plumbing: protocol/packp, Add validation for decodeLine

Signed-off-by: Paulo Gomes <pjbgf@linux.com>

plumbing/protocol/packp/srvresp.go

@@ -101,6 +101,11 @@ func (r *ServerResponse) decodeLine(line []byte) error {
 		return fmt.Errorf("unexpected flush")
 	}
 
+	err := fmt.Errorf("unexpected content %q", string(line))
+	if len(line) < 3 {
+		return err
+	}
+
 	if bytes.Equal(line[0:3], ack) {
 		return r.decodeACKLine(line)
 	}
@@ -109,7 +114,7 @@ func (r *ServerResponse) decodeLine(line []byte) error {
 		return nil
 	}
 
-	return fmt.Errorf("unexpected content %q", string(line))
+	return err
 }
 
 func (r *ServerResponse) decodeACKLine(line []byte) error {

plumbing/protocol/packp/srvresp_test.go

@@ -3,6 +3,7 @@ package packp
 import (
 	"bufio"
 	"bytes"
+	"fmt"
 
 	"github.com/go-git/go-git/v5/plumbing"
 
@@ -23,6 +24,32 @@ func (s *ServerResponseSuite) TestDecodeNAK(c *C) {
 	c.Assert(sr.ACKs, HasLen, 0)
 }
 
+func (s *ServerResponseSuite) TestDecodeNewLine(c *C) {
+	raw := "\n"
+
+	sr := &ServerResponse{}
+	err := sr.Decode(bufio.NewReader(bytes.NewBufferString(raw)), false)
+	c.Assert(err, NotNil)
+	c.Assert(err.Error(), Equals, "invalid pkt-len found")
+}
+
+func (s *ServerResponseSuite) TestDecodeEmpty(c *C) {
+	raw := ""
+
+	sr := &ServerResponse{}
+	err := sr.Decode(bufio.NewReader(bytes.NewBufferString(raw)), false)
+	c.Assert(err, IsNil)
+}
+
+func (s *ServerResponseSuite) TestDecodePartial(c *C) {
+	raw := "000600\n"
+
+	sr := &ServerResponse{}
+	err := sr.Decode(bufio.NewReader(bytes.NewBufferString(raw)), false)
+	c.Assert(err, NotNil)
+	c.Assert(err.Error(), Equals, fmt.Sprintf("unexpected content %q", "00"))
+}
+
 func (s *ServerResponseSuite) TestDecodeACK(c *C) {
 	raw := "0031ACK 6ecf0ef2c2dffb796033e5a02219af86ec6584e5\n"