Fun with Gmail and Go

Many of you at the “free” Go programming course have been asking “How do I use Gmail with Go?” To answer that question, we will quickly build a fun Go web app that uses Gmail to send off emails.

I am assuming that you have downloaded and installed Go and have set the GOPATH properly. If new to Go, then my previous article has this covered.

In one of my previous articles, we learned about Golang’s package template (namely text/template and html/template). We shall use html/template here. Also, we shall use Golang’s net/smtp package to connect to Gmail.

Create the folder C:/go_projects/go/src/github.com/SatishTalim/webgmail. In this folder, create a file webgmail.go as follows:

package main

import (
        "fmt"
        "html/template"
        "net/http"
        "net/smtp"
        "os"
)

func main() {
        http.HandleFunc("/", root)
        http.HandleFunc("/mail", mail)
        fmt.Println("listening...")
        err := http.ListenAndServe(GetPort(), nil)
        if err != nil {
                panic(err)
        }
}

func GetPort() string {
        var port = os.Getenv("PORT")
        // Set a default port if there is nothing in the environment
        if port == "" {
                port = "4747"
                fmt.Println("INFO: No PORT environment variable detected, defaulting to " + port)
        }
        return ":" + port
}

func root(w http.ResponseWriter, r *http.Request) {
        fmt.Fprint(w, rootForm)
}

const rootForm = `
  <!DOCTYPE html>
    <html>
      <head>
        <meta charset="utf-8">
        <title>Enter your mail</title>
        <link rel="stylesheet" href="http://yui.yahooapis.com/pure/0.4.2/pure-min.css">
      </head>
      <body>
        <h2>Enter your Email</h2>
        <form action="/mail" method="post" accept-charset="utf-8" class="pure-form">
          To:<input type="text" name="to" />
          Subject<:input type="text" name="subject" />
          Message:<input type="text" name="msg" />
          <input type="submit" value="... and check the mail!"  class="pure-button pure-button-primary" />
        </form>
        <div>
          <p><b>© 2014 RubyLearning. All rights reserved.</b></p>
        </div>
      </body>
    </html>
`

const mailTemplateHTML = ` 
  <!DOCTYPE html>
    <html>
      <head>
        <meta charset="utf-8">
        <title>Email Result</title>
        <link rel="stylesheet" href="http://yui.yahooapis.com/pure/0.4.2/pure-min.css">
      </head>
      <body>
        <h2>Email Result</h2>
        <p>Your email has been sent to: </p>
        <pre>{{html .}}</pre>
        <p><a href="/">Start again!</a></p>
        <div>
          <p><b>© 2014 RubyLearning. All rights reserved.</b></p>
        </div>
      </body>
    </html>
`

var mailTemplate = template.Must(template.New("mail").Parse(mailTemplateHTML))

func mail(w http.ResponseWriter, r *http.Request) {
        to := r.FormValue("to")
        subject := r.FormValue("subject")
        message := r.FormValue("msg")

        body := "To: " + to + "\r\nSubject: " +
          subject + "\r\n\r\n" + message

        auth := smtp.PlainAuth("", "satish.talim", "password", "smtp.gmail.com")
        err := smtp.SendMail("smtp.gmail.com:587", auth, "satish.talim@gmail.com", 
          []string{to},[]byte(body))
        if err != nil {
                panic(err)
        } 

        err1 := mailTemplate.Execute(w, to)
        if err1 != nil {
                http.Error(w, err1.Error(), http.StatusInternalServerError)
        }
}

From the folder C:/go_projects/go/src/github.com/SatishTalim/webgmail you can now run the program by typing:

$ go run webgmail.go

Point your browser to http://localhost:4747 and you should see something like this in your browser:

Note:

You call smtp.PlainAuth with your gmail username, password and domain name, and it returns you back an instance of smtp.Auth that you can use to send e-mails.
If you have setup the 2-Step Verification process in Gmail, then you need to set an application-specific password. Use this password in the above program.
You can send mail with smtp.SendMail.
SMTP on port 587 uses TLS. SSL and TLS both provide a way to encrypt a communication channel between two computers (e.g. your computer and a server). TLS is the successor to SSL and the terms SSL and TLS are used interchangeably unless you’re referring to a specific version of the protocol.

You can learn more about writing and deploying web apps with Go from my new book.

I hope you’ve enjoyed this post, please leave any feedback in the comments section.