[PATCH wayland] client: Allow absolute paths in WAYLAND_DISPLAY

[Matt Hoosier]

From: Matt Hoosier <matt.hoosier at garmin.com>

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:

https://lists.freedesktop.org/archives/wayland-devel/2017-November/035664.html

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
at:

https://lists.freedesktop.org/archives/wayland-devel/2015-August/023838.html.
---
 doc/man/wl_display_connect.xml | 11 ++++++++---
 src/wayland-client.c           | 34 +++++++++++++++++++++++-----------
 2 files changed, 31 insertions(+), 14 deletions(-)

diff --git a/doc/man/wl_display_connect.xml b/doc/man/wl_display_connect.xml
index 7e6e05c..e86ee26 100644
--- a/doc/man/wl_display_connect.xml
+++ b/doc/man/wl_display_connect.xml
@@ -55,14 +55,19 @@
     <title>Description</title>
     <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> or exist at the absolute
+          path referred to by <envar>WAYLAND_DISPLAY</envar> for this function
+          to find it. 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
           <function>wl_display_connect_to_fd</function> with the file-descriptor
-          number taken from the environment variable.</para>
+          number taken from the environment variable. If
+          <envar>WAYLAND_SOCKET</envar> is not set and <envar>WAYLAND_DISPLAY</envar>
+          is an absolute path then <varname>name</varname> is ignored and the
+          path stored in <envar>WAYLAND_DISPLAY</envar> is used as the Wayland
+          socket to which the connection is attempted.</para>
 
     <para><function>wl_display_connect_to_fd</function> connects to a Wayland
           socket with an explicit file-descriptor. The file-descriptor is passed
diff --git a/src/wayland-client.c b/src/wayland-client.c
index 3d7361e..2263d06 100644
--- a/src/wayland-client.c
+++ b/src/wayland-client.c
@@ -858,8 +858,13 @@ connect_to_socket(const char *name)
 	const char *runtime_dir;
 	int name_size, fd;
 
+	if (name == NULL)
+		name = getenv("WAYLAND_DISPLAY");
+	if (name == NULL)
+		name = "wayland-0";
+
 	runtime_dir = getenv("XDG_RUNTIME_DIR");
-	if (!runtime_dir) {
+	if (!runtime_dir && (name[0] != '/')) {
 		wl_log("error: XDG_RUNTIME_DIR not set in the environment.\n");
 		/* to prevent programs reporting
 		 * "failed to create display: Success" */
@@ -867,25 +872,32 @@ 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 (name[0] != '/') {
+		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 (name[0] != '/') {
+			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));
+		}
 		close(fd);
 		/* to prevent programs reporting
 		 * "failed to add socket: Success" */
-- 
2.13.6