Fix a bug in noise.readMessage.

Was returning nil in case of an error from io.ReadFull, and even then it
should have been io.ErrUnexpectedEOF, not io.EOF.

noise/noise.go

@@ -21,14 +21,16 @@ func readMessage(r io.Reader) ([]byte, error) {
 	var length uint16
 	err := binary.Read(r, binary.BigEndian, &length)
 	if err != nil {
+		// We may return a real io.EOF only here.
 		return nil, err
 	}
 	msg := make([]byte, int(length))
 	_, err = io.ReadFull(r, msg)
-	if err != nil {
-		return nil, nil
+	// Here we must change io.EOF to io.ErrUnexpectedEOF.
+	if err == io.EOF {
+		err = io.ErrUnexpectedEOF
 	}
-	return msg, nil
+	return msg, err
 }
 
 func writeMessage(w io.Writer, msg []byte) error {

noise/noise_test.go

@@ -2,9 +2,74 @@ package noise
 
 import (
 	"bytes"
+	"io"
 	"testing"
 )
 
+func allMessages(buf []byte) ([][]byte, error) {
+	var messages [][]byte
+	r := bytes.NewReader(buf)
+	for {
+		msg, err := readMessage(r)
+		if err != nil {
+			return messages, err
+		}
+		messages = append(messages, msg)
+	}
+}
+
+func messagesEqual(a, b [][]byte) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if !bytes.Equal(a[i], b[i]) {
+			return false
+		}
+	}
+	return true
+}
+
+func TestReadMessage(t *testing.T) {
+	for _, test := range []struct {
+		input    string
+		messages [][]byte
+		err      error
+	}{
+		{"", [][]byte{}, io.EOF},
+		{"\x00", [][]byte{}, io.ErrUnexpectedEOF},
+		{"\x00\x00", [][]byte{{}}, io.EOF},
+		{"\x00\x00\x00", [][]byte{{}}, io.ErrUnexpectedEOF},
+		{"\x00\x01", [][]byte{}, io.ErrUnexpectedEOF},
+		{"\x00\x05hello\x00\x05world", [][]byte{[]byte("hello"), []byte("world")}, io.EOF},
+	} {
+		packets, err := allMessages([]byte(test.input))
+		if !messagesEqual(packets, test.messages) || err != test.err {
+			t.Errorf("%x\nreturned %x %v\nexpected %x %v",
+				test.input, packets, err, test.messages, test.err)
+		}
+	}
+}
+
+func TestMessageRoundTrip(t *testing.T) {
+	for _, messages := range [][][]byte{
+		{},
+	} {
+		var buf bytes.Buffer
+		for _, msg := range messages {
+			err := writeMessage(&buf, msg)
+			if err != nil {
+				panic(err)
+			}
+		}
+		output, err := allMessages(buf.Bytes())
+		if !messagesEqual(output, messages) || err != io.EOF {
+			t.Errorf("%x roundtripped to %x %v",
+				messages, output, err)
+		}
+	}
+}
+
 func TestReadKey(t *testing.T) {
 	for _, test := range []struct {
 		input  string