Telethon/client/doc/concepts/messages.rst

Messages
========

.. currentmodule:: telethon

.. role:: underline
    :class: underline

.. role:: strikethrough
    :class: strikethrough

.. role:: spoiler
    :class: spoiler

Messages are at the heart of a messaging platform.
In Telethon, you will be using the :class:`~types.Message` class to interact with them.


Fetching messages
-----------------

The most common way to actively fetch messages using the :meth:`Client.get_messages` method:

.. code-block:: python

    # Get the last message in a chat (by setting the limit to 1).
    last_message = (await client.get_messages(chat, 1))[0]

    # Iterate over all messages in a chat, starting from the oldest message (by using reversed).
    async for message in reversed(client.get_messages(chat)):
        print(message.sender.name, message.text_html)

You can also perform a fuzzy text search with the :meth:`Client.search_messages` method.
The search will be performed server-side by Telegram, so the rules for how it works are also fuzzy.

If you want to search for messages in all the chats you're part of, you can use :meth:`Client.search_all_messages`.

Lastly, :meth:`Client.send_message` *also* returns the :class:`~types.Message` that you just sent.

The most common way to passively listen to incoming messages is using the :class:`~events.NewMessage` event:

.. code-block:: python

    from telethon import events

    @client.on(events.NewMessage)
    async def first(event):
        print(event.chat.name, ':', event.text)

.. seealso::

    The :doc:`updates` concept for an in-depth explanation on using events.


.. _formatting:

Formatting messages
-------------------

The library supports 3 formatting modes: no formatting, CommonMark, HTML.

Telegram does not natively support markdown or HTML.
Clients such as Telethon parse the text into a list of formatting :tl:`MessageEntity` at different offsets.

Note that `CommonMark's markdown <https://commonmark.org/>`_ is not fully compatible with :term:`HTTP Bot API`'s
`MarkdownV2 style <https://core.telegram.org/bots/api#markdownv2-style>`_, and does not support spoilers::

    *italic* and _italic_
    **bold** and __bold__
    # headings are underlined
    ~~strikethrough~~
    [inline URL](https://www.example.com/)
    [inline mention](tg://user?id=ab1234cd6789)
    custom emoji image with ![👍](tg://emoji?id=1234567890)
    `inline code`
    ```python
    multiline pre-formatted
    block with optional language
    ```

HTML is also not fully compatible with :term:`HTTP Bot API`'s
`HTML style <https://core.telegram.org/bots/api#html-style>`_,
and instead favours more standard `HTML elements <https://developer.mozilla.org/en-US/docs/Web/HTML/Element>`_:

* ``strong`` and ``b`` for **bold**.
* ``em`` and ``i`` for *italics*.
* ``u`` for :underline:`underlined text`.
* ``del`` and ``s`` for :strikethrough:`strikethrough`.
* ``blockquote`` for quotes.
* ``details`` for :spoiler:`hidden text` (spoiler).
* ``code`` for ``inline code``
* ``pre`` for multiple lines of code.
* ``a`` for links.
* ``img`` for inline images (only custom emoji).

Both markdown and HTML recognise the following special URLs using the ``tg:`` protocol:

* ``tg://user?id=ab1234cd6789`` for inline mentions.
  To make sure the mention works, use :attr:`types.PeerRef.hex`.
  You can also use :attr:`types.User.id`, but the mention will fail if the user is not in cache.
* ``tg://emoji?id=1234567890`` for custom emoji.
  You must use the document identifier as the value.
  The alt-text of the image **must** be a emoji such as 👍.


To obtain a message's text formatted, use :attr:`types.Message.text_markdown` or :attr:`types.Message.text_html`.

To send a message with formatted text, use the ``markdown`` or ``html`` parameters in :meth:`Client.send_message`.

When sending files, the format is appended to the name of the ``caption`` parameter, either ``caption_markdown`` or ``caption_html``.


Link previews
^^^^^^^^^^^^^

Link previews are treated as a type of media automatically generated by Telegram.
This means you cannot have both a link preview and other media in the same message.

The ``link_preview`` parameter indicates whether link previews are *allowed* to be present.
If Telegram is unable to generate a link preview for any of the links, there won't be a link preview.

By default, link previews are not enabled.
This is done to prevent sending things you did not explicitly intend to send.
Unlike the official clients, which do not have a GUI to "enable" the preview, you can easily enable them from code.

Telegram will attempt to generate a preview for all links contained in the message in order.
You can use this to your advantage, and hide a link to a photo in the first space or invisible character like ``'\u2063'``.
Note that avid users *will* be able to find out the link. It is not secret!

