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server.go
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server.go
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package smtp
import (
"context"
"crypto/tls"
"errors"
"io"
"log"
"net"
"os"
"sync"
"time"
)
var ErrServerClosed = errors.New("smtp: server already closed")
// Logger interface is used by Server to report unexpected internal errors.
type Logger interface {
Printf(format string, v ...interface{})
Println(v ...interface{})
}
// A SMTP server.
type Server struct {
// The type of network, "tcp" or "unix".
Network string
// 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 bool
Domain string
MaxRecipients int
MaxMessageBytes int64
MaxLineLength int
AllowInsecureAuth 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 (RFC 8689) capability.
// Should be used only if backend supports it.
EnableREQUIRETLS bool
// Advertise BINARYMIME (RFC 3030) capability.
// Should be used only if backend supports it.
EnableBINARYMIME bool
// Advertise DSN (RFC 3461) capability.
// Should be used only if backend supports it.
EnableDSN bool
// Advertise XOORG capability.
// Should be used only if backend supports it.
EnableXOORG bool
// The server backend.
Backend Backend
wg sync.WaitGroup
done chan struct{}
locker sync.Mutex
listeners []net.Listener
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),
conns: make(map[*Conn]struct{}),
}
}
// Serve accepts incoming connections on the Listener l.
func (s *Server) Serve(l net.Listener) error {
s.locker.Lock()
s.listeners = append(s.listeners, l)
s.locker.Unlock()
var tempDelay time.Duration // how long to sleep on accept failure
for {
c, err := l.Accept()
if err != nil {
select {
case <-s.done:
// we called Close()
return nil
default:
}
if ne, ok := err.(net.Error); ok && ne.Temporary() {
if tempDelay == 0 {
tempDelay = 5 * time.Millisecond
} else {
tempDelay *= 2
}
if max := 1 * time.Second; tempDelay > max {
tempDelay = max
}
s.ErrorLog.Printf("accept error: %s; retrying in %s", err, tempDelay)
time.Sleep(tempDelay)
continue
}
return err
}
s.wg.Add(1)
go func() {
defer s.wg.Done()
err := s.handleConn(newConn(c, s))
if err != nil {
s.ErrorLog.Printf("error handling %v: %s", c.RemoteAddr(), err)
}
}()
}
}
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()
}()
if tlsConn, ok := c.conn.(*tls.Conn); ok {
if d := s.ReadTimeout; d != 0 {
c.conn.SetReadDeadline(time.Now().Add(d))
}
if d := s.WriteTimeout; d != 0 {
c.conn.SetWriteDeadline(time.Now().Add(d))
}
if err := tlsConn.Handshake(); err != nil {
return err
}
}
c.greet()
for {
line, err := c.readLine()
if err == nil {
cmd, arg, err := parseCmd(line)
if err != nil {
c.protocolError(501, EnhancedCode{5, 5, 2}, "Bad command")
continue
}
c.handle(cmd, arg)
} else {
if err == io.EOF || errors.Is(err, net.ErrClosed) {
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(421, EnhancedCode{4, 4, 2}, "Idle timeout, bye bye")
return nil
}
c.writeResponse(421, EnhancedCode{4, 4, 0}, "Connection error, sorry")
return err
}
}
}
func (s *Server) network() string {
if s.Network != "" {
return s.Network
}
if s.LMTP {
return "unix"
}
return "tcp"
}
// 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 := s.network()
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 and LMTP is disabled, ":smtps" is used.
func (s *Server) ListenAndServeTLS() error {
network := s.network()
addr := s.Addr
if !s.LMTP && addr == "" {
addr = ":smtps"
}
l, err := tls.Listen(network, addr, s.TLSConfig)
if err != nil {
return err
}
return s.Serve(l)
}
// Close immediately closes all active listeners and connections.
//
// Close returns any error returned from closing the server's underlying
// listener(s).
func (s *Server) Close() error {
select {
case <-s.done:
return ErrServerClosed
default:
close(s.done)
}
var err error
s.locker.Lock()
for _, l := range s.listeners {
if lerr := l.Close(); lerr != nil && err == nil {
err = lerr
}
}
for conn := range s.conns {
conn.Close()
}
s.locker.Unlock()
return err
}
// Shutdown gracefully shuts down the server without interrupting any
// active connections. Shutdown works by first closing all open
// listeners and then waiting indefinitely for connections to return to
// idle and then shut down.
// If the provided context expires before the shutdown is complete,
// Shutdown returns the context's error, otherwise it returns any
// error returned from closing the Server's underlying Listener(s).
func (s *Server) Shutdown(ctx context.Context) error {
select {
case <-s.done:
return ErrServerClosed
default:
close(s.done)
}
var err error
s.locker.Lock()
for _, l := range s.listeners {
if lerr := l.Close(); lerr != nil && err == nil {
err = lerr
}
}
s.locker.Unlock()
connDone := make(chan struct{})
go func() {
defer close(connDone)
s.wg.Wait()
}()
select {
case <-ctx.Done():
return ctx.Err()
case <-connDone:
return err
}
}