What type should I use in my POST request for gorest?

I'm very new to Go so please forgive me if this is stupid obvious.

I'm trying to post a form to a REST API written in Go using gorest. I've successfully done this using GET, but I can't get the POST data to parse into a map. Here is my Go code

gotest.go:

package main
import (
  "code.google.com/p/gorest"
  "net/http"
  "fmt"
)

func main() {
  gorest.RegisterService(new(HelloService)) //Register our service                                        
  http.Handle("/",gorest.Handle())
  http.ListenAndServe(":8787",nil)
}

//Service Definition                                                                                      
type HelloService struct {
  gorest.RestService `root:"/api/"`
  save   gorest.EndPoint `method:"POST" path:"/save/" output:"string" postdata:"map[string]string"`
}

func(serv HelloService) Save(PostData map[string]string) {
  fmt.Println(PostData)
}

And my awesome html form:

<form method="POST" action="http://127.0.0.1:8787/api/save/">
  key: <input type="text" name="key" /><br />  
  json: <input type="text" name="json" /><br />
  <input type="submit" />
</form>

I would think that would turn my post data into a nice map that I could access. I fill out the form, hit submit, and it returns an error:

Error Unmarshalling data using application/json. Client sent incompetible data format in entity. (invalid character 'k' looking for beginning of value)

EDIT: As greggory.hz points out, the program seems to think that the post data is a json. This error is because a json has to start with a brace, bracket or quote.

If map[string]string with string it prints the following to the bash terminal where I am running this:

key=arst&json=%7B%27arst%27%3A%27arst%27%7D

In the go rest documentation the only example of this that I could find is:

posted gorest.EndPoint method:"POST" path:"/post/"  postdata:"User" 
func(serv HelloService) Posted(posted User)

But my attempts at creating a custom struct have also fails with the same unmarshalling error seen above.

type MyStruct struct {
  key,json string
}

Can someone please tell me what data type I should be using?

You are trying to post an html form to a service expecting a json body. But your browser isn't going to format the post as application/json. It will instead format it as a urlencoded body. The problem isn't in your go server code it's in the html form. You probably want to use javascript to package up and send your post instead of a standard html form.

<div>
  <input type="hidden" name="endpont" value="http://127.0.0.1:8787/api/save/" />
  key: <input type="text" name="key" /><br /> <!-- this should be used in your post url -->
  json: <input type="text" name="json" /><br /> <!-- this will get sent by your javascript as the post body -->
  <input type="button" onclick="send_using_ajax();" />
</div>