/
bot.go
601 lines (571 loc) · 18.5 KB
/
bot.go
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// Package bot provides the replbot main functionality
package bot
import (
"context"
_ "embed" // go:embed requires this
"errors"
"fmt"
"github.com/gliderlabs/ssh"
gossh "golang.org/x/crypto/ssh"
"golang.org/x/sync/errgroup"
"heckel.io/replbot/config"
"heckel.io/replbot/util"
"log"
"net"
"net/http"
"net/http/httputil"
"os"
"strings"
"sync"
)
const (
welcomeMessage = "Hi there 👋! "
mentionMessage = "I'm a robot for running interactive REPLs and shells from right here. To start a new session, simply tag me " +
"and name one of the available REPLs, like so: %s %s\n\nAvailable REPLs: %s.\n\nTo run the session in a `thread`, " +
"the main `channel`, or in `split` mode, use the respective keywords (default: `%s`). To define the terminal size, use the words " +
"`tiny`, `small`, `medium` or `large` (default: `%s`). Use `full` or `trim` to set the window mode (default: `%s`), and `everyone` " +
"or `only-me` to define who can send commands (default: `%s`). Send `record` or `norecord` to define if your session should be " +
"recorded (default: `%s`)."
webMessage = "Use the word `web` or `noweb` to enable a web-based terminal for this session (default: `%s`)."
shareMessage = "Using the word `share` will allow you to share your own terminal here in the chat. Terminal sharing " +
"sessions are always started in `only-me` mode, unless overridden."
unknownCommandMessage = "I am not quite sure what you mean by _%s_ ⁉"
misconfiguredMessage = "😭 Oh no. It looks like REPLbot is misconfigured. I couldn't find any scripts to run."
maxTotalSessionsExceededMessage = "😭 There are too many active sessions. Please wait until another session is closed."
maxUserSessionsExceededMessage = "😭 You have too many active sessions. Please close a session to start a new one."
helpRequestedCommand = "help"
recordCommand = "record"
noRecordCommand = "norecord"
webCommand = "web"
noWebCommand = "noweb"
shareCommand = "share"
shareServerScriptFile = "/tmp/replbot_share_server.sh"
)
// Key exchange algorithms, ciphers,and MACs (see `ssh-audit` output)
const (
kexCurve25519SHA256 = "curve25519-sha256@libssh.org"
macHMACSHA256ETM = "hmac-sha2-256-etm@openssh.com"
cipherAES128GCM = "aes128-gcm@openssh.com"
cipherSSHRSA = "ssh-rsa"
cipherED25519 = "ssh-ed25519"
sshVersion = "OpenSSH_7.6p1" // fake!
)
var (
//go:embed share_server.sh
shareServerScriptSource string
errNoScript = errors.New("no script defined")
errHelpRequested = errors.New("help requested")
)
// Bot is the main struct that provides REPLbot
type Bot struct {
config *config.Config
conn conn
sessions map[string]*session
shareUser map[string]*session
webPrefix map[string]*session
cancelFn context.CancelFunc
mu sync.RWMutex
}
// New creates a new REPLbot instance using the given configuration
func New(conf *config.Config) (*Bot, error) {
if len(conf.Scripts()) == 0 {
return nil, errors.New("no REPL scripts found in script dir")
} else if err := util.Run("tmux", "-V"); err != nil {
return nil, fmt.Errorf("tmux check failed: %s", err.Error())
}
var conn conn
switch conf.Platform() {
case config.Slack:
conn = newSlackConn(conf)
case config.Discord:
conn = newDiscordConn(conf)
case config.Mem:
conn = newMemConn(conf)
default:
return nil, fmt.Errorf("invalid type: %s", conf.Platform())
}
return &Bot{
config: conf,
conn: conn,
sessions: make(map[string]*session),
shareUser: make(map[string]*session),
webPrefix: make(map[string]*session),
}, nil
}
// Run runs the bot in the foreground indefinitely or until Stop is called.
