Don't send if message body is too long

_locales/en/messages.json

@@ -1378,6 +1378,10 @@
     "description":
       "Timestamp format string for displaying month and day (but not the year) of a date within the current year, ex: use 'MMM D' for 'Aug 8', or 'D MMM' for '8 Aug'."
   },
+  "messageBodyTooLong": {
+    "message": "Message body is too long.",
+    "description": "Shown if the user tries to send more than 64kb of text"
+  },
   "unblockToSend": {
     "message": "Unblock this contact to send a message.",
     "description": "Brief message shown when trying to message a blocked number"

js/views/conversation_view.js

@@ -64,6 +64,13 @@
     },
   });
 
+  const MAX_MESSAGE_BODY_LENGTH = 64 * 1024;
+  Whisper.MessageBodyTooLongToast = Whisper.ToastView.extend({
+    render_attributes() {
+      return { toastMessage: i18n('messageBodyTooLong') };
+    },
+  });
+
   Whisper.ConversationLoadingScreen = Whisper.View.extend({
     templateName: 'conversation-loading-screen',
     className: 'conversation-loading-screen',
@@ -1653,6 +1660,9 @@
       this.closeEmojiPanel();
       this.model.clearTypingTimers();
 
+      const input = this.$messageField;
+      const message = window.Signal.Emoji.replaceColons(input.val()).trim();
+
       let toast;
       if (extension.expired()) {
         toast = new Whisper.ExpiredToast();
@@ -1666,6 +1676,9 @@
       if (!this.model.isPrivate() && this.model.get('left')) {
         toast = new Whisper.LeftGroupToast();
       }
+      if (message.length > MAX_MESSAGE_BODY_LENGTH) {
+        toast = new Whisper.MessageBodyTooLongToast();
+      }
 
       if (toast) {
         toast.$el.appendTo(this.$el);
@@ -1674,9 +1687,6 @@
         return;
       }
 
-      const input = this.$messageField;
-      const message = window.Signal.Emoji.replaceColons(input.val()).trim();
-
       try {
         if (!message.length && !this.fileInput.hasFiles()) {
           return;