t *testing.T) {
+	tempFile, err := ioutil.TempFile("", "gitlab-workhorse-test")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer tempFile.Close()
+
+	// Deliberately cause an EEXIST error: we know tempFile.Name() already exists
+	err = finalizeCachedArchive(tempFile, tempFile.Name())
+	if err != nil {
+		t.Fatalf("expected nil from finalizeCachedArchive, received %v", err)
+	}
+}