smtp/conn.go

   1 package smtp
   2
   3 import (
   4         "crypto/rand"
   5         "crypto/tls"
   6         "fmt"
   7         "net"
   8         "net/mail"
   9         "net/textproto"
  10         "strings"
  11         "time"
  12
  13         "github.com/uber-go/zap"
  14 )
  15
  16 type state int
  17
  18 const (
  19         stateNew state = iota // Before EHLO.
  20         stateInitial
  21         stateMail
  22         stateRecipient
  23         stateData
  24 )
  25
  26 type connection struct {
  27         server Server
  28
  29         tp *textproto.Conn
  30
  31         nc         net.Conn
  32         remoteAddr net.Addr
  33
  34         esmtp bool
  35         tls   *tls.ConnectionState
  36
  37         log zap.Logger
  38
  39         state
  40         line string
  41
  42         ehlo     string
  43         mailFrom *mail.Address
  44         rcptTo   []mail.Address
  45 }
  46
  47 func AcceptConnection(netConn net.Conn, server Server, log zap.Logger) {
  48         conn := connection{
  49                 server:     server,
  50                 tp:         textproto.NewConn(netConn),
  51                 nc:         netConn,
  52                 remoteAddr: netConn.RemoteAddr(),
  53                 log:        log.With(zap.Stringer("client", netConn.RemoteAddr())),
  54                 state:      stateNew,
  55         }
  56
  57         conn.log.Info("accepted connection")
  58         conn.writeReply(220, fmt.Sprintf("%s ESMTP [%s] (mailpopbox)",
  59                 server.Name(), netConn.LocalAddr()))
  60
  61         for {
  62                 var err error
  63                 conn.line, err = conn.tp.ReadLine()
  64                 if err != nil {
  65                         conn.log.Error("ReadLine()", zap.Error(err))
  66                         conn.tp.Close()
  67                         return
  68                 }
  69
  70                 conn.log.Info("ReadLine()", zap.String("line", conn.line))
  71
  72                 var cmd string
  73                 if _, err = fmt.Sscanf(conn.line, "%s", &cmd); err != nil {
  74                         conn.reply(ReplyBadSyntax)
  75                         continue
  76                 }
  77
  78                 switch strings.ToUpper(cmd) {
  79                 case "QUIT":
  80                         conn.writeReply(221, "Goodbye")
  81                         conn.tp.Close()
  82                         return
  83                 case "HELO":
  84                         conn.esmtp = false
  85                         fallthrough
  86                 case "EHLO":
  87                         conn.esmtp = true
  88                         conn.doEHLO()
  89                 case "STARTTLS":
  90                         conn.doSTARTTLS()
  91                 case "MAIL":
  92                         conn.doMAIL()
  93                 case "RCPT":
  94                         conn.doRCPT()
  95                 case "DATA":
  96                         conn.doDATA()
  97                 case "RSET":
  98                         conn.doRSET()
  99                 case "VRFY":
 100                         conn.writeReply(252, "I'll do my best")
 101                 case "EXPN":
 102                         conn.writeReply(550, "access denied")
 103                 case "NOOP":
 104                         conn.reply(ReplyOK)
 105                 case "HELP":
 106                         conn.writeReply(250, "https://tools.ietf.org/html/rfc5321")
 107                 default:
 108                         conn.writeReply(500, "unrecognized command")
 109                 }
 110         }
 111 }
 112
 113 func (conn *connection) reply(reply ReplyLine) error {
 114         return conn.writeReply(reply.Code, reply.Message)
 115 }
 116
 117 func (conn *connection) writeReply(code int, msg string) error {
 118         conn.log.Info("writeReply", zap.Int("code", code))
 119         var err error
 120         if len(msg) > 0 {
 121                 err = conn.tp.PrintfLine("%d %s", code, msg)
 122         } else {
 123                 err = conn.tp.PrintfLine("%d", code)
 124         }
 125         if err != nil {
 126                 conn.log.Error("writeReply",
 127                         zap.Int("code", code),
 128                         zap.Error(err))
 129         }
 130         return err
 131 }
 132
 133 // parsePath parses out either a forward-, reverse-, or return-path from the
 134 // current connection line. Returns a (valid-path, ReplyOK) if it was
 135 // successfully parsed.
