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