// This method does not return unless there is an error, or if gracefully shut down via Stop.
func (b *Bot) Run() error {
var ctx context.Context
ctx, b.cancelFn = context.WithCancel(context.Background())
g, ctx := errgroup.WithContext(ctx)
eventChan, err := b.conn.Connect(ctx)
if err != nil {
return err
}
g.Go(func() error {
return b.handleEvents(ctx, eventChan)
})
if b.config.ShareHost != "" {
g.Go(func() error {
return b.runShareServer(ctx)
})
}
if b.config.WebHost != "" {
g.Go(func() error {
return b.runWebServer(ctx)
})
}
return g.Wait()
}
// Stop gracefully shuts down the bot, closing all active sessions gracefully
func (b *Bot) Stop() {
b.mu.Lock()
defer b.mu.Unlock()
for sessionID, sess := range b.sessions {
log.Printf("[%s] Force-closing session", sessionID)
if err := sess.ForceClose(); err != nil {
log.Printf("[%s] Force-closing failed: %s", sessionID, err.Error())
}
delete(b.sessions, sessionID)
if sess.conf.share != nil {
delete(b.shareUser, sess.conf.share.user)
}
if sess.webPrefix != "" {
delete(b.webPrefix, sess.webPrefix)
}
}
b.cancelFn() // This must be at the end, see app.go
}
func (b *Bot) handleEvents(ctx context.Context, eventChan <-chan event) error {
for {
select {
case <-ctx.Done():
return nil
case ev := <-eventChan:
if err := b.handleEvent(ev); err != nil {
return err
}
}
}
}
func (b *Bot) handleEvent(e event) error {
switch ev := e.(type) {
case *messageEvent:
return b.handleMessageEvent(ev)
case *errorEvent:
return ev.Error
default:
return nil // Ignore other events
}
}
func (b *Bot) handleMessageEvent(ev *messageEvent) error {
if b.maybeForwardMessage(ev) {
return nil // We forwarded the message
} else if ev.ChannelType == channelTypeUnknown {
return nil
} else if ev.ChannelType == channelTypeChannel && !strings.Contains(ev.Message, b.conn.MentionBot()) {
return nil
}
conf, err := b.parseSessionConfig(ev)
if err != nil {
return b.handleHelp(ev.Channel, ev.Thread, err)
}
if allowed, err := b.checkSessionAllowed(ev.Channel, ev.Thread, conf); err != nil || !allowed {
return err
}
switch conf.controlMode {
case config.Channel:
return b.startSessionChannel(ev, conf)
case config.Thread:
return b.startSessionThread(ev, conf)
case config.Split:
return b.startSessionSplit(ev, conf)
default:
return fmt.Errorf("unexpected mode: %s", conf.controlMode)
}
}
func (b *Bot) maybeForwardMessage(ev *messageEvent) bool {
b.mu.Lock()
defer b.mu.Unlock()
sessionID := util.SanitizeNonAlphanumeric(fmt.Sprintf("%s_%s", ev.Channel, ev.Thread)) // Thread may be empty, that's ok
if sess, ok := b.sessions[sessionID]; ok && sess.Active() {
sess.UserInput(ev.User, ev.Message)
return true
}
return false
}
func (b *Bot) parseSessionConfig(ev *messageEvent) (*sessionConfig, error) {
conf := &sessionConfig{
global: b.config,
user: ev.User,
record: b.config.DefaultRecord,
web: b.config.DefaultWeb,
notifyWeb: b.webUpdated,
}
fields := strings.Fields(ev.Message)
for _, field := range fields {
switch field {
case b.conn.MentionBot():
// Ignore
case helpRequestedCommand:
return nil, errHelpRequested
case string(config.Thread), string(config.Channel), string(config.Split):
conf.controlMode = config.ControlMode(field)
case string(config.Full), string(config.Trim):
conf.windowMode = config.WindowMode(field)
case string(config.OnlyMe), string(config.Everyone):
conf.authMode = config.AuthMode(field)
case config.Tiny.Name, config.Small.Name, config.Medium.Name, config.Large.Name:
conf.size = config.Sizes[field]
case recordCommand, noRecordCommand:
conf.record = field == recordCommand
default:
if b.config.ShareEnabled() && field == shareCommand {
relayPort, err := util.RandomPort()
if err != nil {
return nil, err
}
hostKeyPair, err := util.GenerateSSHKeyPair()
if err != nil {
return nil, err
}
clientKeyPair, err := util.GenerateSSHKeyPair()
if err != nil {
return nil, err
}
conf.script = shareServerScriptFile
conf.share = &shareConfig{
