Golang json.decoder fails to decode requests coming from the browser ONLY

My golang app fails to decode forms coming from the browsers but succeed when using curl and httpie.

#Given this code:

    type Member struct {
Username string `json:"username"`
Email string `json:"email"`
Password string `json:"password"`
}
func Register(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
var t Member
json.NewDecoder(r.Body).Decode(&t)
log.Println(t.Username)
log.Println(t.Email)
log.Println(t.Password)
w.WriteHeader(204)
}

#this prints!
curl -H "Content-Type: application/json" -X POST -d '{"username":"cesco","email":"cesco@gmail.com","password":"password"}' http://localhost:5000/register

#also this!

http -v -j  --form POST localhost:5000/register username="cesco" email="cesco@gmail.com" password="sadsa"

#this does not

<form id="register" action="register"  method="post">
<input type="text" name="username"><br>
<input type="email" name="email"><br>
<input type="password" name="password"><br>
<input type="submit" value="Submit">
</form>

#neither this

var data = $('#register').serialize();
$.ajax({
url: 'register', // php script to retern json encoded string
data: data,  // serialized data to send on server
beforeSend: function (xhr) {
xhr.setRequestHeader("Content-type", "*/*");
},
dataType: 'json', // set recieving type - JSON in case of a question
type: 'POST', // set sending HTTP Request type
async: false,
success: function (data) { // callback method for further manipulations
},
error: function (data) { // if error occured
}
});

#Logs on the same order as the question

2016/02/09 13:56:12 cesco
2016/02/09 13:56:12 cesco@gmail.com
2016/02/09 13:56:12 password
2016/02/09 13:56:12 key: Accept value: [*/*]
2016/02/09 13:56:12 key: Content-Type value: [application/json]
2016/02/09 13:56:12 key: Content-Length value: [68]
2016/02/09 13:56:12 key: User-Agent value: [Mozilla/5.0 Gecko]
[13:56:12] 127.0.0.1 - - [09/Feb/2016:13:56:12 -0200] "POST /register HTTP/1.1" 204 0
2016/02/09 13:56:18 cesco
2016/02/09 13:56:18 cesco@gmail.com
2016/02/09 13:56:18 sadsa
2016/02/09 13:56:18 key: Accept-Encoding value: [gzip, deflate]
2016/02/09 13:56:18 key: Accept value: [application/json]
2016/02/09 13:56:18 key: User-Agent value: [HTTPie/0.8.0]
2016/02/09 13:56:18 key: Connection value: [keep-alive]
2016/02/09 13:56:18 key: Content-Type value: [application/json; charset=utf-8]
2016/02/09 13:56:18 key: Content-Length value: [70]
[13:56:18] 127.0.0.1 - - [09/Feb/2016:13:56:18 -0200] "POST /register HTTP/1.1" 204 0
[13:56:30] 127.0.0.1 - - [09/Feb/2016:13:56:30 -0200] "GET / HTTP/1.1" 200 747
2016/02/09 13:56:40 
2016/02/09 13:56:40 
2016/02/09 13:56:40 
2016/02/09 13:56:40 key: User-Agent value: [Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.103 Safari/537.36]
2016/02/09 13:56:40 key: Content-Type value: [application/x-www-form-urlencoded]
2016/02/09 13:56:40 key: Referer value: [http://localhost:5000/]
2016/02/09 13:56:40 key: Accept-Language value: [en-US,en;q=0.8,pt;q=0.6,es;q=0.4]
2016/02/09 13:56:40 key: Connection value: [keep-alive]
2016/02/09 13:56:40 key: Content-Length value: [53]
2016/02/09 13:56:40 key: Cache-Control value: [max-age=0]
2016/02/09 13:56:40 key: Accept value: [text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8]
2016/02/09 13:56:40 key: Origin value: [http://localhost:5000]
2016/02/09 13:56:40 key: Upgrade-Insecure-Requests value: [1]
2016/02/09 13:56:40 key: Accept-Encoding value: [gzip, deflate]
[13:56:40] 127.0.0.1 - - [09/Feb/2016:13:56:40 -0200] "POST /register HTTP/1.1" 204 0
2016/02/09 13:56:59 
2016/02/09 13:56:59 
2016/02/09 13:56:59 
2016/02/09 13:56:59 key: Content-Type value: [*/*]
2016/02/09 13:56:59 key: Referer value: [http://localhost:5000/]
2016/02/09 13:56:59 key: Connection value: [keep-alive]
2016/02/09 13:56:59 key: Content-Length value: [53]
2016/02/09 13:56:59 key: X-Requested-With value: [XMLHttpRequest]
2016/02/09 13:56:59 key: User-Agent value: [Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.103 Safari/537.36]
2016/02/09 13:56:59 key: Accept value: [application/json, text/javascript, */*; q=0.01]
2016/02/09 13:56:59 key: Origin value: [http://localhost:5000]
2016/02/09 13:56:59 key: Accept-Encoding value: [gzip, deflate]
2016/02/09 13:56:59 key: Accept-Language value: [en-US,en;q=0.8,pt;q=0.6,es;q=0.4]
[13:56:59] 127.0.0.1 - - [09/Feb/2016:13:56:59 -0200] "POST /register HTTP/1.1" 204 0

Your curl example is posting a json encoded body with Content-Type: application/json. A browser isn't going to somehow encode an html form into json. As you can see in the logs, you're receiving Content-Type: application/x-www-form-urlencoded

If you want to get the values from a form, use Request.FormValue, or Request.PostFormValue