 136 func (conn *connection) parsePath(command string) (string, ReplyLine) {
 137         if len(conn.line) < len(command) {
 138                 return "", ReplyBadSyntax
 139         }
 140         if strings.ToUpper(command) != strings.ToUpper(conn.line[:len(command)]) {
 141                 return "", ReplyLine{500, "unrecognized command"}
 142         }
 143         params := conn.line[len(command):]
 144         idx := strings.Index(params, ">")
 145         if idx == -1 {
 146                 return "", ReplyBadSyntax
 147         }
 148         return strings.ToLower(params[:idx+1]), ReplyOK
 149 }
 150
 151 func (conn *connection) doEHLO() {
 152         conn.resetBuffers()
 153
 154         var cmd string
 155         _, err := fmt.Sscanf(conn.line, "%s %s", &cmd, &conn.ehlo)
 156         if err != nil {
 157                 conn.reply(ReplyBadSyntax)
 158                 return
 159         }
 160
 161         if cmd == "HELO" {
 162                 conn.writeReply(250, fmt.Sprintf("Hello %s [%s]", conn.ehlo, conn.remoteAddr))
 163         } else {
 164                 conn.tp.PrintfLine("250-Hello %s [%s]", conn.ehlo, conn.remoteAddr)
 165                 if conn.server.TLSConfig() != nil && conn.tls == nil {
 166                         conn.tp.PrintfLine("250-STARTTLS")
 167                 }
 168                 conn.tp.PrintfLine("250 SIZE %d", 40960000)
 169         }
 170
 171         conn.log.Info("doEHLO()", zap.String("ehlo", conn.ehlo))
 172
 173         conn.state = stateInitial
 174 }
 175
 176 func (conn *connection) doSTARTTLS() {
 177         if conn.state != stateInitial {
 178                 conn.reply(ReplyBadSequence)
 179                 return
 180         }
 181
 182         tlsConfig := conn.server.TLSConfig()
 183         if !conn.esmtp || tlsConfig == nil {
 184                 conn.writeReply(500, "unrecognized command")
 185                 return
 186         }
 187
 188         conn.log.Info("doSTARTTLS()")
 189         conn.writeReply(220, "initiate TLS connection")
 190
 191         tlsConn := tls.Server(conn.nc, tlsConfig)
 192         if err := tlsConn.Handshake(); err != nil {
 193                 conn.log.Error("failed to do TLS handshake", zap.Error(err))
 194                 return
 195         }
 196
 197         conn.nc = tlsConn
 198         conn.tp = textproto.NewConn(tlsConn)
 199         conn.state = stateNew
 200
 201         connState := tlsConn.ConnectionState()
 202         conn.tls = &connState
 203
 204         conn.log.Info("TLS connection done", zap.String("state", conn.getTransportString()))
 205 }
 206
 207 func (conn *connection) doMAIL() {
 208         if conn.state != stateInitial {
 209                 conn.reply(ReplyBadSequence)
 210                 return
 211         }
 212
 213         mailFrom, reply := conn.parsePath("MAIL FROM:")
 214         if reply != ReplyOK {
 215                 conn.reply(reply)
 216                 return
 217         }
 218
 219         var err error
 220         conn.mailFrom, err = mail.ParseAddress(mailFrom)
 221         if err != nil || conn.mailFrom == nil {
 222                 conn.reply(ReplyBadSyntax)
 223                 return
 224         }
 225
 226         conn.log.Info("doMAIL()", zap.String("address", conn.mailFrom.Address))
 227
 228         conn.state = stateMail
 229         conn.reply(ReplyOK)
 230 }
 231
 232 func (conn *connection) doRCPT() {
 233         if conn.state != stateMail && conn.state != stateRecipient {
 234                 conn.reply(ReplyBadSequence)
 235                 return
 236         }
 237
 238         rcptTo, reply := conn.parsePath("RCPT TO:")
 239         if reply != ReplyOK {
 240                 conn.reply(reply)
 241                 return
 242         }
 243
 244         address, err := mail.ParseAddress(rcptTo)
 245         if err != nil {
 246                 conn.reply(ReplyBadSyntax)
 247                 return
 248         }
 249
 250         if reply := conn.server.VerifyAddress(*address); reply != ReplyOK {
 251                 conn.log.Warn("invalid address",
 252                         zap.String("address", address.Address),
 253                         zap.Stringer("reply", reply))
 254                 conn.reply(reply)
 255                 return
 256         }
 257
 258         conn.log.Info("doRCPT()", zap.String("address", address.Address))
 259
 260         conn.rcptTo = append(conn.rcptTo, *address)
 261
 262         conn.state = stateRecipient
 263         conn.reply(ReplyOK)
 264 }
 265
 266 func (conn *connection) doDATA() {
 267         if conn.state != stateRecipient {
 268                 conn.reply(ReplyBadSequence)
 269                 return
 270         }
 271
 272         conn.writeReply(354, "Start mail input; end with <CRLF>.<CRLF>")
 273         conn.log.Info("doDATA()")
 274
 275         data, err := conn.tp.ReadDotBytes()
 276         if err != nil {
 277                 conn.log.Error("failed to ReadDotBytes()",
 278                         zap.Error(err),
 279                         zap.String("bytes", fmt.Sprintf("%x", data)))
 280                 conn.writeReply(552, "transaction failed")
 281                 return
 282         }
 283
 284         received := time.Now()
 285         env := Envelope{
 286                 RemoteAddr: conn.remoteAddr,
 287                 EHLO:       conn.ehlo,
 288                 MailFrom:   *conn.mailFrom,
 289                 RcptTo:     conn.rcptTo,
 290                 Received:   received,
 291                 ID:         conn.envelopeID(received),
 292         }
 293
 294         conn.log.Info("received message",
 295                 zap.Int("bytes", len(data)),
 296                 zap.Time("date", received),
 297                 zap.String("id", env.ID))
 298
 299         trace := conn.getReceivedInfo(env)
 300
 301         env.Data = append(trace, data...)
