[PATCH] libwayland: Add WAYLAND_DEBUG_INTERFACES

[wl at ongy.net]

From: Markus Ongyerth <wl at ongy.net>

Add environment variable WAYLAND_DEBUG_INTERFACES for filtering the
output of WAYLAND_DEBUG logs.
While WAYLAND_DEBUG is a pretty powerful and useful debug tool, printing
everything has a few downsides.

1) It's a full keylogger (getting debug-logs from users)
2) It can be overly spammy with wl_buffer/wl_surface actions (e.g. when
   playing a video))

With this addition it's possible to supply another environment
variable, to filter on the interfaces one is interested in.
E.g. when interested in the behaviour of xdg-shell popups the filter could be
WAYLAND_DEBUG_INTERFACES=xdg_positioner,xdg_surface,xdg_popup
greatly improving SNR on the output and hiding potentially sensitive
information such as keystrokes.
---
 src/wayland-client.c | 85 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 81 insertions(+), 4 deletions(-)

diff --git a/src/wayland-client.c b/src/wayland-client.c
index efeb745..9de8e4e 100644
--- a/src/wayland-client.c
+++ b/src/wayland-client.c
@@ -118,6 +118,31 @@ struct wl_display {
 /** \endcond */
 
 static int debug_client = 0;
+static size_t debug_client_count = 0;
+static char **debug_client_interfaces = NULL;
+
+static void
+wl_client_debug_print(struct wl_closure *closure,
+                      struct wl_object *target, int send)
+{
+	if (debug_client_interfaces) {
+		bool found = false;
+		size_t i;
+		for (i = 0; i < debug_client_count; ++i) {
+			if (!strcmp(target->interface->name,
+			            debug_client_interfaces[i])) {
+				found = true;
+				break;
+			}
+		}
+
+		if (!found) {
+			return;
+		}
+	}
+
+	wl_closure_print(closure, target, send);
+}
 
 /**
  * This helper function wakes up all threads that are
@@ -748,7 +773,7 @@ wl_proxy_marshal_array_constructor_versioned(struct wl_proxy *proxy,
 		wl_abort("Error marshalling request: %s\n", strerror(errno));
 
 	if (debug_client)
-		wl_closure_print(closure, &proxy->object, true);
+		wl_client_debug_print(closure, &proxy->object, true);
 
 	if (wl_closure_send(closure, proxy->display->connection))
 		wl_abort("Error sending request: %s\n", strerror(errno));
@@ -1016,6 +1041,56 @@ connect_to_socket(const char *name)
 	return fd;
 }
 
+/* Set up the filter list for WAYLAND_DEBUG output.
+ * This reads WAYLAND_DEBUG_INTERFACEs and splits the provided string on every
+ * ','.
+ * The resulting list of strings is used as whitelist for interfaces printed by
+ * the WAYLAND_DEBUG mechanism.
+ * Sadly this leaks the memory required to strdup() the environment variable,
+ * but since this is a debug feature, and it should be constant over the
+ * lifetime of a single process, I consider it a minor problem
+ */
+static void
+setup_interface_filter(void)
+{
+	char *saveptr;
+	char *token;
+	size_t count = 0;
+	size_t i;
+	char *env;
+
+	/* We set this up before (on another wl_display_connect probably) so we
+	 * don't have to do anything this time
+	 */
+	if (debug_client_interfaces)
+		return;
+
+	if (!(env = getenv("WAYLAND_DEBUG_INTERFACES")))
+		return;
+
+	if (!(env = strdup(env))) {
+		wl_log("error: Could not allocate memory for WAYLAND_DEBUG_INTERFACES\n");
+		return;
+	}
+
+	for (i = 0; env[i]; ++i) {
+		if (env[i] == ',')
+			++count;
+	}
+
+	/* The maximum possible interfaces is the number of ',' found + 1 */
+	debug_client_interfaces = calloc(count + 1, sizeof(char *));
+	if (!debug_client_interfaces) {
+		wl_log("error: Could not allocate memory for WAYLAND_DEBUG_INTERFACES\n");
+		free(env);
+		return;
+	}
+
+	for (token = strtok_r(env, ",", &saveptr); token; token = strtok_r(NULL, ",", &saveptr)) {
+		debug_client_interfaces[debug_client_count++] = token;
+	}
+}
+
 /** Connect to Wayland display on an already open fd
  *
  * \param fd The fd to use for the connection
@@ -1034,8 +1109,10 @@ wl_display_connect_to_fd(int fd)
 	const char *debug;
 
 	debug = getenv("WAYLAND_DEBUG");
-	if (debug && (strstr(debug, "client") || strstr(debug, "1")))
+	if (debug && (strstr(debug, "client") || strstr(debug, "1"))) {
 		debug_client = 1;
+		setup_interface_filter();
+	}
 
 	display = zalloc(sizeof *display);
 	if (display == NULL) {
@@ -1423,13 +1500,13 @@ dispatch_event(struct wl_display *display, struct wl_event_queue *queue)
 
 	if (proxy->dispatcher) {
 		if (debug_client)
-			wl_closure_print(closure, &proxy->object, false);
+			wl_client_debug_print(closure, &proxy->object, false);
 
 		wl_closure_dispatch(closure, proxy->dispatcher,
 				    &proxy->object, opcode);
 	} else if (proxy->object.implementation) {
 		if (debug_client)
-			wl_closure_print(closure, &proxy->object, false);
+			wl_client_debug_print(closure, &proxy->object, false);
 
 		wl_closure_invoke(closure, WL_CLOSURE_INVOKE_CLIENT,
 				  &proxy->object, opcode, proxy->user_data);
-- 
2.18.0