xcb_parse_display: support XDG_RUNTIME_DIR/X11-socketxdg-implicitly

If a client doesn't give a display we should just assume they want
to connect to a well known name in their runtime directory.  This
gets rid of one more environment variable in the wild.

1 files changed, 15 insertions, 2 deletions

diff --git a/src/xcb_util.c b/src/xcb_util.c
index 9bdfa86..c63648c 100644
--- a/src/xcb_util.c
+++ b/src/xcb_util.c
@@ -83,11 +83,24 @@ static int _xcb_parse_display(const char *name, char **host, char **protocol,
 {
     int len, display, screen;
     char *slash, *colon, *dot, *end;
+    char socket_path[PATH_MAX];
 
     if(!name || !*name)
         name = getenv("DISPLAY");
-    if(!name)
-        return 0;
+
+    if(!name) {
+        const char *runtime_dir = getenv ("XDG_RUNTIME_DIR");
+
+        if(!runtime_dir || runtime_dir[0] != '/')
+            goto error_out;
+
+        snprintf(socket_path, sizeof(socket_path), "%s/X11-socket", runtime_dir);
+
+        if(access(socket_path, F_OK) < 0)
+            goto error_out;
+
+        name = socket_path;
+    }
 
     if(name[0] == '/')
         slash = NULL;