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/transport/PushTransport.java

@@ -22,6 +22,7 @@ import android.util.Log;
 
 import com.google.protobuf.ByteString;
 
+import org.thoughtcrime.securesms.crypto.KeyExchangeProcessor;
 import org.thoughtcrime.securesms.crypto.KeyExchangeProcessorV2;
 import org.thoughtcrime.securesms.database.DatabaseFactory;
 import org.thoughtcrime.securesms.database.model.SmsMessageRecord;
@@ -85,12 +86,15 @@ public class PushTransport extends BaseTransport {
       Recipient         recipient = message.getIndividualRecipient();
       long              threadId  = message.getThreadId();
       PushServiceSocket socket    = PushServiceSocketFactory.create(context);
-      byte[]            plaintext = PushMessageContent.newBuilder()
-                                                      .setBody(message.getBody().getBody())
-                                                      .build().toByteArray();
+      byte[]            plaintext = getPlaintextMessage(message);
 
       deliver(socket, recipient, threadId, plaintext);
 
+      if (message.isEndSession()) {
+        SessionRecordV2.deleteAll(context, recipient);
+        KeyExchangeProcessor.broadcastSecurityUpdateEvent(context, threadId);
+      }
+
       context.sendBroadcast(constructSentIntent(context, message.getId(), message.getType(), true));
 
     } catch (InvalidNumberException e) {
@@ -295,6 +299,17 @@ public class PushTransport extends BaseTransport {
     return builder.build().toByteArray();
   }
 
+  private byte[] getPlaintextMessage(SmsMessageRecord record) {
+    PushMessageContent.Builder builder = PushMessageContent.newBuilder()
+                                                           .setBody(record.getBody().getBody());
+
+    if (record.isEndSession()) {
+      builder.setFlags(PushMessageContent.Flags.END_SESSION_VALUE);
+    }
+
+    return builder.build().toByteArray();
+  }
+
   private OutgoingPushMessageList getEncryptedMessages(PushServiceSocket socket, long threadId,
                                                        Recipient recipient, byte[] plaintext)
       throws IOException, InvalidNumberException, UntrustedIdentityException
@@ -352,8 +367,4 @@ public class PushTransport extends BaseTransport {
       throw new AssertionError("Unknown ciphertext type: " + message.getType());
     }
   }
-
-  private void destroySessions(Recipient recipient) {
-    SessionRecordV2.deleteAll(context, recipient);
-  }
 }

src/org/thoughtcrime/securesms/transport/SmsTransport.java

@@ -33,6 +33,7 @@ import org.whispersystems.textsecure.crypto.MasterSecret;
 import org.whispersystems.textsecure.crypto.SessionCipher;
 import org.whispersystems.textsecure.crypto.protocol.CiphertextMessage;
 import org.whispersystems.textsecure.storage.RecipientDevice;
+import org.whispersystems.textsecure.util.Hex;
 
 import java.util.ArrayList;
 
@@ -47,7 +48,7 @@ public class SmsTransport extends BaseTransport {
   }
 
   public void deliver(SmsMessageRecord message) throws UndeliverableMessageException {
-    if (message.isSecure() || message.isKeyExchange()) {
+    if (message.isSecure() || message.isKeyExchange() || message.isEndSession()) {
       deliverSecureMessage(message);
     } else {
       deliverPlaintextMessage(message);
@@ -58,7 +59,7 @@ public class SmsTransport extends BaseTransport {
     MultipartSmsMessageHandler multipartMessageHandler = new MultipartSmsMessageHandler();
     OutgoingTextMessage transportMessage               = OutgoingTextMessage.from(message);
 
-    if (message.isSecure()) {
+    if (message.isSecure() || message.isEndSession()) {
       transportMessage = getAsymmetricEncrypt(masterSecret, transportMessage);
     }