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extract a javascript object value from a html page using goquery and otto
package main
import (
"errors"
"log"
"os"
"github.com/PuerkitoBio/goquery"
"github.com/robertkrimen/otto"
)
func getMP4URL(id string) string {
doc, err := goquery.NewDocument("https://vine.co/v/" + id)
check(err)
// we want the first <script> tag from the html
firstScript := doc.Find("script").First()
vm := otto.New()
// otherwise window.POST_DATA will raise an reference error `ReferenceError: 'window' is not defined`
_, err = vm.Run("var window = {};")
check(err)
// eval the javascript inside the <script> tag
_, err = vm.Run(firstScript.Text())
check(err)
// traverse down the object path: window > POST_DATA > <videoID> > videoDashURL
wVal, err := vm.Get("window")
check(err)
pdata, err := getValueFromObject(wVal, "POST_DATA")
check(err)
videoData, err := getValueFromObject(*pdata, id)
check(err)
videoDashUrl, err := getValueFromObject(*videoData, "videoDashUrl")
check(err)
// finally the video url...
videoUrl, err := videoDashUrl.ToString()
check(err)
return videoUrl
}
func main() {
if len(os.Args) != 2 {
log.Fatalln("Usage: vineUrl <videoID>")
}
log.Println("Video URL:", getMP4URL(os.Args[1]))
}
// fatal if there is an error
func check(err error) {
if err != nil {
log.Fatal(err)
}
}
func getValueFromObject(val otto.Value, key string) (*otto.Value, error) {
if !val.IsObject() {
return nil, errors.New("passed val is not an Object")
}
valObj := val.Object()
obj, err := valObj.Get(key)
if err != nil {
return nil, err
}
return &obj, nil
}
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