TelnetServer: Port to LibMain

This is only a very basic change, since the fallible function calls are
all inside the `on_ready_to_accept` callback.

Userland/Services/TelnetServer/CMakeLists.txt

@@ -10,4 +10,4 @@ set(SOURCES
 )
 
 serenity_bin(TelnetServer)
-target_link_libraries(TelnetServer LibCore)
+target_link_libraries(TelnetServer LibCore LibMain)

Userland/Services/TelnetServer/main.cpp

@@ -11,6 +11,7 @@
 #include <LibCore/ArgsParser.h>
 #include <LibCore/EventLoop.h>
 #include <LibCore/TCPServer.h>
+#include <LibMain/Main.h>
 #include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -21,7 +22,7 @@ static void run_command(int ptm_fd, String command)
 {
     pid_t pid = fork();
     if (pid == 0) {
-        const char* tty_name = ptsname(ptm_fd);
+        char const* tty_name = ptsname(ptm_fd);
         if (!tty_name) {
             perror("ptsname");
             exit(1);
@@ -65,12 +66,12 @@ static void run_command(int ptm_fd, String command)
             perror("ioctl(TIOCSCTTY)");
             exit(1);
         }
-        const char* args[4] = { "/bin/Shell", nullptr, nullptr, nullptr };
+        char const* args[4] = { "/bin/Shell", nullptr, nullptr, nullptr };
         if (!command.is_empty()) {
             args[1] = "-c";
             args[2] = command.characters();
         }
-        const char* envs[] = { "TERM=xterm", "PATH=/usr/local/bin:/usr/bin:/bin", nullptr };
+        char const* envs[] = { "TERM=xterm", "PATH=/usr/local/bin:/usr/bin:/bin", nullptr };
         rc = execve("/bin/Shell", const_cast<char**>(args), const_cast<char**>(envs));
         if (rc < 0) {
             perror("execve");
@@ -80,15 +81,15 @@ static void run_command(int ptm_fd, String command)
     }
 }
 
-int main(int argc, char** argv)
+ErrorOr<int> serenity_main(Main::Arguments arguments)
 {
     int port = 23;
-    const char* command = "";
+    char const* command = "";
 
     Core::ArgsParser args_parser;
     args_parser.add_option(port, "Port to listen on", nullptr, 'p', "port");
     args_parser.add_option(command, "Program to run on connection", nullptr, 'c', "command");
-    args_parser.parse(argc, argv);
+    args_parser.parse(arguments);
 
     if ((u16)port != port) {
         warnln("Invalid port number: {}", port);
@@ -148,11 +149,5 @@ int main(int argc, char** argv)
         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;
+    return event_loop.exec();
 }