internal/wayland: improve error handling

Note: wl_registry_add_listener is undocumented everywhere. Its implementation calls wl_proxy_add_listener which returns 0 on success or -1 on failure.
Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/system/output.go

@@ -40,6 +40,10 @@ func (e *OpError) Error() string {
 }
 
 func (e *OpError) Message() string {
+	if m, ok := message.GetMessage(e.Err); ok {
+		return m
+	}
+
 	switch {
 	case e.Msg != "":
 		return e.Error()

internal/wayland/wayland-client-helper.c

@@ -31,67 +31,84 @@ static const struct wl_registry_listener registry_listener = {
     .global_remove = registry_handle_global_remove,
 };
 
-int32_t hakurei_bind_wayland_fd(
+hakurei_wayland_res hakurei_bind_wayland_fd(
     char *socket_path,
     int fd,
     const char *app_id,
     const char *instance_id,
     int sync_fd) {
-  int32_t res = 0; /* refer to resErr for corresponding Go error */
+  hakurei_wayland_res res = HAKUREI_WAYLAND_SUCCESS; /* see wayland.go for handling */
+
+  struct wl_display *display = NULL;
+  struct wl_registry *registry;
+  struct wp_security_context_manager_v1 *security_context_manager = NULL;
+  int event_cnt;
+  int listen_fd = -1;
+  struct sockaddr_un sockaddr = {0};
+  struct wp_security_context_v1 *security_context;
 
-  struct wl_display *display;
   display = wl_display_connect_to_fd(fd);
-  if (!display) {
+  if (display == NULL) {
-    res = 1;
+    res = HAKUREI_WAYLAND_CONNECT;
     goto out;
   };
 
-  struct wl_registry *registry;
   registry = wl_display_get_registry(display);
-
+  if (wl_registry_add_listener(registry, &registry_listener, &security_context_manager) < 0) {
-  struct wp_security_context_manager_v1 *security_context_manager = NULL;
+    res = HAKUREI_WAYLAND_LISTENER;
-  wl_registry_add_listener(registry, &registry_listener, &security_context_manager);
-  int ret;
-  ret = wl_display_roundtrip(display);
-  wl_registry_destroy(registry);
-  if (ret < 0)
     goto out;
-
+  }
-  if (!security_context_manager) {
+  event_cnt = wl_display_roundtrip(display);
-    res = 2;
+  wl_registry_destroy(registry);
+  if (event_cnt < 0) {
+    res = HAKUREI_WAYLAND_ROUNDTRIP;
     goto out;
   }
 
-  int listen_fd = -1;
+  if (security_context_manager == NULL) {
-  listen_fd = socket(AF_UNIX, SOCK_STREAM, 0);
+    res = HAKUREI_WAYLAND_NOT_AVAIL;
-  if (listen_fd < 0)
     goto out;
+  }
+
+  listen_fd = socket(AF_UNIX, SOCK_STREAM, 0);
+  if (listen_fd < 0) {
+    res = HAKUREI_WAYLAND_SOCKET;
+    goto out;
+  }
 
-  struct sockaddr_un sockaddr = {0};
   sockaddr.sun_family = AF_UNIX;
   snprintf(sockaddr.sun_path, sizeof(sockaddr.sun_path), "%s", socket_path);
-  if (bind(listen_fd, (struct sockaddr *)&sockaddr, sizeof(sockaddr)) != 0)
+  if (bind(listen_fd, (struct sockaddr *)&sockaddr, sizeof(sockaddr)) != 0) {
+    res = HAKUREI_WAYLAND_BIND;
     goto out;
+  }
 
-  if (listen(listen_fd, 0) != 0)
+  if (listen(listen_fd, 0) != 0) {
+    res = HAKUREI_WAYLAND_LISTEN;
     goto out;
+  }
 
