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

3 files changed, 33 insertions, 11 deletions

diff --git a/storage/memory/object.go b/storage/memory/object.go
index eda6ab7..125e887 100644
--- a/storage/memory/object.go
+++ b/storage/memory/object.go
@@ -2,7 +2,7 @@ package memory
 
 import (
 	"bytes"
-	"io"
+	"io/ioutil"
 
 	"gopkg.in/src-d/go-git.v3/core"
 )
@@ -39,17 +39,21 @@ func (o *Object) Size() int64 { return o.size }
 // SetSize set the object size, the given size should be written afterwards
 func (o *Object) SetSize(s int64) { o.size = s }
 
-// Reader returns a io.Reader used to read the object content
-func (o *Object) Reader() io.Reader {
-	return bytes.NewBuffer(o.content)
+// Reader returns a core.ObjectReader used to read the object's content.
+func (o *Object) Reader() (core.ObjectReader, error) {
+	return ioutil.NopCloser(bytes.NewBuffer(o.content)), nil
 }
 
-// Writer returns a io.Writed used to write the object content
-func (o *Object) Writer() io.Writer {
-	return o
+// Writer returns a core.ObjectWriter used to write the object's content.
+func (o *Object) Writer() (core.ObjectWriter, error) {
+	return o, nil
 }
 
 func (o *Object) Write(p []byte) (n int, err error) {
 	o.content = append(o.content, p...)
 	return len(p), nil
 }
+
+// Close releases any resources consumed by the object when it is acting as a
+// core.ObjectWriter.
+func (o *Object) Close() error { return nil }
diff --git a/storage/memory/object_test.go b/storage/memory/object_test.go
index f9dd25d..f2873fa 100644
--- a/storage/memory/object_test.go
+++ b/storage/memory/object_test.go
@@ -51,7 +51,11 @@ func (s *ObjectSuite) TestSize(c *C) {
 func (s *ObjectSuite) TestReader(c *C) {
 	o := &Object{content: []byte("foo")}
 
-	b, err := ioutil.ReadAll(o.Reader())
+	reader, err := o.Reader()
+	c.Assert(err, IsNil)
+	defer func() { c.Assert(reader.Close(), IsNil) }()
+
+	b, err := ioutil.ReadAll(reader)
 	c.Assert(err, IsNil)
 	c.Assert(b, DeepEquals, []byte("foo"))
 }
@@ -59,7 +63,11 @@ func (s *ObjectSuite) TestReader(c *C) {
 func (s *ObjectSuite) TestWriter(c *C) {
 	o := &Object{}
 
-	n, err := o.Writer().Write([]byte("foo"))
+	writer, err := o.Writer()
+	c.Assert(err, IsNil)
+	defer func() { c.Assert(writer.Close(), IsNil) }()
+
+	n, err := writer.Write([]byte("foo"))
 	c.Assert(err, IsNil)
 	c.Assert(n, Equals, 3)
 
diff --git a/storage/memory/storage_test.go b/storage/memory/storage_test.go
index ba7e224..f2fd3da 100644
--- a/storage/memory/storage_test.go
+++ b/storage/memory/storage_test.go
@@ -25,7 +25,12 @@ func (s *ObjectStorageSuite) TestSet(c *C) {
 
 	o.SetType(core.CommitObject)
 	o.SetSize(3)
-	o.Writer().Write([]byte("foo"))
+
+	writer, err := o.Writer()
+	c.Assert(err, IsNil)
+	defer func() { c.Assert(writer.Close(), IsNil) }()
+
+	writer.Write([]byte("foo"))
 
 	h, err := os.Set(o)
 	c.Assert(h.String(), Equals, "bc9968d75e48de59f0870ffb71f5e160bbbdcf52")
@@ -39,7 +44,12 @@ func (s *ObjectStorageSuite) TestGet(c *C) {
 
 	o.SetType(core.CommitObject)
 	o.SetSize(3)
-	o.Writer().Write([]byte("foo"))
+
+	writer, err := o.Writer()
+	c.Assert(err, IsNil)
+	defer func() { c.Assert(writer.Close(), IsNil) }()
+
+	writer.Write([]byte("foo"))
 
 	h, err := os.Set(o)
 	c.Assert(err, IsNil)