如何通过Gmail Go SDK将html模板正文作为电子邮件发送？

I have created a html file(i.e. email.html) which would finally serve me as my email body template. I tried the following code but my email body is a plain text with all the html that I have written in (email.html).

Can you suggest by looking into the code. Where is it going wrong??

Note: Template Parsing and Execute are working fine.

Code:

package main

import (
    "encoding/base64"
    "fmt"
    "html/template"
)

func getMessageString(fromEmail, To, ReplyTo, CC, BCC, Subject, emailBody string) []byte {
    return []byte("Reply-To: " + ReplyTo + "
" + "From: " + fromEmail + "
" + "To: " + To + "
" + "Cc: " + CC + "
" + "Bcc: " + BCC + "
" + "Subject: " + Subject + "

" + "MIME-Version: 1.0
" + "Content-Type: text/html; charset=\"utf-8\"
" + emailBody + "

")
}

func main() {
    t, tempErr := template.New("template.html").ParseFiles("template.html")
    if tempErr != nil {
        fmt.Println(tempErr.Error())
        return
    }

    execErr := t.Execute(buf, data)
    if execErr != nil {
        fmt.Println(execErr.Error())
    } else {
        messageStr := getMessageString("xyz@gmail.com", "abc@ionosnetworks.com", "pqr@gmail.com", "", "", "Test Subject", buf.String())

        var message gmail.Message
        message.Raw = base64.URLEncoding.EncodeToString(messageStr)

        _, err = svc.Users.Messages.Send("me", &message).Do()
        if err != nil {
            fmt.Println(err.Error())
        }
    }
}

The error is in the getMessageString func:

"Subject: " + Subject + "

"

Notice the double sequence, mail server parses everything after double as email content. In your case it skipped Content-Type header. So just remove one and result code should look like:

func getMessageString(fromEmail, To, ReplyTo, CC, BCC, Subject, emailBody string) []byte {
    return []byte("Reply-To: " + ReplyTo + "
" + "From: " + fromEmail + "
" + "To: " + To + "
" + "Cc: " + CC + "
" + "Bcc: " + BCC + "
" + "Subject: " + Subject + "
" + "MIME-Version: 1.0
" + "Content-Type: text/html; charset=\"utf-8\"

" + emailBody + "
")
}