使用golang发送邮件

目前大多应用都是手机登录，但是作为开源的一个软件，或者是私有的一个应用，那么使用手机短信接收验证码成本比较高，使用邮箱相对更容易，

这里从tinode中取出发邮件的部分做一个测试，

其中邮箱一般需要设置后才能使用SMTP方式发送邮件，设置方式参考：

使用tinode架设自己的私有聊天服务

邮件其实是有格式的，不是随便发一个字符串过去就好了

func randomBoundary() string {
	var buf [24]byte
	rand.Read(buf[:])
	return fmt.Sprintf("tinode--%x", buf[:])
}

func GetMessage(SendFrom, to, title, dataType, content string) ([]byte, error) {
	message := &bytes.Buffer{}

	// Common headers.
	fmt.Fprintf(message, "From: %s\r\n", SendFrom)
	fmt.Fprintf(message, "To: %s\r\n", to)
	message.WriteString("Subject: ")
	// Old email clients may barf on UTF-8 strings.
	// Encode as quoted printable with 75-char strings separated by spaces, split by spaces, reassemble.
	message.WriteString(strings.Join(strings.Split(mime.QEncoding.Encode("utf-8", title), " "), "\r\n    "))
	message.WriteString("\r\n")
	message.WriteString("MIME-version: 1.0;\r\n")

	if dataType == "plain" {
		// Plain text message
		message.WriteString("Content-Type: text/plain; charset=\"UTF-8\"; format=flowed; delsp=yes\r\n")
		message.WriteString("Content-Transfer-Encoding: base64\r\n\r\n")
		b64w := base64.NewEncoder(base64.StdEncoding, message)
		b64w.Write([]byte(content))
		b64w.Close()
	} else if dataType == "html" {
		// HTML-formatted message
		message.WriteString("Content-Type: text/html; charset=\"UTF-8\"\r\n")
		message.WriteString("Content-Transfer-Encoding: quoted-printable\r\n\r\n")
		qpw := qp.NewWriter(message)
		qpw.Write([]byte(content))
		qpw.Close()
	} else {
		// Multipart-alternative message includes both HTML and plain text components.
		boundary := randomBoundary()
		message.WriteString("Content-Type: multipart/alternative; boundary=\"" + boundary + "\"\r\n\r\n")

		message.WriteString("--" + boundary + "\r\n")
		message.WriteString("Content-Type: text/plain; charset=\"UTF-8\"; format=flowed; delsp=yes\r\n")
		message.WriteString("Content-Transfer-Encoding: base64\r\n\r\n")
		b64w := base64.NewEncoder(base64.StdEncoding, message)
		b64w.Write([]byte(content))
		b64w.Close()

		message.WriteString("\r\n")

		message.WriteString("--" + boundary + "\r\n")
		message.WriteString("Content-Type: text/html; charset=\"UTF-8\"\r\n")
		message.WriteString("Content-Transfer-Encoding: quoted-printable\r\n\r\n")
		qpw := qp.NewWriter(message)
		qpw.Write([]byte(content))
		qpw.Close()

		message.WriteString("\r\n--" + boundary + "--")
	}

	message.WriteString("\r\n")
	return message.Bytes(), nil
}

这里使用了用户名密码验证：

SMTP（Simple Mail Transfer Protocol）支持多种认证方式，其中常见的包括：

1. PLAIN: 客户端将用户名和密码以明文形式发送给服务器进行认证。这是一种最简单的认证方式，但是由于信息以明文形式传输，安全性较低。

2. LOGIN: 客户端发送用户名和密码，但是这次发送的是经过 BASE64 编码的形式。尽管没有以明文形式传输，但仍然不够安全，因为 BASE64 编码可以容易地解码。

3. CRAM-MD5: 客户端和服务器之间进行挑战-响应式的认证。服务器发送一个挑战给客户端，客户端使用密码进行哈希处理后的响应进行回复。这种方式更加安全，因为密码不会以明文形式传输。

import (
	"bytes"
	"crypto/tls"
	"encoding/base64"
	"fmt"
	"math/rand"
	"mime"
	qp "mime/quotedprintable"
	"net/smtp"
	"strings"
)

type Validator struct {
	SMTPAddr              string
	SMTPPort              string
	SMTPHeloHost          string
	TLSInsecureSkipVerify bool
	auth                  smtp.Auth
}

type loginAuth struct {
	username, password []byte
}

func (a *loginAuth) Start(server *smtp.ServerInfo) (string, []byte, error) {
	return "LOGIN", []byte(a.username), nil
}

// Next continues the authentication. Exported only to satisfy the interface definition.
func (a *loginAuth) Next(fromServer []byte, more bool) ([]byte, error) {
	if more {
		switch strings.ToLower(string(fromServer)) {
		case "username:":
			return a.username, nil
		case "password:":
			return a.password, nil
		default:
			return nil, fmt.Errorf("LOGIN AUTH unknown server response '%s'", string(fromServer))
		}
	}
	return nil, nil
}

发送一个邮件：

var user string = "[email protected]"
var touser string = "[email protected]"
var pass string = "1234566"

func TestMail() {

	auth := &loginAuth{[]byte(user), []byte(pass)}
	v := Validator{"smtp.sina.com",
		"25",
		"sina.com",
		false,
		auth,
	}

	msg, _ := GetMessage(user, touser, "it is a test.", "plain", "这是一个测试")
	err := v.SendMail([]string{touser}, msg)
	fmt.Println(err)
}


func (v *Validator) SendMail(rcpt []string, msg []byte) error {

	client, err := smtp.Dial(v.SMTPAddr + ":" + v.SMTPPort)
	if err != nil {
		return err
	}
	defer client.Close()
	if err = client.Hello(v.SMTPHeloHost); err != nil {
		return err
	}
	if istls, _ := client.Extension("STARTTLS"); istls {
		tlsConfig := &tls.Config{
			InsecureSkipVerify: v.TLSInsecureSkipVerify,
			ServerName:         v.SMTPAddr,
		}
		if err = client.StartTLS(tlsConfig); err != nil {
			return err
		}
	}
	if v.auth != nil {
		if isauth, _ := client.Extension("AUTH"); isauth {
			err = client.Auth(v.auth)
			if err != nil {
				fmt.Println(err)
				return err
			}
		}
	}
	if err = client.Mail(user); err != nil {
		fmt.Println(err)
		return err
	}
	for _, to := range rcpt {
		if err = client.Rcpt(strings.ReplaceAll(strings.ReplaceAll(to, "\r", " "), "\n", " ")); err != nil {
			return err
		}
	}
	w, err := client.Data()
	if err != nil {
		return err
	}

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

如果不报错，就去收件箱接收邮件就好了。