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Mango Wayland Compositor implements the dwl-ipc-unstable-v2 protocol for inter-process communication. This allows external clients to query compositor state and control window management operations.

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Protocol Architecture

The IPC protocol is built on Wayland’s native protocol system and consists of two main interfaces:

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zdwl_ipc_manager_v2

The manager interface is exposed as a global in wl_registry. It provides:
  • Tag Information: Announces the number of tags configured in the compositor
  • Layout Enumeration: Lists all available layouts
  • Output Access: Creates zdwl_ipc_output_v2 objects for specific outputs
After binding to the manager, clients receive tags and layout events that expose the compositor’s configuration.

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zdwl_ipc_output_v2

The output interface allows observing and controlling individual outputs (monitors). It provides: Events (compositor → client):
  • Tag state updates (active, urgent, client count)
  • Layout changes
  • Client information (title, appid)
  • Fullscreen and floating status
  • Client geometry (x, y, width, height)
  • Keyboard layout and keybind mode
  • Scale factor
Requests (client → compositor):
  • Set active tags
  • Modify client tags
  • Change layout
  • Dispatch internal commands
  • Quit compositor

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Event Double-Buffering

Events from zdwl_ipc_output_v2 are double-buffered. Clients should:
  1. Cache incoming events
  2. Wait for the frame event
  3. Redraw/update when frame is received
This ensures atomic updates and prevents visual tearing in status bars.

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mmsg Client Tool

Mango includes mmsg, a command-line IPC client that implements the dwl-ipc-unstable-v2 protocol. It provides three operation modes:

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Operation Modes

# Query compositor state
mmsg -g [options]

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Common Use Cases

# Get selected tags with occupancy and urgency info
mmsg -g -t

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Building IPC Clients

To build custom IPC clients:
  1. Generate Protocol Bindings 
    wayland-scanner client-header \
  protocols/dwl-ipc-unstable-v2.xml \
  dwl-ipc-unstable-v2-protocol.h

wayland-scanner private-code \
  protocols/dwl-ipc-unstable-v2.xml \
  dwl-ipc-unstable-v2-protocol.c
  2. Connect to Wayland Display 
    struct wl_display *display = wl_display_connect(NULL);
struct wl_registry *registry = wl_display_get_registry(display);
  3. Bind IPC Manager 
    // In registry global_add callback
if (strcmp(interface, zdwl_ipc_manager_v2_interface.name) == 0) {
    dwl_ipc_manager = wl_registry_bind(registry, name,
        &zdwl_ipc_manager_v2_interface, 2);
    zdwl_ipc_manager_v2_add_listener(dwl_ipc_manager,
        &dwl_ipc_listener, NULL);
}
  4. Get Output Interface 
    // For wl_output objects
struct zdwl_ipc_output_v2 *dwl_ipc_output =
    zdwl_ipc_manager_v2_get_output(dwl_ipc_manager, output);
zdwl_ipc_output_v2_add_listener(dwl_ipc_output,
    &dwl_ipc_output_listener, data);
  5. Dispatch Events 
    // Single update
wl_display_roundtrip(display);

// Continuous watching
while (wl_display_dispatch(display) != -1);

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Protocol Stability

The dwl-ipc-unstable-v2 protocol is experimental and may change. Backward incompatible changes are indicated by version bumps in protocol and interface names.
The protocol will be stabilized by:
  • Removing the ‘z’ prefix
  • Removing version numbers from names
  • Resetting interface version to 1

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See Also

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