1 files changed, 123 insertions, 0 deletions
diff --git a/formats/objfile/reader.go b/formats/objfile/reader.go
new file mode 100644
index 0000000..b3c2e5c
--- /dev/null
+++ b/formats/objfile/reader.go
@@ -0,0 +1,123 @@
+package objfile
+
+import (
+	"errors"
+	"io"
+
+	"gopkg.in/src-d/go-git.v3/core"
+
+	"github.com/klauspost/compress/zlib"
+)
+
+var (
+	// ErrZLib is returned when the objfile contains invalid zlib data.
+	ErrZLib = errors.New("objfile: invalid zlib data")
+)
+
+// Reader reads and decodes compressed objfile data from a provided io.Reader.
+//
+// Reader implements io.ReadCloser. Close should be called when finished with
+// the Reader. Close will not close the underlying io.Reader.
+type Reader struct {
+	header header
+	hash   core.Hash // final computed hash stored after Close
+
+	r            io.Reader     // provided reader wrapped in decompressor and tee
+	decompressor io.ReadCloser // provided reader wrapped in decompressor, retained for calling Close
+	h            core.Hasher   // streaming SHA1 hash of decoded data
+}
+
+// NewReader returns a new Reader reading from r.
+//
+// Calling NewReader causes it to immediately read in header data from r
+// containing size and type information. Any errors encountered in that
+// process will be returned in err.
+//
+// The returned Reader implements io.ReadCloser. Close should be called when
+// finished with the Reader. Close will not close the underlying io.Reader.
+func NewReader(r io.Reader) (*Reader, error) {
+	reader := &Reader{}
+	return reader, reader.init(r)
+}
+
+// init prepares the zlib decompressor for the given input as well as a hasher
+// for computing its hash.
+//
+// init immediately reads header data from the input and stores it. This leaves
+// the Reader in a state that is ready to read content.
+func (r *Reader) init(input io.Reader) (err error) {
+	r.decompressor, err = zlib.NewReader(input)
+	if err != nil {
+		// TODO: Make this error match the ZLibErr in formats/packfile/reader.go?
+		return ErrZLib
+	}
+
+	err = r.header.Read(r.decompressor)
+	if err != nil {
+		r.decompressor.Close()
+		return
+	}
+
+	r.h = core.NewHasher(r.header.t, r.header.size)
+	r.r = io.TeeReader(r.decompressor, r.h) // All reads from the decompressor also write to the hash
+
+	return
+}
+
+// Read reads len(p) bytes into p from the object data stream. It returns
+// the number of bytes read (0 <= n <= len(p)) and any error encountered. Even
+// if Read returns n < len(p), it may use all of p as scratch space during the
+// call.
+//
+// If Read encounters the end of the data stream it will return err == io.EOF,
+// either in the current call if n > 0 or in a subsequent call.
+func (r *Reader) Read(p []byte) (n int, err error) {
+	if r.r == nil {
+		return 0, ErrClosed
+	}
+
+	return r.r.Read(p)
+}
+
+// Type returns the type of the object.
+func (r *Reader) Type() core.ObjectType {
+	return r.header.t
+}
+
+// Size returns the uncompressed size of the object in bytes.
+func (r *Reader) Size() int64 {
+	return r.header.size
+}
+
+// Hash returns the hash of the object data stream that has been read so far.
+// It can be called before or after Close.
+func (r *Reader) Hash() core.Hash {
+	if r.r != nil {
+		return r.h.Sum() // Not yet closed, return hash of data read so far
+	}
+	return r.hash
+}
+
+// Close releases any resources consumed by the Reader.
+//
+// Calling Close does not close the wrapped io.Reader originally passed to
+// NewReader.
+func (r *Reader) Close() (err error) {
+	if r.r == nil {
+		// TODO: Consider returning ErrClosed here?
+		return nil // Already closed
+	}
+
+	// Release the decompressor's resources
+	err = r.decompressor.Close()
+
+	// Save the hash because we're about to throw away the hasher
+	r.hash = r.h.Sum()
+
+	// Release references
+	r.r = nil // Indicates closed state
+	r.decompressor = nil
+	r.h.Hash = nil
+
+	return
+}