go-bbs/main.go

// go-bbs provides a basic framework for a multiuser bulletin board server application
// it is indended to be customized by the operator of the bulletin board
package main

import (
	"bytes"
	"context"
	"errors"
	"flag"
	"fmt"
	"io"
	"log"
	"net"
	"os"
	"os/exec"
	"strconv"
	"strings"
	"sync"
	"text/template"
	"time"

	"github.com/creack/pty"
	"github.com/xtaci/gaio"
	"golang.org/x/term"
	"versestudios.com/go-bbs/openconn"
)

type InChanKey string
type OutChanKey string

// ioHandler is the gaio.Watcher's main loop
// it wait for I/O calls to the watcher's Read and Write methods
// and tracks the state of the call, dispatching the appropriate gaio.OpResult
// to the proper channel based on whether it was a read (input from the remote client)
// or a write (output to the remote client)
func ioHandler(w *gaio.Watcher, WatcherControl *chan string) {
	for {
		select {
		case msg := <-*WatcherControl:
			switch msg {
			case "":
				log.Println("empty WatcherControl command")
			case "stop":
				log.Println("stopping ioHandler via WatcherControl stop command")
				return
			default:
				log.Println("unknown WatcherControl command:", msg)
			}
		default:
			// loop wait for any IO events
			results, err := w.WaitIO()
			if err != nil {
				log.Println(err)
				return
			}

		IOLoop:
			for _, res := range results {
				if res.Context != nil && nil != res.Context.(context.Context) {
					if inChan, _, ok := openconn.FromContext(res.Context.(context.Context)); ok {
						switch res.Operation {
						case gaio.OpRead: // read completion event
							inChan <- res
							// queue next read
							w.Read(res.Context, res.Conn, nil)
						default: // anything else (meaning write completions)
							continue IOLoop
						}
					} else {
						log.Printf("error getting inChan and outChan from context: %v\n", res.Context)
					}
				} else {
					log.Printf("nil context! res: %v\n", res)
				}
			}
		}
		time.Sleep(time.Millisecond)
	}
}

// main is the main loop of the server
// it sets up both the network listener as well as the gaio.Watcher that will handle
// I/O for each incoming network connection
func main() {
	port := flag.Int("port", 3333, "Port to accept connections on.")
	host := flag.String("host", "127.0.0.1", "Host or IP to bind to")
	flag.Parse()

	w, err := gaio.NewWatcher()
	if err != nil {
		log.Fatal(err)
	}
	defer w.Close()
	l, err := net.Listen("tcp", *host+":"+strconv.Itoa(*port))
	if err != nil {
		log.Panicln(err)
	}
	log.Println("Listening to connections at '"+*host+"' on port", strconv.Itoa(*port))
	log.Println("(If you want to run this on a different address or port, the command line flags -host and -port are available to you.)")
	defer l.Close()

	for {
		conn, err := l.Accept()
		if err != nil {
			log.Panicln(err)
		}

		log.Println("new client: ", conn.RemoteAddr())
		// chan to terminate ioHandler when neccessary
		WatcherControl := make(chan string)

		// get new context with inChan and outChan for this client connection
		ctx := openconn.NewContext(context.Background())
		log.Printf("new context for client %v: %v\n", conn.RemoteAddr(), ctx)

		// submit the first async write IO request
		welcomeScreen, err := screenHandler("welcome", nil)
		if err != nil {
			log.Printf("err loading initial welcome screen: %v\n", err)
		}
		err = w.Write(ctx, conn, welcomeScreen)
		if err != nil {
			log.Printf("err sending welcomeHandler: %v\n", err)
			return
		}
		// now that a prompt is (or will be) displayed, go ahead and listen for input
		err = w.Read(ctx, conn, nil)
		if err != nil {
			log.Printf("err queueing w.Read: %v\n", err)
			return
		}

		time.Sleep(time.Millisecond)

