The following steps will guide you to build MEGAchat library (including tests and QtApp). In summary, you need to:

• Build WebRTC
• Clone MEGAchat
• Clone MEGA SDK in <MEGAchat>/third-party/
• Build MEGAchat library, QtApp example, automated tests...

You may need to install the following packages in your system

• cmake and ccmake
• autoconf
• automake
• libtool
• python
• g++
• qt (for QtApp example)
• gtest (for automated tests)
• libglib2.0-dev libgtk-3-dev libpulse-dev libasound2-dev libuv1-dev libcap-dev libfreeimage-dev ffmpeg (Ubuntu 20.04.2)

*NOTE: gtests are only needed if you want to compile and execute MEGAchat automatic tests. Versions under 1.7.0 could cause incompatibilities.

*Windows: the cygwin version of cmake will not be sufficient, you need to install the native cmake for Windows from the official site, and instead of ccmake use cmake-gui. You will also need to add the path to Cmake to Cygwin.

1. $ chmod +x ./requirements.sh
2. $ ./requirements.sh

Create a directory to download Webrtc (webrtc_dir) and add it to $PATH

• cd webrtc_dir
• fetch --nohooks webrtc
• gclient sync
• cd ./src
• git checkout 93081d594f7efff72958a79251f53731b99e902b
• gclient sync

In case the fetch command above failed, you may need to get the Chromium build system to get WebRTC itself. Create a directory to get it (<chromium_build_dir>).

• cd <chromium_build_dir>
• git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
• export PATH="$PATH:/<chromium_build_dir>"

For more information about WebRTC compilation for Android, you can visit this link WebRTC for Android.

Checkout the MEGAchat repository:

• git clone --recursive https://github.com/meganz/MEGAchat.git

The MEGAchat sources are at MEGAchat/src

*NOTE the --recursive switch - the repository contains git submodules that need to be checked out as well.

Clone the SDK repository inside <MEGAchat>/third-party/mega:

• cd <MEGAchat>/third-party/
• git clone https://github.com/meganz/sdk.git mega
• cd mega
• ./autogen.sh
• ./configure

You can configure the SDK with following optional parameters:

• --enable-debug
• --enable-chat
• --enable-tests --with-gtest=<path_to_gtest>

In order to build MEGAchat, simply execute the script build_with_webrtc.sh, which downloads, configure and build some additional dependencies.

• cd <MEGAchat>/third-party/mega/bindings/qt/ (This step is neccesary to set the right current path for the script)

• ./build_with_webrtc.sh <all | clean> [withExamples]

Now that you're ready, you can open <MEGAchat>/contrib/qt/MEGAchat.pro in QtCreator and hit Build button, edit sources and play around.

You may need to change the "Build directory" in the project setting to <MEGAchat>/build if building complains about files not found.

*NOTE: When building with ./configure --enable-debug --enable-chat --enable-tests --with-gtest=<path_to_gtest> ./build_with_webrtc.sh all withExamples linking failed due to missing symbols, which was resolved by additional linker options -lavformat -lavcodec -lavutil -lswscale in sdk.pri (in need of a proper fix).

MacOS disclaimer:

Note: You may need to (re)configure the SDK to use openssl linked by ./build_with_webrtc.sh at 3rdparty/lib/ (webrtc's boringssl) and disabling certain features in MAC:

• ./configure --disable-examples --without-freeimage --with-openssl=<MEGAchat>/third-party/mega/bindings/qt/3rdparty

And also have all the other requirements at /third-party/mega/bindings/qt/3rdparty/libs.

If you specified the [withExamples] option when you executed build_with_webrtc.sh, the example QtApp would be already built. Otherwise, by building the Qt Project aforementioned, the QtApp will be also built.

In any case, it will be found at <MEGAchat>/build/MEGAChatQt/megachat.

*NOTE: In some operating systems the qmake command could have different name (i.e Fedora). To be able to compile with qmake command, we have to ensure that it exists and that it's included in the $PATH

To check where is qmake version, run: ls /usr/bin | grep -i qmake The output for a Fedora system is:

• qmake-qt5
• qmake-qt5.sh

Finally we have to create a soft link to qmake.

• ln -s /usr/bin/qmake-qt5 /usr/bin/qmake

MEGAchat provides a set of automatic tests to ease the continuous integration. In order to build these tests, you need to configure the SDK with the parameters --enable-tests --with-gtest = <path_to_gtest>, as it's explained above.

The executable can be located at <MEGAchat>/build/MEGAchatTests/megachat_tests.

Follow the instructions given by the program to setup your testing accounts and other parameters.

From within the build directory, provided that you generated a make build (<MEGAchat>/build), type:

• make doc

To abstract the code complexity, MEGAchat provides an intermediate layer that enables to quickly create new applications.