user: util.RandomString(10),
relayPort: relayPort,
hostKeyPair: hostKeyPair,
clientKeyPair: clientKeyPair,
}
} else if b.config.WebHost != "" && (field == webCommand || field == noWebCommand) {
conf.web = field == webCommand
} else if s := b.config.Script(field); conf.script == "" && s != "" {
conf.script = s
} else {
return nil, fmt.Errorf(unknownCommandMessage, field) //lint:ignore ST1005 we'll pass this to the client
}
}
}
if conf.script == "" {
return nil, errNoScript
}
return b.applySessionConfigDefaults(ev, conf)
}
func (b *Bot) applySessionConfigDefaults(ev *messageEvent, conf *sessionConfig) (*sessionConfig, error) {
if conf.share != nil { // sane defaults for terminal sharing
if conf.authMode == "" {
conf.authMode = config.OnlyMe
}
}
if conf.controlMode == "" {
if ev.Thread != "" {
conf.controlMode = config.Thread // special handling, because it'd be weird otherwise
} else {
conf.controlMode = b.config.DefaultControlMode
}
}
if b.config.Platform() == config.Discord && ev.ChannelType == channelTypeDM && conf.controlMode != config.Channel {
conf.controlMode = config.Channel // special case: Discord does not support threads in direct messages
}
if conf.windowMode == "" {
if conf.controlMode == config.Thread {
conf.windowMode = config.Trim
} else {
conf.windowMode = b.config.DefaultWindowMode
}
}
if conf.authMode == "" {
conf.authMode = b.config.DefaultAuthMode
}
if conf.size == nil {
if conf.controlMode == config.Thread {
conf.size = config.Tiny // special case: make it tiny in a thread
} else {
conf.size = b.config.DefaultSize
}
}
return conf, nil
}
func (b *Bot) startSessionChannel(ev *messageEvent, conf *sessionConfig) error {
conf.id = util.SanitizeNonAlphanumeric(fmt.Sprintf("%s_%s", ev.Channel, ""))
conf.control = &channelID{Channel: ev.Channel, Thread: ""}
conf.terminal = conf.control
return b.startSession(conf)
}
func (b *Bot) startSessionThread(ev *messageEvent, conf *sessionConfig) error {
if ev.Thread == "" {
conf.id = util.SanitizeNonAlphanumeric(fmt.Sprintf("%s_%s", ev.Channel, ev.ID))
conf.control = &channelID{Channel: ev.Channel, Thread: ev.ID}
conf.terminal = conf.control
return b.startSession(conf)
}
conf.id = util.SanitizeNonAlphanumeric(fmt.Sprintf("%s_%s", ev.Channel, ev.Thread))
conf.control = &channelID{Channel: ev.Channel, Thread: ev.Thread}
conf.terminal = conf.control
return b.startSession(conf)
}
func (b *Bot) startSessionSplit(ev *messageEvent, conf *sessionConfig) error {
if ev.Thread == "" {
conf.id = util.SanitizeNonAlphanumeric(fmt.Sprintf("%s_%s", ev.Channel, ev.ID))
conf.control = &channelID{Channel: ev.Channel, Thread: ev.ID}
conf.terminal = &channelID{Channel: ev.Channel, Thread: ""}
return b.startSession(conf)
}
conf.id = util.SanitizeNonAlphanumeric(fmt.Sprintf("%s_%s", ev.Channel, ev.Thread))
conf.control = &channelID{Channel: ev.Channel, Thread: ev.Thread}
conf.terminal = &channelID{Channel: ev.Channel, Thread: ""}
return b.startSession(conf)
}
func (b *Bot) startSession(conf *sessionConfig) error {
b.mu.Lock()
defer b.mu.Unlock()
sess := newSession(conf, b.conn)
b.sessions[conf.id] = sess
if conf.share != nil {
b.shareUser[conf.share.user] = sess
}
log.Printf("[%s] Starting session, requested by %s", conf.id, conf.user)
go func() {
if err := sess.Run(); err != nil {
log.Printf("[%s] Session exited with error: %s", conf.id, err.Error())
} else {
log.Printf("[%s] Session exited successfully", conf.id)
}
b.mu.Lock()
delete(b.sessions, conf.id)
if conf.share != nil {
delete(b.shareUser, conf.share.user)
}
if sess.webPrefix != "" {
delete(b.webPrefix, sess.webPrefix)
}
b.mu.Unlock()
}()
return nil
}
func (b *Bot) handleHelp(channel, thread string, err error) error {
target := &channelID{Channel: channel, Thread: thread}
scripts := b.config.Scripts()
if len(scripts) == 0 {
return b.conn.Send(target, misconfiguredMessage)
}
var messageTemplate string
if err == nil || err == errNoScript || err == errHelpRequested {
