libQuotient (former libQMatrixClient)

The Quotient project aims to produce a Qt5-based SDK to develop applications for Matrix. libQuotient is a library that enables client applications. It is the backbone of Quaternion, NeoChat and other projects. Versions 0.5.x and older use the previous name - libQMatrixClient.

Contacts

You can find Quotient developers in the Matrix room: #quotient:matrix.org.

You can file issues at the project issue tracker. If you find what looks like a security issue, please use instructions in SECURITY.md.

Getting and using libQuotient

Depending on your platform, the library can be obtained from a package management system. Recent releases of Debian and openSUSE, e.g., already have it. Alternatively, just build the library from the source and bundle it with your application, as described below.

Pre-requisites

• A recent Linux, macOS or Windows system (desktop versions are known to work; mobile operating systems where Qt is available might work too)
  • Recent enough Linux examples: Debian Bullseye; Fedora 35; openSUSE Leap 15.4; Ubuntu 22.04 LTS.
• Qt 5 (either Open Source or Commercial), 5.15 or higher
• CMake 3.16 or newer (from your package management system or the official website)
• A C++ toolchain with that supports at least some subset of C++20:
  • GCC 11 (Windows, Linux, macOS), Clang 11 (Linux), Apple Clang 12 (macOS) and Visual Studio 2019 (Windows) are the oldest officially supported.
• Any build system that works with CMake should be fine: GNU Make and ninja on any platform, NMake and jom on Windows are known to work. Ninja is recommended.

Linux

Just install things from the list above using your preferred package manager. If your Qt package base is fine-grained you might want to run cmake and look at error messages. The library is entirely offscreen but aside from QtCore and QtNetwork it also depends on QtGui in order to handle avatar thumbnails.

macOS

brew install qt5 should get you a recent Qt5. You may need to pass -DCMAKE_PREFIX_PATH=$(brew --prefix qt5) to make it aware of the Qt location.

Windows

Install Qt5 using their official installer; make sure to tick the CMake box in the list of installed components unless you already have it installed.

The commands in further sections imply that cmake is in your PATH, otherwise you have to prepend those commands with actual paths. It's a good idea to run a qtenv2.bat script that can be found in C:\Qt\<Qt version>\<toolchain>\bin (assuming you installed Qt to C:\Qt) if you're building from the command line; the script adds necessary paths to PATH. You might not want to run that script on system startup but it's very handy to setup the environment before building. Alternatively you can add the Qt path to CMAKE_PREFIX_PATH and leave PATH unchanged.

Using the library

If you're just starting a project using libQuotient from scratch, you can copy quotest/CMakeLists.txt to your project and change quotest to your project name. If you already have an existing CMakeLists.txt, you need to insert a find_package(Quotient REQUIRED) line to an appropriate place in it (use find_package(Quotient) if libQuotient is not a hard dependency for you) and then add Quotient to your target_link_libraries() line.

Building with dynamic linkage is only tested on Linux at the moment and is a recommended way of linking your application with libQuotient on this platform. Static linkage is the default on Windows/macOS; feel free to experiment with dynamic linking and submit PRs if you get reusable results.

As for the actual API usage, a (very basic) overview can be found at the respective wiki page. Beyond that, looking at Quotest - the test application that comes with libQuotient - may help you with most common use cases such as sending messages, uploading files, setting room state etc. For more extensive usage feel free to check out (and copy, with appropriate attribution) the source code of Quaternion (the reference client for libQuotient) or NeoChat.

Building the library

The source code is at GitHub. Checking out a certain commit or tag (rather than downloading the archive) along with submodules is strongly recommended. If you want to hack on the library as a part of another project (e.g. you are working on Quaternion but need to do some changes to the library code), it makes sense to make a recursive check out of that project (in this case, Quaternion) and update the library submodule (also recursively) within the appropriate branch. Be mindful of API compatibility restrictions: e.g., Quaternion 0.0.95 will not build with the master branch of libQuotient.

Tags consisting of digits and periods represent released versions; tags ending with -betaN or -rcN mark pre-releases. If/when packaging pre-releases, it is advised to replace a dash with a tilde.

The following commands issued in the root directory of the project sources:

mkdir build_dir
cd build_dir
cmake .. # [-D<cmake-variable>=<value>...], see below
cmake --build . --target all

will get you a compiled library in build_dir inside your project sources. Static builds are tested on all supported platforms, building the library as a shared object (aka dynamic library) is supported on Linux and macOS but is very likely to be broken on Windows.

