~cellsoftware/telegram-app/1583929

# Telegram for Ubuntu - development guide

Last updated: 2015-11-17

The goal of this document is to familiarize you, the developer and/or maintainer,
with some details which you may find helpful while developing or maintaining
Telegram for Ubuntu.

Most of the details required for building the app can be found in the README.md

This document provides some more context around the development and the team,
so that you know where to look for things, who to ask, and where to land.

## History

Telegram for Ubuntu consists of three components/layers (branch names):
 - the UI (libqtelegram/app)
 - the QML plugin (libqtelegram/plugin subdir)
 - the API library (libqtelegram)
and is packaged with:
 - a push helper
 - a scope

Initially the lowest level library was based on telegram-cli project
(https://github.com/vysheng/tg) but was heavily scrubbed and effectively
mostly re-written for the needs of better API based on Qt's signal/slots.
Most of this work has been done by
 - Roberto Mier Escandon - irc:rmescandon@irc.freenode.net)
 - Tiago Herrmann - irc:salem_@irc.freenode.net)

A stateful QML plugin, written by Roberto, with little contribution from me,
wrapped the lower API library and provided a higher level API for managing
a Telegram instance from QML.

The QML plugin lived under the `plugin` directory in the libqtelegram library.

Those two components where wrapped in a QML UI by yours truly.

A push helper by me as well as a Telegram scope by Victor Palau
were shipped with the app to the Ubuntu store.

At some point in time, the team advised management of some critical changes
needed to be done, as the glue code (the QML plugin) was not as reliable
as we wished and it introduced some performance issues as well. There was
parallel development undergoing on an open source Cutgram Telegram client
by the Aseman team (mostly Bardia Daneshvar), which we did not want to
ignore, and thus we made the call to leverage that instead!

It was a turning point for Telegram for Ubuntu, because:
 1. this allowed us to make use of a more reliable Cutegram backend
 2. and provided very up to date high layer Telegram API access
This also meant I effectively had to transplant the UI on top of new code,
which in practice turned out to cause a major rewrite, but with the latest
Ubuntu.Components 2.3, it gave the app a completely fresh look.

Feature wise this was a small step backward, as we no longer had secret
chat self-destruct on messages or a few minor features, but the stability
and reliability of the back-end itself was very much worth it. This was
the primary reason to make the switch in the first place.

I should make you aware the QML source is not up to standard. There's still
some blocks of comments left for adaptation from the old source, and not all
Cutegram features are yet surfaced in the UI. However, because a lot of
components map directly to the ones in Cutegram, it should be really easy to
add the missing subset of features, without having to start them from scratch.

## Present

Currently Telegram for Ubuntu consists of three components/layers:
 - the UI          lp:telegram-app/v2 - contains whole app, pulls dependencies
 - the QML plugin  https://github.com/Aseman-Land/TelegramQML
 - the API library https://github.com/Aseman-Land/libqtelegram-aseman-edition
and is packaged with:
 - a push helper
 - a scope

Bardia Daneshvar (find him on github) is a great developer, he has put
a significant effort into maintaining libqtelegram (as we now call it short,
libqtelegram-ae), and adding latest API features. Because of that, we
abandoned our own master branch of the library, and continued to develop
libqtelegram-ae with Bardia. He does most of the hard work, and we are
very greatful for that.

TelegramQML has been authored by Bardia, and this was the component that
replaced our libqtelegram/plugin implementation. It is a solid work, but
usually libqtelegram-ae exposes more features than TelegramQML consumes.
Effectively, this means contributions are welcome, because we already can
do much more on the lower level, but not all of it is yet exposed to QML apps.
So, we invite you to contribute!

As mentioned in the previus paragraph, the UI part of Telegram for Ubuntu
has been mostly rewritten, as well as the Telegram scope. The push helper
was cleaned-up.

I think it's worth mentioning the core developers, so you know who you
can reach out to in case you need:

Tiago - was involved early in the project, and it's been a long time,
    so unless you have some Telepathy or Messaging Framework questions,
    you probably don't want to bother him with Telegram questions.
Roberto - was involved even before he joined Canonical, up till ~half a year
    ago, when he moved to work on the Messaging Framework full time.
    He still provides his knowledge and expertise on the back-end and how
    Telegram works. Do note that, he may not be familiar with the new
    TelegramQML library much, but the old libqtelegram - very much so.
Michal - (which is myself) was involved over whole length of the project,
    mosty working on the UI, contributing to the back-end, and managing
    project priorities, releases and external contributions
    (we have fantastic community!). Over the last few months I was solely
    responsible for all of the re-work that went into the major 2.x update.

I am only mentioning 'core' developers here, but I have always been
appreciative of all contributions we've had from people around the world,
you are champs and we are greatful to every one of you!

## Technical overview

The project lives under
 - https://launchpad.net/telegram-app
It previously lived under
 - https://launchpad.net/libqtelegram
which now is an alias to the former one.

Development focus is:
 - lp:telegram-app/v2

Project was internally tracked in Asana, but has now been archived, and the
pending tasks have been moved over to more general one.

From the README.md you already know Telegram builds in an
armhf ubuntu-sdk-15.04 click chroot. Note that click chroot (or schroot,
that it uses indirectly) is known for having trouble when working on a machine
with encrypted home directory. Hence, while potentially inconvenient, we advise
you work on a machine with an un-encrypted home directory to avoid those
problems. Do note that by the time you read this, this may have been resolved,
feel free to Google.