messageTemplate = welcomeMessage + mentionMessage
} else {
messageTemplate = err.Error() + "\n\n" + mentionMessage
}
if b.config.WebHost != "" {
defaultWebCommand := webCommand
if !b.config.DefaultWeb {
defaultWebCommand = noWebCommand
}
messageTemplate += " " + fmt.Sprintf(webMessage, defaultWebCommand)
}
if b.config.ShareEnabled() {
messageTemplate += "\n\n" + shareMessage
scripts = append(scripts, shareCommand)
}
replList := fmt.Sprintf("`%s`", strings.Join(scripts, "`, `"))
defaultRecordCommand := recordCommand
if !b.config.DefaultRecord {
defaultRecordCommand = noRecordCommand
}
message := fmt.Sprintf(messageTemplate, b.conn.MentionBot(), scripts[0], replList, b.config.DefaultControlMode, b.config.DefaultSize.Name, b.config.DefaultWindowMode, b.config.DefaultAuthMode, defaultRecordCommand)
return b.conn.Send(target, message)
}
func (b *Bot) runWebServer(ctx context.Context) error {
_, port, err := net.SplitHostPort(b.config.WebHost)
if err != nil {
return err
}
if port == "" {
port = "80"
}
errChan := make(chan error)
go func() {
http.HandleFunc("/", b.webHandler)
errChan <- http.ListenAndServe(":"+port, nil)
}()
select {
case err := <-errChan:
return err
case <-ctx.Done():
return nil
}
}
func (b *Bot) webHandler(w http.ResponseWriter, r *http.Request) {
if err := b.webHandlerInternal(w, r); err != nil {
log.Printf("[web] error: %s, returning 404", err.Error())
http.NotFound(w, r)
}
}
func (b *Bot) webHandlerInternal(w http.ResponseWriter, r *http.Request) error {
parts := strings.Split(r.URL.Path, "/")
if len(parts) < 2 {
return errors.New("invalid prefix")
}
prefix := parts[1]
b.mu.RLock()
var webPort int
session := b.webPrefix[prefix]
if session != nil {
webPort = session.webPort
}
b.mu.RUnlock()
if session == nil || webPort == 0 {
return fmt.Errorf("session with prefix %s not found", prefix)
}
if len(parts) < 3 { // must be /prefix/, not just /prefix
http.Redirect(w, r, r.URL.String()+"/", http.StatusTemporaryRedirect)
return nil
}
proxy := &httputil.ReverseProxy{Director: func(r *http.Request) {
r.URL.Scheme = "http"
r.URL.Host = fmt.Sprintf("127.0.0.1:%d", webPort)
r.URL.Path = strings.TrimPrefix(r.URL.Path, "/"+prefix)
r.URL.RawPath = strings.TrimPrefix(r.URL.Path, "/"+prefix)
r.Header.Set("Origin", fmt.Sprintf("http://%s", b.config.WebHost))
}}
proxy.ServeHTTP(w, r)
return nil
}
func (b *Bot) runShareServer(ctx context.Context) error {
if err := os.WriteFile(shareServerScriptFile, []byte(shareServerScriptSource), 0700); err != nil {
return err
}
_, port, err := net.SplitHostPort(b.config.ShareHost)
if err != nil {
return err
}
server, err := b.sshServer(port)
if err != nil {
return err
}
errChan := make(chan error)
go func() {
errChan <- server.ListenAndServe()
}()
select {
case err := <-errChan:
return err
case <-ctx.Done():
return nil
}
}
func (b *Bot) sshServer(port string) (*ssh.Server, error) {
forwardHandler := &ssh.ForwardedTCPHandler{}
server := &ssh.Server{
Addr: fmt.Sprintf(":%s", port),
Version: sshVersion,
PasswordHandler: nil,
PublicKeyHandler: nil,
KeyboardInteractiveHandler: nil,
PtyCallback: b.sshPtyCallback,
ReversePortForwardingCallback: b.sshReversePortForwardingCallback,
Handler: b.sshSessionHandler,
ServerConfigCallback: b.sshServerConfigCallback,
RequestHandlers: map[string]ssh.RequestHandler{
"tcpip-forward": forwardHandler.HandleSSHRequest,
"cancel-tcpip-forward": forwardHandler.HandleSSHRequest,
},
ChannelHandlers: map[string]ssh.ChannelHandler{
"session": ssh.DefaultSessionHandler,
},
}
if err := server.SetOption(ssh.HostKeyFile(b.config.ShareKeyFile)); err != nil {
return nil, err
}
return server, nil
}
// sshSessionHandler is the main SSH session handler. It returns the share script which creates a local tmux session
// and opens the reverse tunnel. The session is identified by the SSH user name. If the session is not found, the
// handler exits immediately.