The documentation is available at src/megachatapi.h

The MEGAchat threading model is similar to the javascript threading model - everything runs in the main (GUI) thread, blocking is never allowed, and external events (network, timers etc, webrtc events etc) trigger callbacks on the main thread. For this to work, MEGAchat must be able to interact with the application's event loop - this is usually the event/message loop of the GUI framework in case of a GUI application, or a custom message loop in case of a console application. As this message loop is very platform-specific, it is the application developer's responsibility to implement the interface between it and MEGAchat. This may sound more complicated than it is in reality - the interface consists of two parts. One part is the implementation of megaPostMessageToGui(void*) function, which posts an opaque void* pointer to the application's message loop. This function is normally called by threads other than the main thread, but can also be called by the GUI thread itself. The other part is the code in the application's message loop that recognizes this type of messages and passes them back to MEGAchat, by calling megaProcessMessage(void* with that same pointer - this time in the context of the main (GUI) thread. All this is implemented in /src/base/gcm.h and /src/base/gcm.hpp. These files contain detiled documentation. An example of implementing this on Windows is: megaPostMessageToGui(void*) would do a PostMessage() with a user message type, and the void* as the lParam or wParam of the message, and in the event processing switch statement, there will be an entry for that message type, getting the void* pointer by casting the lParam or wParam of the message, and passing it to megaProcessMessage(void*).

MEGAchat relies on libuv, running in its own dedicated thread, to monitor multiple sockets for raw I/O events, and to implement timers. It also relies on the higher-level I/O functionality of libuv such as DNS resolution and SSL sockets. A thin layer on top of libuv, called 'services' (/src/base/?services\*.\*) is implemented on top of libuv and the GCM to have simple, javascript-like async C++11 APIs for timers (src/base/timer.h), DNS resolution (/src/base/services-dns.hpp), http client (/src/base/services-http.hpp). This layer was originally designed to have a lower-level component with plain C interface (cservices*.cpp/h files), so that the services can be used by several DLLs built with different compilers, and a high-level header-only C++11 layer that is the frontend and contains the public API - these are the .hpp files.

All network libraries in MEGAchat (libcurl) use libuv for network operation and timers (C libraries use libuv directly, C++ code uses the C++11 layer, i.e. timers.hpp). It is strongly recommended that the SDK user also does the same, although it is possible for example to have a dedicated worker thread blocking on a socket, and posting events to the GUI thread via the GCM.

The usage pattern is as follows: a callback is registered for a certain event (socket I/O event, timer, etc), and that callback is called by the libuv thread when the event occurs. If the event may propagate outside the library whose callback is called, and especially to the GUI, then, at some point, event processing must be marshalled to the GUI thread, using the GCM mechanism. However, if the event is internal and never propagates outside the library then it can be handled directly in the context of the libuv thread (provided that it never blocks it). This saves the performance cost of marshalling it to the GUI thread, and is recommended if the event occurs at a high frequency, e.g. an incoming data chunk event that only needs the data appended to a buffer. When the transfer is complete, a completion event can be marshalled on the GUI thread once per transfer, combining the advantages of both approaches.

MEGAchat has an advanced logging facility that supports file and console logging with color, log file rotation, multiple log channels, each with individual log level. Log levels are configured at runtime (at startup), and not at compile time (i.e. not by disabling log macros). This allows a release-built app to enable full debug logging for any channels. Log channels are defined and default-configured in src/base/loggerChannelConfig.h. The file contains detailed documentation. For convenience, dedicated logging macros for each channel are usually defined in the code that uses it - see the XXX_LOG_DEBUG/WARN/ERROR macros in karereCommon.h for examples. The SDK user is free to create additional log channels if needed. A GUI log channel is already defined. Log channel configuration can be overriden at runtime by the KRLOG environment variable. Its format is as follows:
KRLOG=<chan name>=<log level>,<chan name2>=<log level2>...
Log levels are 'off', 'error', 'warn', 'info', 'verbose', 'debug', 'debugv'.
There is one special channel name - 'all'. Setting the log level of this channel sets the log levels of all channels. This allows for example to easily silence all channels except one (or few), by:
KRLOG=all=warn,mychannel=debug,myotherchannel=info
The same channel can be configured multiple times, and only the last setting will be effective, which makes the above trick possible.
MEGAchat requires the function karere::getAppDir() to be defined by the application at compile time, in order to know where to create the log file and start logging as early as possible, before main() is entered. If MEGAchat is built as a static lib, this is not a problem. In case of dynamic lib, this function has to be a weak symbol, so that MEGAchat itself can compile without the function implementation, and the implementation to be linked when the MEGAchat shared lib is loaded at app startup. Weak symbols are not really portable across compilers, and this may be a problem. However they are supported by both gcc and clang. If no weak symbols are supported, karer ehas to be built as static lib.

