[PATCH 2/2] proto, server: Add internal server error message.

[raof at ubuntu.com]

From: Christopher James Halse Rogers <christopher.halse.rogers at canonical.com>

Many languages such as C++ or Rust have an unwinding error-reporting
mechanism. Code in these languages can (and must!) wrap request handling
callbacks in unwind guards to avoid undefined behaviour.

As a consequence such code will detect internal server errors, but have
no way to communicate such failures to the client.

This adds a WL_DISPLAY_ERROR_INTERNAL error to wl_display so that
such code can notify (and disconnect) client which hit internal bugs.

Signed-off-by: Christopher James Halse Rogers <christopher.halse.rogers at canonical.com>
---
 protocol/wayland.xml      |  2 ++
 src/wayland-client.c      |  3 +++
 src/wayland-server-core.h |  4 ++++
 src/wayland-server.c      | 23 +++++++++++++++++++++++
 tests/display-test.c      | 40 ++++++++++++++++++++++++++++++++++++++++
 5 files changed, 72 insertions(+)

diff --git a/protocol/wayland.xml b/protocol/wayland.xml
index b5662e0..1db31a6 100644
--- a/protocol/wayland.xml
+++ b/protocol/wayland.xml
@@ -94,6 +94,8 @@
 	     summary="method doesn't exist on the specified interface"/>
       <entry name="no_memory" value="2"
 	     summary="server is out of memory"/>
+      <entry name="internal" value="3"
+	     summary="internal server error"/>
     </enum>
 
     <event name="delete_id">
diff --git a/src/wayland-client.c b/src/wayland-client.c
index c1369b8..7c442b1 100644
--- a/src/wayland-client.c
+++ b/src/wayland-client.c
@@ -192,6 +192,9 @@ display_protocol_error(struct wl_display *display, uint32_t code,
 		case WL_DISPLAY_ERROR_NO_MEMORY:
 			err = ENOMEM;
 			break;
+		case WL_DISPLAY_ERROR_INTERNAL:
+			err = EPROTO;
+			break;
 		default:
 			err = EFAULT;
 		}
diff --git a/src/wayland-server-core.h b/src/wayland-server-core.h
index 2e725d9..7137da6 100644
--- a/src/wayland-server-core.h
+++ b/src/wayland-server-core.h
@@ -324,6 +324,10 @@ wl_client_get_object(struct wl_client *client, uint32_t id);
 void
 wl_client_post_no_memory(struct wl_client *client);
 
+void
+wl_client_post_internal_error(struct wl_client *client,
+			      const char* msg, ...) WL_PRINTF(2,3);
+
 void
 wl_client_add_resource_created_listener(struct wl_client *client,
                                         struct wl_listener *listener);
diff --git a/src/wayland-server.c b/src/wayland-server.c
index 00c93f7..6317f8f 100644
--- a/src/wayland-server.c
+++ b/src/wayland-server.c
@@ -650,6 +650,29 @@ wl_client_post_no_memory(struct wl_client *client)
 			       WL_DISPLAY_ERROR_NO_MEMORY, "no memory");
 }
 
+/** Report an internal server error
+ *
+ * \param client The client object
+ * \param msg A printf-style format string
+ * \param ... Format string arguments
+ *
+ * Report an unspecified internal error and disconnect the client.
+ *
+ * \memberof wl_client
+ */
+WL_EXPORT void
+wl_client_post_internal_error(struct wl_client *client,
+			      char const *msg, ...)
+{
+	va_list ap;
+
+	va_start(ap, msg);
+	wl_resource_post_error_vargs(client->display_resource,
+				     WL_DISPLAY_ERROR_INTERNAL,
+				     msg, ap);
+	va_end(ap);
+}
+
 WL_EXPORT void
 wl_resource_post_no_memory(struct wl_resource *resource)
 {
diff --git a/tests/display-test.c b/tests/display-test.c
index 9b49a0e..63f8b5a 100644
--- a/tests/display-test.c
+++ b/tests/display-test.c
@@ -419,6 +419,46 @@ TEST(post_nomem_tst)
 	display_destroy(d);
 }
 
+static void
+post_internal_error_main(void)
+{
+	struct client *c = client_connect();
+	struct wl_seat *seat = client_get_seat(c);
+	uint32_t object_id, protocol_error;
+	const struct wl_interface *interface;
+
+	assert(stop_display(c, 1) == -1);
+	int err = wl_display_get_error(c->wl_display);
+	fprintf(stderr, "Err is %i\n", err);
+	assert(err == EPROTO);
+	protocol_error = wl_display_get_protocol_error(c->wl_display,
+						       &interface,
+						       &object_id);
+	assert(protocol_error == WL_DISPLAY_ERROR_INTERNAL);
+	assert(interface == &wl_display_interface);
+
+	wl_proxy_destroy((struct wl_proxy *) seat);
+	client_disconnect_nocheck(c);
+}
+
+TEST(post_internal_error_tst)
+{
+	struct display *d = display_create();
+	struct client_info *cl;
+
+	wl_global_create(d->wl_display, &wl_seat_interface,
+			 1, d, bind_seat);
+
+	cl = client_create_noarg(d, post_internal_error_main);
+	display_run(d);
+
+	wl_client_post_internal_error(cl->wl_client, "Error %i", 20);
+
+	display_resume(d);
+
+	display_destroy(d);
+}
+
 static void
 register_reading(struct wl_display *display)
 {
-- 
2.15.1