From 3d403c2471f38d93fd89fad78e714727242a454b Mon Sep 17 00:00:00 2001
From: Tulir Asokan <tulir@maunium.net>
Date: Sat, 19 Dec 2020 13:15:27 +0200
Subject: [PATCH] Add option to resolve redirects in invite links. Fixes #559

---
 mautrix_telegram/commands/telegram/misc.py | 12 +++++++++++-
 mautrix_telegram/config.py                 |  1 +
 mautrix_telegram/example-config.yaml       |  3 +++
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/mautrix_telegram/commands/telegram/misc.py b/mautrix_telegram/commands/telegram/misc.py
index 976fdf17..0060619c 100644
--- a/mautrix_telegram/commands/telegram/misc.py
+++ b/mautrix_telegram/commands/telegram/misc.py
@@ -18,6 +18,8 @@ import codecs
 import base64
 import re
 
+from aiohttp import ClientSession, InvalidURL
+
 from telethon.errors import (InviteHashInvalidError, InviteHashExpiredError, OptionsTooMuchError,
                              UserAlreadyParticipantError, ChatIdInvalidError,
                              TakeoutInitDelayError, EmoticonInvalidError)
@@ -145,9 +147,17 @@ async def join(evt: CommandEvent) -> Optional[EventID]:
     if len(evt.args) == 0:
         return await evt.reply("**Usage:** `$cmdprefix+sp join <invite link>`")
 
+    url = evt.args[0]
+    if evt.config["bridge.invite_link_resolve"]:
+        try:
+            async with ClientSession() as sess, sess.get(url) as resp:
+                url = resp.url
+        except InvalidURL:
+            return await evt.reply("That doesn't look like a Telegram invite link.")
+
     regex = re.compile(r"(?:https?://)?t(?:elegram)?\.(?:dog|me)"
                        r"(?:/(?P<type>joinchat|s))?/(?P<id>[^/]+)/?", flags=re.IGNORECASE)
-    arg = regex.match(evt.args[0])
+    arg = regex.match(url)
     if not arg:
         return await evt.reply("That doesn't look like a Telegram invite link.")
 
diff --git a/mautrix_telegram/config.py b/mautrix_telegram/config.py
index 3613a374..f2a5f97c 100644
--- a/mautrix_telegram/config.py
+++ b/mautrix_telegram/config.py
@@ -114,6 +114,7 @@ class Config(BaseBridgeConfig):
         else:
             copy("bridge.login_shared_secret_map")
         copy("bridge.telegram_link_preview")
+        copy("bridge.invite_link_resolve")
         copy("bridge.inline_images")
         copy("bridge.image_as_file_size")
         copy("bridge.max_document_size")
diff --git a/mautrix_telegram/example-config.yaml b/mautrix_telegram/example-config.yaml
index 4401afd8..f73b4733 100644
--- a/mautrix_telegram/example-config.yaml
+++ b/mautrix_telegram/example-config.yaml
@@ -194,6 +194,9 @@ bridge:
         example.com: foobar
     # Set to false to disable link previews in messages sent to Telegram.
     telegram_link_preview: true
+    # Whether or not the !tg join command should do a HTTP request
+    # to resolve redirects in invite links.
+    invite_link_resolve: false
     # Use inline images instead of a separate message for the caption.
     # N.B. Inline images are not supported on all clients (e.g. Riot iOS).
     inline_images: false