		// menu handler for this connection
		go menuHandler(ctx, conn, w)
		// io handler for this connection
		go ioHandler(w, &WatcherControl)

		log.Println("main thread looping")
	}
}

// menuHandler is the main loop for each individual remote connection
// it receives input over the connection's InChan channel (part of its context)
// as a gaio.OpResult
func menuHandler(ctx context.Context, conn net.Conn, w *gaio.Watcher) {
	var wg sync.WaitGroup

	MenuControl := make(chan string)

	var inChan, outChan chan gaio.OpResult
	var ok bool

	if inChan, outChan, ok = openconn.FromContext(ctx); !ok {
		log.Println("Could not get inChan/outChan from context!", ok, ctx)
	}

	wg.Add(1)
	go func(inChan, outChan chan gaio.OpResult, MenuControl chan string) {
		defer wg.Done()
		log.Println("starting menu loop")
		paused := false
	ControlLoop:
		for {
			select {
			case msg := <-MenuControl:
				log.Println("msg on MenuControl:", msg)
				switch string(msg) {

				case "stop":
					log.Println("closing menu loop")
					paused = true
					break ControlLoop

				case "pause":
					log.Println("pausing menu loop via menucontrol")
					paused = true

				case "unpause":
					log.Println("unpausing menu loop via menucontrol")
					paused = false

				default:
					log.Println("menu received unknown command: ", msg)
				}

			default:
				if !paused {
					select {
					case res := <-inChan:
						if res.Error != nil {
							log.Println("error on inChan: ", res.Error)
						}
						if res.Operation == gaio.OpRead && res.Size > 0 && res.Conn == conn {
							log.Printf("received on inChan: conn: %v, buffer size: %v\n", res.Conn.RemoteAddr(), res.Size)
							log.Println("menu receive: ", strings.TrimSpace(string(res.Buffer[:res.Size-1])))
							switch string(strings.TrimSpace(string(res.Buffer[:res.Size-1]))) {

							case "welcome":
								welcomeStr, err := screenHandler("welcome", nil)
								if err != nil {
									log.Printf("err loading welcome screen: %v\n", err)
								}
								if err := w.Write(ctx, conn, welcomeStr); err != nil {
									log.Printf("error sending screenHandler from cmd `welcome`: %v", err)
								}

							case "help":
								helpStr, err := screenHandler("help", nil)
								if err != nil {
									log.Printf("err loading help screen: %v\n", err)
								}
								if err := w.Write(ctx, conn, helpStr); err != nil {
									log.Printf("error sending screenHandler from cmd `help`: %v", err)
								}

							case "contact":
								contactStr, err := screenHandler("contact", nil)
								if err != nil {
									log.Printf("err loading contact screen: %v\n", err)
								}
								if err := w.Write(ctx, conn, contactStr); err != nil {
									log.Printf("error sending screenHandler from cmd `contact`: %v", err)
								}

							case "operator":
								opStr, err := screenHandler("operator", nil)
								if err != nil {
									log.Printf("err loading operator screen: %v\n", err)
								}
								var lineNum int
								var line string
								baudrate := 40 // 300 baud is ~ 30 characters per second; I'll be nice and bump it to 400
								for lineNum, line = range strings.Split(string(opStr), "\n") {
									// changed my mind - I actually like it at a nice steady 400 baud, tyvm
									// if baudrate < 120 && i > 1 { // 1200 baud is still very readable in realtime without being too fast
									//	baudrate += 1
									//}
									if lineNum < 10 { // spit the banner text out quickly
										if err := w.Write(ctx, conn, []byte(line+"\r\n")); err != nil {
											log.Printf("error sending rune from cmd `operator`: %v", err)
										}
									} else {
										ms := float64(1) / float64(baudrate)
										for _, c := range line {
											if err := w.Write(ctx, conn, []byte{byte(c)}); err != nil {
												log.Printf("error sending rune from cmd `operator`: %v", err)
											}

											time.Sleep(time.Duration(ms*1000) * time.Millisecond)
										}
										if err := w.Write(ctx, conn, []byte("\r\n")); err != nil {
											log.Printf("error sending rune from cmd `operator`: %v", err)
										}
									}
								}
								// add prompt at end
								if err := w.Write(ctx, conn, []byte("\r\n> ")); err != nil {
									log.Printf("error sending rune from cmd `operator`: %v", err)
								}

