Refactor type 2 message decoding, drop any extra lines from subject.

This allows other clients to insert headers in extra lines of text between
the Subject and Body fields of the message, as discussed on the 24x7 mailing
list. The PyBitmessage client was never able to meaningfully display
multi-line subjects, so this does not break anything. The extra lines are
thrown away and never stored anywhere, so this also protects against
watermarking attacks.

src/class_receiveDataThread.py

@@ -528,13 +528,7 @@ class receiveDataThread(threading.Thread):
                     print 'fromAddress:', fromAddress
 
                 if messageEncodingType == 2:
-                    bodyPositionIndex = string.find(message, '\nBody:')
-                    if bodyPositionIndex > 1:
-                        subject = message[8:bodyPositionIndex]
-                        body = message[bodyPositionIndex + 6:]
-                    else:
-                        subject = ''
-                        body = message
+                    subject, body = self.decodeType2Message(message)
                 elif messageEncodingType == 1:
                     body = message
                     subject = ''
@@ -684,13 +678,7 @@ class receiveDataThread(threading.Thread):
                 print 'fromAddress:', fromAddress
 
             if messageEncodingType == 2:
-                bodyPositionIndex = string.find(message, '\nBody:')
-                if bodyPositionIndex > 1:
-                    subject = message[8:bodyPositionIndex]
-                    body = message[bodyPositionIndex + 6:]
-                else:
-                    subject = ''
-                    body = message
+                subject, body = self.decodeType2Message(message)
             elif messageEncodingType == 1:
                 body = message
                 subject = ''
@@ -1005,15 +993,7 @@ class receiveDataThread(threading.Thread):
                     toLabel = toAddress
 
                 if messageEncodingType == 2:
-                    bodyPositionIndex = string.find(message, '\nBody:')
-                    if bodyPositionIndex > 1:
-                        subject = message[8:bodyPositionIndex]
-                        subject = subject[
-                            :500]  # Only save and show the first 500 characters of the subject. Any more is probably an attak.
-                        body = message[bodyPositionIndex + 6:]
-                    else:
-                        subject = ''
-                        body = message
+                    subject, body = self.decodeType2Message(message)
                 elif messageEncodingType == 1:
                     body = message
                     subject = ''
@@ -1086,6 +1066,21 @@ class receiveDataThread(threading.Thread):
                 print 'Time to decrypt this message successfully:', timeRequiredToAttemptToDecryptMessage
                 print 'Average time for all message decryption successes since startup:', sum / len(shared.successfullyDecryptMessageTimings)
 
+    def decodeType2Message(self, message):
+        bodyPositionIndex = string.find(message, '\nBody:')
+        if bodyPositionIndex > 1:
+            subject = message[8:bodyPositionIndex]
+            # Only save and show the first 500 characters of the subject.
+            # Any more is probably an attack.
+            subject = subject[:500]
+            body = message[bodyPositionIndex + 6:]
+        else:
+            subject = ''
+            body = message
+        # Throw away any extra lines (headers) after the subject.
+        if subject:
+            subject = subject.splitlines()[0]
+        return subject, body
 
     def isAckDataValid(self, ackData):
         if len(ackData) < 24: