bufio half closed tcp connections

bufio-smtp.go

package main

import (
	"fmt"
	"io"
	"log"
	"os"
	"os/exec"
	"strings"
	"time"

	"github.com/emersion/go-smtp"
)

const listenAddr = ":1025"

var timeout = time.Second * 1

type Logger struct{}

func (l *Logger) Printf(_ *smtp.Conn, format string, v ...interface{}) {
	log.Printf(format, v...)
}

func (l *Logger) Println(_ *smtp.Conn, v ...interface{}) {
	log.Println(v...)
}

type backend struct{}

func (be *backend) Login(state *smtp.ConnectionState, username, password string) (smtp.Session, error) {
	return &session{}, nil
}

func (be *backend) AnonymousLogin(state *smtp.ConnectionState) (smtp.Session, error) {
	return &session{}, nil
}

type session struct{}

func (s *session) Data(r io.Reader) error {
	return nil
}

func (s *session) Mail(from string, opts *smtp.MailOptions) error {
	return nil
}

func (s *session) Rcpt(to string) error {
	return nil
}

func (s *session) Reset() {
	return
}

func (s *session) Logout() error {
	return nil
}

func init() {
	be := &backend{}
	smtpServer := smtp.NewServer(be)
	smtpServer.Addr = listenAddr
	smtpServer.AllowInsecureAuth = true
	smtpServer.ReadTimeout = timeout
	smtpServer.WriteTimeout = timeout
	smtpServer.ErrorLog = &Logger{}
	smtpServer.Debug = os.Stderr

	// run SMTP server
	go func() {
		err := smtpServer.ListenAndServe()
		if err != nil && !strings.Contains(err.Error(), "use of closed network connection") {
			log.Fatalf("failed to listen: %v", err)
		}
	}()
}

func main() {
	// wait for listener
	time.Sleep(timeout)
	msg := strings.NewReader("test")
	err := sendMail("test@test.com", "test@test.com", msg)
	if err != nil {
		log.Fatalf("failed to send an email: %v", err)
	}

	// wait for timeout closed TCP
	time.Sleep(2 * timeout)
	cmd := exec.Command("sh", "-c", fmt.Sprintf("netstat -ntp | grep %d", os.Getpid()))
	stdout, err := cmd.Output()
	if err != nil {
		log.Fatalf("failed to run netstat: %v", err)
	}
	log.Println(string(stdout))
}

func sendMail(from, to string, r io.Reader) error {
	c, err := smtp.Dial(listenAddr)
	if err != nil {
		return err
	}
	//defer c.Close()
	if err = c.Hello("client"); err != nil {
		return err
	}
	if err = c.Mail(from, nil); err != nil {
		return err
	}
	if err = c.Rcpt(to); err != nil {
		return err
	}
	w, err := c.Data(nil)
	if err != nil {
		return err
	}
	_, err = io.Copy(w, r)
	if err != nil {
		return err
	}
	err = w.Close()
	if err != nil {
		return err
	}
	//return c.Quit()
	return nil
}