respond to unreadable OTR messages with error message. fixed #1021

src/main/java/eu/siacs/conversations/crypto/OtrEngine.java

@@ -201,9 +201,21 @@ public class OtrEngine extends OtrCryptoEngineImpl implements OtrEngineHost {
 	}
 
 	@Override
-	public void messageFromAnotherInstanceReceived(SessionID id) {
+	public void messageFromAnotherInstanceReceived(SessionID session) {
-		Log.d(Config.LOGTAG,
+		try {
-				"unreadable message received from " + id.getAccountID());
+			Jid jid = Jid.fromSessionID(session);
+			Conversation conversation = mXmppConnectionService.find(account, jid);
+			String id = conversation == null ? null : conversation.getLastReceivedOtrMessageId();
+			if (id != null) {
+				MessagePacket packet = mXmppConnectionService.getMessageGenerator().generateOtrError(jid,id);
+				packet.setFrom(account.getJid());
+				mXmppConnectionService.sendMessagePacket(account,packet);
+				Log.d(Config.LOGTAG,packet.toString());
+				Log.d(Config.LOGTAG,account.getJid().toBareJid().toString()+": unreadable OTR message in "+conversation.getName());
+			}
+		} catch (InvalidJidException e) {
+			return;
+		}
 	}
 
 	@Override

src/main/java/eu/siacs/conversations/entities/Conversation.java

@@ -78,6 +78,7 @@ public class Conversation extends AbstractEntity implements Blockable {
 	private boolean messagesLeftOnServer = true;
 	private ChatState mOutgoingChatState = Config.DEFAULT_CHATSTATE;
 	private ChatState mIncomingChatState = Config.DEFAULT_CHATSTATE;
+	private String mLastReceivedOtrMessageId = null;
 
 	public boolean hasMessagesLeftOnServer() {
 		return messagesLeftOnServer;
@@ -234,6 +235,14 @@ public class Conversation extends AbstractEntity implements Blockable {
 		return getContact().getBlockedJid();
 	}
 
+	public String getLastReceivedOtrMessageId() {
+		return this.mLastReceivedOtrMessageId;
+	}
+
+	public void setLastReceivedOtrMessageId(String id) {
+		this.mLastReceivedOtrMessageId = id;
+	}
+
 
 	public interface OnMessageFound {
 		public void onMessageFound(final Message message);

src/main/java/eu/siacs/conversations/generator/MessageGenerator.java

@@ -171,4 +171,17 @@ public class MessageGenerator extends AbstractGenerator {
 		received.setAttribute("id", originalMessage.getId());
 		return receivedPacket;
 	}
+
+	public MessagePacket generateOtrError(Jid to, String id) {
+		MessagePacket packet = new MessagePacket();
+		packet.setType(MessagePacket.TYPE_ERROR);
+		packet.setAttribute("id",id);
+		packet.setTo(to);
+		Element error = packet.addChild("error");
+		error.setAttribute("code","406");
+		error.setAttribute("type","modify");
+		error.addChild("not-acceptable","urn:ietf:params:xml:ns:xmpp-stanzas");
+		error.addChild("text").setContent("unreadable OTR message received");
+		return packet;
+	}
 }

src/main/java/eu/siacs/conversations/parser/MessageParser.java

@@ -118,6 +118,7 @@ public class MessageParser extends AbstractParser implements
 			}
 		}
 		try {
+			conversation.setLastReceivedOtrMessageId(packet.getId());
 			Session otrSession = conversation.getOtrSession();
 			SessionStatus before = otrSession.getSessionStatus();
 			body = otrSession.transformReceiving(body);
@@ -145,6 +146,7 @@ public class MessageParser extends AbstractParser implements
 			finishedMessage.markable = isMarkable(packet);
 			finishedMessage.setCounterpart(from);
 			extractChatState(conversation, packet);
+			conversation.setLastReceivedOtrMessageId(null);
 			return finishedMessage;
 		} catch (Exception e) {
 			conversation.resetOtrSession();

src/main/java/eu/siacs/conversations/xmpp/stanzas/MessagePacket.java

@@ -39,6 +39,9 @@ public class MessagePacket extends AbstractStanza {
 			break;
 		case TYPE_NORMAL:
 			break;
+		case TYPE_ERROR:
+			this.setAttribute("type","error");
+			break;
 		default:
 			this.setAttribute("type", "chat");
 			break;