How to retrieve object from Go http.Request?

I have a working app that recieves HTTP GET parameters. They've been Strings and ints until now and it has worked fine getting each field using

http.Request.FormValue("field")

But now I've added an array of simple objects in the parameters and I don't know how to transform it to a slice of Go structs.

The array in question is

mods:[{
    name : x,
    max : 1,
    min : 2
 },{
    name:y,...
 }]

So I'm not sure how to proceed to map it to a Go struct. Should I create the struct first and map the result of r.FormValue using JSON?

Let's say you want to fetch a set of github users and want to print their nicknames (Login field in api.github.com).

Given a User array example:

[{
  "login": "simonjefford",
  "id": 136,
  "avatar_url": "https://avatars1.githubusercontent.com/u/136?v=3",
  "gravatar_id": "",
  "url": "https://api.github.com/users/simonjefford",
  "html_url": "https://github.com/simonjefford",
  "followers_url": "https://api.github.com/users/simonjefford/followers",
  "following_url": "https://api.github.com/users/simonjefford/following{/other_user}",
  "gists_url": "https://api.github.com/users/simonjefford/gists{/gist_id}",
  "starred_url": "https://api.github.com/users/simonjefford/starred{/owner}{/repo}",
  "subscriptions_url": "https://api.github.com/users/simonjefford/subscriptions",
  "organizations_url": "https://api.github.com/users/simonjefford/orgs",
  "repos_url": "https://api.github.com/users/simonjefford/repos",
  "events_url": "https://api.github.com/users/simonjefford/events{/privacy}",
  "received_events_url": "https://api.github.com/users/simonjefford/received_events",
  "type": "User",
  "site_admin": false
}]

You need a proper struct to handle it:

type Users []struct {
  Login string `json:"login"`
  ID int `json:"id"`
  AvatarURL string `json:"avatar_url"`
  GravatarID string `json:"gravatar_id"`
  URL string `json:"url"`
  HTMLURL string `json:"html_url"`
  FollowersURL string `json:"followers_url"`
  FollowingURL string `json:"following_url"`
  GistsURL string `json:"gists_url"`
  StarredURL string `json:"starred_url"`
  SubscriptionsURL string `json:"subscriptions_url"`
  OrganizationsURL string `json:"organizations_url"`
  ReposURL string `json:"repos_url"`
  EventsURL string `json:"events_url"`
  ReceivedEventsURL string `json:"received_events_url"`
  Type string `json:"type"`
  SiteAdmin bool `json:"site_admin"`
}

I suggest you to use json-to-go to have a nice a clean struct given a json.

Then you can do the following:

package main

import (
  "fmt"
  "encoding/json"
  "net/http"
  "log"
  "io/ioutil"
)

func main() {

  response, err := http.Get("https://api.github.com/users?since=135")
  if err != nil {
     log.Fatal(err)
  } else {

    defer response.Body.Close()
    users := UnmarshalUsers(response)
    for _, u := range users {
        //Print each user's Login nickname
        fmt.Println(u.Login)
    }

  }

}

Where UnmarshalUsers is

func UnmarshalUsers(r *http.Response) Users {
	body, err := ioutil.ReadAll(r.Body)
	if err != nil {
		panic(err)
	}
	var users Users
	err = json.Unmarshal(body, &users)
	if err != nil {
		panic(err)
	}

	return users
}

Check out the encoding/json package. In Go, you have to marshal and unmarshal your Go structures into and out of their encoding. It isn't quick an easy, but it's an good modern solution for a strictly typed language like Go.

In your case, you'll want to create a struct that matches the structure of the json you are trying to extract, and then unmarshal the json into a variable of the struct type you created.