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Name

ipc - Unix socket Inter Process Communication protocols

Synopsis

IPC endpoints are provided as Unix sockets in /tmp/portal. All services have their own formats, automatically implemented through LibIPC.

Description

The specifics of each service's format depend on the corresponding source .ipc file.

The format can be identified by the format magic, which is derived in Meta/Lagom/Tools/CodeGenerators/IPCCompiler/main.cpp from the service-endpoint name, e.g. "ClipboardClient" (which hashes to 4008793515) or "ClipboardServer" (which hashes to 1329211611).

In general, communication works by packets, which might have been sent in response to other packets. Everything is host endianness. Each packet consists of:

  • a 32-bit message size (see Connection::try_parse_messages in Userland/Libraries/LibIPC/Connection.h)
  • the 32-bit endpoint magic (note that responses use the endpoint of the requesting packet, so the Clipboard server might use the endpoint magic 4008793515 to signal that this packet is a response)
  • the 32-bit message ID within that endpoint (sequentially assigned, starting at 1)
  • the data of that message itself (e.g. see Messages::ClipboardServer::SetClipboardData::{en,de}code in Build/*/Userland/Services/Clipboard/ClipboardServerEndpoint.h).

See Also

  • ipc(5) (IPC file format documentation)