reddit.go

// simple program to use json and download images from a subreddit

package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"image"
	"image/gif"
	"image/jpeg"
	"image/png"
	"io/ioutil"
	"log"
	"net/http"
	"os"
	"time"
)

type Item struct {
	Title   string
	URL     string
	Is_self bool
}

type Response struct {
	Data struct {
		Children []struct {
			Data Item
		}
		After  string
		Before string
	}
}

func (i Item) String() string {
	return fmt.Sprintf("%s\n%s\n%v", i.Title, i.URL, i.Is_self)
}

func decode(subreddit string) ([]Item, error) {
	url := fmt.Sprintf("http://www.reddit.com/r/%s.json", subreddit)
	r, err := http.Get(url)
	if err != nil {
		return nil, err
	}

	defer r.Body.Close()
	if r.StatusCode != http.StatusOK {
		return nil, errors.New(r.Status)
	}

	resp := new(Response)
	err = json.NewDecoder(r.Body).Decode(resp)
	if err != nil {
		return nil, err
	}

	items := make([]Item, len(resp.Data.Children))
	for i, child := range resp.Data.Children {
		items[i] = child.Data
	}
	//    after := resp.Data.After
	//    fmt.Printf("%s\n", after)
	return items, nil
}

func init() {

	image.RegisterFormat("png", "png", png.Decode, png.DecodeConfig)

	image.RegisterFormat("jpeg", "jpeg", jpeg.Decode, jpeg.DecodeConfig)

	image.RegisterFormat("gif", "gif", gif.Decode, gif.DecodeConfig)
}

func download_images(url string, title string, sema chan bool) {

	fmt.Println("Go routine waiting to start")

	// We will not start work until we get something from the channel
	<-sema

	// Make a http Get request to the url
	// We get back a response and an error
	r, err := http.Get(url)

	if err != nil {
		log.Fatalf("http.Get error %v", err)
		//return err
	}

	// We read all the bytes of the image
	data, err := ioutil.ReadAll(r.Body)

	if err != nil {
		log.Fatalf("io.ReadAll error %v", err)
		//return err
	}

	// close the response body
	r.Body.Close()

	// Create a temp file to store image
	file, err := ioutil.TempFile(os.TempDir(), "prefix")
	defer os.Remove(file.Name())
	if err != nil {
		log.Fatalf("tempfile creating error %v", err)
	}

	// Store image in temp file
	ioutil.WriteFile(file.Name(), data, 0666)

	// Open temp file
	f, _ := os.Open(file.Name())
	defer f.Close()

	// Find out format of image
	_, format, _ := image.Decode(f)

	if format == "jpeg" || format == "png" || format == "gif" {
		// Now we save the file to disk
		filename := fmt.Sprintf("(%s).%s", title, format)
		log.Println("Saving image ", title)
		ioutil.WriteFile(filename, data, 0666)
	}

	sema <- true

}

func main() {
	// Call the Get function to get our structs filled with reddit data
	items, err := decode("aww")

	if err != nil {
		log.Fatalf("Error while decoding %v", err)
	}

	// Create a channel of booleans. The capacity of the channel will decide,
	// how many goroutines will be working at any point
	sema := make(chan bool, 5)

	// Download images from the link
	for _, item := range items {
		if !item.Is_self {
			go download_images(item.URL, item.Title, sema)
		} else {
			continue
		}
	}

	// Activate go routines
	for i := 0; i < cap(sema); i++ {
		sema <- true
	}

	time.Sleep(40 * time.Second)
}