Commit 1b6521e6 authored by Matthew Hoosier's avatar Matthew Hoosier Committed by Pekka Paalanen

client: Allow absolute paths in WAYLAND_DISPLAY

In order to support system compositor instances, it is necessary to
allow clients' wl_display_connect() to find the compositor's listening
socket somewhere outside of XDG_RUNTIME_DIR. For a full account, see
the discussion beginning here:

This change adjusts the client-side connection logic so that, if
WAYLAND_DISPLAY is formatted as an absolute pathname, the socket
connection attempt is made to just $WAYLAND_DISPLAY rather than
usual user-private location $XDG_RUNTIME_DIR/$WAYLAND_DISPLAY.

This change is based on Davide Bettio's submission of the same concept

v4 changes:

* Improved internal comments and some boundary-condition
  error checks in test case.
* Refer to compositor as "Wayland server" rather than "Wayland
  display" in wl_display_connect() doxygen comments.
* Remove redundant descriptions of parameter-interpretation
  mechanics from wl_display_connect() manpage. Reworked things
  to make it clear that 'name' and $WAYLAND_DISLAY are each
  capable of encoding absolute server socket paths.
* Remove callout to reference implementation behavior in protocol
  documented. In its place there is now a simple statement that
  implementations can optionally support absolute socket paths.

v3 changes:

* Added test case.
* Clarified documentation to note that 'name' parameter to wl_display_connect()
  can also be an absolute path.

v2 changes:

