Don't display the same message multiple times.

core/src/main/scala/com/nutomic/ensichat/core/ConnectionHandler.scala

@@ -69,7 +69,7 @@ final class ConnectionHandler(settings: SettingsInterface, database: DatabaseInt
 
       val msg = new Message(header, body)
       val encrypted = crypto.encryptAndSign(msg)
-      router.onReceive(encrypted)
+      router.forwardMessage(encrypted)
       onNewMessage(msg)
     }
   }
@@ -81,13 +81,15 @@ final class ConnectionHandler(settings: SettingsInterface, database: DatabaseInt
    * Decrypts and verifies incoming messages, forwards valid ones to [[onNewMessage()]].
    */
   def onMessageReceived(msg: Message): Unit = {
-    if (msg.header.target == crypto.localAddress) {
+    if (router.isMessageSeen(msg)) {
+      Log.v(Tag, "Ignoring message from " + msg.header.origin + " that we already received")
+    } else if (msg.header.target == crypto.localAddress) {
       crypto.verifyAndDecrypt(msg) match {
         case Some(m) => onNewMessage(m)
         case None => Log.i(Tag, "Ignoring message with invalid signature from " + msg.header.origin)
       }
     } else {
-      router.onReceive(msg)
+      router.forwardMessage(msg)
     }
   }
 

core/src/main/scala/com/nutomic/ensichat/core/Router.scala

@@ -9,17 +9,32 @@ final private[core] class Router(activeConnections: () => Set[Address], send: (A
 
   private var messageSeen = Set[(Address, Int)]()
 
-  def onReceive(msg: Message): Unit = {
+  /**
+   * Returns true if we have received the same message before.
+   */
+  def isMessageSeen(msg: Message): Boolean = {
     val info = (msg.header.origin, msg.header.seqNum)
-    if (messageSeen.contains(info))
-      return
+    val seen = messageSeen.contains(info)
+    markMessageSeen(info)
+    seen
+  }
 
+  /**
+   * Sends message to all connected devices. Should only be called if [[isMessageSeen()]] returns
+   * true.
+   */
+  def forwardMessage(msg: Message): Unit = {
+    val info = (msg.header.origin, msg.header.seqNum)
     val updated = incHopCount(msg)
     if (updated.header.hopCount >= updated.header.hopLimit)
       return
 
     activeConnections().foreach(a => send(a, updated))
 
+    markMessageSeen(info)
+  }
+
+  private def markMessageSeen(info: (Address, Int)): Unit = {
     trimMessageSeen(info._1, info._2)
     messageSeen += info
   }