4 files changed, 37 insertions, 5 deletions
diff --git a/plumbing/protocol/packp/advrefs_decode.go b/plumbing/protocol/packp/advrefs_decode.go
index fddd69b..e0a449e 100644
--- a/plumbing/protocol/packp/advrefs_decode.go
+++ b/plumbing/protocol/packp/advrefs_decode.go
@@ -55,8 +55,12 @@ type decoderStateFn func(*advRefsDecoder) decoderStateFn
 
 // fills out the parser stiky error
 func (d *advRefsDecoder) error(format string, a ...interface{}) {
-	d.err = fmt.Errorf("pkt-line %d: %s", d.nLine,
-		fmt.Sprintf(format, a...))
+	msg := fmt.Sprintf(
+		"pkt-line %d: %s", d.nLine,
+		fmt.Sprintf(format, a...),
+	)
+
+	d.err = NewErrUnexpectedData(msg, d.line)
 }
 
 // Reads a new pkt-line from the scanner, makes its payload available as
diff --git a/plumbing/protocol/packp/advrefs_decode_test.go b/plumbing/protocol/packp/advrefs_decode_test.go
index 2cc2568..e9a01f8 100644
--- a/plumbing/protocol/packp/advrefs_decode_test.go
+++ b/plumbing/protocol/packp/advrefs_decode_test.go
@@ -46,7 +46,7 @@ func (s *AdvRefsDecodeSuite) TestShortForHash(c *C) {
 		pktline.FlushString,
 	}
 	r := toPktLines(c, payloads)
-	s.testDecoderErrorMatches(c, r, ".*too short")
+	s.testDecoderErrorMatches(c, r, ".*too short.*")
 }
 
 func (s *AdvRefsDecodeSuite) testDecoderErrorMatches(c *C, input io.Reader, pattern string) {
diff --git a/plumbing/protocol/packp/common.go b/plumbing/protocol/packp/common.go
index 93dfaed..ab07ac8 100644
--- a/plumbing/protocol/packp/common.go
+++ b/plumbing/protocol/packp/common.go
@@ -1,5 +1,9 @@
 package packp
 
+import (
+	"fmt"
+)
+
 type stateFn func() stateFn
 
 const (
@@ -44,3 +48,23 @@ var (
 func isFlush(payload []byte) bool {
 	return len(payload) == 0
 }
+
+// ErrUnexpectedData represents an unexpected data decoding a message
+type ErrUnexpectedData struct {
+	Msg  string
+	Data []byte
+}
+
+// NewErrUnexpectedData returns a new ErrUnexpectedData containing the data and
+// the message given
+func NewErrUnexpectedData(msg string, data []byte) error {
+	return &ErrUnexpectedData{Msg: msg, Data: data}
+}
+
+func (err *ErrUnexpectedData) Error() string {
+	if len(err.Data) == 0 {
+		return err.Msg
+	}
+
+	return fmt.Sprintf("%s (%s)", err.Msg, err.Data)
+}
diff --git a/plumbing/protocol/packp/ulreq_decode.go b/plumbing/protocol/packp/ulreq_decode.go
index 541a077..bcd642d 100644
--- a/plumbing/protocol/packp/ulreq_decode.go
+++ b/plumbing/protocol/packp/ulreq_decode.go
@@ -45,8 +45,12 @@ func (d *ulReqDecoder) Decode(v *UploadRequest) error {
 
 // fills out the parser stiky error
 func (d *ulReqDecoder) error(format string, a ...interface{}) {
-	d.err = fmt.Errorf("pkt-line %d: %s", d.nLine,
-		fmt.Sprintf(format, a...))
+	msg := fmt.Sprintf(
+		"pkt-line %d: %s", d.nLine,
+		fmt.Sprintf(format, a...),
+	)
+
+	d.err = NewErrUnexpectedData(msg, d.line)
 }
 
 // Reads a new pkt-line from the scanner, makes its payload available as