slack bridge: Add legacy mode for Slack Bridge.

Slack Bridge now uses the Slack Webhook integration
to get messages accross from Slack instead of the
legacy RTM API based connection our Slack Bridge
use.

This commit adds a "--legacy" argument to the script,
it acts as a toggle to run the RTM API based connection
to get messages accross to Zulip. It is used to ensure
backwards compitability for users who want to maintain
any ongoing Slack mirror.

Fixes #825.

zulip/integrations/bridge_with_slack/bridge_with_slack_config.py

@@ -13,8 +13,8 @@
     "channel_mapping": {
         # Slack channel; must be channel ID
         "C5Z5N7R8A": {
-            # Zulip stream
-            "stream": "test here",
+            # Zulip channel
+            "channel": "test here",
             # Zulip topic
             "topic": "<- slack-bridge",
         },

zulip/integrations/bridge_with_slack/run-slack-bridge

@@ -49,7 +49,7 @@ class SlackBridge:
 
         self.slack_to_zulip_map: Dict[str, Dict[str, str]] = config["channel_mapping"]
         self.zulip_to_slack_map: Dict[StreamTopicT, str] = {
-            (z["stream"], z["topic"]): s for s, z in config["channel_mapping"].items()
+            (z["channel"], z["topic"]): s for s, z in config["channel_mapping"].items()
         }
 
         # zulip-specific
@@ -123,7 +123,7 @@ class SlackBridge:
             zulip_endpoint = self.slack_to_zulip_map[event["channel"]]
             msg_data = dict(
                 type="stream",
-                to=zulip_endpoint["stream"],
+                to=zulip_endpoint["channel"],
                 subject=zulip_endpoint["topic"],
                 content=content,
             )
@@ -141,6 +141,10 @@ if __name__ == "__main__":
 
     sys.path.append(os.path.join(os.path.dirname(__file__), ".."))
     parser = argparse.ArgumentParser(usage=usage)
+    parser.add_argument(
+        "--legacy", action="store_true", help="Run the bridge using the legacy Slack RTM API"
+    )
+    args = parser.parse_args()
 
     config: Dict[str, Any] = bridge_with_slack_config.config
     if "channel_mapping" not in config:
@@ -154,6 +158,7 @@ if __name__ == "__main__":
     print("MAKE SURE THE BOT IS SUBSCRIBED TO THE RELEVANT ZULIP STREAM(S) & SLACK CHANNEL(S)!")
 
     # We have to define rtm outside of SlackBridge because the rtm variable is used as a method decorator.
+    # the RTM API is a legacy Slack SDK, we keep using them only to provide backwards compitability.
     rtm = RTMClient(token=config["slack"]["token"])
 
     backoff = zulip.RandomExponentialBackoff(timeout_success_equivalent=300)
@@ -164,14 +169,26 @@ if __name__ == "__main__":
             zp = threading.Thread(
                 target=sb.zulip_client.call_on_each_message, args=(sb.zulip_to_slack(),)
             )
-            sp = threading.Thread(target=sb.run_slack_listener, args=())
             print("Starting message handler on Zulip client")
             zp.start()
-            print("Starting message handler on Slack client")
-            sp.start()
 
-            zp.join()
-            sp.join()
+            if args.legacy:
+                sp = threading.Thread(target=sb.run_slack_listener, args=())
+                print(
+                    "Warning! Running on legacy Slack SDK\n"
+                    "Starting message handler on Slack client"
+                )
+                sp.start()
+                sp.join()
+                zp.join()
+            else:
+                print(
+                    "Warning! if you haven't moved to the new Slack app,\n"
+                    "please run the script with the --legacy argument.\n"
+                    "Make sure your Slack Webhook integration is running\n"
+                    "to receive messages from Slack."
+                )
+                zp.join()
         except Exception:
             traceback.print_exc()
         backoff.fail()