 302
 303         if reply := conn.server.OnMessageDelivered(env); reply != nil {
 304                 conn.log.Warn("message was rejected", zap.String("id", env.ID))
 305                 conn.reply(*reply)
 306                 return
 307         }
 308
 309         conn.state = stateInitial
 310         conn.reply(ReplyOK)
 311 }
 312
 313 func (conn *connection) envelopeID(t time.Time) string {
 314         var idBytes [4]byte
 315         rand.Read(idBytes[:])
 316         return fmt.Sprintf("m.%d.%x", t.UnixNano(), idBytes)
 317 }
 318
 319 func (conn *connection) getReceivedInfo(envelope Envelope) []byte {
 320         rhost, _, err := net.SplitHostPort(conn.remoteAddr.String())
 321         if err != nil {
 322                 rhost = conn.remoteAddr.String()
 323         }
 324
 325         rhosts, err := net.LookupAddr(rhost)
 326         if err == nil {
 327                 rhost = fmt.Sprintf("%s [%s]", rhosts[0], rhost)
 328         }
 329
 330         base := fmt.Sprintf("Received: from %s (%s)\r\n        ", conn.ehlo, rhost)
 331
 332         with := "SMTP"
 333         if conn.esmtp {
 334                 with = "E" + with
 335         }
 336         if conn.tls != nil {
 337                 with += "S"
 338         }
 339         base += fmt.Sprintf("by %s (mailpopbox) with %s id %s\r\n        ", conn.server.Name(), with, envelope.ID)
 340
 341         base += fmt.Sprintf("for <%s>\r\n        ", envelope.RcptTo[0].Address)
 342
 343         transport := conn.getTransportString()
 344         date := envelope.Received.Format(time.RFC1123Z) // Same as RFC 5322 § 3.3
 345         base += fmt.Sprintf("(using %s);\r\n        %s\r\n", transport, date)
 346
 347         return []byte(base)
 348 }
 349
 350 func (conn *connection) getTransportString() string {
 351         if conn.tls == nil {
 352                 return "PLAINTEXT"
 353         }
 354
 355         ciphers := map[uint16]string{
 356                 tls.TLS_RSA_WITH_RC4_128_SHA:                "TLS_RSA_WITH_RC4_128_SHA",
 357                 tls.TLS_RSA_WITH_3DES_EDE_CBC_SHA:           "TLS_RSA_WITH_3DES_EDE_CBC_SHA",
 358                 tls.TLS_RSA_WITH_AES_128_CBC_SHA:            "TLS_RSA_WITH_AES_128_CBC_SHA",
 359                 tls.TLS_RSA_WITH_AES_256_CBC_SHA:            "TLS_RSA_WITH_AES_256_CBC_SHA",
 360                 tls.TLS_RSA_WITH_AES_128_GCM_SHA256:         "TLS_RSA_WITH_AES_128_GCM_SHA256",
 361                 tls.TLS_RSA_WITH_AES_256_GCM_SHA384:         "TLS_RSA_WITH_AES_256_GCM_SHA384",
 362                 tls.TLS_ECDHE_ECDSA_WITH_RC4_128_SHA:        "TLS_ECDHE_ECDSA_WITH_RC4_128_SHA",
 363                 tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA:    "TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA",
 364                 tls.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA:    "TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA",
 365                 tls.TLS_ECDHE_RSA_WITH_RC4_128_SHA:          "TLS_ECDHE_RSA_WITH_RC4_128_SHA",
 366                 tls.TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA:     "TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA",
 367                 tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA:      "TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA",
 368                 tls.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA:      "TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA",
 369                 tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256:   "TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256",
 370                 tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256: "TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256",
 371                 tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384:   "TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384",
 372                 tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384: "TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384",
 373         }
 374         versions := map[uint16]string{
 375                 tls.VersionSSL30: "SSLv3.0",
 376                 tls.VersionTLS10: "TLSv1.0",
 377                 tls.VersionTLS11: "TLSv1.1",
 378                 tls.VersionTLS12: "TLSv1.2",
 379         }
 380
 381         state := conn.tls
 382
 383         version := versions[state.Version]
 384         cipher := ciphers[state.CipherSuite]
 385
 386         if version == "" {
 387                 version = fmt.Sprintf("%x", state.Version)
 388         }
 389         if cipher == "" {
 390                 cipher = fmt.Sprintf("%x", state.CipherSuite)
 391         }
 392
 393         name := ""
 394         if state.ServerName != "" {
 395                 name = fmt.Sprintf(" name=%s", state.ServerName)
 396         }
 397
 398         return fmt.Sprintf("%s cipher=%s%s", version, cipher, name)
 399 }
 400
 401 func (conn *connection) doRSET() {
 402         conn.log.Info("doRSET()")
 403         conn.state = stateInitial
 404         conn.resetBuffers()
 405         conn.reply(ReplyOK)
 406 }
 407
 408 func (conn *connection) resetBuffers() {
 409         conn.mailFrom = nil
 410         conn.rcptTo = make([]mail.Address, 0)
 411 }