如何从Go http.Request中检索对象？

Question

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?

Answer 1

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
}