This documentation refers to individual protocol features, it links to the implementation and technical documentation for each subsystem.
Each subsystem should be using its own prefix for capabilities and packet types. (most already do)
Most modules are optional, see security considerations.
A client or server may choose to completely disable a
subsystem.
When this is the case, it will not load the module into memory and will
not know how to handle requests for this feature.
Most subsystems are independent of each other. The diagram below
shows the dependencies enforced at subsystem load time (see xpra/server/features.py).
Solid arrows mark a hard requirement — the dependent subsystem
cannot be enabled unless its parent is also enabled. Dashed arrows mark
soft or alternative dependencies — the subsystem can use the
parent if it is available, or has an alternative code path on some
platforms.
graph LR
classDef core fill:#fde,stroke:#a04,stroke-width:2px,color:#000;
classDef group fill:#eef,stroke:#446,color:#000;
Core["Server core<br/>(sockets, auth, dispatch)"]:::core
subgraph Backend["Display backend (mutually exclusive)"]
X11[x11]
Wayland[wayland]
end
subgraph Surface["Display surface"]
Window[window]
Keyboard[keyboard]
Pointer[pointer]
Display[display]
Cursor[cursor]
OpenGL[opengl]
Bell[bell]
end
Window --> Display
Keyboard --> Display
Pointer --> Display
Display --> Cursor
Display --> OpenGL
Display --> Bell
subgraph Media["Media pipeline"]
GStreamer[gstreamer]
Audio[audio]
Pulseaudio[pulseaudio]
AVSync[av_sync]
Webcam[webcam]
Encoding[encoding]
end
GStreamer --> Audio
Audio --> Pulseaudio
Audio --> AVSync
GStreamer -.-> Webcam
GStreamer -.-> Encoding
subgraph X11Ext["X11-only extensions"]
ICC[icc]
BellSrv[bell server]
SysTray[systray]
end
X11 --> ICC
Display --> ICC
X11 --> BellSrv
Bell --> BellSrv
X11 --> SysTray
subgraph UI["UI / lifecycle"]
GTK[gtk]
Tray[tray]
Watcher[watcher]
Power[power]
Suspend[suspend]
Idle[idle]
Debug[debug]
Splash[splash]
end
GTK --> Tray
SysTray -.-> Tray
subgraph Net["Network / transport"]
SSL[ssl]
SSH[ssh]
HTTP[http]
MDNS[mdns]
RFB[rfb]
Control[control]
SSHAgent[ssh_agent]
end
SSL -.-> HTTP
SSH --> SSHAgent
subgraph Session["Session features"]
Clipboard[clipboard]
FileT[file]
Printer[printer]
Notification[notification]
Command[command]
Logging[logging]
Ping[ping]
Bandwidth[bandwidth]
Shell[shell]
MMap[mmap]
DBus[dbus]
Encryption[encryption]
Sharing[sharing]
ClientSession[client_session]
end
Printer --> FileT
DBus --> Notification
DBus -.-> Tray
Core --> Backend
Core --> Surface
Core --> Media
Core --> UI
Core --> Net
Core --> Session
class Backend,Surface,Media,X11Ext,UI,Net,Session group;Notes:
display is auto-enabled when any of
window, keyboard or pointer is
enabled — it is the union of those features rather than a
prerequisite.notification requires dbus on Linux, but
has native code paths on Windows and macOS (shown as dashed via
DBus).tray requires gtk and (for the system tray
icon on X11) the systray extension.ICC, bell server and
systray subsystems are loaded only on X11 sessions, and
require both x11 and the corresponding feature flag.pulseaudio and av_sync are strict
refinements of audio, which itself requires
gstreamer.These subsystems involve communication between client and server.
| Subsystem | Client Module | Server Module | Client Connection Module | User Documentation | |---------------------------------|----------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------|-------------------------------------------------------| | Audio | audio | audio | audio | audio feature | | Bandwidth | bandwidth | bandwidth | bandwidth | n/a | | Clipboard | clipboard | clipboard | clipboard | clipboard feature | | Command | command | command | none | n/a | | Cursor | cursor | cursor | cursor | n/a | | Display | display | display | display | Automatically configured | | Encoding | encoding | encoding | encoding | Automatically configured | | Encryption | n/a | encryption | n/a | encryption | | File | n/a | file | file | file transfers | | Info | server_info | info | n/a | | | Keyboard | keyboard | keyboard | keyboard | keyboard feature | | Logging | logging | logging | none | logging usage | | Menu | n/a | menu | menu | n/a | | MMAP | mmap | mmap | mmap | enabled automatically | | Notification | notification | notification | notification | notifications feature | | Ping | ping | ping | ping | n/a | | Pointer | pointer | pointer | pointer | | | Power | power | power | n/a | | | Printer | n/a | printer | printer | printing feature | | Sharing | n/a | sharing | sharing | n/a | | Shell | n/a | shell | shell | n/a | | Socket | socket | n/a | n/a | | | SSH Agent | ssh_agent | ssh_agent | none | n/a | | Tray | tray | tray | none | n/a | | Webcam | webcam | webcam | webcam | webcam usage | | Window | window | window | window | |
These subsystems handle server-side infrastructure and have no corresponding client module or client connection module.
| Subsystem | Server Module | User Documentation | |----------------|----------------------------------------------------------------------------------------------------|--------------------------------------------------| | Auth | auth | authentication | | ClientSession | client_session | n/a | | Control | control | n/a | | Daemon | daemon | n/a | | DBUS | dbus | n/a | | Debug | debug | n/a | | DRM | drm | n/a | | GTK | gtk | n/a | | HTTP | http | n/a | | ID | id | n/a | | Idle | idle | n/a | | MDNS | mdns | multicast DNS | | OpenGL | opengl | OpenGL usage | | Platform | platform | n/a | | Process | process | n/a | | PulseAudio | pulseaudio | audio feature | | RFB | rfb | n/a | | SessionFiles | sessionfiles | n/a | | Shutdown | shutdown | n/a | | Splash | splash | n/a | | Suspend | suspend | n/a | | Version | version | n/a | | Watcher | watcher | n/a | | Xvfb | xvfb | n/a |