-  struct wp_security_context_v1 *security_context;
   security_context = wp_security_context_manager_v1_create_listener(security_context_manager, listen_fd, sync_fd);
+  if (security_context == NULL) { /* not reached */
+    res = HAKUREI_WAYLAND_NOT_AVAIL;
+    goto out;
+  }
   wp_security_context_v1_set_sandbox_engine(security_context, "app.hakurei");
   wp_security_context_v1_set_app_id(security_context, app_id);
   wp_security_context_v1_set_instance_id(security_context, instance_id);
   wp_security_context_v1_commit(security_context);
   wp_security_context_v1_destroy(security_context);
-  if (wl_display_roundtrip(display) < 0)
+  if (wl_display_roundtrip(display) < 0) {
+    res = HAKUREI_WAYLAND_ROUNDTRIP;
     goto out;
+  }
 
 out:
   if (listen_fd >= 0)
     close(listen_fd);
-  if (security_context_manager)
+  if (security_context_manager != NULL)
     wp_security_context_manager_v1_destroy(security_context_manager);
-  if (display)
+  if (display != NULL)
     wl_display_disconnect(display);
 
   free((void *)socket_path);

internal/wayland/wayland-client-helper.h

@@ -1,6 +1,22 @@
-#include <stdint.h>
+typedef enum {
+  HAKUREI_WAYLAND_SUCCESS,
+  /* wl_display_connect_to_fd failed, errno */
+  HAKUREI_WAYLAND_CONNECT,
+  /* wl_registry_add_listener failed, errno */
+  HAKUREI_WAYLAND_LISTENER,
+  /* wl_display_roundtrip failed, errno */
+  HAKUREI_WAYLAND_ROUNDTRIP,
+  /* compositor does not implement wp_security_context_v1 */
+  HAKUREI_WAYLAND_NOT_AVAIL,
+  /* socket failed, errno */
+  HAKUREI_WAYLAND_SOCKET,
+  /* bind failed, errno */
+  HAKUREI_WAYLAND_BIND,
+  /* listen failed, errno */
+  HAKUREI_WAYLAND_LISTEN,
+} hakurei_wayland_res;
 
-int32_t hakurei_bind_wayland_fd(
+hakurei_wayland_res hakurei_bind_wayland_fd(
     char *socket_path,
     int fd,
     const char *app_id,

internal/wayland/wayland.go

@@ -12,7 +12,6 @@ package wayland
 */
 import "C"
 import (
-	"errors"
 	"strings"
 	"syscall"
 )
@@ -31,18 +30,96 @@ const (
 	FallbackName = "wayland-0"
 )
 
-var resErr = [...]error{
+type (
-	0: nil,
+	// Res is the outcome of a call to hakurei_bind_wayland_fd.
-	1: errors.New("wl_display_connect_to_fd() failed"),
+	Res = C.hakurei_wayland_res
-	2: errors.New("wp_security_context_v1 not available"),
+
+	// An Error represents a failure during hakurei_bind_wayland_fd.
+	Error struct {
+		// Where the failure occurred.
+		Cause Res
+		// Global errno value set during the fault.
+		Errno error
+	}
+)
+
+// withPrefix returns prefix suffixed with errno description if available.
+func (e *Error) withPrefix(prefix string) string {
+	if e.Errno == nil {
+		return prefix
+	}
+	return prefix + ": " + e.Errno.Error()
 }
 
