Support for an 'end session' protocol message.

1) On the push side, this message is a flag in PushMessageContent.
   Any secure message with that flag will terminate the current
   sessin.

2) On the SMS side, there is an "end session" wire type and
   the convention that a message with this wire type must be
   secure and contain the string "TERMINATE."

src/org/thoughtcrime/securesms/sms/IncomingEndSessionMessage.java

@@ -0,0 +1,22 @@
+package org.thoughtcrime.securesms.sms;
+
+public class IncomingEndSessionMessage extends IncomingTextMessage {
+
+  public IncomingEndSessionMessage(IncomingTextMessage base) {
+    this(base, base.getMessageBody());
+  }
+
+  public IncomingEndSessionMessage(IncomingTextMessage base, String newBody) {
+    super(base, newBody);
+  }
+
+  @Override
+  public IncomingEndSessionMessage withMessageBody(String messageBody) {
+    return new IncomingEndSessionMessage(this, messageBody);
+  }
+
+  @Override
+  public boolean isEndSession() {
+    return true;
+  }
+}

src/org/thoughtcrime/securesms/sms/IncomingTextMessage.java

@@ -216,6 +216,10 @@ public class IncomingTextMessage implements Parcelable {
     return false;
   }
 
+  public boolean isEndSession() {
+    return false;
+  }
+
   public boolean isIdentityUpdate() {
     return false;
   }

src/org/thoughtcrime/securesms/sms/MultipartSmsMessageHandler.java

@@ -71,6 +71,8 @@ public class MultipartSmsMessageHandler {
       return new IncomingKeyExchangeMessage(message.getBaseMessage(), strippedMessage);
     } else if (message.getWireType() == MultipartSmsTransportMessage.WIRETYPE_PREKEY) {
       return new IncomingPreKeyBundleMessage(message.getBaseMessage(), strippedMessage);
+    } else if (message.getWireType() == MultipartSmsTransportMessage.WIRETYPE_END_SESSION) {
+      return new IncomingEndSessionMessage(message.getBaseMessage(), strippedMessage);
     } else {
       return new IncomingEncryptedMessage(message.getBaseMessage(), strippedMessage);
     }

src/org/thoughtcrime/securesms/sms/MultipartSmsTransportMessage.java

@@ -2,12 +2,14 @@ package org.thoughtcrime.securesms.sms;
 
 import android.util.Log;
 
+import org.thoughtcrime.securesms.protocol.EndSessionWirePrefix;
 import org.thoughtcrime.securesms.protocol.KeyExchangeWirePrefix;
 import org.thoughtcrime.securesms.protocol.PrekeyBundleWirePrefix;
 import org.thoughtcrime.securesms.protocol.SecureMessageWirePrefix;
 import org.thoughtcrime.securesms.protocol.WirePrefix;
 import org.whispersystems.textsecure.util.Base64;
 import org.whispersystems.textsecure.util.Conversions;
+import org.whispersystems.textsecure.util.Hex;
 
 import java.io.IOException;
 import java.util.ArrayList;
@@ -21,9 +23,10 @@ public class MultipartSmsTransportMessage {
   public static final int MULTI_MESSAGE_MULTIPART_OVERHEAD       = 3;
   public static final int FIRST_MULTI_MESSAGE_MULTIPART_OVERHEAD = 2;
 
-  public static final int WIRETYPE_SECURE = 1;
-  public static final int WIRETYPE_KEY    = 2;
-  public static final int WIRETYPE_PREKEY = 3;
+  public static final int WIRETYPE_SECURE      = 1;
+  public static final int WIRETYPE_KEY         = 2;
+  public static final int WIRETYPE_PREKEY      = 3;
+  public static final int WIRETYPE_END_SESSION = 4;
 
   private static final int VERSION_OFFSET    = 0;
   private static final int MULTIPART_OFFSET  = 1;
@@ -39,6 +42,7 @@ public class MultipartSmsTransportMessage {
 
     if      (WirePrefix.isEncryptedMessage(message.getMessageBody())) wireType = WIRETYPE_SECURE;
     else if (WirePrefix.isPreKeyBundle(message.getMessageBody()))     wireType = WIRETYPE_PREKEY;
+    else if (WirePrefix.isEndSession(message.getMessageBody()))       wireType = WIRETYPE_END_SESSION;
     else                                                              wireType = WIRETYPE_KEY;
 
     Log.w(TAG, "Decoded message with version: " + getCurrentVersion());
@@ -158,6 +162,7 @@ public class MultipartSmsTransportMessage {
 
       if      (message.isKeyExchange())  prefix = new KeyExchangeWirePrefix();
       else if (message.isPreKeyBundle()) prefix = new PrekeyBundleWirePrefix();
+      else if (message.isEndSession())   prefix = new EndSessionWirePrefix();
       else                               prefix = new SecureMessageWirePrefix();
 
       if (count == 1) return getSingleEncoded(decoded, prefix);

src/org/thoughtcrime/securesms/sms/OutgoingEndSessionMessage.java

@@ -0,0 +1,22 @@
+package org.thoughtcrime.securesms.sms;
+
+public class OutgoingEndSessionMessage extends OutgoingTextMessage {
+
+  public OutgoingEndSessionMessage(OutgoingTextMessage base) {
+    this(base, base.getMessageBody());
+  }
+
+  public OutgoingEndSessionMessage(OutgoingTextMessage message, String body) {
+    super(message, body);
+  }
+
+  @Override
+  public boolean isEndSession() {
+    return true;
+  }
+
+  @Override
+  public OutgoingTextMessage withBody(String body) {
+    return new OutgoingEndSessionMessage(this, body);
+  }
+}

src/org/thoughtcrime/securesms/sms/OutgoingTextMessage.java

@@ -52,6 +52,10 @@ public class OutgoingTextMessage {
     return false;
   }
 
+  public boolean isEndSession() {
+    return false;
+  }
+
   public boolean isPreKeyBundle() {
     return false;
   }
@@ -61,6 +65,8 @@ public class OutgoingTextMessage {
       return new OutgoingEncryptedMessage(record.getIndividualRecipient(), record.getBody().getBody());
     } else if (record.isKeyExchange()) {
       return new OutgoingKeyExchangeMessage(record.getIndividualRecipient(), record.getBody().getBody());
+    } else if (record.isEndSession()) {
+      return new OutgoingEndSessionMessage(new OutgoingTextMessage(record.getIndividualRecipient(), record.getBody().getBody()));
     } else {
       return new OutgoingTextMessage(record.getIndividualRecipient(), record.getBody().getBody());
     }