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         ReplyAuthOK           = ReplyLine{235, "auth success"}
  35         ReplyBadSyntax        = ReplyLine{501, "syntax error"}
  36         ReplyBadSequence      = ReplyLine{503, "bad sequence of commands"}
  37         ReplyBadMailbox       = ReplyLine{550, "mailbox unavailable"}
  38         ReplyMailboxUnallowed = ReplyLine{553, "mailbox name not allowed"}
  39 )
  40
  41 func DomainForAddress(addr mail.Address) string {
  42         return DomainForAddressString(addr.Address)
  43 }
  44
  45 func DomainForAddressString(address string) string {
  46         domainIdx := strings.LastIndex(address, "@")
  47         if domainIdx == -1 {
  48                 return ""
  49         }
  50         return address[domainIdx+1:]
  51 }
  52
  53 type Envelope struct {
  54         RemoteAddr net.Addr
  55         EHLO       string
  56         MailFrom   mail.Address
  57         RcptTo     []mail.Address
  58         Data       []byte
  59         Received   time.Time
  60         ID         string
  61 }
  62
  63 func WriteEnvelopeForDelivery(w io.Writer, e Envelope) {
  64         fmt.Fprintf(w, "Delivered-To: <%s>\r\n", e.RcptTo[0].Address)
  65         fmt.Fprintf(w, "Return-Path: <%s>\r\n", e.MailFrom.Address)
  66         w.Write(e.Data)
  67 }
  68
  69 func generateEnvelopeId(prefix string, t time.Time) string {
  70         var idBytes [4]byte
  71         rand.Read(idBytes[:])
  72         return fmt.Sprintf("%s.%d.%x", prefix, t.UnixNano(), idBytes)
  73 }
  74
  75 // lookupRemoteHost attempts to reverse look-up the provided IP address. On
  76 // success, it returns the hostname and the IP as formatted for a receive
  77 // trace. If the lookup fails, it just returns the original IP.
  78 func lookupRemoteHost(addr net.Addr) string {
  79         rhost, _, err := net.SplitHostPort(addr.String())
  80         if err != nil {
  81                 rhost = addr.String()
  82         }
  83
  84         rhosts, err := net.LookupAddr(rhost)
  85         if err == nil {
  86                 rhost = fmt.Sprintf("%s [%s]", rhosts[0], rhost)
  87         }
  88
  89         return rhost
  90 }
  91
  92 type Server interface {
  93         Name() string
  94         TLSConfig() *tls.Config
  95         VerifyAddress(mail.Address) ReplyLine
  96         // Verify that the authc+passwd identity can send mail as authz.
  97         Authenticate(authz, authc, passwd string) bool
  98         DeliverMessage(Envelope) *ReplyLine
  99
 100         // RelayMessage instructs the server to send the Envelope to another
 101         // MTA for outbound delivery.
 102         RelayMessage(Envelope)
 103 }
 104
 105 type EmptyServerCallbacks struct{}
 106
 107 func (*EmptyServerCallbacks) TLSConfig() *tls.Config {
 108         return nil
 109 }
 110
 111 func (*EmptyServerCallbacks) VerifyAddress(mail.Address) ReplyLine {
 112         return ReplyOK
 113 }
 114
 115 func (*EmptyServerCallbacks) Authenticate(authz, authc, passwd string) bool {
 116         return false
 117 }
 118
 119 func (*EmptyServerCallbacks) DeliverMessage(Envelope) *ReplyLine {
 120         return nil
 121 }
 122
 123 func (*EmptyServerCallbacks) RelayMessage(Envelope) {
 124 }