smtp/conn.go

   1 // mailpopbox
   2 // Copyright 2020 Blue Static <https://www.bluestatic.org>
   3 // This program is free software licensed under the GNU General Public License,
   4 // version 3.0. The full text of the license can be found in LICENSE.txt.
   5 // SPDX-License-Identifier: GPL-3.0-only
   6
   7 package smtp
   8
   9 import (
  10         "crypto/rand"
  11         "crypto/tls"
  12         "fmt"
  13         "net"
  14         "net/mail"
  15         "net/textproto"
  16         "strings"
  17         "time"
  18
  19         "go.uber.org/zap"
  20 )
  21
  22 type state int
  23
  24 const (
  25         stateNew state = iota // Before EHLO.
  26         stateInitial
  27         stateMail
  28         stateRecipient
  29         stateData
  30 )
  31
  32 type connection struct {
  33         server Server
  34
  35         tp *textproto.Conn
  36
  37         nc         net.Conn
  38         remoteAddr net.Addr
  39
  40         esmtp bool
  41         tls   *tls.ConnectionState
  42
  43         log *zap.Logger
  44
  45         state
  46         line string
  47
  48         ehlo     string
  49         mailFrom *mail.Address
  50         rcptTo   []mail.Address
  51 }
  52
  53 func AcceptConnection(netConn net.Conn, server Server, log *zap.Logger) {
  54         conn := connection{
  55                 server:     server,
  56                 tp:         textproto.NewConn(netConn),
  57                 nc:         netConn,
  58                 remoteAddr: netConn.RemoteAddr(),
  59                 log:        log.With(zap.Stringer("client", netConn.RemoteAddr())),
  60                 state:      stateNew,
  61         }
  62
  63         conn.log.Info("accepted connection")
  64         conn.writeReply(220, fmt.Sprintf("%s ESMTP [%s] (mailpopbox)",
  65                 server.Name(), netConn.LocalAddr()))
  66
  67         for {
  68                 var err error
  69                 conn.line, err = conn.tp.ReadLine()
  70                 if err != nil {
  71                         conn.log.Error("ReadLine()", zap.Error(err))
  72                         conn.tp.Close()
  73                         return
  74                 }
  75
  76                 conn.log.Info("ReadLine()", zap.String("line", conn.line))
  77
  78                 var cmd string
  79                 if _, err = fmt.Sscanf(conn.line, "%s", &cmd); err != nil {
  80                         conn.reply(ReplyBadSyntax)
  81                         continue
  82                 }
  83
  84                 switch strings.ToUpper(cmd) {
  85                 case "QUIT":
  86                         conn.writeReply(221, "Goodbye")
  87                         conn.tp.Close()
  88                         return
  89                 case "HELO":
  90                         conn.esmtp = false
  91                         fallthrough
  92                 case "EHLO":
  93                         conn.esmtp = true
  94                         conn.doEHLO()
  95                 case "STARTTLS":
  96                         conn.doSTARTTLS()
  97                 case "MAIL":
  98                         conn.doMAIL()
  99                 case "RCPT":
 100                         conn.doRCPT()
 101                 case "DATA":
 102                         conn.doDATA()
 103                 case "RSET":
 104                         conn.doRSET()
 105                 case "VRFY":
 106                         conn.writeReply(252, "I'll do my best")
 107                 case "EXPN":
 108                         conn.writeReply(550, "access denied")
 109                 case "NOOP":
 110                         conn.reply(ReplyOK)
 111                 case "HELP":
 112                         conn.writeReply(250, "https://tools.ietf.org/html/rfc5321")
 113                 default:
 114                         conn.writeReply(500, "unrecognized command")
 115                 }
 116         }
 117 }
 118
 119 func (conn *connection) reply(reply ReplyLine) error {
 120         return conn.writeReply(reply.Code, reply.Message)
 121 }
 122
 123 func (conn *connection) writeReply(code int, msg string) error {
 124         conn.log.Info("writeReply", zap.Int("code", code))
 125         var err error
 126         if len(msg) > 0 {
 127                 err = conn.tp.PrintfLine("%d %s", code, msg)
 128         } else {
 129                 err = conn.tp.PrintfLine("%d", code)
 130         }
 131         if err != nil {
 132                 conn.log.Error("writeReply",
 133                         zap.Int("code", code),
 134                         zap.Error(err))
 135         }
 136         return err
 137 }
 138
 139 // parsePath parses out either a forward-, reverse-, or return-path from the
 140 // current connection line. Returns a (valid-path, ReplyOK) if it was
 141 // successfully parsed.
