Golang 通过net/smtp发送邮件在正文中添加图片(附件/非附件)

背景

遇到一个需求需要发送带有图片的邮件
于是参考:http://www.cnblogs.com/zengchunyun/p/9485444.html
完成了带图片附件的邮件发送功能
但是！！
产品竟然说图片需要在正文里！！正文！！个人觉得在附件里很好呀0.0

尝试

产品说什么就是什么吧。。
于是疯狂尝试怎么把图片从附件里显示到正文当中

multipart类型，有三种子类型：mixed、alternative、related
multipart/mixed可以包含附件。
multipart/related可以包含内嵌资源。
multipart/alternative 纯文本与超文本共存
multipart可以发送若干个内容并使用boundary来分割

一开始以为是mixed的缘故改成了related
但是一点都没用。。该在附件里的还是出现在了附件了

最后自己本地发邮件抓包发现了原来可以发送html格式的邮件把图片放到‘’img‘’中来实现正文中添加图片的功能

废话不多说上代码

代码

package main

import (
    "bytes"
    "encoding/base64"
    "fmt"
    "io/ioutil"
    "net/smtp"
    "strings"
    "time"
)

type SendMail struct {
    user     string
    password string
    host     string
    port     string
    auth     smtp.Auth
}

type Attachment struct {
    name        []string
    contentType string
    withFile    bool
}

type Message struct {
    from        string
    to          []string
    cc          []string
    bcc         []string
    subject     string
    body        string
    contentType string
    attachment  Attachment
}

func (mail *SendMail) Auth() {
    mail.auth = smtp.PlainAuth("", mail.user, mail.password, mail.host)
}

func (mail SendMail) Send(message Message) error {
    mail.Auth()
    buffer := bytes.NewBuffer(nil)
    boundary := "GoBoundary"
    Header := make(map[string]string)
    Header["From"] = message.from
    Header["To"] = strings.Join(message.to, ";")
    Header["Cc"] = strings.Join(message.cc, ";")
    Header["Bcc"] = strings.Join(message.bcc, ";")
    Header["Subject"] = message.subject
    Header["Content-Type"] = "multipart/related;boundary=" + boundary
    Header["Date"] = time.Now().String()
    mail.writeHeader(buffer, Header)

    var imgsrc string
    if message.attachment.withFile {
        //多图片发送
        for _, graphname := range message.attachment.name {
            attachment := "\r\n--" + boundary + "\r\n"
            attachment += "Content-Transfer-Encoding:base64\r\n"
            attachment += "Content-Type:" + message.attachment.contentType + ";name=\"" + graphname + "\"\r\n"
            attachment += "Content-ID: <" + graphname + "> \r\n\r\n"
            buffer.WriteString(attachment)

            //拼接成html
            imgsrc += "<p><img src=\"cid:" + graphname + "\" height=200 width=300></p><br>\r\n\t\t\t"

            defer func() {
                if err := recover(); err != nil {
                    fmt.Printf(err.(string))
                }
            }()
            mail.writeFile(buffer, graphname)
        }
    }

    //需要在正文中显示的html格式
    var template = `
    <html>
        <body>
            <p>text:%s</p><br>
            %s          
        </body>
    </html>
    `
    var content = fmt.Sprintf(template, message.body, imgsrc)
    body := "\r\n--" + boundary + "\r\n"
    body += "Content-Type: text/html; charset=UTF-8 \r\n"
    body += content
    buffer.WriteString(body)

    buffer.WriteString("\r\n--" + boundary + "--")
    fmt.Println(buffer.String())
    smtp.SendMail(mail.host+":"+mail.port, mail.auth, message.from, message.to, buffer.Bytes())
    return nil
}

func (mail SendMail) writeHeader(buffer *bytes.Buffer, Header map[string]string) string {
    header := ""
    for key, value := range Header {
        header += key + ":" + value + "\r\n"
    }
    header += "\r\n"
    buffer.WriteString(header)
    return header
}

func (mail SendMail) writeFile(buffer *bytes.Buffer, fileName string) {
    file, err := ioutil.ReadFile(fileName)
    if err != nil {
        panic(err.Error())
    }
    payload := make([]byte, base64.StdEncoding.EncodedLen(len(file)))
    base64.StdEncoding.Encode(payload, file)
    buffer.WriteString("\r\n")
    for index, line := 0, len(payload); index < line; index++ {
        buffer.WriteByte(payload[index])
        if (index+1)%76 == 0 {
            buffer.WriteString("\r\n")
        }
    }
}

func main() {
    mail := &SendMail{user: "[email protected]", password: "password", host: "smtp.qq.com", port: "25"}
    message := Message{
        from:        "[email protected]",
        to:          []string{"[email protected]"},
        cc:          []string{},
        bcc:         []string{},
        subject:     "test", //邮件标题
        body:        "msg body!", //正文内容
        contentType: "text/plain;charset=utf-8",
        attachment: Attachment{
            name:        []string{"1.png"}, //可以放入多张图片
            contentType: "image/png",
            withFile:    true,
        },
    }
    mail.Send(message)
}

下面再附上最终组合成的发送格式：

From:[email protected]
To:[email protected]
Cc:
Bcc:
Subject:test
Content-Type:multipart/related;boundary=GoBoundary
Date:2018-08-22 14:42:04.529271 +0800 CST m=+0.006003700


--GoBoundary
Content-Transfer-Encoding:base64
Content-Type:image/png;name="1.png"
Content-ID: <1.png> 

//图片base64编码内容 太长就不显示了

--GoBoundary
Content-Type: text/html; charset=UTF-8 

    <html>
        <body>
            <p>text:msg body!</p><br>
            <p><img src="cid:1.png" height=200 width=300></p><br>

        </body>
    </html>

--GoBoundary--

总结

以上代码可以实现在正文中添加多张图片的功能
当然只要修改template 想怎么发送就怎么发送~~~

因为使用的是QQ邮箱在password中填入QQ邮箱的授权码
这里写图片描述

这个方法是将图片按原先附件的方法添加
关键就是在之后的html中通过 img src=”cid:1.png” 来引用附件中的图片从而在正文中显示
这里写图片描述

这只是我通过抓包发现的一种方法总感觉有点麻烦
感觉应该存在其它更优的方法希望能够一起交流谢谢！！

Golang 通过net/smtp发送邮件 在正文中添加图片(附件/非附件)

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