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 // lookupRemoteHost attempts to reverse look-up the provided IP address. On
  75 // success, it returns the hostname and the IP as formatted for a receive
  76 // trace. If the lookup fails, it just returns the original IP.
  77 func lookupRemoteHost(addr net.Addr) string {
  78         rhost, _, err := net.SplitHostPort(addr.String())
  79         if err != nil {
  80                 rhost = addr.String()
  81         }
  82
  83         rhosts, err := net.LookupAddr(rhost)
  84         if err == nil {
  85                 rhost = fmt.Sprintf("%s [%s]", rhosts[0], rhost)
  86         }
  87
  88         return rhost
  89 }
  90
  91 type Server interface {
  92         Name() string
  93         TLSConfig() *tls.Config
  94         VerifyAddress(mail.Address) ReplyLine
  95         // Verify that the authc+passwd identity can send mail as authz.
  96         Authenticate(authz, authc, passwd string) bool
  97         DeliverMessage(Envelope) *ReplyLine
  98
  99         // RelayMessage instructs the server to send the Envelope to another
 100         // MTA for outbound delivery.
 101         RelayMessage(Envelope)
 102 }
 103
 104 type EmptyServerCallbacks struct{}
 105
 106 func (*EmptyServerCallbacks) TLSConfig() *tls.Config {
 107         return nil
 108 }
 109
 110 func (*EmptyServerCallbacks) VerifyAddress(mail.Address) ReplyLine {
 111         return ReplyOK
 112 }
 113
 114 func (*EmptyServerCallbacks) Authenticate(authz, authc, passwd string) bool {
 115         return false
 116 }
 117
 118 func (*EmptyServerCallbacks) DeliverMessage(Envelope) *ReplyLine {
 119         return nil
 120 }
 121
 122 func (*EmptyServerCallbacks) RelayMessage(Envelope) {
 123 }