submessages: Add update_message() function.

We want to update message.submessages for new events, even
though our couple of widgets (poll/tictactoe) that can process
"update" events currently just apply events as "deltas"
to their current data.

This does fix a subtle issue where you may get incoming
events for a message that the client knows about but which
it hasn't yet activated as a widget.  Up until now,
we've rarely seen the bug that's fixed here, since it's
usually the case that as soon as we receive a message, we
widgetize it right away.

frontend_tests/node_tests/submessage.js

@@ -2,6 +2,7 @@ zrequire('submessage');
 
 set_global('channel', {});
 set_global('widgetize', {});
+set_global('message_store', {});
 
 run_test('get_message_events', () => {
     var msg = {};
@@ -64,6 +65,7 @@ run_test('handle_event', () => {
     };
 
     const event = {
+        id: 11,
         msg_type: 'widget',
         sender_id: 99,
         message_id: message.id,
@@ -75,6 +77,11 @@ run_test('handle_event', () => {
         args = opts;
     };
 
+    message_store.get = (msg_id) => {
+        assert.equal(msg_id, message.id);
+        return message;
+    };
+
     submessage.handle_event(event);
 
     assert.deepEqual(args, {
@@ -82,4 +89,6 @@ run_test('handle_event', () => {
         message_id: 42,
         data: 'some_data',
     });
+
+    assert.deepEqual(message.submessages[0], event);
 });

static/js/submessage.js

@@ -81,7 +81,39 @@ exports.do_process_submessages = function (in_opts) {
     });
 };
 
+exports.update_message = function (submsg) {
+    var message = message_store.get(submsg.message_id);
+
+    if (message === undefined) {
+        // This is generally not a problem--the server
+        // can send us events without us having received
+        // the original message, since the server doesn't
+        // track that.
+        return;
+    }
+
+    var existing = _.find(message.submessages, function (sm) {
+        return sm.id === submsg.id;
+    });
+
+    if (existing !== undefined) {
+        blueslip.warn("Got submessage multiple times: " + submsg.id);
+        return;
+    }
+
+    if (message.submessages === undefined) {
+        message.submessages = [];
+    }
+
+    message.submessages.push(submsg);
+};
+
 exports.handle_event = function (submsg) {
+    // Update message.submessages in case we haven't actually
+    // activated the widget yet, so that when the message does
+    // come in view, the data will be complete.
+    exports.update_message(submsg);
+
     // Right now, our only use of submessages is widgets.
     var msg_type = submsg.msg_type;