outboxActions: Show dialog if message send fails with informative Api…

…Error

This is our minimal support for zulip#5870 in this legacy codebase.
Supporting it properly with a client-side check of the setting is
more effort than we can spare right now.

Probably more error handling is called for in general (like for
network or server issues), but zulip#3881 ("Sending outbox messages is
fraught with issues") is complicated and it's probably best to leave
it be.

Fixes: zulip#5870

src/outbox/outboxActions.js

@@ -3,6 +3,8 @@
 import parseMarkdown from 'zulip-markdown-parser';
 import invariant from 'invariant';
 
+import { ApiError } from '../api/apiErrors';
+import { showErrorAlert } from '../utils/info';
 import * as logging from '../utils/logging';
 import type {
   PerAccountState,
@@ -79,14 +81,30 @@ const trySendMessages = (dispatch, getState): boolean => {
             //   CSV, then a literal. To avoid misparsing, always use JSON.
           : JSON.stringify([streamNameOfStreamMessage(item)]);
 
-      await api.sendMessage(auth, {
-        type: item.type,
-        to,
-        subject: item.subject,
-        content: item.markdownContent,
-        localId: item.timestamp,
-        eventQueueId: state.session.eventQueueId ?? undefined,
-      });
+      try {
+        await api.sendMessage(auth, {
+          type: item.type,
+          to,
+          subject: item.subject,
+          content: item.markdownContent,
+          localId: item.timestamp,
+          eventQueueId: state.session.eventQueueId ?? undefined,
+        });
+      } catch (errorIllTyped) {
+        const error: mixed = errorIllTyped; // https://github.com/facebook/flow/issues/2470
+
+        if (error instanceof ApiError && error.message.length > 0) {
+          showErrorAlert(
+            // TODO(i18n) nontrivial to plumb through GetText;
+            //   skip for now in this legacy codebase
+            'Failed to send message',
+            // E.g., "You do not have permission to send direct messages to this recipient."
+            `The server at ${auth.realm.toString()} said:\n\n${error.message}`,
+          );
+          dispatch(deleteOutboxMessage(item.id));
+          return;
+        }
+      }
       dispatch(messageSendComplete(item.timestamp));
     });
     return true;