Golang & Javascript : How to save cropped image to file on server
While building my web application to manage my tenants and rental properties, I need a solution to capture the cropped image and save the bytes produced by https://github.com/fengyuanchen/cropperjs into my server(or upload directly to S3). Cropping image helps to reduce the image size and provides a clearer representation on which part of the original image to focus on.
The example code below demonstrates how to crop an image and store the image bytes into a file. Before compiling and executing the code, make sure that you have:
Download chi package by
go get -u github.com/go-chi/chi
Create a directory named
cropped
An image file to crop
package main
import (
"bytes"
"encoding/base64"
"fmt"
"image"
"image/png"
"net/http"
"os"
"path/filepath"
"strings"
"github.com/go-chi/chi"
)
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))
currentDir, _ := os.Getwd()
imgFile, err := os.Create(currentDir + "/cropped/croppedimage.png")
if err != nil {
panic(err)
}
// save to file on your webserver
png.Encode(imgFile, img)
fmt.Println("croppedimage.png file saved")
}
}
func CropImage(w http.ResponseWriter, r *http.Request) {
html := `<!DOCTYPE html>
<html lang="en">
<head>
<title>Golang and Cropper JS demo</title>
<!-- cropper js -->
<link href="https://cdnjs.cloudflare.com/ajax/libs/cropperjs/1.5.6/cropper.min.css" rel="stylesheet">
<script src="https://cdnjs.cloudflare.com/ajax/libs/cropperjs/1.5.6/cropper.min.js"></script>
<!-- jquery -->
<script src="https://code.jquery.com/jquery-3.4.1.min.js" integrity="sha256-CSXorXvZcTkaix6Yvo6HppcZGetbYMGWSFlBw8HfCJo=" crossorigin="anonymous"></script>
</head><body>
<input type="file" name="img[]" class="file-upload-default" id="cropperImageUpload">
<div>
<input type="text" class="form-control file-upload-info" disabled="" placeholder="Upload Image">
<button class="file-upload-browse" type="button">Upload</button>
</div>
<div>
<label>Width (px) :</label>
<input type="number" value="300" class="img-w" placeholder="Image width">
<button class="btn btn-primary crop mb-2 mb-md-0">Crop</button>
<a href="javascript:;" class="save">Save</a>
</div>
<style>
w-100 {
max-width: 100%; /* This rule is very important, please do not ignore this! */
}
</style>
<div>
<img src="" class="w-100" id="croppingImage" alt="cropper">
</div>
<div class="col-md-4 ml-auto">
<h6>Cropped Image: </h6>
<img class="w-100 cropped-img" src="#" alt="">
</div>
<script type="text/javascript">
$(function() {
'use strict';
var croppingImage = document.querySelector('#croppingImage'),
img_w = document.querySelector('.img-w'),
cropBtn = document.querySelector('.crop'),
croppedImg = document.querySelector('.cropped-img'),
saveBtn = document.querySelector('.save'),
upload = document.querySelector('#cropperImageUpload'),
cropper = '';
$('.file-upload-browse').on('click', function(e) {
var file = $(this).parent().parent().parent().find('.file-upload-default');
file.trigger('click');
});
cropper = new Cropper(croppingImage);
// on change show image with crop options
upload.addEventListener('change', function (e) {
$(this).parent().find('.form-control').val($(this).val().replace(/C:\\fakepath\\/i, ''));
if (e.target.files.length) {
cropper.destroy();
// start file reader
const reader = new FileReader();
reader.onload = function (e) {
if(e.target.result){
croppingImage.src = e.target.result;
cropper = new Cropper(croppingImage);
}
};
reader.readAsDataURL(e.target.files[0]);
}
});
// crop on click
cropBtn.addEventListener('click',function(e) {
e.preventDefault();
// get result to data uri
let imgSrc = cropper.getCroppedCanvas({
width: img_w.value // input value
}).toDataURL();
croppedImg.src = imgSrc;
saveBtn.setAttribute('href', imgSrc);
});
// save on click
saveBtn.addEventListener('click',function(e) {
e.preventDefault();
// get result to data uri
let imgSrc = cropper.getCroppedCanvas({
//width: img_w.value // input value
width: 300 // input value
}).toDataURL();
//post base64 image data to saveCroppedPhoto function then redirect to the /cropped directory show the actual file
$.post("/saveCroppedPhoto", {data: imgSrc}, function () {window.location.href = "/cropped/"});
});
});
</script>`
w.Write([]byte(html))
}
func main() {
mux := chi.NewRouter()
mux.HandleFunc("/", CropImage)
mux.HandleFunc("/saveCroppedPhoto", SaveFile)
// expose our /cropped directory
workDir, _ := os.Getwd()
croppedDir := filepath.Join(workDir, "/cropped")
fileServer(mux, "/cropped", http.Dir(croppedDir))
http.ListenAndServe(":8080", mux)
}
func fileServer(r chi.Router, path string, root http.FileSystem) {
if strings.ContainsAny(path, "{}*") {
panic("FileServer does not permit URL parameters.")
}
fs := http.StripPrefix(path, http.FileServer(root))
if path != "/" && path[len(path)-1] != '/' {
r.Get(path, http.RedirectHandler(path+"/", 301).ServeHTTP)
path += "/"
}
path += "*"
r.Get(path, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
fs.ServeHTTP(w, r)
}))
}
Start the program and point to localhost:8080
with your browser. Upload
an image file, crop
and save
the cropped image.
Happy coding!
References:
https://www.socketloop.com/tutorials/golang-upload-to-s3-with-official-aws-sdk-go-package
https://github.com/fengyuanchen/cropperjs/blob/master/README.md#features
https://www.socketloop.com/tutorials/golang-take-screen-shot-of-browser-with-jquery-example
See also : Golang : Upload to S3 with official aws-sdk-go package
By Adam Ng(黃武俊)
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