A simple Telegram bot that can forward messages from a Telegram group to a Zulip stream. The bot must be given the permission to access the messages of the group (you can turn this option on/off with the /setprivacy command sent to the BotFather).

Currently, it supports:

1. Text-only messages, including replies

2. Messages with attachments:

   • Photo
   • Audio
   • Voice message
   • Video
   • Document (i.e., generic file)

3. @-mentions (i.e., a user mentioned in Telegram will be mentioned in the message forwarded to Zulip. This feature requires a JSON file mapping Telegram with Zulip's usernames)

4. Message editing as long as the edit occurs no later than 60 minutes after the message has been sent on Telegram

At present, the attachments are not uploaded to Zulip's storage but are directly linked with an URL from Telegram API. This might be a security issue if your Zulip workspace is open to anyone since the link to the attachment retrieved by the bot exposes the bot's token.

When forwarding a reply, the message sent to Zulip will follow this format:

> *Original author (HH:MM):*
> Original message

*Replying author:*
Reply message

Markdown syntax will be rendered automatically by Zulip. If the original message's date differs from that of the reply, the timestamp will include the date for an easier reference.

Look into config.sample to know which parameters are necessary. Telegram bot's token and API key/email of your Zulip bot are compulsory.

Specifying paths with string interpolation, might be a more robust solution to avoid FileNotFound errors. For example, you can define a [paths] section in your config file and then specify the database path as db_path = %{paths:custom_dir}/{db_name}.

[paths]
my_dir = /home

[db]
db_name = data.db
db_path = ${paths:my_dir}/${db_name}

The JSON file should be as simple as

{ 
    "telegram_user_1": "zulip_user_1",
    "telegram_user_2": "zulip_user_2",
}

Note: if a user has a Telegram @-username, the bot will receive a mention without first_name or last_name. For these users, you should add their @-usernames as their keys in the JSON file.

The path to this file can be specified in the config in the [zulip] section as zulip_users. The default is zulip_users.json in the current working directory.

• Add a customizable format for replies
• Add a customizable time-interval for message editing
• Add the possibility to download a file from Telegram and upload it to Zulip's server (partially implemented)