Services: Add a WebSocket service

The WebSocket service isolates communication with a WebSocket to its
own isolated process. Similar to other isolating services, it has its
own user and group.

Userland/Services/WebSocket/main.cpp

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2021, Dex♪ <dexes.ttp@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibCore/EventLoop.h>
+#include <LibCore/LocalServer.h>
+#include <LibIPC/ClientConnection.h>
+#include <LibTLS/Certificate.h>
+#include <WebSocket/ClientConnection.h>
+
+int main(int, char**)
+{
+    if (pledge("stdio inet accept unix rpath cpath fattr sendfd recvfd", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    // Ensure the certificates are read out here.
+    [[maybe_unused]] auto& certs = DefaultRootCACertificates::the();
+
+    Core::EventLoop event_loop;
+    // FIXME: Establish a connection to LookupServer and then drop "unix"?
+    if (pledge("stdio inet accept unix sendfd recvfd", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+    if (unveil("/tmp/portal/lookup", "rw") < 0) {
+        perror("unveil");
+        return 1;
+    }
+    if (unveil(nullptr, nullptr) < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    auto socket = Core::LocalSocket::take_over_accepted_socket_from_system_server();
+    VERIFY(socket);
+    IPC::new_client_connection<WebSocket::ClientConnection>(socket.release_nonnull(), 1);
+    return event_loop.exec();
+}