smtp/server.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         "io"
  14         "net"
  15         "net/mail"
  16         "regexp"
  17         "strings"
  18         "time"
  19 )
  20
  21 type ReplyLine struct {
  22         Code    int
  23         Message string
  24 }
  25
  26 func (l ReplyLine) String() string {
  27         return fmt.Sprintf("%d %s", l.Code, l.Message)
  28 }
  29
  30 var SendAsSubject = regexp.MustCompile(`(?i)\[sendas:\s*([a-zA-Z0-9\.\-_]+)\]`)
  31
  32 var (
  33         ReplyOK               = ReplyLine{250, "OK"}
  34         ReplyBadSyntax        = ReplyLine{501, "syntax error"}
  35         ReplyBadSequence      = ReplyLine{503, "bad sequence of commands"}
  36         ReplyBadMailbox       = ReplyLine{550, "mailbox unavailable"}
  37         ReplyMailboxUnallowed = ReplyLine{553, "mailbox name not allowed"}
  38 )
  39
  40 func DomainForAddress(addr mail.Address) string {
  41         return DomainForAddressString(addr.Address)
  42 }
  43
  44 func DomainForAddressString(address string) string {
  45         domainIdx := strings.LastIndex(address, "@")
  46         if domainIdx == -1 {
  47                 return ""
  48         }
  49         return address[domainIdx+1:]
  50 }
  51
  52 type Envelope struct {
  53         RemoteAddr net.Addr
  54         EHLO       string
  55         MailFrom   mail.Address
  56         RcptTo     []mail.Address
  57         Data       []byte
  58         Received   time.Time
  59         ID         string
  60 }
  61
  62 func WriteEnvelopeForDelivery(w io.Writer, e Envelope) {
  63         fmt.Fprintf(w, "Delivered-To: <%s>\r\n", e.RcptTo[0].Address)
  64         fmt.Fprintf(w, "Return-Path: <%s>\r\n", e.MailFrom.Address)
  65         w.Write(e.Data)
  66 }
  67
  68 func generateEnvelopeId(prefix string, t time.Time) string {
  69         var idBytes [4]byte
  70         rand.Read(idBytes[:])
  71         return fmt.Sprintf("%s.%d.%x", prefix, t.UnixNano(), idBytes)
  72 }
  73
  74 type Server interface {
  75         Name() string
  76         TLSConfig() *tls.Config
  77         VerifyAddress(mail.Address) ReplyLine
  78         // Verify that the authc+passwd identity can send mail as authz.
  79         Authenticate(authz, authc, passwd string) bool
  80         OnMessageDelivered(Envelope) *ReplyLine
  81
  82         // RelayMessage instructs the server to send the Envelope to another
  83         // MTA for outbound delivery.
  84         RelayMessage(Envelope)
  85 }
  86
  87 type EmptyServerCallbacks struct{}
  88
  89 func (*EmptyServerCallbacks) TLSConfig() *tls.Config {
  90         return nil
  91 }
  92
  93 func (*EmptyServerCallbacks) VerifyAddress(mail.Address) ReplyLine {
  94         return ReplyOK
  95 }
  96
  97 func (*EmptyServerCallbacks) Authenticate(authz, authc, passwd string) bool {
  98         return false
  99 }
 100
 101 func (*EmptyServerCallbacks) OnMessageDelivered(Envelope) *ReplyLine {
 102         return nil
 103 }
 104
 105 func (*EmptyServerCallbacks) RelayMessage(Envelope) {
 106 }