The first CMake invocation above configures the build. You can pass CMake variables (such as -DCMAKE_PREFIX_PATH="path1;path2;..." and -DCMAKE_INSTALL_PREFIX=path) here if needed. CMake documentation (pick the CMake version at the top of the page that you use) describes the standard variables coming with CMake. On top of them, Quotient introduces:

• Quotient_INSTALL_TESTS=<ON/OFF>, ON by default - install quotest along with the library files when install target is invoked. quotest is a small command-line program that (assuming correct parameters, see quotest --help) that tries to connect to a given room as a given user and perform some basic Matrix operations, such as sending messages and small files, redaction, setting room tags etc. This is useful to check the sanity of your library installation. As of now, quotest expects the used homeserver to be able to get the contents of #quotient:matrix.org; this is being fixed in #401.
• Quotient_ENABLE_E2EE=<ON/OFF>, OFF by default - enable work-in-progress E2EE code in the library. As of 0.6, this code is very incomplete and leaks memory; only set this to ON if you want to help making this code work. Switching this on will define Quotient_E2EE_ENABLED macro (note the difference from the CMake switch) for compiler invocations on all Quotient and Quotient-dependent (if it uses find_package(Quotient 0.6)) code; so you can use #ifdef Quotient_E2EE_ENABLED to guard the code using E2EE parts of Quotient.
• MATRIX_SPEC_PATH and GTAD_PATH - these two variables are used to point CMake to the directory with the matrix-doc repository containing API files and to a GTAD binary. These two are used to generate C++ files from Matrix Client-Server API description made in OpenAPI notation. This is not needed if you just need to build the library; if you're really into hacking on it, CONTRIBUTING.md elaborates on what these two variables are for.

You can install the library with CMake:

cmake --build . --target install

This will also install cmake package config files; once this is done, you should be able to use quotest/CMakeLists.txt to compile quotest with the installed library. Installation of the quotest binary along with the rest of the library can be skipped by setting Quotient_INSTALL_TESTS to OFF.

Troubleshooting

Building fails

• If cmake fails with

  CMake Warning at CMakeLists.txt:11 (find_package):
    By not providing "FindQt5Widgets.cmake" in CMAKE_MODULE_PATH this project
    has asked CMake to find a package configuration file provided by
    "Qt5Widgets", but CMake did not find one.
  

  then you need to set the right -DCMAKE_PREFIX_PATH variable, see above.

• If you use GCC and get an "unknown declarator" compilation error in the file qtconcurrentthreadengine.h - unfortunately, it is an actual error in Qt 5.15 sources, see https://bugreports.qt.io/browse/QTBUG-90568 (or https://bugreports.qt.io/browse/QTBUG-91909). The Qt company did not make an open source release with the fix, therefore:

  • if you're on Linux - try to use Qt from your package management system, as most likely this bug is already fixed in the packages
  • if you're on Windows, or if you have to use Qt (5.15) from download.qt.io for any other reason, you should apply the fix to Qt sources: locate the file (the GCC error message tells exactly where it is), find the line with the (strange-looking) ThreadEngineStarter constructor definition:

    ThreadEngineStarter<void>(ThreadEngine<void> \*_threadEngine)
    

    and remove the template specialisation from the constructor name so that it looks like

    ThreadEngineStarter(ThreadEngine<void> \*_threadEngine)
    

    This will fix your build (and any other build involving QtConcurrent from this installation of Qt - the fix is not specific to Quotient in any way).

Logging configuration

libQuotient uses Qt's logging categories to make switching certain types of logging easier. In case of troubles at runtime (bugs, crashes) you can increase logging if you add the following to the QT_LOGGING_RULES environment variable:

quotient.<category>.<level>=<flag>

where

• <category> is one of: main, jobs, jobs.sync, jobs.thumbnail, events, events.state (covering both the "usual" room state and account data), events.messages, events.ephemeral, e2ee and profiler (you can always find the full list in lib/logging.cpp);
• <level> is one of debug, info, and warning;
• <flag> is either true or false.

* can be used as a wildcard for any part between two dots, and semicolon is used for a separator. Latter statements override former ones, so if you want to switch on all debug logs except jobs you can set

QT_LOGGING_RULES="quotient.*.debug=true;quotient.jobs.debug=false"

Note that quotient is a prefix that only works since version 0.6 of the library; 0.5.x and older used libqmatrixclient instead. If you happen to deal with both libQMatrixClient-era and Quotient-era versions, it's reasonable to use both prefixes, to make sure you're covered with no regard to the library version. For example, the above setting could look like

QT_LOGGING_RULES="libqmatrixclient.*.debug=true;libqmatrixclient.jobs.debug=false;quotient.*.debug=true;quotient.jobs.debug=false"

Cache format

In case of troubles with room state and caching it may be useful to switch cache format from binary to JSON. To do that, set the following value in your client's configuration file/registry key (you might need to create the libQuotient key for that): libQuotient/cache_type to json. This will make cache saving and loading work slightly slower but the cache will be in text JSON files (possibly very long and unindented so prepare a good JSON viewer or text editor with JSON formatting capabilities).