Golang : Submit web forms without browser by http.PostForm example

Writing this tutorial on how to submit a web form without using a browser. We submit web forms almost every time when we go online, such as login form, sign up form or purchasing order form. All these are done with a browser and require human input.

In this tutorial, we will learn how to post form input with Golang and get the status to see if the submission is successful or otherwise. For demonstration purpose, a server program will wait for input from client program and a client program will submit the login data to the server program. If the submission is successful, the server program prints out the accepted input from the client.

First, run this server program and prepare to accept submission from a client program.

loginserver.go

 package main

 import (
  "fmt"
  "html/template"
  "log"
  "net/http"
 )

 const logUserPage = `<html><body>
 {{if .LoginError}}<p style="color:red">Either username or password is not in our record! Sign Up?</p>{{end}}

 <form method="post" action="/login">
 {{if .Username}}
 <p><b>{{.Username}}</b>, you're already logged in! <a href="/logout">Logout!</a></p>
 {{else}}
 <label>Username:</label>
 <input type="text" name="Username"><br>

 <label>Password:</label>
 <input type="password" name="Password">

 <input type="submit" name="Login" value="Let me in!">
 {{end}}
 </form>
 </body></html>`

 var logUserTemplate = template.Must(template.New("").Parse(logUserPage))

 func LoginPageHandler(w http.ResponseWriter, r *http.Request) {

  conditionsMap := map[string]interface{}{}

  // verify username and password
  if r.FormValue("Password") != "" && r.FormValue("Username") != "" {
 username := r.FormValue("Username")
 password := r.FormValue("Password")

 log.Println("Logged in :", username)
 log.Println("With password :", password)

 conditionsMap["Username"] = username
 conditionsMap["LoginError"] = false

  }

  if err := logUserTemplate.Execute(w, conditionsMap); err != nil {
 log.Println(err)
  }
 }

 func main() {
  fmt.Println("Server started, submit web forms to localhost:8080/login")
  http.HandleFunc("/login", LoginPageHandler)
  http.ListenAndServe(":8080", nil)
 }

Execute

go run loginserver.go &

Next, run this client program. NOTE: Remember, the client must have the matching form variable names in order to execute a successful submission. The names should be case sensitive.

submitwebform.go

 package main

 import (
  "fmt"
  "net/http"
  "net/url"
 )

 func main() {
  username := "adamng"
  password := "theultimatepassword"

  loginURL := "http://localhost:8080/login"

  urlData := url.Values{}
  urlData.Set("Username", username)
  urlData.Set("Password", password)

  resp, err := http.PostForm(loginURL, urlData)

  if err != nil {
 fmt.Println(err)
  }

  fmt.Println("Status : ", resp.Status)
  fmt.Println("Header: ", resp.Header)
  fmt.Println("Body: ", resp.Body)

 }

Output from server program upon receiving correct login input:

Server started, submit web forms to localhost:8080/login

2017/08/30 16:07:56 Logged in : adamng

2017/08/30 16:07:56 With password : theultimatepassword

Happy coding!

References:

https://www.socketloop.com/references/golang-net-http-postform-function-example

https://www.socketloop.com/tutorials/golang-login-and-logout-a-user-after-password-verification-and-redirect-example

Golang : Submit web forms without browser by http.PostForm example

See also : Golang : Login and logout a user after password verification and redirect example

By Adam Ng

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