Refactor to use core.ObjectReader and core.ObjectWriter

* New function signatures provide the necessary interface to stream data from disk when using filesystem-based storage in the future
* New function signatures provide proper error handling
* ObjectReader and ObjectWriter interfaces added to avoid future refactoring, currently are type aliases for io.ReadCloser and io.WriteCloser respectively
* Object.Reader now returns (ObjectReader, error)
* Object.Writer now returns (ObjectWriter, error)
* File.Contents now returns (string, error)
* File.Lines now returns ([]string, error)
* Blob.Reader now returns (core.ObjectReader, error)
* Added internal close helper function for deferred calls to Close that need to check the return value

1 files changed, 20 insertions, 0 deletions

diff --git a/formats/packfile/common.go b/formats/packfile/common.go
index 57bc0b9..d207563 100644
--- a/formats/packfile/common.go
+++ b/formats/packfile/common.go
@@ -41,3 +41,23 @@ func (t *trackingReader) ReadByte() (c byte, err error) {
 	t.position++
 	return p[0], nil
 }
+
+// close is used with defer to close the given io.Closer and check its
+// returned error value. If Close returns an error and the given *error
+// is not nil, *error is set to the error returned by Close.
+//
+// close is typically used with named return values like so:
+//
+//   func do(obj *Object) (err error) {
+//     w, err := obj.Writer()
+//     if err != nil {
+//       return nil
+//     }
+//     defer close(w, &err)
+//     // work with w
+//   }
+func close(c io.Closer, err *error) {
+	if cerr := c.Close(); cerr != nil && *err == nil {
+		*err = cerr
+	}
+}