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Version 4 (modified by ahuillet, 7 years ago) (diff)

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Project Ideas

Xpra is a remote desktop tool providing many exciting features as compared to other open source tools. It is developed with a mix of Python and C, and works on many platforms. The list below describes Google Summer of Code project ideas, aimed both at improving Xpra and at teaching the students about how a remote desktop solution works.

1) Xorg-related improvements

Xpra acts as an X11 compositor, and uses many different X APIs and features to achieve its purpose. We have run into some limitations related to X11 features.
For example, Xpra has to be able to dynamically adapt the remote (server-side) virtual framebuffer to match the client configuration. This is not feasible on-the-fly even with xf86-video-dummy, so an improvement in this area is needed - ability to change the resolution, and DPI, on the fly. There also are some tearing issues when using Xpra, because of seemingly incorrect use of VSync. Someone interested in the world of X.org may be interested in this project. All changes will have to be incorporated in upstream X.org.

Difficulty: hard
Keywords: C, X11, X.org

2) Automated problem reports

The Xpra client, like any piece of software, has bugs. It sometimes crashes. It's not a big deal: you just have to restart the client, and you'll get your applications back (unless the server crashed also, but it happens less often). However, whenever it crashes, and especially on Win32 platforms, there is very little information that can be sent to the developers to help them fix the bug, and reproducing the crash is not always straightforward.
This project is about making Xpra easier to debug. Ideas are :

  • Integrate an automated stack trace mechanism
  • Generate automatic crash reports, including screenshots if necessary, to enable easy bug reporting for users
  • Allow building of the client with debug symbols

Difficulty: medium
Keywords: Python, backtrace, automated bug reporting

3) Android client support

The objective is for Xpra to support as many platforms as possible for the client. An Android client exists but is not completely up-to-date in terms of feature, and its usability is far from perfect. This project consists in improving Android client support, or, alternatively, implement Xpra client support for another mobile platform (be it Linux - Raspberry Pi, Android, or any other OS).
The tasks for Android consist in the following:

  • Support keyboard
  • Support pinch to zoom
  • Support video scaling
  • Add any required feature for comfortable, seamless remote desktop

The applicant is encouraged to propose implementing support for any other low-power/mobile platform, with an extensive list of tasks to be carried out and prior technical research.

Difficulty: Hard
Keywords: Android

4) Wayland

With the advent of Wayland, a modern replacement to X11, the basis of Xpra (the X Composite extension) disappears. Xpra is conceptually a X compositor, and it could be modified to also become a Wayland compositor. This project is about making Xpra Wayland-compatible so that Wayland gets a network "transparency" layer that is efficient.
Tasks are :

  • Understand Wayland
  • Make Xpra behave (optionally and in addition to X11) as a Wayland compositor
  • Promote the work towards the Wayland community, and submit it for review

Difficulty: medium/easy
Keywords: Wayland, compositor, X.org, X11, network transparency

5) Latency improvements through hardware-accelerated video decoding

Remote desktop software is very sensitive to latency. Too high of a latency can kill the user experience. Latency sources are obviously the network, but also and usually more importantly, the video encoding on the server side, the video decoding on the client side, and the video presentation on the client side.
We have preliminary support for OpenGL presentation on the client side (doing YUV to RGB conversion and drawing), which helps with latency. However, there is the technical possibility of offloading the video decoding process to the GPU using such APIs as VAAPI (Linux) or DxVA (Windows), possibly both through libva which we already use. This project is about improving latency of Xpra, with the following tasks :

  • Offload video decoding to the GPU through libva
  • Make this work on Windows clients as well as Linux clients
  • Make this work with OpenGL presentation on the client-side
  • Do whatever else is necessary to improve latency

Difficulty: medium
Keywords: OpenGL, libav, video decoding, Windows, Linux, Python, C

6) Keyboard mapping improvements

The applications running on the server need to receive mouse and keyboard input. It is easy to map the client-side mouse-input to mouse events on the server side, but it's more difficult for the keyboard, because the keyboard mapping on the client side can be different from one client to another (US, french, german, ...). What transits over the wires are keycodes (the physical position of the key on the keyboard), and they are translated back to keysyms (the keymap-dependant symbol produced when the key is pressed) on the server side. Xpra uses obsolete X APIs to do this translation work, and often gets it wrong. In addition, running virtual machines with e.g. VirtualBox? inside Xpra adds another layer of keyboard translation, and the end result is often wrong.
The tasks for this project are:

  • Learn and understand the X11 keyboard input system (specifically Xkb)
  • Re-implement keyboard mapping logic using Xkb instead of core keyboard API

Difficulty: hard
Keywords: Xkb, X11, input, C

7) Encryption

At the moment, Xpra can use AES encrypted communication over TCP. It supports password authentication, but the key exchange system is open to MITM attacks.
Xpra supports a mode where it connects through an SSH connection. That mode is good, but doesn't answer all needs: it requires an ssh server and each user connecting to the session to have shell access on the system, no matter what application needs to be run.
The objective of this project is to implement a secure transport mechanism, based on known good cryptographic algorithms.
Tasks are:

  • Implement secure key exchange
  • Implement correct AES CBC mode
  • Assess performance impact in terms of latency, bandwidth, and CPU requirements

Difficulty: Medium, knowledge of good crypto practices
Keywords: (py)crypto, AES

8) Win32 server (shadow mode)

Xpra's client works on many platforms, but the server is restricted to Linux. This means that Xpra can only be used to remotely access a Linux-based desktop. It would be very interesting to make Xpra's server able to work on a Windows machine. Currently there is preliminary support for this feature but it uses polling which is very inefficient.
This project is about improving support for Windows-based server, so that it achieves satisfying performance. Tasks would include:

  • Implement screen update detection code so xpra can forward only the parts of the screen that have actually changed (as it does on *nix)
  • Implement win32 socket code so "xpra info" can be used on win32 servers
  • Rely on benchmarks to assess which improvements to make and

Applicants are required to have some Windows development experience.

Difficulty: Medium
Keywords: Windows named pipes, GDI