.. _sessions:

==============
Session Files
==============

The first parameter you pass to the constructor of the ``TelegramClient`` is
the ``session``, and defaults to be the session name (or full path). That is,
if you create a ``TelegramClient('anon')`` instance and connect, an
``anon.session`` file will be created on the working directory.

These database files using ``sqlite3`` contain the required information to
talk to the Telegram servers, such as to which IP the client should connect,
port, authorization key so that messages can be encrypted, and so on.

These files will by default also save all the input entities that you've seen,
so that you can get information about an user or channel by just their ID.
Telegram will **not** send their ``access_hash`` required to retrieve more
information about them, if it thinks you have already seem them. For this
reason, the library needs to store this information offline.

The library will by default too save all the entities (chats and channels
with their name and username, and users with the phone too) in the session
file, so that you can quickly access them by username or phone number.

If you're not going to work with updates, or don't need to cache the
``access_hash`` associated with the entities' ID, you can disable this
by setting ``client.session.save_entities = False``, or pass it as a
parameter to the ``TelegramClient``.

If you don't want to save the files as a database, you can also create
your custom ``Session`` subclass and override the ``.save()`` and ``.load()``
methods. For example, you could save it on a database:

    .. code-block:: python

        class DatabaseSession(Session):
            def save():
                # serialize relevant data to the database

            def load():
                # load relevant data to the database


You should read the ````session.py```` source file to know what "relevant
data" you need to keep track of.


Sessions and Heroku
-------------------

You probably have a newer version of SQLite installed (>= 3.8.2). Heroku uses
SQLite 3.7.9 which does not support ``WITHOUT ROWID``. So, if you generated
your session file on a system with SQLite >= 3.8.2 your session file will not
work on Heroku's platform and will throw a corrupted schema error.

There are multiple ways to solve this, the easiest of which is generating a
session file on your Heroku dyno itself. The most complicated is creating
a custom buildpack to install SQLite >= 3.8.2.


Generating a Session File on a Heroku Dyno
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. note::
    Due to Heroku's ephemeral filesystem all dynamically generated
    files not part of your applications buildpack or codebase are destroyed
    upon each restart.

.. warning::
    Do not restart your application Dyno at any point prior to retrieving your
    session file. Constantly creating new session files from Telegram's API
    will result in a 24 hour rate limit ban.

Due to Heroku's ephemeral filesystem all dynamically generated
files not part of your applications buildpack or codebase are destroyed upon
each restart.

Using this scaffolded code we can start the authentication process:

    .. code-block:: python

        client = TelegramClient('login.session', api_id, api_hash).start()

At this point your Dyno will crash because you cannot access stdin. Open your
Dyno's control panel on the Heroku website and "Run console" from the "More"
dropdown at the top right. Enter ``bash`` and wait for it to load.

You will automatically be placed into your applications working directory.
So run your application ``python app.py`` and now you can complete the input
requests such as "what is your phone number" etc.

Once you're successfully authenticated exit your application script with
CTRL + C and ``ls`` to confirm ``login.session`` exists in your current
directory. Now you can create a git repo on your account and commit
``login.session`` to that repo.

You cannot ``ssh`` into your Dyno instance because it has crashed, so unless
you programatically upload this file to a server host this is the only way to
get it off of your Dyno.

You now have a session file compatible with SQLite <= 3.8.2. Now you can
programatically fetch this file from an external host (Firebase, S3 etc.)
and login to your session using the following scaffolded code:

    .. code-block:: python

        fileName, headers = urllib.request.urlretrieve(file_url, 'login.session')
        client = TelegramClient(os.path.abspath(fileName), api_id, api_hash).start()

.. note::
    - ``urlretrieve`` will be depreciated, consider using ``requests``.
    - ``file_url`` represents the location of your file.