1 files changed, 79 insertions, 0 deletions
diff --git a/formats/objfile/common.go b/formats/objfile/common.go
new file mode 100644
index 0000000..2f0585f
--- /dev/null
+++ b/formats/objfile/common.go
@@ -0,0 +1,79 @@
+package objfile
+
+import (
+	"errors"
+	"io"
+	"strconv"
+
+	"gopkg.in/src-d/go-git.v3/core"
+)
+
+var (
+	// ErrClosed is returned when the objfile Reader or Writer is already closed.
+	ErrClosed = errors.New("objfile: already closed")
+	// ErrHeader is returned when the objfile has an invalid header.
+	ErrHeader = errors.New("objfile: invalid header")
+	// ErrNegativeSize is returned when a negative object size is declared.
+	ErrNegativeSize = errors.New("objfile: negative object size")
+)
+
+type header struct {
+	t    core.ObjectType
+	size int64
+}
+
+func (h *header) Read(r io.Reader) error {
+	t, err := h.readSlice(r, ' ')
+	if err != nil {
+		return err
+	}
+
+	h.t, err = core.ParseObjectType(string(t))
+	if err != nil {
+		return err
+	}
+
+	size, err := h.readSlice(r, 0)
+	if err != nil {
+		return err
+	}
+
+	h.size, err = strconv.ParseInt(string(size), 10, 64)
+	if err != nil {
+		return ErrHeader
+	}
+
+	if h.size < 0 {
+		return ErrNegativeSize
+	}
+
+	return nil
+}
+
+func (h *header) Write(w io.Writer) error {
+	b := h.t.Bytes()
+	b = append(b, ' ')
+	b = append(b, []byte(strconv.FormatInt(h.size, 10))...)
+	b = append(b, 0)
+	_, err := w.Write(b)
+	return err
+}
+
+// readSlice reads one byte at a time from r until it encounters delim or an
+// error.
+func (h *header) readSlice(r io.Reader, delim byte) ([]byte, error) {
+	var buf [1]byte
+	value := make([]byte, 0, 16)
+	for {
+		if n, err := r.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])
+	}
+}