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
  14 type state int
  15
  16 const (
  17         stateNew state = iota // Before EHLO.
  18         stateInitial
  19         stateMail
  20         stateRecipient
  21         stateData
  22 )
  23
  24 type connection struct {
  25         server Server
  26
  27         tp *textproto.Conn
  28
  29         nc         net.Conn
  30         tlsNc      *tls.Conn
  31         remoteAddr net.Addr
  32
  33         esmtp bool
  34
  35         state
  36         line string
  37
  38         ehlo     string
  39         mailFrom *mail.Address
  40         rcptTo   []mail.Address
  41 }
  42
  43 func AcceptConnection(netConn net.Conn, server Server) error {
  44         conn := connection{
  45                 server:     server,
  46                 tp:         textproto.NewConn(netConn),
  47                 nc:         netConn,
  48                 remoteAddr: netConn.RemoteAddr(),
  49                 state:      stateNew,
  50         }
  51
  52         var err error
  53
  54         conn.writeReply(220, fmt.Sprintf("%s ESMTP [%s] (mailpopbox)", server.Name(), netConn.LocalAddr()))
  55
  56         for {
  57                 conn.line, err = conn.tp.ReadLine()
  58                 if err != nil {
  59                         conn.writeReply(500, "line too long")
  60                         continue
  61                 }
  62
  63                 var cmd string
  64                 if _, err = fmt.Sscanf(conn.line, "%s", &cmd); err != nil {
  65                         conn.reply(ReplyBadSyntax)
  66                         continue
  67                 }
  68
  69                 switch strings.ToUpper(cmd) {
  70                 case "QUIT":
  71                         conn.writeReply(221, "Goodbye")
  72                         conn.tp.Close()
  73                         break
  74                 case "HELO":
  75                         conn.esmtp = false
  76                         fallthrough
  77                 case "EHLO":
  78                         conn.esmtp = true
  79                         conn.doEHLO()
  80                 case "STARTTLS":
  81                         conn.doSTARTTLS()
  82                 case "MAIL":
  83                         conn.doMAIL()
  84                 case "RCPT":
  85                         conn.doRCPT()
  86                 case "DATA":
  87                         conn.doDATA()
  88                 case "RSET":
  89                         conn.doRSET()
  90                 case "VRFY":
  91                         conn.writeReply(252, "I'll do my best")
  92                 case "EXPN":
  93                         conn.writeReply(550, "access denied")
  94                 case "NOOP":
  95                         conn.reply(ReplyOK)
  96                 case "HELP":
  97                         conn.writeReply(250, "https://tools.ietf.org/html/rfc5321")
  98                 default:
  99                         conn.writeReply(500, "unrecognized command")
 100                 }
 101         }
 102
 103         return err
 104 }
 105
 106 func (conn *connection) reply(reply ReplyLine) error {
 107         return conn.writeReply(reply.Code, reply.Message)
 108 }
 109
 110 func (conn *connection) writeReply(code int, msg string) error {
 111         if len(msg) > 0 {
 112                 return conn.tp.PrintfLine("%d %s", code, msg)
 113         } else {
 114                 return conn.tp.PrintfLine("%d", code)
 115         }
 116 }
 117
 118 // parsePath parses out either a forward-, reverse-, or return-path from the
 119 // current connection line. Returns a (valid-path, ReplyOK) if it was
 120 // successfully parsed.
 121 func (conn *connection) parsePath(command string) (string, ReplyLine) {
 122         if len(conn.line) < len(command) {
 123                 return "", ReplyBadSyntax
 124         }
 125         if strings.ToUpper(command) != strings.ToUpper(conn.line[:len(command)]) {
 126                 return "", ReplyLine{500, "unrecognized command"}
 127         }
 128         return conn.line[len(command):], ReplyOK
 129 }
 130
 131 func (conn *connection) doEHLO() {
 132         conn.resetBuffers()
 133
 134         var cmd string
 135         _, err := fmt.Sscanf(conn.line, "%s %s", &cmd, &conn.ehlo)
 136         if err != nil {
 137                 conn.reply(ReplyBadSyntax)
 138                 return
 139         }
 140
 141         if cmd == "HELO" {
 142                 conn.writeReply(250, fmt.Sprintf("Hello %s [%s]", conn.ehlo, conn.remoteAddr))
 143         } else {
 144                 conn.tp.PrintfLine("250-Hello %s [%s]", conn.ehlo, conn.remoteAddr)
 145                 if conn.server.TLSConfig() != nil && conn.tlsNc == nil {
 146                         conn.tp.PrintfLine("250-STARTTLS")
 147                 }
 148                 conn.tp.PrintfLine("250 SIZE %d", 40960000)
 149         }
 150
 151         conn.state = stateInitial
 152 }
 153
 154 func (conn *connection) doSTARTTLS() {
 155         if conn.state != stateInitial {
 156                 conn.reply(ReplyBadSequence)
 157                 return
 158         }
 159
 160         tlsConfig := conn.server.TLSConfig()