							case "adventure":
								// start the door and wait
								var wg sync.WaitGroup
								log.Println("starting door handler...")
								wg.Add(1)
								go doorHandler(ctx, conn, w, &wg)
								log.Println("menu handler waiting for wg to return from door")
								wg.Wait()
								log.Println("returning from door")
								// welcome back and prompt
								err := w.Write(ctx, conn, []byte("Welcome back from your adventure!\n\n> "))
								if err != nil {
									log.Printf("error writing to connection: %v", err)
								}

							case "info":
								wg := new(sync.WaitGroup)
								wg.Add(2)
								uptime := getUptime(wg)
								tubes := getTubePeers(wg)
								wg.Wait()
								data := struct{ Uptime, TubesInfo string }{uptime, tubes}
								infoStr, err := screenHandler("info", data)
								if err != nil {
									log.Printf("err loading info screen: %v\n", err)
								}
								if err := w.Write(ctx, conn, infoStr); err != nil {
									log.Printf("error sending screenHandler from cmd `info`: %v", err)
								}

							case "exit":
								exitStr, err := screenHandler("exit", nil)
								if err != nil {
									log.Printf("err loading exit screen: %v\n", err)
								}
								if err := w.Write(ctx, conn, exitStr); err != nil {
									log.Printf("error sending exitHandler from cmd `exit`: %v", err)
								}
								// wait a second before really closing the connection
								time.Sleep(time.Second)
								w.Free(conn)

							default:
								err := w.Write(ctx, conn, []byte("huh?\n\n> "))
								if err != nil {
									log.Printf("error writing to connection: %v", err)
								}
							}

						} else {
							// noop
							log.Printf("received on inChan: conn: %v, buffer: %v\n", res.Conn.RemoteAddr(), string(res.Buffer))
						}
					default:
						// noop - wait a lil bit
						time.Sleep(time.Millisecond)
					}
					if conn == nil {
						log.Println("conn is nil!")
					}
				}
			}
			time.Sleep(time.Millisecond)
		}
		log.Println("menu controlloop closed!")
	}(inChan, outChan, MenuControl)

	log.Println("menu waiting on waitgroup")
	wg.Wait()
	log.Println("terminating menucontrol for client")
}

// screenHandler handles non-interactive commands
// it takes a screen name and an optional struct of data to be parsed into the screen's template
// it returns the populated screen as a byte array and an error if there's a problem loading the template
// screen templates are simple text files with optional go template directives. if the text file includes
// ANSI control sequences they will be passed on to the remote client as well.
// TODO: add caching of static screens, move ANSI handling out to optional template directives as well
func screenHandler(screenName string, tplData interface{}) (screen []byte, err error) {
	var screenBuf *bytes.Buffer
	if tmpl, err := template.ParseFiles("screens/" + screenName + ".ans"); err != nil {
		log.Printf("err loading welcome template: %v\n", err) // // TODO: better error handling
	} else {
		screenBuf = new(bytes.Buffer)
		tmpl.Execute(screenBuf, tplData)
	}

	return screenBuf.Bytes(), err
}

// doorHandler handles interactive commands
// it halts the processing of the menuHandler and allows the doorHandler full duplex I/O
// between the remote connection and a local program's stdin/stdout
// doorHandler returns control to menuHandler once the program completes and exits
// TODO: add argument for program, program's prompt, launch text, and exit text
func doorHandler(ctx context.Context, c net.Conn, w *gaio.Watcher, menuwg *sync.WaitGroup) error {
	defer menuwg.Done()

	var wg sync.WaitGroup

	var inChan, _ chan gaio.OpResult
	var ok bool

	if inChan, _, ok = openconn.FromContext(ctx); !ok {
		log.Println("Could not get inChan/outChan from context!", ok, ctx) // TODO: better error handling
	}

	cmd := exec.Command("/usr/games/adventure") // TODO: move command path and args to an argument to doorHandler

	ptmx, err := pty.Start(cmd)
	if err != nil {
		return err
	}
	// Make sure to close the pty at the end.
	defer func() { _ = ptmx.Close() }() // Best effort.  TODO: better error handling, better zombie handling

	if term.IsTerminal(int(ptmx.Fd())) {
		oldState, _ := term.MakeRaw(int(ptmx.Fd()))
		defer term.Restore(int(ptmx.Fd()), oldState)
	}