 142 func (conn *connection) parsePath(command string) (string, ReplyLine) {
 143         if len(conn.line) < len(command) {
 144                 return "", ReplyBadSyntax
 145         }
 146         if strings.ToUpper(command) != strings.ToUpper(conn.line[:len(command)]) {
 147                 return "", ReplyLine{500, "unrecognized command"}
 148         }
 149         params := conn.line[len(command):]
 150         idx := strings.Index(params, ">")
 151         if idx == -1 {
 152                 return "", ReplyBadSyntax
 153         }
 154         return strings.ToLower(params[:idx+1]), ReplyOK
 155 }
 156
 157 func (conn *connection) doEHLO() {
 158         conn.resetBuffers()
 159
 160         var cmd string
 161         _, err := fmt.Sscanf(conn.line, "%s %s", &cmd, &conn.ehlo)
 162         if err != nil {
 163                 conn.reply(ReplyBadSyntax)
 164                 return
 165         }
 166
 167         if cmd == "HELO" {
 168                 conn.writeReply(250, fmt.Sprintf("Hello %s [%s]", conn.ehlo, conn.remoteAddr))
 169         } else {
 170                 conn.tp.PrintfLine("250-Hello %s [%s]", conn.ehlo, conn.remoteAddr)
 171                 if conn.server.TLSConfig() != nil && conn.tls == nil {
 172                         conn.tp.PrintfLine("250-STARTTLS")
 173                 }
 174                 conn.tp.PrintfLine("250 SIZE %d", 40960000)
 175         }
 176
 177         conn.log.Info("doEHLO()", zap.String("ehlo", conn.ehlo))
 178
 179         conn.state = stateInitial
 180 }
 181
 182 func (conn *connection) doSTARTTLS() {
 183         if conn.state != stateInitial {
 184                 conn.reply(ReplyBadSequence)
 185                 return
 186         }
 187
 188         tlsConfig := conn.server.TLSConfig()
 189         if !conn.esmtp || tlsConfig == nil {
 190                 conn.writeReply(500, "unrecognized command")
 191                 return
 192         }
 193
 194         conn.log.Info("doSTARTTLS()")
 195         conn.writeReply(220, "initiate TLS connection")
 196
 197         tlsConn := tls.Server(conn.nc, tlsConfig)
 198         if err := tlsConn.Handshake(); err != nil {
 199                 conn.log.Error("failed to do TLS handshake", zap.Error(err))
 200                 return
 201         }
 202
 203         conn.nc = tlsConn
 204         conn.tp = textproto.NewConn(tlsConn)
 205         conn.state = stateNew
 206
 207         connState := tlsConn.ConnectionState()
 208         conn.tls = &connState
 209
 210         conn.log.Info("TLS connection done", zap.String("state", conn.getTransportString()))
 211 }
 212
 213 func (conn *connection) doMAIL() {
 214         if conn.state != stateInitial {
 215                 conn.reply(ReplyBadSequence)
 216                 return
 217         }
 218
 219         mailFrom, reply := conn.parsePath("MAIL FROM:")
 220         if reply != ReplyOK {
 221                 conn.reply(reply)
 222                 return
