Services: Renamed from Servers

It didn't feel right to have a "DHCPClient" in a "Servers" directory.
Rename this to Services to better reflect the type of programs we'll
be putting in there.

Services/TelnetServer/main.cpp

@@ -0,0 +1,177 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "Client.h"
+#include <AK/BufferStream.h>
+#include <AK/ByteBuffer.h>
+#include <AK/HashMap.h>
+#include <AK/IPv4Address.h>
+#include <AK/String.h>
+#include <AK/StringBuilder.h>
+#include <AK/Types.h>
+#include <LibCore/EventLoop.h>
+#include <LibCore/TCPServer.h>
+#include <LibCore/TCPSocket.h>
+#include <fcntl.h>
+#include <getopt.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/ioctl.h>
+
+static void run_command(int ptm_fd, String command)
+{
+    pid_t pid = fork();
+    if (pid == 0) {
+        const char* tty_name = ptsname(ptm_fd);
+        if (!tty_name) {
+            perror("ptsname");
+            exit(1);
+        }
+        close(ptm_fd);
+        int pts_fd = open(tty_name, O_RDWR);
+        if (pts_fd < 0) {
+            perror("open");
+            exit(1);
+        }
+
+        // NOTE: It's okay if this fails.
+        (void)ioctl(0, TIOCNOTTY);
+
+        close(0);
+        close(1);
+        close(2);
+
+        int rc = dup2(pts_fd, 0);
+        if (rc < 0) {
+            perror("dup2");
+            exit(1);
+        }
+        rc = dup2(pts_fd, 1);
+        if (rc < 0) {
+            perror("dup2");
+            exit(1);
+        }
+        rc = dup2(pts_fd, 2);
+        if (rc < 0) {
+            perror("dup2");
+            exit(1);
+        }
+        rc = close(pts_fd);
+        if (rc < 0) {
+            perror("close");
+            exit(1);
+        }
+        rc = ioctl(0, TIOCSCTTY);
+        if (rc < 0) {
+            perror("ioctl(TIOCSCTTY)");
+            exit(1);
+        }
+        const char* args[4] = { "/bin/Shell", nullptr, nullptr, nullptr };
+        if (!command.is_empty()) {
+            args[1] = "-c";
+            args[2] = command.characters();
+        }
+        const char* envs[] = { "TERM=xterm", "PATH=/bin:/usr/bin:/usr/local/bin", nullptr };
+        rc = execve("/bin/Shell", const_cast<char**>(args), const_cast<char**>(envs));
+        if (rc < 0) {
+            perror("execve");
+            exit(1);
+        }
+        ASSERT_NOT_REACHED();
+    }
+}
+
+int main(int argc, char** argv)
+{
+    Core::EventLoop event_loop;
+    auto server = Core::TCPServer::construct();
+
+    int opt;
+    u16 port = 23;
+    const char* command = "";
+    while ((opt = getopt(argc, argv, "p:c:")) != -1) {
+        switch (opt) {
+        case 'p':
+            port = atoi(optarg);
+            break;
+        case 'c':
+            command = optarg;
+            break;
+        default:
+            fprintf(stderr, "Usage: %s [-p port] [-c command]", argv[0]);
+            exit(1);
+        }
+    }
+
+    if (!server->listen({}, port)) {
+        perror("listen");
+        exit(1);
+    }
+
+    HashMap<int, NonnullRefPtr<Client>> clients;
+    int next_id = 0;
+
+    server->on_ready_to_accept = [&next_id, &clients, &server, command] {
+        int id = next_id++;
+
+        auto client_socket = server->accept();
+        if (!client_socket) {
+            perror("accept");
+            return;
+        }
+
+        int ptm_fd = posix_openpt(O_RDWR);
+        if (ptm_fd < 0) {
+            perror("posix_openpt");
+            client_socket->close();
+            return;
+        }
+        if (grantpt(ptm_fd) < 0) {
+            perror("grantpt");
+            client_socket->close();
+            return;
+        }
+        if (unlockpt(ptm_fd) < 0) {
+            perror("unlockpt");
+            client_socket->close();
+            return;
+        }
+
+        run_command(ptm_fd, command);
+
+        auto client = Client::create(id, move(client_socket), ptm_fd);
+        client->on_exit = [&clients, id] { clients.remove(id); };
+        clients.set(id, client);
+    };
+
+    int rc = event_loop.exec();
+    if (rc != 0) {
+        fprintf(stderr, "event loop exited badly; rc=%d", rc);
+        exit(1);
+    }
+
+    return 0;
+}