[FEATURE] Telnet command #66

Author: Thidas Senavirathna

src/main/java/com/mycmd/App.java

@@ -96,6 +96,7 @@ private static void registerCommands(Map<String, Command> commands) {
         commands.put("date", new DateCommand());
         commands.put("history", new HistoryCommand());
         commands.put("ping", new PingCommand());
+        commands.put("telnet", new TelnetCommand());
         commands.put("pwd", new PwdCommand());
         commands.put("uptime", new UptimeCommand());
         commands.put("clearhistory", new ClearHistoryCommand());

src/main/java/com/mycmd/commands/TelnetCommand.java

@@ -0,0 +1,83 @@
+package com.mycmd.commands;
+
+import com.mycmd.ShellContext;
+
+import java.io.*;
+import java.net.Socket;
+
+/**
+ * TelnetCommand - simple TCP client for interactive sessions.
+ * Usage: telnet <host> [port]
+ *
+ * Notes:
+ * - This is a minimal implementation (no Telnet option negotiation).
+ * - It will take over stdin while connected; type 'exit' to return to the shell.
+ */
+public class TelnetCommand implements Command {
+
+    @Override
+    public void execute(String[] args, ShellContext context) throws Exception {
+        if (args.length < 1) {
+            System.out.println("Usage: telnet <host> [port]");
+            return;
+        }
+
+        String host = args[0];
+        int port = 23;
+        if (args.length >= 2) {
+            try {
+                port = Integer.parseInt(args[1]);
+            } catch (NumberFormatException e) {
+                System.out.println("Invalid port: " + args[1]);
+                return;
+            }
+        }
+
+        try (Socket socket = new Socket(host, port)) {
+            socket.setSoTimeout(0); // blocking reads
+            System.out.println("Connected to " + host + ":" + port + " (type 'exit' to quit)");
+
+            // Reader thread: prints remote data to stdout
+            Thread reader = new Thread(() -> {
+                try (InputStream in = socket.getInputStream();
+                     InputStreamReader isr = new InputStreamReader(in);
+                     BufferedReader br = new BufferedReader(isr)) {
+
+                    char[] buffer = new char[2048];
+                    int read;
+                    while ((read = br.read(buffer)) != -1) {
+                        System.out.print(new String(buffer, 0, read));
+                        System.out.flush();
+                    }
+                } catch (IOException ignored) {
+                    // socket closed or stream ended
+                }
+            }, "telnet-reader");
+            reader.setDaemon(true);
+            reader.start();
+
+            // Writer loop: read stdin and send to remote
+            try (OutputStream out = socket.getOutputStream();
+                 OutputStreamWriter osw = new OutputStreamWriter(out);
+                 BufferedWriter bw = new BufferedWriter(osw);
+                 BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in))) {
+
+                String line;
+                while ((line = stdin.readLine()) != null) {
+                    if ("exit".equalsIgnoreCase(line.trim())) break;
+                    bw.write(line);
+                    bw.write("\r\n"); // typical telnet line ending
+                    bw.flush();
+                }
+            } catch (IOException ignored) {
+                // stdin/socket error, will disconnect
+            }
+
+            // ensure socket closes to stop reader
+            try { socket.close(); } catch (IOException ignored) {}
+            System.out.println("\nDisconnected.");
+        } catch (IOException e) {
+            System.out.println("Connection failed: " + e.getMessage());
+        }
+    }
+}