 223         }
 224
 225         var err error
 226         conn.mailFrom, err = mail.ParseAddress(mailFrom)
 227         if err != nil || conn.mailFrom == nil {
 228                 conn.reply(ReplyBadSyntax)
 229                 return
 230         }
 231
 232         conn.log.Info("doMAIL()", zap.String("address", conn.mailFrom.Address))
 233
 234         conn.state = stateMail
 235         conn.reply(ReplyOK)
 236 }
 237
 238 func (conn *connection) doRCPT() {
 239         if conn.state != stateMail && conn.state != stateRecipient {
 240                 conn.reply(ReplyBadSequence)
 241                 return
 242         }
 243
 244         rcptTo, reply := conn.parsePath("RCPT TO:")
 245         if reply != ReplyOK {
 246                 conn.reply(reply)
 247                 return
 248         }
 249
 250         address, err := mail.ParseAddress(rcptTo)
 251         if err != nil {
 252                 conn.reply(ReplyBadSyntax)
 253                 return
 254         }
 255
 256         if reply := conn.server.VerifyAddress(*address); reply != ReplyOK {
 257                 conn.log.Warn("invalid address",
 258                         zap.String("address", address.Address),
 259                         zap.Stringer("reply", reply))
 260                 conn.reply(reply)
 261                 return
 262         }
 263
 264         conn.log.Info("doRCPT()", zap.String("address", address.Address))
 265
 266         conn.rcptTo = append(conn.rcptTo, *address)
 267
 268         conn.state = stateRecipient
 269         conn.reply(ReplyOK)
 270 }
 271
 272 func (conn *connection) doDATA() {
 273         if conn.state != stateRecipient {
 274                 conn.reply(ReplyBadSequence)
 275                 return
 276         }
 277
 278         conn.writeReply(354, "Start mail input; end with <CRLF>.<CRLF>")
 279         conn.log.Info("doDATA()")
 280
 281         data, err := conn.tp.ReadDotBytes()
 282         if err != nil {
 283                 conn.log.Error("failed to ReadDotBytes()",
 284                         zap.Error(err),
 285                         zap.String("bytes", fmt.Sprintf("%x", data)))
 286                 conn.writeReply(552, "transaction failed")
 287                 return
 288         }
 289
 290         received := time.Now()
 291         env := Envelope{
 292                 RemoteAddr: conn.remoteAddr,
 293                 EHLO:       conn.ehlo,
 294                 MailFrom:   *conn.mailFrom,
 295                 RcptTo:     conn.rcptTo,
 296                 Received:   received,
 297                 ID:         conn.envelopeID(received),
 298         }
 299
 300         conn.log.Info("received message",
 301                 zap.Int("bytes", len(data)),
 302                 zap.Time("date", received),
 303                 zap.String("id", env.ID))
 304
 305         trace := conn.getReceivedInfo(env)
 306
 307         env.Data = append(trace, data...)