	Terminator := make(chan bool)

	wg.Add(1)
	go func() {
		defer wg.Done()
		waitingForInput := false
	IOLoop:
		for {
			select {
			case result, ok := <-inChan:
				var l int
				if ok {
					if result.Operation == gaio.OpRead && result.Size > 0 {
						l, err = ptmx.Write(result.Buffer[:result.Size])
						if err != nil {
							if err == io.EOF {
								log.Println("EOF on cmd.write!!!") // TODO: better error handling
								break IOLoop
							}
						}
						if l > 0 {
							waitingForInput = false
						}

					}
				} else {
					log.Println("yikes, problem getting a result from inChan in doorHandler!") // TODO: better error handling
				}
			case <-Terminator:
				log.Println("Terminator'd!!!")
				break IOLoop
			default:
				if !waitingForInput {
					ptmx.SetReadDeadline(time.Now().Add(1 * time.Second))
					var l int
					outBuf := make([]byte, 4096)
					if l, err = ptmx.Read(outBuf); err != nil {
						if err == io.EOF {
							// EOF isn't actually an error in this case, it just means we're done
							break IOLoop
						} else if errors.Is(err, os.ErrDeadlineExceeded) {
							// output deadline exceeded - get some input instead
							w.Read(ctx, c, nil)
							waitingForInput = true
						} else if errors.Is(err, os.ErrClosed) {
							// program exited - get outta here
							break IOLoop
						} else {
							log.Printf("err reading from cmd term: %v\n", err) // TODO: better error handling
							break IOLoop
						}
					}
					if l > 0 {
						w.Write(ctx, c, outBuf[:l])
						if strings.Contains(string(outBuf[:l]), ">") { // TODO: abstract out prompt string as argument to doorHandler
							// a prompt appeared!
							waitingForInput = true
						}
					} else {
						// zero output? let's get some input opportunistically
						w.Read(ctx, c, nil)
					}
				}
			}
			time.Sleep(time.Millisecond)
		}
	}()
	wg.Wait()
	log.Println("waiting for cmd")
	exitErr := cmd.Wait()
	if exitErr != nil {
		log.Printf("cmd exited with err: %v\n", exitErr) // TODO: better error handling
	}
	log.Println("leaving door handler")
	return nil
}

// returns output of `uptime` as a string
func getUptime(wg *sync.WaitGroup) string {
	defer wg.Done()
	out, err := exec.Command("uptime").Output()
	if err != nil {
		return string(err.Error()) // TODO: better error handling
	}
	return string(out)
}

// returns output of a bash script that collects current wireguard peering connections and their traffic totals
func getTubePeers(wg *sync.WaitGroup) string {
	defer wg.Done()
	out, err := exec.Command("/usr/local/bin/getTubesPeers.bash").Output()
	outStr := ""
	// clean up the output formatting a little
	for _, line := range strings.Split(string(out), "\n") {
		formattedLine := ""
		for j, field := range strings.Fields(line) {
			switch j {
			case 0:
				formattedLine = field
			case 1:
				formattedLine += "\x1b[9G" + field
			case 2:
				offset := 10 - len(field) + 57
				formattedLine += "\x1b[" + fmt.Sprintf("%d", offset) + "G" + field
			case 3:
				offset := 10 - len(field) + 74
				formattedLine += "\x1b[" + fmt.Sprintf("%d", offset) + "G" + field
			}
		}
		outStr = outStr + formattedLine + "\n"
	}

	if err != nil {
		log.Printf("err loading getTubePeers: %v\n", err)
		return string(err.Error()) // TODO: better error handling
	}
	return outStr
}