Golang : Take screen shot of browser with JQuery example
In this tutorial, we will learn how to do a screen capture of a client(browser) and send the capture screen shot back to the web server to be saved as a PNG file and download into the client's computer afterward(need user permission).
This tutorial uses JQuery & JavaScript HTML renderer - html2canvas to capture the browser content either by targeting certain <div> or entire page and pass the base64 data back to Golang web server.
This feature can be useful in situation where you want download a page screen shot at certain interval or use in tech support(with permission from client).
Here you go!
package main
import (
"bytes"
"encoding/base64"
"fmt"
"image"
"image/png"
"io/ioutil"
"net/http"
"os"
)
func SaveFile(w http.ResponseWriter, r *http.Request) {
if r.Method == "POST" {
imgBase64 := r.FormValue("data")
// remove "data:image/png;base64,"
imgBase64cleaned := imgBase64[len("data:image/png;base64,"):len(imgBase64)]
// decode base64 to buffer bytes
imgBytes, _ := base64.StdEncoding.DecodeString(imgBase64cleaned)
// convert []byte to image for saving to file
img, _, _ := image.Decode(bytes.NewReader(imgBytes))
imgFile, err := os.Create("./screen-capture.png")
if err != nil {
panic(err)
}
// save to file on your webserver
png.Encode(imgFile, img)
fmt.Println("screen-capture.png file saved")
}
// NOTE : For some odd reason this part has to be outside the r.Method == "POST"
// in order for the streaming/download straight to browser to work
streamBytes, _ := ioutil.ReadFile("./screen-capture.png")
//output to browser
w.Header().Set("Content-Disposition", "attachment; filename='screen-capture.png'")
w.Header().Set("Content-Type", "image/png")
w.Header().Set("Content-Transfer-Encoding", "binary")
w.Header().Set("Content-Description", "File Transfer")
//w.Header().Set("Content-Length", string(len(streamBytes)))
// will produce warning message : http: invalid Content-Length of "뚴"
// ok, pump it out to the browser!
b := bytes.NewBuffer(streamBytes)
if _, err := b.WriteTo(w); err != nil {
fmt.Fprintf(w, "%s", err)
}
}
func ScreenCapture(w http.ResponseWriter, r *http.Request) {
html := `<html><body>
<script type="text/javascript" src="https://code.jquery.com/jquery-1.11.3.js"></script>
<script type="text/javascript" src="https://socketloop.com/public/tutorial/html2canvas.js"></script>
<style type="text/css">
#buttons-area
{
margin:30px auto;
padding:5px;
border:solid #cdcdcd 1px;
width:700px;
text-color:white;
background:#f4f4f4;
}
#target-area
{
margin:50px auto;
padding:15px;
border:solid #cdcdcd 1px;
width:700px;
background:blue;
}
button
{
text-align:center;
width:48%;
height:80px;
border:1px solid #c3d825;
font-family:Verdana, Geneva, sans-serif;
border-radius:3px;
background:#c3d825;
color:#355105;
text-shadow: 0 1pm #ecffba;
font-weight:bolder;
font-size:18px;
border-radius:10px;
}
</style>
<div id="target-area"></div>
<div id="buttons-area">
<h1>Take a screenshot with JQuery and Golang example.</h1>
<button type="button" onclick="captureDiv()">capture div and replace</button>
<button type="button" onclick="capturePage()">capture entire page & save</button>
</div>
</body></html>
<script type="text/javascript">
function captureDiv() {
html2canvas([document.getElementById('buttons-area')], {
onrendered: function(canvas)
{
var imgBase64 = canvas.toDataURL() // already base64
var img2html = '<img src=' + imgBase64 + '>'
document.getElementById('target-area').innerHTML = img2html;
}
});
}
function capturePage() {
html2canvas(document.body, {
onrendered: function(canvas)
{
var imgBase64 = canvas.toDataURL() // already base64
var img2html = '<img src=' + imgBase64 + '>'
// too big to fit into target-area div
// so, we save to file
//document.getElementById('target-area').innerHTML = img2html;
//post screen capture base64 image data to save function
$.post("/save", {data: imgBase64}, function () {
window.location.href = "save"});
}
});
}
</script>`
w.Write([]byte(html))
}
func main() {
mux := http.NewServeMux()
mux.HandleFunc("/", ScreenCapture)
mux.HandleFunc("/save", SaveFile)
http.ListenAndServe(":8080", mux)
}
Hope this helps and happy coding!
References:
Affiliate :
Hire Golang Developers
Tags : golang screen-capture html2canvas jquery
By Adam Ng
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