Earlier this month we had a contribution from faenil, who prepared desktop
based build setup, which you can find here:
 - lp:~libqtelegram-team/telegram-app/telegram2-all-platforms
I didn't point directly to his branch as I already resolved some minor issues.
I am very careful about landing this branch, which is the only reason
I'm taking my time for this. Feel free to give it a go, and run the app on
a 15.04 based desktop, assuming you're okay to install the vivid phone overlay
(which is not what we would normally recommend, beyond development purposes).

Regardless which branch you pick, the bootstrap/setup process will pull
the dependencies for you (libqtelegram-ae, TelegramQML) and build them as well.

The /telegram directory contains three directories (+po for translations):
 - app - is the core application
 - push - is the push helper
 - scope - is the app's scope

### Build

In the build scripts you will notice the scope is build separately, and not
as part of the qmake subdirs template. This is because of a conflict, caused
by lack of namespaces in one of the two libraries. If this is fixed, the scope
could be build as part of the subdirs, which would be much cleaner.

### App

As you'd expect, main.cpp is the entry point to the app.

#### Version

The versioning needs a little work. In v1 we had this nicely done,
in v2 however there's three places that contain the version string
currently:
 - telegram/app/main.cpp (setApplicationVersion))
 - telegram/app/qml/js/version.js
 - telegram/manifest.json.in ("version")
plus bzr tag on release day, so it's something to fix/pay attention to.

We stick to semver, MAJOR.MINOR.PATCH and append .REVISION,
which does not need to match bzr revision, although it would be a good
idea if it did. It was the situation with Tg v1, it hasn't been set up
for Tg v2 yet.

#### Manifest

The app's manifest (located one directory up) contains 3 hooks.
 - telegram - the hook for the app
 - push - the hook for the push helper
 - sctelegram - the hook for the scope (legacy name we can't change)

Let's talk about the telegram hook, the other two are self explanatory.

account-application allows us to show Telegram entry in
  Settings > Notifications

apparmor entry lists all permissions required by the app.

content-hub tells Telegram can share pictures, videos, links and text.

urls tells the Telegram app can handle the "telegram" protocol,
which basically means a URI scheme. Interestingly, this is currently
not in use, but should be for links like joining a group chat
via a group invite link.

Moving on, telegram.cpp takes most of Cutegram's goodies, it's a QObject
that exposes a bunch of application properties to QML, as well as a few
utility methods.

tg-server.pub is the public key required by libqtelegram-ae to
talk to Telegram servers. It's installed next to the telegram app binary.

upgradev2 is used by users, who used Telegram v1 and launch v2 for the
first time. It persists user session over the upgrade, as well as 
the secret chats. Part of the class is overly complex and uses fictional
values (which doesn't affect users at all, as the attachments have already
been downloaded and are no longer on the server), because some critical
metadata relating to media attachments has not been stored by the old
libqtelegram in the sqlite database. Hence, the upgrade process was
more challenging thatn I wished :')

TODO karni: explain the QML file relations a bit.

There's a few items currently not used, like unitysystemtray.

### Push

There's not too much to say about the push helper other than basic
documentation available about push helpers on developer.ubuntu.com.
It's a simple program that takes the push message payload and outputs
it in the format that the notifications expect it.

If you end up having to hack on the push helper, I suggest you output
the raw payload and let it through json_pp so you get the idea of the
payload format. The format is not optimal (some redundant fields),
it's a long story. We haven't reviewed this with Telegram push team,
because it would require some work on their end, but once there's a new
spec on how we'd like to do it, it would be time to talk to the Telegram
server team, and also request push messages about read read messages,
which I believe are the only ones that we are actually not getting.

### Scope

The scope has read access to the applications SQLite database files. See:
 - /telegram/scope/apparmor-scope.json

This is the reason why it gets red-flagged by click-review. Alan Pope, who
does our releases to the store, is aware of this, and the app gets a +1
on manual review.

You will notice the config.h file contains some hardcoded paths, as well as
enum types. The paths should rather be queried by the scope source, and
enums should come from the library to avoid duplication. We simply didn't
have time to do this properly, which I'm very sad about.

The 'Today' and 'Photos' aggregator scopes depend on these two values:
 - KEYWORD_RECENT
 - KEYWORD_PHOTOS_TELEGRAM
So they most probably should never change. If for any reason you do need
to change them, this should be closely consulted with Kyle Nitsche.
These same keywords are mentioned in the scope's .ini file under Keywords=

In the context of the scope, it is probably worth mentioning a pending
bug report filed here:
 - https://bugs.launchpad.net/ubuntu/+source/unity-scope-mediascanner/+bug/1472755
The reason is not yet known for the crasher, but it's the most common
crasher on the phone. The scope's code has been reviewed, and it is not
even clear whether the scope is actually to blame. But because this affects
multiple users, I thought it was the right thing to mention it here.
We do not know whether this only affects Telegram within the aggregator
(like 'Today') or not, but it was reported that disabling Telegram under
'Today' scope's settings works around the crasher.

## Foot notes

Authored by: Michał Karnicki - irc:karni@irc.freenode.net | 2015-11-17