Link previews of photos won't show under the photos of the chat,
but it requires a server hosting the image, a public address, and Telegram to be able to generate a preview.

To regenerate a preview, send the corresponding link to `@WebpageBot <https://t.me/WebpageBot>`_.


Message identifiers
-------------------

This is an in-depth explanation for how the :attr:`types.Message.id` works.

.. note::

    You can safely skip this section if you're not interested.

Every account, whether it's an user account or bot account, has its own message counter.
This counter starts at 1, and is incremented by 1 every time a new message is received.
In private conversations or small groups, each account will receive a copy each message.
The message identifier will be based on the message counter of the receiving account.

In megagroups and broadcast channels, the message counter instead belongs to the channel itself.
It also starts at 1 and is incremented by 1 for every message sent to the group or channel.
This means every account will see the same message identifier for a given mesasge in a group or channel.

This design has the following implications:

* The message identifier alone is enough to uniquely identify a message only if it's not from a megagroup or channel.
  This is why :class:`events.MessageDeleted` does not need to (and doesn't always) include chat information.
* Messages cannot be deleted for one-side only in megagroups or channels.
  Because every account shares the same identifier for the message, it cannot be deleted only for some.
* Links to messages only work for everyone inside megagroups or channels.
  In private conversations and small groups, each account will have their own counter, and the identifiers won't match.

Let's look at a concrete example.

* You are logged in as User-A.
* Both User-B and User-C are your mutual contacts.
* You have share a small group called Group-S with User-B.
* You also share a megagroup called Group-M with User-C.

.. graphviz::
    :caption: Demo scenario

    digraph scenario {
        "User A" [shape=trapezium];
        "User B" [shape=box];
        "User C" [shape=box];

        "User A" -> "User B";
        "User A" -> "User C";

        "Group-S" -> "User A";
        "Group-S" -> "User B";

        "Group-M" -> "User A";
        "Group-M" -> "User C";
    }

Every account and channel has just been created.
This means everyone has a message counter of one.

First, User-A will sent a welcome message to both User-B and User-C::

    User-A → User-B: Hey, welcome!
    User-A → User-C: ¡Bienvenido!

* For User-A, "Hey, welcome!" will have the message identifier 1. The message with "¡Bienvenido!" will have an ID of 2.
* For User-B, "Hey, welcome" will have ID 1.
* For User-B, "¡Bienvenido!" will have ID 1.

.. csv-table:: Message identifiers
   :header: "Message", "User-A", "User-B", "User-C", "Group-S", "Group-M"

   "Hey, welcome!", 1, 1, "", "", ""
   "¡Bienvenido!", 2, "", 1, "", ""

Next, User-B and User-C will respond to User-A::

    User-B → User-A: Thanks!
    User-C → User-A: Gracias :)

.. csv-table:: Message identifiers
   :header: "Message", "User-A", "User-B", "User-C", "Group-S", "Group-M"

   "Hey, welcome!", 1, 1, "", "", ""
   "¡Bienvenido!", 2, "", 1, "", ""
   "Thanks!", 3, 2, "", "", ""
   "Gracias :)", 4, "", 2, "", ""

Notice how for each message, the counter goes up by one, and they are independent.

Let's see what happens when User-B sends a message to Group-S::

    User-B → Group-S: Nice group

.. csv-table:: Message identifiers
   :header: "Message", "User-A", "User-B", "User-C", "Group-S", "Group-M"

   "Hey, welcome!", 1, 1, "", "", ""
   "¡Bienvenido!", 2, "", 1, "", ""
   "Thanks!", 3, 2, "", "", ""
   "Gracias :)", 4, "", 2, "", ""
   "Nice group", 5, 3, "", "", ""

While the message was sent to a different chat, the group itself doesn't have a counter.
The message identifiers are still unique for each account.
The chat where the message was sent can be completely ignored.

Megagroups behave differently::

    User-C → Group-M: Buen grupo

.. csv-table:: Message identifiers
   :header: "Message", "User-A", "User-B", "User-C", "Group-S", "Group-M"

   "Hey, welcome!", 1, 1, "", "", ""
   "¡Bienvenido!", 2, "", 1, "", ""
   "Thanks!", 3, 2, "", "", ""
   "Gracias :)", 4, "", 2, "", ""
   "Nice group", 5, 3, "", "", ""
   "Buen grupo", "", "", "", "", 1

The group has its own message counter.
Each user won't get a copy of the message with their own identifier, but rather everyone sees the same message.