18-rest-api-fetch.go

/**
 * rest-api-fetch.go
 *
 * Example fetching data from a REST API endpoint parsing and displaying
 * This example using new listing in Reddit golang group. The key to
 * understanding JSON decoding is understanding the data structure you
 * receive the data. Once data structs are mapped, it becomes relatively
 * straight forward
 *
 */

package main

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

// create data structures to hold JSON data
// this needs to match the fields in the JSON feed
// see sample data fetch at bottom of this file

// create an individual entry data structure
// this does not need to hold every field, just the ones we want
type Entry struct {
	Title     string
	Author    string
	URL       string
	Permalink string
}

// the feed is the full JSON data structure
// this sets up the array of Entry types (defined above)
type Feed struct {
	Data struct {
		Children []struct {
			Data Entry
		}
	}
}

func main() {
	// url of REST endpoint we are grabbing data from
	url := "http://www.reddit.com/r/golang/new.json"

	// fetch url
	resp, err := http.Get(url)
	if err != nil {
		log.Fatalln("Error fetching:", err)
	}
	// defer response close
	defer resp.Body.Close()

	// confirm we received an OK status
	if resp.StatusCode != http.StatusOK {
		log.Fatalln("Error Status not OK:", resp.StatusCode)
	}

	// read the entire body of the response
	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		log.Fatalln("Error reading body:", err)
	}

	// create an empty instance of Feed struct
	// this is what gets filled in when unmarshaling JSON
	var entries Feed
	if err := json.Unmarshal(body, &entries); err != nil {
		log.Fatalln("Error decoing JSON", err)
	}

	// loop through the children and create entry objects
	for _, ed := range entries.Data.Children {
		entry := ed.Data
		log.Println(">>>")
		log.Println("Title   :", entry.Title)
		log.Println("Author  :", entry.Author)
		log.Println("URL     :", entry.URL)
		log.Printf("Comments: http://reddit.com%s \n", entry.Permalink)
	}
}

/* Example Data Listing

{"kind": "Listing",
	"data": {
		"modhash": "",
		"children": [
			{ "kind": "t3", "data":
				{
					"domain": "austingwalters.com", "banned_by": null, "media_embed": {}, "subreddit": "golang", "selftext_html": null, "selftext": "", "likes": null, "secure_media": null, "link_flair_text": null, "id": "26l1by", "gilded": 0, "secure_media_embed": {}, "clicked": false, "stickied": false, "author": "dgryski", "media": null, "score": 2, "approved_by": null, "over_18": false, "hidden": false, "thumbnail": "", "subreddit_id": "t5_2rc7j", "edited": false, "link_flair_css_class": null, "author_flair_css_class": null, "downs": 8, "saved": false, "is_self": false,
					"permalink": "/r/golang/comments/26l1by/building_a_web_server_in_go_database_accesses/", "name": "t3_26l1by", "created": 1401198126.0,
					"url": "http://austingwalters.com/building-a-web-server-in-go-database-accesses/", "author_flair_text": null,
					"title": "Building a Web Server in Go: Database Accesses", "created_utc": 1401169326.0, "ups": 10, "num_comments": 1, "visited": false, "num_reports": null, "distinguished": null
				}
			},
			{ "kind": "t3", "data":
				{
					"domain": "self.golang", "banned_by": null, "media_embed": {}, "subreddit": "golang", "selftext_html": "<!-- SC_OFF --><div class=\"md\"><p>Hello champs!</p>\n\n<p>Again with a short-question</p>\n\n<p>As I'm a ruby/RoR/sinatra api developer I would like to convinced my CTO to move some of the stack to golang.</p>\n\n<p>I know some of the webframework in golang</p>\n\n<ul>\n<li>revel</li>\n<li>martini</li>\n<li>negroni</li>\n<li>goji</li>\n</ul>\n\n<p>and libraries like gorila.</p>\n\n<p>But, always all the people seems to say: start with net/http</p>\n\n<p>Totally agree, but I found documentation a little bit random :)</p>\n\n<p>So, my CTO ask me:</p>\n\n<ul>\n<li>how stable are the api</li>\n<li>how hot and active are the frameworks</li>\n<li>if I use net/http do I have all the rack, sinatra, API libraries</li>\n</ul>\n\n<p>There any long save tutorial for net/http (json response, json parse, auth, REST, etc)?</p>\n\n<p>all the best</p>\n</div><!-- SC_ON -->", "selftext": "Hello champs!\n\nAgain with a short-question\n\nAs I'm a ruby/RoR/sinatra api developer I would like to convinced my CTO to move some of the stack to golang.\n\nI know some of the webframework in golang\n\n* revel\n* martini\n* negroni\n* goji\n\nand libraries like gorila.\n\nBut, always all the people seems to say: start with net/http\n\nTotally agree, but I found documentation a little bit random :)\n\nSo, my CTO ask me:\n\n* how stable are the api\n* how hot and active are the frameworks\n* if I use net/http do I have all the rack, sinatra, API libraries\n\n\nThere any long save tutorial for net/http (json response, json parse, auth, REST, etc)?\n\nall the best", "likes": null, "secure_media": null, "link_flair_text": null, "id": "26jiyc", "gilded": 0, "secure_media_embed": {}, "clicked": false, "stickied": false, "author": "claudiug1", "media": null, "score": 10, "approved_by": null, "over_18": false, "hidden": false, "thumbnail": "", "subreddit_id": "t5_2rc7j", "edited": false, "link_flair_css_class": null, "author_flair_css_class": null, "downs": 5, "saved": false, "is_self": true,
					"permalink": "/r/golang/comments/26jiyc/where_to_look_to_start_with_golang_web/", "name": "t3_26jiyc", "created": 1401160182.0,
					"url": "http://www.reddit.com/r/golang/comments/26jiyc/where_to_look_to_start_with_golang_web/", "author_flair_text": null,
					"title": "where to look to start with golang web", "created_utc": 1401131382.0, "ups": 15, "num_comments": 9, "visited": false, "num_reports": null, "distinguished": null
				}
			},
			...
*/