+const (
+	// RSuccess is returned on a successful call.
+	RSuccess Res = C.HAKUREI_WAYLAND_SUCCESS
+	// RConnect is returned if wl_display_connect_to_fd failed. The global errno is set.
+	RConnect Res = C.HAKUREI_WAYLAND_CONNECT
+	// RListener is returned if wl_registry_add_listener failed. The global errno is set.
+	RListener Res = C.HAKUREI_WAYLAND_LISTENER
+	// RRoundtrip is returned if wl_display_roundtrip failed. The global errno is set.
+	RRoundtrip Res = C.HAKUREI_WAYLAND_ROUNDTRIP
+	// RNotAvail is returned if compositor does not implement wp_security_context_v1.
+	RNotAvail Res = C.HAKUREI_WAYLAND_NOT_AVAIL
+	// RSocket is returned if socket failed. The global errno is set.
+	RSocket Res = C.HAKUREI_WAYLAND_SOCKET
+	// RBind is returned if bind failed. The global errno is set.
+	RBind Res = C.HAKUREI_WAYLAND_BIND
+	// RListen is returned if listen failed. The global errno is set.
+	RListen Res = C.HAKUREI_WAYLAND_LISTEN
+)
+
+func (e *Error) Unwrap() error   { return e.Errno }
+func (e *Error) Message() string { return e.Error() }
+func (e *Error) Error() string {
+	switch e.Cause {
+	case RSuccess:
+		if e.Errno == nil {
+			return "success"
+		}
+		return e.Errno.Error()
+
+	case RConnect:
+		return e.withPrefix("wl_display_connect_to_fd failed")
+	case RListener:
+		return e.withPrefix("wl_registry_add_listener failed")
+	case RRoundtrip:
+		return e.withPrefix("wl_display_roundtrip failed")
+	case RNotAvail:
+		return "compositor does not implement security_context_v1"
+
+	case RSocket, RBind, RListen:
+		if e.Errno == nil {
+			return "socket operation failed"
+		}
+		return e.Errno.Error()
+
+	default:
+		return e.withPrefix("impossible outcome") /* not reached */
+	}
+}
+
+// bindWaylandFd calls hakurei_bind_wayland_fd. A non-nil error has concrete type [Error].
 func bindWaylandFd(socketPath string, fd uintptr, appID, instanceID string, syncFd uintptr) error {
 	if hasNull(appID) || hasNull(instanceID) {
 		return syscall.EINVAL
 	}
-	res := C.hakurei_bind_wayland_fd(C.CString(socketPath), C.int(fd), C.CString(appID), C.CString(instanceID), C.int(syncFd))
+
-	return resErr[int32(res)]
+	var e Error
+	e.Cause, e.Errno = C.hakurei_bind_wayland_fd(
+		C.CString(socketPath),
+		C.int(fd),
+		C.CString(appID),
+		C.CString(instanceID),
+		C.int(syncFd),
+	)
+
+	if e.Cause == RSuccess {
+		return nil
+	}
+	return &e
 }
 
+// hasNull returns whether s contains the NUL character.
 func hasNull(s string) bool { return strings.IndexByte(s, 0) > -1 }

internal/wayland/wayland_test.go

@@ -0,0 +1,79 @@
+package wayland_test
+
+import (
+	"syscall"
+	"testing"
+
+	"hakurei.app/container/stub"
+	"hakurei.app/internal/wayland"
+)
+
+func TestError(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name string
+		err  wayland.Error
+		want string
+	}{
+		{"success", wayland.Error{
+			Cause: wayland.RSuccess,
+		}, "success"},
+
+		{"success errno", wayland.Error{
+			Cause: wayland.RSuccess,
+			Errno: stub.UniqueError(0),
+		}, "unique error 0 injected by the test suite"},
+
+		{"wl_display_connect_to_fd", wayland.Error{
+			Cause: wayland.RConnect,
+			Errno: stub.UniqueError(1),
+		}, "wl_display_connect_to_fd failed: unique error 1 injected by the test suite"},
+
+		{"wl_registry_add_listener", wayland.Error{
+			Cause: wayland.RListener,
+			Errno: stub.UniqueError(2),
+		}, "wl_registry_add_listener failed: unique error 2 injected by the test suite"},
+
+		{"wl_display_roundtrip", wayland.Error{
+			Cause: wayland.RRoundtrip,
+			Errno: stub.UniqueError(3),
+		}, "wl_display_roundtrip failed: unique error 3 injected by the test suite"},
+
+		{"not available", wayland.Error{
+			Cause: wayland.RNotAvail,
+		}, "compositor does not implement security_context_v1"},
+
+		{"not available errno", wayland.Error{
+			Cause: wayland.RNotAvail,
+			Errno: syscall.EAGAIN,
+		}, "compositor does not implement security_context_v1"},
+
+		{"socket", wayland.Error{
+			Cause: wayland.RSocket,
+			Errno: stub.UniqueError(4),
+		}, "unique error 4 injected by the test suite"},
+
+		{"socket invalid", wayland.Error{
+			Cause: wayland.RSocket,
+		}, "socket operation failed"},
+
+		{"invalid", wayland.Error{
+			Cause: 0xbad,
+		}, "impossible outcome"},
+
+		{"invalid errno", wayland.Error{
+			Cause: 0xbad,
+			Errno: stub.UniqueError(5),
+		}, "impossible outcome: unique error 5 injected by the test suite"},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			if got := tc.err.Message(); got != tc.want {
+				t.Errorf("Message: %q, want %q", got, tc.want)
+			}
+		})
+	}
+}