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server.go
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server.go
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package smtp
import (
"crypto/tls"
"errors"
"io"
"log"
"net"
"os"
"sync"
"time"
"github.com/emersion/go-sasl"
)
var errTCPAndLMTP = errors.New("smtp: cannot start LMTP server listening on a TCP socket")
// SaslServerFactory creates SASL servers.
type SaslServerFactory func(conn *Conn) sasl.Server
// Logger interface is used by Server to report unexpected internal errors.
type Logger interface {
Printf(format string, v ...interface{})
Println(v ...interface{})
}
// Server represents a SMTP Server.
type Server struct {
// TCP or Unix address to listen on.
Addr string
// The server TLS configuration.
TLSConfig *tls.Config
// Enable LMTP mode, as defined in RFC 2033. LMTP mode cannot be used with a
// TCP listener.
LMTP bool
Domain string
MaxRecipients int
MaxMessageBytes int
MaxLineLength int
AllowInsecureAuth bool
Strict bool
Debug io.Writer
ErrorLog Logger
ReadTimeout time.Duration
WriteTimeout time.Duration
// Advertise SMTPUTF8 (RFC 6531) capability.
// Should be used only if backend supports it.
EnableSMTPUTF8 bool
// Advertise REQUIRETLS (draft-ietf-uta-smtp-require-tls-09) capability.
// Should be used only if backend supports it.
EnableREQUIRETLS bool
// If set, the AUTH command will not be advertised and authentication
// attempts will be rejected. This setting overrides AllowInsecureAuth.
AuthDisabled bool
// The server backend.
Backend Backend
listeners []net.Listener
caps []string
auths map[string]SaslServerFactory
done chan struct{}
locker sync.Mutex
conns map[*Conn]struct{}
}
// New creates a new SMTP server.
func NewServer(be Backend) *Server {
return &Server{
// Doubled maximum line length per RFC 5321 (Section 4.5.3.1.6)
MaxLineLength: 2000,
Backend: be,
done: make(chan struct{}, 1),
ErrorLog: log.New(os.Stderr, "smtp/server ", log.LstdFlags),
caps: []string{"PIPELINING", "8BITMIME", "ENHANCEDSTATUSCODES"},
auths: map[string]SaslServerFactory{
sasl.Plain: func(conn *Conn) sasl.Server {
return sasl.NewPlainServer(func(identity, username, password string) error {
if identity != "" && identity != username {
return errors.New("Identities not supported")
}
state := conn.State()
session, err := be.Login(&state, username, password)
if err != nil {
return err
}
conn.SetSession(session)
return nil
})
},
},
conns: make(map[*Conn]struct{}),
}
}
// Serve accepts incoming connections on the Listener l.
func (s *Server) Serve(l net.Listener) error {
s.listeners = append(s.listeners, l)
for {
c, err := l.Accept()
if err != nil {
select {
case <-s.done:
// we called Close()
return nil
default:
return err
}
}
go s.handleConn(newConn(c, s))
}
}
func (s *Server) handleConn(c *Conn) error {
s.locker.Lock()
s.conns[c] = struct{}{}
s.locker.Unlock()
defer func() {
c.Close()
s.locker.Lock()
delete(s.conns, c)
s.locker.Unlock()
}()
c.greet()
for {
line, err := c.ReadLine()
if err == nil {
cmd, arg, err := parseCmd(line)
if err != nil {
c.nbrErrors++
c.WriteResponse(501, EnhancedCode{5, 5, 2}, "Bad command")
continue
}
c.handle(cmd, arg)
} else {
if err == io.EOF {
return nil
}
if err == ErrTooLongLine {
c.WriteResponse(500, EnhancedCode{5, 4, 0}, "Too long line, closing connection")
return nil
}
if neterr, ok := err.(net.Error); ok && neterr.Timeout() {
c.WriteResponse(221, EnhancedCode{2, 4, 2}, "Idle timeout, bye bye")
return nil
}
c.WriteResponse(221, EnhancedCode{2, 4, 0}, "Connection error, sorry")
return err
}
}
}
// ListenAndServe listens on the network address s.Addr and then calls Serve
// to handle requests on incoming connections.
//
// If s.Addr is blank and LMTP is disabled, ":smtp" is used.
func (s *Server) ListenAndServe() error {
network := "tcp"
if s.LMTP {
network = "unix"
}
addr := s.Addr
if !s.LMTP && addr == "" {
addr = ":smtp"
}
l, err := net.Listen(network, addr)
if err != nil {
return err
}
return s.Serve(l)
}
// ListenAndServeTLS listens on the TCP network address s.Addr and then calls
// Serve to handle requests on incoming TLS connections.
//
// If s.Addr is blank, ":smtps" is used.
func (s *Server) ListenAndServeTLS() error {
if s.LMTP {
return errTCPAndLMTP
}
addr := s.Addr
if addr == "" {
addr = ":smtps"
}
l, err := tls.Listen("tcp", addr, s.TLSConfig)
if err != nil {
return err
}
return s.Serve(l)
}
// Close stops the server.
func (s *Server) Close() {
close(s.done)
for _, l := range s.listeners {
l.Close()
}
s.locker.Lock()
defer s.locker.Unlock()
for conn := range s.conns {
conn.Close()
}
}
// EnableAuth enables an authentication mechanism on this server.
//
// This function should not be called directly, it must only be used by
// libraries implementing extensions of the SMTP protocol.
func (s *Server) EnableAuth(name string, f SaslServerFactory) {
s.auths[name] = f
}
// ForEachConn iterates through all opened connections.
func (s *Server) ForEachConn(f func(*Conn)) {
s.locker.Lock()
defer s.locker.Unlock()
for conn := range s.conns {
f(conn)
}
}