• The Promise lib in base/promise.h and example usage for example in /src/test-promise.cpp
• The setTimeout() and setInterval() timer functions in /src/base/timers.hpp
• The marshallCall() function marshalls lambda calls from a worker thread to the GUI thread. Examples of use can be seen for example in /src/webrtcAdapter.h and in many different places. This mechanism should not be directly needed in high-level code that runs in the GUI thread.
• The overall client structure in /src/chatClient.h;.cpp
• The intermediate layer shows how to implement megaPostMessageToGui(), how to start the 'services', and how to instantiate the MEGAchat client. Also shows how to implement the getAppDir() method, which is a weak symbol needed by the MEGAchat library in order to create the log file and start logging as early as possible, before main() is entered.
• The video module public interface in src/rtcModile/IRtcModule.h and related headers

MEGAchat provides platform-specific video renderer widgets for Qt and iOS (probably will work also for MacOS with no or minimal changes). These widgets are implemented as subclasses of standard widgets. Their code is in src/videoRenderer_xxx.cpp;mm;h. They can be used directly in the platform's GUI designer by placing the corresponding standard widget and then selecting the VideoRenderer_xxx class name from the menu to tell the GUI designer to use that subclass. You must include these files in your project, including the headers, to make the subclass visible to the GUI designer.

• The rtctestapp above is the reference app. Build it, study it, experiment with it.
  Note that there is one critical and platform-dependent function that each app that uses MEGAchat must provide, which will be referenced as megaPostMessageToGui(), but it can have any name, provided that the signature is extern "C" void(void*). This function is the heart of the message passing mechanism (called the Gui Call Marshaller, or GCM) that MEGAchat relies on. You must pass a pointer to this function to services_init().
  For more details, read the comments in base/gcm.h, and for reference implementation study rtctestapp/main.cpp
• IRtcModule, IEventHandler in /src/IRtcModule.h. These are used to initiate rtc calls and receive events.
• IVideoRenderer in /src/IVideoRenderer.h is used to implement video playback in arbitrary GUI environments. Example implementation for Qt is in src/videoRenderer_Qt.h;.cpp. The example usage can be seen from the rtctestapp application.

• To integrate with the environment, a simple bridge class called MyMegaApi is implemented in /src/sdkApi.h. Example usage of it is in /src/chatClient.cpp.

• Android
  Install the android NDK, and create a standalone CLang toolchain, using the make-standalone-toolchain.sh scrpt included in the NDK, using following example commandline:
  ./android-ndk-r11b/build/tools/make-standalone-toolchain.sh --toolchain=arm-linux-androideabi-clang --install-dir=/home/user/android-dev/toolchain --stl=libc++ --platform=android-21
  Then, you need to prepare a cross-compile environment for android. For this purpose, you need to use the /platforms/android/env-android.sh shell script. Please read the Readme.md in the same directory on how to use that script.

Notes on building webrtc with Android
Building of webrtc is supported only on Linux. This is a limitation of Google's webrtc/chromium build system.
Although webrtc comes with its own copy of the NDK, we are going to use the standard one for building the MEGAchat code, and let webrtc build with its own NDK. Both compilers are binary compatible. Forcing webrtc to build with an external NDK will not work. For some operations, like assembly code transformations, a host compiler is used, which is the clang version that comes with webrtc. To use an external NDK, we would need to specify explicitly specify the --sysroot path of the external NDK, which also gets passed to the clang host compiler, causing errors.

• iOS
  Building of webrtc and MEGAchat is supported only on MacOS. XCode is required. Then, you need to prepare a cross-compile environment for android. For this purpose, you need to use the /platforms/ios/env-ios.sh shell script. Please read the Readme.md in the same directory no how to use that script.

• Windows Microsoft Visual Studio 2015 or later (only C++ compiler), and the Cygwin environment are required. You need to setup the start shortcut/batfile of the Cygwin shell to run the vcvars32.bat with the cmd.exe shell inside the cygwin shell, in order to add the compiler and system library paths to the Cygwin shell. Building of MEGAchat, webrtc and dependencies will be done under the Cygwin shell.

Since the Chromium build system (at least the curent revision) relies heavily on python, and it assumes the python version is 2.7, the python command must map to python2 instead of python3. This may not be true on more recent systems. To check, just type python --version. If it says version 2.x, then you are ok and can skip the rest of this section. To easily make python2 default in the current shell, you can create a symlink named python that points to /usr/bin/python2. Put that symlink in a private directory that doesn't contain other executables with names clashing with ones in the system path, and include this directory to be first in the system PATH in the shell where you build webrtc, before invoking build-webrtc.sh:
export PATH=/path/to/dir-with-python-symlink:$PATH