Add a new 'rejected' disconnect reason

This reason will be used in a future commit that will reject erroneous
messages.

src/locales/en.json

@@ -90,6 +90,9 @@
   "pad.modals.rateLimited": "Rate Limited.",
   "pad.modals.rateLimited.explanation": "You sent too many messages to this pad so it disconnected you.",
 
+  "pad.modals.rejected.explanation": "The server rejected a message that was sent by your browser.",
+  "pad.modals.rejected.cause": "The server may have been updated while you were viewing the pad, or maybe there is a bug in Etherpad. Try reloading the page.",
+
   "pad.modals.disconnected": "You have been disconnected.",
   "pad.modals.disconnected.explanation": "The connection to the server was lost",
   "pad.modals.disconnected.cause": "The server may be unavailable. Please notify the service administrator if this continues to happen.",

src/static/js/pad_connectionstatus.js

@@ -63,9 +63,26 @@ var padconnectionstatus = (function()
         what: 'disconnected',
         why: msg
       };
-      var k = String(msg); // known reason why
-      if (!(k == 'userdup' || k == 'deleted' || k == 'looping' || k == 'slowcommit' || k == 'initsocketfail' || k == 'unauth' || k == 'rateLimited' || k == 'badChangeset' || k == 'corruptPad'))
-      {
+
+      // These message IDs correspond to localized strings that are presented to the user. If a new
+      // message ID is added here then a new div must be added to src/templates/pad.html and the
+      // corresponding l10n IDs must be added to the language files in src/locales.
+      const knownReasons = [
+        'badChangeset',
+        'corruptPad',
+        'deleted',
+        'disconnected',
+        'initsocketfail',
+        'looping',
+        'rateLimited',
+        'rejected',
+        'slowcommit',
+        'unauth',
+        'userdup',
+      ];
+      let k = String(msg);
+      if (knownReasons.indexOf(k) === -1) {
+        // Fall back to a generic message.
         k = 'disconnected';
       }
 

src/templates/pad.html

@@ -283,6 +283,11 @@
             <h1 data-l10n-id="pad.modals.rateLimited"></h1>
             <p data-l10n-id="pad.modals.rateLimited.explanation"></p>
           </div>
+          <div class="rejected">
+            <h1 data-l10n-id="pad.modals.disconnected"></h1>
+            <h2 data-l10n-id="pad.modals.rejected.explanation"></h2>
+            <p data-l10n-id="pad.modals.rejected.cause"></p>
+          </div>
           <div class="disconnected with_reconnect_timer">
             <% e.begin_block("disconnected"); %>
             <h1 data-l10n-id="pad.modals.disconnected"></h1>