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

2 files changed, 74 insertions, 10 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
+	}
+}
diff --git a/formats/packfile/reader.go b/formats/packfile/reader.go
index 6f30f8a..e14b84e 100644
--- a/formats/packfile/reader.go
+++ b/formats/packfile/reader.go
@@ -187,7 +187,7 @@ func (r *Reader) newObject() (core.Object, error) {
 	return raw, err
 }
 
-func (r *Reader) readREFDelta(raw core.Object) error {
+func (r *Reader) readREFDelta(raw core.Object) (err error) {
 	var ref core.Hash
 	if _, err := io.ReadFull(r.r, ref[:]); err != nil {
 		return err
@@ -206,7 +206,17 @@ func (r *Reader) readREFDelta(raw core.Object) error {
 		return err
 	}
 
-	d, _ := ioutil.ReadAll(referenced.Reader())
+	reader, err := referenced.Reader()
+	if err != nil {
+		return err
+	}
+	defer close(reader, &err)
+
+	d, err := ioutil.ReadAll(reader)
+	if err != nil {
+		return err
+	}
+
 	patched := patchDelta(d, buf.Bytes())
 	if patched == nil {
 		return PatchingErr.n("hash %q", ref)
@@ -214,12 +224,19 @@ func (r *Reader) readREFDelta(raw core.Object) error {
 
 	raw.SetType(referenced.Type())
 	raw.SetSize(int64(len(patched)))
-	raw.Writer().Write(patched)
+
+	writer, err := raw.Writer()
+	if err != nil {
+		return err
+	}
+	defer close(writer, &err)
+
+	writer.Write(patched)
 
 	return nil
 }
 
-func (r *Reader) readOFSDelta(raw core.Object, steps int64) error {
+func (r *Reader) readOFSDelta(raw core.Object, steps int64) (err error) {
 	start := r.r.position
 	offset, err := decodeOffset(r.r, steps)
 	if err != nil {
@@ -227,7 +244,7 @@ func (r *Reader) readOFSDelta(raw core.Object, steps int64) error {
 	}
 
 	buf := bytes.NewBuffer(nil)
-	if err := r.inflate(buf); err != nil {
+	if err = r.inflate(buf); err != nil {
 		return err
 	}
 
@@ -236,8 +253,22 @@ func (r *Reader) readOFSDelta(raw core.Object, steps int64) error {
 		return PackEntryNotFoundErr.n("offset %d", start+offset)
 	}
 
-	referenced, _ := r.s.Get(ref) // FIXME: Handle error returned from Get()
-	d, _ := ioutil.ReadAll(referenced.Reader())
+	referenced, err := r.s.Get(ref)
+	if err != nil {
+		return err
+	}
+
+	reader, err := referenced.Reader()
+	if err != nil {
+		return err
+	}
+	defer close(reader, &err)
+
+	d, err := ioutil.ReadAll(reader)
+	if err != nil {
+		return err
+	}
+
 	patched := patchDelta(d, buf.Bytes())
 	if patched == nil {
 		return PatchingErr.n("hash %q", ref)
@@ -245,13 +276,26 @@ func (r *Reader) readOFSDelta(raw core.Object, steps int64) error {
 
 	raw.SetType(referenced.Type())
 	raw.SetSize(int64(len(patched)))
-	raw.Writer().Write(patched)
+
+	writer, err := raw.Writer()
+	if err != nil {
+		return err
+	}
+	defer close(writer, &err)
+
+	writer.Write(patched)
 
 	return nil
 }
 
-func (r *Reader) readObject(raw core.Object) error {
-	return r.inflate(raw.Writer())
+func (r *Reader) readObject(raw core.Object) (err error) {
+	writer, err := raw.Writer()
+	if err != nil {
+		return err
+	}
+	defer close(writer, &err)
+
+	return r.inflate(writer)
 }
 
 func (r *Reader) inflate(w io.Writer) error {