telnetroulette/terminal_handler.go

package main

import (
	"github.com/BRNSystems/go-telnet"
	"github.com/reiver/go-oi"
	"strings"
)

type InternalTerminalHandler struct {
	ShellCharacter  string
	WelcomeMessage  string
	CommandRegistry *CommandRegistry
}

func NewInternalTerminalHandler(shellCharacter, welcomeMessage string, commandRegistry *CommandRegistry) *InternalTerminalHandler {
	return &InternalTerminalHandler{
		ShellCharacter:  shellCharacter,
		WelcomeMessage:  welcomeMessage,
		CommandRegistry: commandRegistry,
	}
}

func (handler *InternalTerminalHandler) ServeTELNET(ctx telnet.Context, w telnet.Writer, r telnet.Reader) {
	clientID := NewClient(&ctx, &w, &r)

	defer RemoveClient(clientID)
	w.RawWrite([]byte{0xff, 0xfb, 0x03}) //send char by char
	w.RawWrite([]byte{0xff, 0xfb, 0x01}) //echo from server
	w.Write([]byte(strings.ReplaceAll(handler.WelcomeMessage, "\n", "\r\n") + "\r\n"))
	//replace every \n with \r\n in WelcomeMessage
	w.Write([]byte(handler.ShellCharacter))

	var lineBuffer []byte

	CSISequence := 0

	for {
		var bt [1]byte
		n, err := r.Read(bt[:])
		if err != nil {
			break
		}

		if n > 0 {
			b := bt[0]

			if b == 0x03 || b == 0x04 {
				return
			} else if b == 0x1B { //escape
				CSISequence = 1
			} else if CSISequence == 1 && b == 0x5B {
				CSISequence = 2
			} else if CSISequence == 2 && b == 'A' {
				if len(lineBuffer) == 0 && len(clients[clientID].History) > 0 {
					if clients[clientID].HistoryIndex < len(clients[clientID].History)-1 {
						clients[clientID].HistoryIndex++
					}
					lineBuffer = []byte(clients[clientID].History[clients[clientID].HistoryIndex])
					w.RawWrite([]byte{0x1B, 0x5B, 0x4B}) //clear line
					w.Write(lineBuffer)
				}
			} else if CSISequence == 2 && b == 'B' {
				if len(lineBuffer) == 0 && len(clients[clientID].History) > 0 {
					if clients[clientID].HistoryIndex > 0 {
						clients[clientID].HistoryIndex--
					}
					lineBuffer = []byte(clients[clientID].History[clients[clientID].HistoryIndex])
					w.RawWrite([]byte{0x1B, 0x5B, 0x4B}) //clear line
					w.Write(lineBuffer)
				}
			} else if b == 0x7F {
				if len(lineBuffer) > 0 {
					w.Write([]byte{0x08, 0x20, 0x08})
					lineBuffer = lineBuffer[:len(lineBuffer)-1]
				}
			} else if b != '\r' && b != '\n' && b != 0 {
				CSISequence = 0
				lineBuffer = append(lineBuffer, b)
				w.RawWrite([]byte{b})
			} else if b == '\r' {
				w.Write([]byte("\r\n"))
				command := string(lineBuffer)
				args := strings.Fields(command)
				var message string

				if len(args) > 0 {
					cmd := args[0]
					if cmd == "exit" {
						return
					}
					handlerFunc, ok, clientID := handler.CommandRegistry.GetCommandHandler(cmd, clientID)
					clients[clientID].HistoryIndex = 0
					if ok {
						message = handlerFunc(args[1:], clientID)
						clients[clientID].History = append(clients[clientID].History, command)
					} else {
						message = "Command not found"
					}
					message += "\n" + handler.ShellCharacter
				} else {
					message = handler.ShellCharacter
				}
				oi.LongWrite(w, []byte(strings.ReplaceAll(message, "\n", "\r\n")))
				lineBuffer = nil
			}
		}
	}
}