net/mail: Fix EOF error while reading header-only message

Author: 0xc0d

src/net/mail/message.go

@@ -54,6 +54,13 @@ func ReadMessage(r io.Reader) (msg *Message, err error) {
 	tp := textproto.NewReader(bufio.NewReader(r))
 
 	hdr, err := tp.ReadMIMEHeader()
+	// Header-Only messages
+	if err == io.EOF && len(hdr) > 0 {
+		return &Message{
+			Header: Header(hdr),
+			Body:   tp.R,
+		}, nil
+	}
 	if err != nil {
 		return nil, err
 	}

src/net/mail/message_test.go

@@ -39,6 +39,19 @@ So, "Hello".
 		},
 		body: "This is a message just to say hello.\nSo, \"Hello\".\n",
 	},
+	{
+		// RFC 5965, Appendix B.1, a part of the multipart message (a header-only sub message)
+		in: `Feedback-Type: abuse
+User-Agent: SomeGenerator/1.0
+Version: 1
+`,
+		header: Header{
+			"Feedback-Type": []string{"abuse"},
+			"User-Agent": []string{"SomeGenerator/1.0"},
+			"Version": []string{"1"},
+		},
+		body: "",
+	},
 }
 
 func TestParsing(t *testing.T) {