smtp.go

// referers:
//     https://gist.github.com/chrisgillis/10888032
//     http://www.oschina.net/code/snippet_166520_34694
package csmtp

import (
	"crypto/tls"
	"fmt"
	"log"
	"net"
	"net/smtp"
	"strings"
)

// only one smtp account for now
var (
	Host string
	Port int    = 465
	Name string // sender name
	From string // sender email
	auth smtp.Auth
)

// Auth setup sender password
func Auth(password string) {
	auth = smtp.PlainAuth("", From, password, Host)
}

// SendMail send a email
func SendMail(subject, body string, to ...string) (err error) {

	header := make(map[string]string)
	header["From"] = fmt.Sprintf("%s <%s>", Name, From)
	header["To"] = strings.Join(to, ", ")
	header["Subject"] = subject
	header["Content-Type"] = "text/html; charset=UTF-8"

	message := ""
	for k, v := range header {
		message += fmt.Sprintf("%s: %s\r\n", k, v)
	}
	message += "\r\n" + body

	err = sendMailUsingTLS(
		fmt.Sprintf("%s:%d", Host, Port),
		auth,
		From,
		to,
		[]byte(message),
	)

	return
}

//return a smtp client
func dial(addr string) (*smtp.Client, error) {
	conn, err := tls.Dial("tcp", addr, nil)
	if err != nil {
		log.Println("Dialing Error:", err)
		return nil, err
	}
	//分解主机端口字符串
	host, _, _ := net.SplitHostPort(addr)
	return smtp.NewClient(conn, host)
}

//参考net/smtp的func SendMail()
//使用net.Dial连接tls(ssl)端口时,smtp.NewClient()会卡住且不提示err
//len(to)>1时,to[1]开始提示是密送
func sendMailUsingTLS(addr string, auth smtp.Auth, from string,
	to []string, msg []byte) error {

	//create smtp client
	c, err := dial(addr)
	if err != nil {
		log.Println("Create smpt client error:", err)
		return err
	}
	defer c.Close()

	if auth != nil {
		if ok, _ := c.Extension("AUTH"); ok {
			if err = c.Auth(auth); err != nil {
				log.Println("Error during AUTH", err)
				return err
			}
		}
	}

	if err = c.Mail(from); err != nil {
		return err
	}

	for _, addr := range to {
		if err = c.Rcpt(addr); err != nil {
			return err
		}
	}

	w, err := c.Data()
	if err != nil {
		return err
	}

	_, err = w.Write(msg)
	if err != nil {
		return err
	}

	err = w.Close()
	if err != nil {
		return err
	}

	return c.Quit()
}