* Added backward incompatibility note to wl_display_connect() manpage.
* Rephased wl_display_connect() manpage changes to precisely match actual
  changed behavior.
* Added mention of new absolute path behavior in wl_display_connect()
  doxygen comments.
* Mentioned new absolute path interpretation of WAYLAND_DISPLAY in
  protocol documentation.
Signed-off-by: Matt Hoosier's avatarMatt Hoosier <>
Acked-by: Jonas Ådahl's avatarJonas Ådahl <>
Reviewed-by: Pekka Paalanen's avatarPekka Paalanen <>
parent de24f4dd
......@@ -55,15 +55,39 @@
<para><function>wl_display_connect</function> connects to a Wayland socket
that was previously opened by a Wayland server. The server socket must
be placed in <envar>XDG_RUNTIME_DIR</envar> for this function to
find it. The <varname>name</varname> argument specifies the name of
be placed in <envar>XDG_RUNTIME_DIR</envar> when <envar>WAYLAND_DISPLAY</envar>
(or <varname>name</varname>, see below) is a simple name, for this
function to find it. The server socket is also allowed to exist at an
arbitrary path; usage details follow. See below for compatibility issue
<para>The <varname>name</varname> argument specifies the name of
the socket or <constant>NULL</constant> to use the default (which is
<constant>"wayland-0"</constant>). The environment variable
<envar>WAYLAND_DISPLAY</envar> replaces the default value. If
<envar>WAYLAND_SOCKET</envar> is set, this function behaves like
<envar>WAYLAND_DISPLAY</envar> replaces the default value.
If <varname>name</varname> is an absolute path, then that path is used
as the Wayland socket to which the connection is attempted. Note that
in combination with the default-value behavior described above, this
implies that setting <envar>WAYLAND_DISPLAY</envar> to an absolute
path will implicitly cause <varname>name</varname> to take on that
absolute path if <varname>name</varname> is <constant>NULL</constant>.
If <envar>WAYLAND_SOCKET</envar> is set, this function behaves like
<function>wl_display_connect_to_fd</function> with the file-descriptor
number taken from the environment variable.</para>
<para>Support for interpreting <envar>WAYLAND_DISPLAY</envar> as an
absolute path is a change in behavior compared to
<function>wl_display_connect</function>'s behavior in versions
1.14 and older of Wayland. It is no longer guaranteed in versions
1.15 and higher that the Wayland socket chosen is equivalent to
manually constructing a socket pathname by concatenating
<envar>XDG_RUNTIME_DIR</envar> and <envar>WAYLAND_DISPLAY</envar>.
Manual construction of the socket path must account for the
possibility that <envar>WAYLAND_DISPLAY</envar> contains an absolute
<para><function>wl_display_connect_to_fd</function> connects to a Wayland
socket with an explicit file-descriptor. The file-descriptor is passed
as argument <varname>fd</varname>.</para>
......@@ -94,7 +94,10 @@
The protocol is sent over a UNIX domain stream socket, where the endpoint
usually is named <systemitem class="service">wayland-0</systemitem>
(although it can be changed via <emphasis>WAYLAND_DISPLAY</emphasis>
in the environment).
in the environment). Beginning in Wayland 1.15, implementations can
optionally support server socket endpoints located at arbitrary
locations in the filesystem by setting <emphasis>WAYLAND_DISPLAY</emphasis>
to the absolute path at which the server endpoint listens.
Every message is structured as 32-bit words; values are represented in the
......@@ -857,9 +857,17 @@ connect_to_socket(const char *name)
socklen_t size;
const char *runtime_dir;
int name_size, fd;
bool path_is_absolute;
if (name == NULL)
name = getenv("WAYLAND_DISPLAY");
if (name == NULL)
name = "wayland-0";
path_is_absolute = name[0] == '/';
runtime_dir = getenv("XDG_RUNTIME_DIR");
if (!runtime_dir) {
if (!runtime_dir && !path_is_absolute) {
wl_log("error: XDG_RUNTIME_DIR not set in the environment.\n");
/* to prevent programs reporting
* "failed to create display: Success" */
......@@ -867,25 +875,32 @@ connect_to_socket(const char *name)
return -1;
if (name == NULL)
name = getenv("WAYLAND_DISPLAY");
if (name == NULL)
name = "wayland-0";
fd = wl_os_socket_cloexec(PF_LOCAL, SOCK_STREAM, 0);
if (fd < 0)
return -1;
memset(&addr, 0, sizeof addr);
addr.sun_family = AF_LOCAL;
name_size =
snprintf(addr.sun_path, sizeof addr.sun_path,
"%s/%s", runtime_dir, name) + 1;
if (!path_is_absolute) {
name_size =
snprintf(addr.sun_path, sizeof addr.sun_path,
"%s/%s", runtime_dir, name) + 1;
} else {
/* absolute path */
name_size =
snprintf(addr.sun_path, sizeof addr.sun_path,
"%s", name) + 1;
assert(name_size > 0);
if (name_size > (int)sizeof addr.sun_path) {
wl_log("error: socket path \"%s/%s\" plus null terminator"
" exceeds 108 bytes\n", runtime_dir, name);
if (!path_is_absolute) {
wl_log("error: socket path \"%s/%s\" plus null terminator"
" exceeds %i bytes\n", runtime_dir, name, (int) sizeof(addr.sun_path));
} else {
wl_log("error: socket path \"%s\" plus null terminator"
" exceeds %i bytes\n", name, (int) sizeof(addr.sun_path));
/* to prevent programs reporting
* "failed to add socket: Success" */
......@@ -994,6 +1009,16 @@ wl_display_connect_to_fd(int fd)
* its value will be replaced with the WAYLAND_DISPLAY environment
* variable if it is set, otherwise display "wayland-0" will be used.
* If \c name is an absolute path, then that path is used as-is for
* the location of the socket at which the Wayland server is listening;
* no qualification inside XDG_RUNTIME_DIR is attempted.
* If \c name is \c NULL and the WAYLAND_DISPLAY environment variable
* is set to an absolute pathname, then that pathname is used as-is
* for the socket in the same manner as if \c name held an absolute
* path. Support for absolute paths in \c name and WAYLAND_DISPLAY
* is present since Wayland version 1.15.
* \memberof wl_display
WL_EXPORT struct wl_display *
......@@ -26,10 +26,14 @@
#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/un.h>
#include <unistd.h>
#include "wayland-client.h"
#include "wayland-os.h"
#include "wayland-server.h"
#include "test-runner.h"
......@@ -173,3 +177,108 @@ TEST(add_socket_auto)
struct client_create_listener {
struct wl_listener listener;
struct wl_display *display;
struct client_destroy_listener {
struct wl_listener listener;
struct wl_display *display;
static void
client_destroy_notify(struct wl_listener *l, void *data)
struct client_destroy_listener *listener =
wl_container_of(l, listener, listener);
static void
client_create_notify(struct wl_listener *l, void *data)
struct wl_client *client = data;
struct client_create_listener *listener =
wl_container_of(l, listener, listener);
struct client_destroy_listener *destroy_listener = (struct client_destroy_listener *)malloc(sizeof *destroy_listener);
assert(destroy_listener != NULL);
destroy_listener->display = listener->display;
destroy_listener->listener.notify = client_destroy_notify;
wl_client_add_destroy_listener(client, &destroy_listener->listener);
struct wl_display *display;
struct client_create_listener client_create_listener;
struct sockaddr_un addr;
int fd;
socklen_t size;
const char *xdg_runtime_dir;
size_t len;
int ret;
pid_t pid;
/* It's a little weird that this test about absolute socket paths
* uses XDG_RUNTIME_DIR, but that's the only location guaranteed
* by test-runner to be both writable and unique. This isn't
* really a problem; we'll just take care that the leaf-level
* filename used for the socket isn't anything that would
* accidentally be generated by a default usage of wl_display_connect(). */
xdg_runtime_dir = require_xdg_runtime_dir();
memset(&addr, 0, sizeof addr);
len = snprintf(addr.sun_path, sizeof addr.sun_path,
"%s/%s", xdg_runtime_dir, "wayland-absolute-0");
assert(len < sizeof addr.sun_path
&& "Bug in test. Path too long");
/* The path must not exist prior to binding. */
assert(access(addr.sun_path, F_OK) == -1);
size = offsetof (struct sockaddr_un, sun_path) + strlen(addr.sun_path);
addr.sun_family = AF_LOCAL;
fd = wl_os_socket_cloexec(PF_LOCAL, SOCK_STREAM, 0);
assert(fd >= 0 );
ret = bind(fd, (struct sockaddr *) &addr, size);
assert(ret >= 0);
ret = listen(fd, 128);
assert(ret >= 0);
/* Start server display. Be careful (by avoiding wl_display_add_socket_auto()
* to offer only the absolutely qualified socket made above. */
display = wl_display_create();
assert(display != NULL);
client_create_listener.listener.notify = client_create_notify;
client_create_listener.display = display;
wl_display_add_client_created_listener(display, &client_create_listener.listener);
ret = wl_display_add_socket_fd(display, fd);
assert(ret == 0);
/* Execute client that connects to the absolutely qualified server socket path. */
pid = fork();
assert(pid != -1);
if (pid == 0) {
ret = setenv("WAYLAND_DISPLAY", addr.sun_path, 1);
assert(ret == 0);
struct wl_display *client_display = wl_display_connect(NULL);
assert(client_display != NULL);
ret = wl_display_roundtrip(client_display);
assert(ret != -1);
ret = waitpid(pid, NULL, 0);
assert(ret == pid);
ret = unlink(addr.sun_path);
assert(ret == 0);
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