 308
 309         if reply := conn.server.OnMessageDelivered(env); reply != nil {
 310                 conn.log.Warn("message was rejected", zap.String("id", env.ID))
 311                 conn.reply(*reply)
 312                 return
 313         }
 314
 315         conn.state = stateInitial
 316         conn.reply(ReplyOK)
 317 }
 318
 319 func (conn *connection) envelopeID(t time.Time) string {
 320         var idBytes [4]byte
 321         rand.Read(idBytes[:])
 322         return fmt.Sprintf("m.%d.%x", t.UnixNano(), idBytes)
 323 }
 324
 325 func (conn *connection) getReceivedInfo(envelope Envelope) []byte {
 326         rhost, _, err := net.SplitHostPort(conn.remoteAddr.String())
 327         if err != nil {
 328                 rhost = conn.remoteAddr.String()
 329         }
 330
 331         rhosts, err := net.LookupAddr(rhost)
 332         if err == nil {
 333                 rhost = fmt.Sprintf("%s [%s]", rhosts[0], rhost)
 334         }
 335
 336         base := fmt.Sprintf("Received: from %s (%s)\r\n        ", conn.ehlo, rhost)
 337
 338         with := "SMTP"
 339         if conn.esmtp {
 340                 with = "E" + with
 341         }
 342         if conn.tls != nil {
 343                 with += "S"
 344         }
 345         base += fmt.Sprintf("by %s (mailpopbox) with %s id %s\r\n        ", conn.server.Name(), with, envelope.ID)
 346
 347         base += fmt.Sprintf("for <%s>\r\n        ", envelope.RcptTo[0].Address)
 348
 349         transport := conn.getTransportString()
 350         date := envelope.Received.Format(time.RFC1123Z) // Same as RFC 5322 § 3.3
 351         base += fmt.Sprintf("(using %s);\r\n        %s\r\n", transport, date)
 352
 353         return []byte(base)
 354 }
 355
 356 func (conn *connection) getTransportString() string {
 357         if conn.tls == nil {
 358                 return "PLAINTEXT"
 359         }
 360
 361         ciphers := map[uint16]string{
 362                 tls.TLS_RSA_WITH_RC4_128_SHA:                "TLS_RSA_WITH_RC4_128_SHA",
 363                 tls.TLS_RSA_WITH_3DES_EDE_CBC_SHA:           "TLS_RSA_WITH_3DES_EDE_CBC_SHA",
 364                 tls.TLS_RSA_WITH_AES_128_CBC_SHA:            "TLS_RSA_WITH_AES_128_CBC_SHA",
 365                 tls.TLS_RSA_WITH_AES_256_CBC_SHA:            "TLS_RSA_WITH_AES_256_CBC_SHA",
 366                 tls.TLS_RSA_WITH_AES_128_GCM_SHA256:         "TLS_RSA_WITH_AES_128_GCM_SHA256",
 367                 tls.TLS_RSA_WITH_AES_256_GCM_SHA384:         "TLS_RSA_WITH_AES_256_GCM_SHA384",
 368                 tls.TLS_ECDHE_ECDSA_WITH_RC4_128_SHA:        "TLS_ECDHE_ECDSA_WITH_RC4_128_SHA",
 369                 tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA:    "TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA",
 370                 tls.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA:    "TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA",
 371                 tls.TLS_ECDHE_RSA_WITH_RC4_128_SHA:          "TLS_ECDHE_RSA_WITH_RC4_128_SHA",
 372                 tls.TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA:     "TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA",
 373                 tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA:      "TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA",
 374                 tls.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA:      "TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA",
 375                 tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256:   "TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256",
 376                 tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256: "TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256",
 377                 tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384:   "TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384",
 378                 tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384: "TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384",
 379         }
 380         versions := map[uint16]string{
 381                 tls.VersionSSL30: "SSLv3.0",
 382                 tls.VersionTLS10: "TLSv1.0",
 383                 tls.VersionTLS11: "TLSv1.1",
 384                 tls.VersionTLS12: "TLSv1.2",
 385         }
 386
 387         state := conn.tls
 388
 389         version := versions[state.Version]
 390         cipher := ciphers[state.CipherSuite]
 391
 392         if version == "" {
 393                 version = fmt.Sprintf("%x", state.Version)
 394         }
 395         if cipher == "" {
 396                 cipher = fmt.Sprintf("%x", state.CipherSuite)
 397         }
 398
 399         name := ""
 400         if state.ServerName != "" {
 401                 name = fmt.Sprintf(" name=%s", state.ServerName)
 402         }
 403
 404         return fmt.Sprintf("%s cipher=%s%s", version, cipher, name)
 405 }
 406
 407 func (conn *connection) doRSET() {
 408         conn.log.Info("doRSET()")
 409         conn.state = stateInitial
 410         conn.resetBuffers()
 411         conn.reply(ReplyOK)
 412 }
 413
 414 func (conn *connection) resetBuffers() {
 415         conn.mailFrom = nil
 416         conn.rcptTo = make([]mail.Address, 0)
 417 }