1 files changed, 118 insertions, 0 deletions
diff --git a/plumbing/format/objfile/reader.go b/plumbing/format/objfile/reader.go
new file mode 100644
index 0000000..e7e119c
--- /dev/null
+++ b/plumbing/format/objfile/reader.go
@@ -0,0 +1,118 @@
+package objfile
+
+import (
+	"compress/zlib"
+	"errors"
+	"io"
+	"strconv"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/plumbing/format/packfile"
+)
+
+var (
+	ErrClosed       = errors.New("objfile: already closed")
+	ErrHeader       = errors.New("objfile: invalid header")
+	ErrNegativeSize = errors.New("objfile: negative object size")
+)
+
+// 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 {
+	multi  io.Reader
+	zlib   io.ReadCloser
+	hasher plumbing.Hasher
+}
+
+// NewReader returns a new Reader reading from r.
+func NewReader(r io.Reader) (*Reader, error) {
+	zlib, err := zlib.NewReader(r)
+	if err != nil {
+		return nil, packfile.ErrZLib.AddDetails(err.Error())
+	}
+
+	return &Reader{
+		zlib: zlib,
+	}, nil
+}
+
+// Header reads the type and the size of object, and prepares the reader for read
+func (r *Reader) Header() (t plumbing.ObjectType, size int64, err error) {
+	var raw []byte
+	raw, err = r.readUntil(' ')
+	if err != nil {
+		return
+	}
+
+	t, err = plumbing.ParseObjectType(string(raw))
+	if err != nil {
+		return
+	}
+
+	raw, err = r.readUntil(0)
+	if err != nil {
+		return
+	}
+
+	size, err = strconv.ParseInt(string(raw), 10, 64)
+	if err != nil {
+		err = ErrHeader
+		return
+	}
+
+	defer r.prepareForRead(t, size)
+	return
+}
+
+// readSlice reads one byte at a time from r until it encounters delim or an
+// error.
+func (r *Reader) readUntil(delim byte) ([]byte, error) {
+	var buf [1]byte
+	value := make([]byte, 0, 16)
+	for {
+		if n, err := r.zlib.Read(buf[:]); err != nil && (err != io.EOF || n == 0) {
+			if err == io.EOF {
+				return nil, ErrHeader
+			}
+			return nil, err
+		}
+
+		if buf[0] == delim {
+			return value, nil
+		}
+
+		value = append(value, buf[0])
+	}
+}
+
+func (r *Reader) prepareForRead(t plumbing.ObjectType, size int64) {
+	r.hasher = plumbing.NewHasher(t, size)
+	r.multi = io.TeeReader(r.zlib, r.hasher)
+}
+
+// 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) {
+	return r.multi.Read(p)
+}
+
+// Hash returns the hash of the object data stream that has been read so far.
+func (r *Reader) Hash() plumbing.Hash {
+	return r.hasher.Sum()
+}
+
+// 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() error {
+	if err := r.zlib.Close(); err != nil {
+		return err
+	}
+
+	return nil
+}