func (b *Bot) sshSessionHandler(s ssh.Session) {
b.mu.RLock()
defer b.mu.RUnlock()
sess, ok := b.shareUser[s.User()]
if !ok {
return
}
if len(s.Command()) != 1 {
return
}
clientUser := s.Command()[0]
if err := sess.WriteShareUserFile(clientUser); err != nil {
log.Printf("cannot write share user file: %s", err.Error())
return
}
if err := sess.WriteShareClientScript(s); err != nil {
log.Printf("cannot write session script: %s", err.Error())
return
}
}
// sshReversePortForwardingCallback checks if the requested reverse tunnel host/port (ssh -R) matches the one
// that was assigned in the REPL share session and rejects/closes the connection if it doesn't
func (b *Bot) sshReversePortForwardingCallback(ctx ssh.Context, host string, port uint32) (allow bool) {
conn, ok := ctx.Value(ssh.ContextKeyConn).(*gossh.ServerConn)
if !ok {
return false
}
defer func() {
if !allow {
log.Printf("rejecting connection %s", conn.RemoteAddr())
conn.Close()
}
}()
if port < 1024 || (host != "localhost" && host != "127.0.0.1") {
return
}
b.mu.RLock()
defer b.mu.RUnlock()
sess, ok := b.shareUser[ctx.User()]
if !ok || sess.conf.share == nil || sess.conf.share.relayPort != int(port) {
return
}
sess.RegisterShareConn(conn)
return true
}
// sshPtyCallback always returns false, thereby refusing any SSH client attempt to request a TTY
func (b *Bot) sshPtyCallback(ctx ssh.Context, pty ssh.Pty) bool {
return false
}
// sshServerConfigCallback configures the SSH server algorithms to be more secure (see `ssh-audit` output)
func (b *Bot) sshServerConfigCallback(ctx ssh.Context) *gossh.ServerConfig {
conf := &gossh.ServerConfig{}
conf.KeyExchanges = []string{kexCurve25519SHA256}
conf.Ciphers = []string{cipherAES128GCM, cipherED25519, cipherSSHRSA}
conf.MACs = []string{macHMACSHA256ETM}
return conf
}
func (b *Bot) checkSessionAllowed(channel, thread string, conf *sessionConfig) (allowed bool, err error) {
b.mu.RLock()
defer b.mu.RUnlock()
if len(b.sessions) >= b.config.MaxTotalSessions {
ch := &channelID{Channel: channel, Thread: thread}
return false, b.conn.Send(ch, maxTotalSessionsExceededMessage)
}
var userSessions int
for _, sess := range b.sessions {
if sess.conf.user == conf.user {
userSessions++
}
}
if userSessions >= b.config.MaxUserSessions {
ch := &channelID{Channel: channel, Thread: thread}
return false, b.conn.Send(ch, maxUserSessionsExceededMessage)
}
return true, nil
}
func (b *Bot) webUpdated(s *session, enabled bool, prefix string) {
b.mu.Lock()
defer b.mu.Unlock()
if enabled {
b.webPrefix[prefix] = s
} else {
delete(b.webPrefix, prefix)
}
}