 161         if !conn.esmtp || tlsConfig == nil {
 162                 conn.writeReply(500, "unrecognized command")
 163                 return
 164         }
 165
 166         conn.writeReply(220, "initiate TLS connection")
 167
 168         newConn := tls.Server(conn.nc, tlsConfig)
 169         if err := newConn.Handshake(); err != nil {
 170                 return
 171         }
 172
 173         conn.tlsNc = newConn
 174         conn.tp = textproto.NewConn(conn.tlsNc)
 175         conn.state = stateInitial
 176
 177         conn.writeReply(220, fmt.Sprintf("%s ESMTPS [%s] (mailpopbox)",
 178                 conn.server.Name(), newConn.LocalAddr()))
 179 }
 180
 181 func (conn *connection) doMAIL() {
 182         if conn.state != stateInitial {
 183                 conn.reply(ReplyBadSequence)
 184                 return
 185         }
 186
 187         mailFrom, reply := conn.parsePath("MAIL FROM:")
 188         if reply != ReplyOK {
 189                 conn.reply(reply)
 190                 return
 191         }
 192
 193         var err error
 194         conn.mailFrom, err = mail.ParseAddress(mailFrom)
 195         if err != nil {
 196                 conn.reply(ReplyBadSyntax)
 197                 return
 198         }
 199
 200         conn.state = stateMail
 201         conn.reply(ReplyOK)
 202 }
 203
 204 func (conn *connection) doRCPT() {
 205         if conn.state != stateMail && conn.state != stateRecipient {
 206                 conn.reply(ReplyBadSequence)
 207                 return
 208         }
 209
 210         rcptTo, reply := conn.parsePath("RCPT TO:")
 211         if reply != ReplyOK {
 212                 conn.reply(reply)
 213                 return
 214         }
 215
 216         address, err := mail.ParseAddress(rcptTo)
 217         if err != nil {
 218                 conn.reply(ReplyBadSyntax)
 219         }
 220
 221         if reply := conn.server.VerifyAddress(*address); reply != ReplyOK {
 222                 conn.reply(reply)
 223                 return
 224         }
 225
 226         conn.rcptTo = append(conn.rcptTo, *address)
 227
 228         conn.state = stateRecipient
 229         conn.reply(ReplyOK)
 230 }
 231
 232 func (conn *connection) doDATA() {
 233         if conn.state != stateRecipient {
 234                 conn.reply(ReplyBadSequence)
 235                 return
 236         }
 237
 238         conn.writeReply(354, "Start mail input; end with <CRLF>.<CRLF>")
 239
 240         data, err := conn.tp.ReadDotBytes()
 241         if err != nil {
 242                 // TODO: log error
 243                 conn.writeReply(552, "transaction failed")
 244                 return
 245         }
 246
 247         received := time.Now()
 248         env := Envelope{
 249                 RemoteAddr: conn.remoteAddr,
 250                 EHLO:       conn.ehlo,
 251                 MailFrom:   *conn.mailFrom,
 252                 RcptTo:     conn.rcptTo,
 253                 Received:   received,
 254                 ID:         conn.envelopeID(received),
 255         }
 256
 257         trace := conn.getReceivedInfo(env)
 258
 259         env.Data = append(trace, data...)
 260
 261         if reply := conn.server.OnMessageDelivered(env); reply != nil {
 262                 conn.reply(*reply)
 263                 return
 264         }
 265
 266         conn.state = stateInitial
 267         conn.reply(ReplyOK)
 268 }
 269
 270 func (conn *connection) envelopeID(t time.Time) string {
 271         var idBytes [4]byte
 272         rand.Read(idBytes[:])
 273         return fmt.Sprintf("m.%d.%x", t.UnixNano(), idBytes)
 274 }
 275
 276 func (conn *connection) getReceivedInfo(envelope Envelope) []byte {
 277         rhost, _, err := net.SplitHostPort(conn.remoteAddr.String())
 278         if err != nil {
 279                 rhost = conn.remoteAddr.String()
 280         }
 281
 282         rhosts, err := net.LookupAddr(rhost)
 283         if err == nil {
 284                 rhost = fmt.Sprintf("%s [%s]", rhosts[0], rhost)
 285         }
 286
 287         base := fmt.Sprintf("Received: from %s (%s)\r\n        ", conn.ehlo, rhost)
 288
 289         with := "SMTP"
 290         if conn.esmtp {
 291                 with = "E" + with
 292         }
 293         if conn.tlsNc != nil {
 294                 with += "S"
 295         }
 296         base += fmt.Sprintf("by %s (mailpopbox) with %s id %s\r\n        ", conn.server.Name(), with, envelope.ID)
 297
 298         base += fmt.Sprintf("for <%s>\r\n        ", envelope.RcptTo[0].Address)
 299
 300         transport := "PLAINTEXT"
 301         if conn.tlsNc != nil {
 302                 // TODO: TLS version, cipher, bits
 303         }
 304         date := envelope.Received.Format(time.RFC1123Z) // Same as RFC 5322 § 3.3
 305         base += fmt.Sprintf("(using %s);\r\n        %s\r\n", transport, date)
 306
 307         return []byte(base)
 308 }
 309
 310 func (conn *connection) doRSET() {
 311         conn.state = stateInitial
 312         conn.resetBuffers()
 313         conn.reply(ReplyOK)
 314 }
 315
 316 func (conn *connection) resetBuffers() {
 317         conn.mailFrom = nil
 318         conn.rcptTo = make([]mail.Address, 0)
 319 }