wlmessage(3) Wayland wlmessage(3)

NAME
       wlmessage -

SYNOPSIS
       #include 

   Data Fields
       const char * name
       const char * signature
       struct wlinterface ** types

Detailed Description
       Protocol message signature

       A wlmessage describes the signature of an actual protocol message,
       such as a request or event, that adheres to the Wayland protocol wire
       format. The protocol implementation uses a wlmessage within its
       demarshal machinery for decoding messages between a compositor and its
       clients. In a sense, a wlmessage is to a protocol message like a class
       is to an object.

       The name of a wlmessage is the name of the corresponding protocol
       message.

       The signature is an ordered list of symbols representing the data types
       of message arguments and, optionally, a protocol version and indicators
       for nullability. A leading integer in the signature indicates the since
       version of the protocol message. A ? preceding a data type symbol
       indicates that the following argument type is nullable. While it is a
       protocol violation to send messages with non-nullable arguments set to
       NULL, event handlers in clients might still get called with non-
       nullable object arguments set to NULL. This can happen when the client
       destroyed the object being used as argument on its side and an event
       referencing that object was sent before the server knew about its
       destruction. As this race cannot be prevented, clients should - as a
       general rule - program their event handlers such that they can handle
       object arguments declared non-nullable being NULL gracefully.

       When no arguments accompany a message, signature is an empty string.

       Symbols:

       · i: int

       · u: uint

       · f: fixed

       · s: string

       · o: object

       · n: newid

       · a: array

       · h: fd

       · ?: following argument is nullable

       While demarshaling primitive arguments is straightforward, when
       demarshaling messages containing object or newid arguments, the
       protocol implementation often must determine the type of the object.
       The types of a wlmessage is an array of wlinterface references that
       correspond to o and n arguments in signature, with NULL placeholders
       for arguments with non-object types.

       Consider the protocol event wldisplay deleteid that has a single uint
       argument. The wlmessage is:

       * { "deleteid", "u", [NULL] }
       *

       Here, the message name is 'deleteid', the signature is 'u', and the
       argument types is [NULL], indicating that the uint argument has no
       corresponding wlinterface since it is a primitive argument.

       In contrast, consider a wlfoo interface supporting protocol request
       bar that has existed since version 2, and has two arguments: a uint and
       an object of type wlbazinterface that may be NULL. Such a wlmessage
       might be:

       * { "bar", "2u?o", [NULL, &wlbazinterface] }
       *

       Here, the message name is 'bar', and the signature is '2u?o'. Notice
       how the 2 indicates the protocol version, the u indicates the first
       argument type is uint, and the ?o indicates that the second argument is
       an object that may be NULL. Lastly, the argument types array indicates
       that no wlinterface corresponds to the first argument, while the type
       wlbazinterface corresponds to the second argument.

       See Also:
           wlargument

           wlinterface

           Wire Format

Field Documentation
   const char* wlmessage::name
       Message name

   const char* wlmessage::signature
       Message signature

   struct wlinterface** wlmessage::types
       Object argument interfaces


Author
       Generated automatically by Doxygen for Wayland from the source code.



Version 1.15.0                  Tue Oct 30 2018                  wlmessage(3)