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How to convert a base64 string into a file?

I used a jquery plugin to crop images. The plugin will crop the image and give it to me as a base64 encoded string. In order to upload it to S3, I need to convert this into a file and pass the file into the upload function. How can I do this? I tried a lot of things including decoding the string using atob. None worked.
Here's the code of the cropping plugin ('croppie') which gives me the encoded string :
imageCropper.croppie('result', {
type: 'canvas',
size: 'viewport',
format: 'jpeg'
}).then(function (resp) {
updateAvatar(resp);
});
I pass it to a function called updateAvatar. Here's the updateAvatar function :
updateAvatar({Meteor, Slingshot}, avatar) {
const uploader = new Slingshot.Upload('userAvatarUpload');
uploader.send(avatar, function (error, downloadUrl) {
if (error) {
// Log service detailed response.
console.error('Error uploading', uploader.xhr.response);
console.log(error);
}
else {
console.log('uploaded', downloadUrl);
}
});
}
The uploader.send function expects a file or a url. It won't accept my encoded string.
The plugin which I use to upload files to S3 : https://github.com/CulturalMe/meteor-slingshot

It seems like the missing 'brick' in your code is a function that would take a base64-encoded image and convert it to a Blob.
So, I'm going to focus on that part exclusively with a short comment for each step.
The following function expects a string such as:
data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2wBDAAMCAgICA...
function base64ImageToBlob(str) {
// extract content type and base64 payload from original string
var pos = str.indexOf(';base64,');
var type = str.substring(5, pos);
var b64 = str.substr(pos + 8);
// decode base64
var imageContent = atob(b64);
// create an ArrayBuffer and a view (as unsigned 8-bit)
var buffer = new ArrayBuffer(imageContent.length);
var view = new Uint8Array(buffer);
// fill the view, using the decoded base64
for(var n = 0; n < imageContent.length; n++) {
view[n] = imageContent.charCodeAt(n);
}
// convert ArrayBuffer to Blob
var blob = new Blob([buffer], { type: type });
return blob;
}

Convert the base64 string to blob, to be used in upload to S3. There are tidier ways of doing this of course! :)
Original SO Answer here: https://stackoverflow.com/a/16245768/1350913
imageCropper.croppie('result', {
type: 'canvas',
size: 'viewport',
format: 'jpeg'
}).then(function(resp) {
var contentType = 'image/png';
var s3Blob = b64toBlob(resp, contentType);
updateAvatar(s3Blob);
});
updateAvatar({
Meteor,
Slingshot
}, avatar) {
const uploader = new Slingshot.Upload('userAvatarUpload');
uploader.send(avatar, function(error, downloadUrl) {
if (error) {
// Log service detailed response.
console.error('Error uploading', uploader.xhr.response);
console.log(error);
} else {
console.log('uploaded', downloadUrl);
}
});
}
function b64toBlob(b64Data, contentType, sliceSize) {
contentType = contentType || '';
sliceSize = sliceSize || 512;
var b64DataString = b64Data.substr(b64Data.indexOf(',') + 1);
var byteCharacters = atob(b64DataString);
var byteArrays = [];
for (var offset = 0; offset < byteCharacters.length; offset += sliceSize) {
var slice = byteCharacters.slice(offset, offset + sliceSize);
var byteNumbers = new Array(slice.length);
for (var i = 0; i < slice.length; i++) {
byteNumbers[i] = slice.charCodeAt(i);
}
var byteArray = new Uint8Array(byteNumbers);
byteArrays.push(byteArray);
}
var blob = new Blob(byteArrays, {
type: contentType
});
return blob;
}

The base64ToFile function (.ts) converts the base64 string into a File. The codeUnits and charCodes part make sure you can read Unicode text as ASCII by converting the string such that each 16-bit unit occupies only one byte.
Finally the download function (.ts) downloads the converted file from your browser to your local machine.
function base64ToFile(base64data: string, myFileNameWithdotExtention: string,
fileType: string): File {
let content = decodeURIComponent(escape(window.atob(base64data)));
let fileName = myFileNameWithdotExtention;
const codeUnits = Uint16Array.from(
{ length: content.length },
( _, index) => content.charCodeAt(index)
);
const charCodes = new Uint8Array(codeUnits.buffer);
const type = fileType; // 'text/csv' for instance
const blob = new Blob([charCodes], { type });
return new File([blob], fileName, { lastModified: new Date().getTime(), type });
}
download(){
let res: string = getMyDataFromSomewhere(); // base64 string
let data = base64ToFile(res);
let element = document.createElement('a');
window.URL = window.URL || window.webkitURL;
element.setAttribute('href', window.URL.createObjectURL(data));
element.setAttribute('download', data.name);
element.style.display = 'none';
document.body.appendChild(element);
element.click();
document.body.removeChild(element);
}

Canvas to .jpg file with Cordova Phonegap

I'm trying to store a canvas in my divice, reading in internet i found that i have to convert my canvas to Base64, nice, i did it...
Then i searched a function to store a base64 with cordova and just found a function that stores a Blob object, so i searched again and found a function that converts my base64 to Blob, and nice again, it apparently works, but when i go to the file explorer i'm just getting a file that says in plain text (and changing its extension to .txt ):
[object Uint8Array][object Uint8Array]
This is my final code:
function draw() {
window.requestFileSystem(window.TEMPORARY, 5 * 1024 * 1024, function (fs) {
console.log('file system open: ' + fs.name);
getSampleFile(fs.root);
}, errorHandler);
}
function getSampleFile(dirEntry) {
var canvas = document.getElementById("mycanvas");
if (canvas.getContext) {
var ctx = canvas.getContext("2d");
//...some code to customize the canvas
//var mURI = canvas.toDataURL();
var mURI = canvas.toDataURL().replace(/data:image\/png;base64,/,'');
var x = Math.floor((Math.random() * 100000) + 1);
saveFile(dirEntry, b64toBlob(mURI,"image/png","512") , x+".png");
}
}
function b64toBlob(b64Data, contentType, sliceSize) {
contentType = contentType || '';
sliceSize = sliceSize || 512;
console.log('Estoy en B64');
var byteCharacters = atob(b64Data);
var byteArrays = [];
for (var offset = 0; offset < byteCharacters.length; offset += sliceSize) {
var slice = byteCharacters.slice(offset, offset + sliceSize);
var byteNumbers = new Array(slice.length);
for (var i = 0; i < slice.length; i++) {
byteNumbers[i] = slice.charCodeAt(i);
}
var byteArray = new Uint8Array(byteNumbers);
byteArrays.push(byteArray);
}
console.log('ByteArrays'+byteArrays);
var blob = new Blob(byteArrays, {type: contentType});
return blob;
}
function saveFile(dirEntry, fileData, fileName) {
console.log('1. DIRENTRY:'+dirEntry+', 2 FILEDATA:'+fileData+',3 FILENAME:'+fileName);
dirEntry.getFile(fileName, { create: true, exclusive: false }, function (fileEntry) {
writeFile(fileEntry, fileData);
}, errorHandler);
}
function writeFile(fileEntry, dataObj, isAppend) {
fileEntry.createWriter(function (fileWriter) {
fileWriter.onwriteend = function() {
console.log("Successful file write...");
};
fileWriter.onerror = function(e) {
console.log("Failed file write: " + e.toString());
};
fileWriter.write(dataObj);
});
}
I hope you can help me, the main goal of this is to store a picture with a watermark, so if you have another idea please tell me, thanks

Since you need to add a water mark you may refer following links
W3School Link
Jsfiddle Link
EDITED
var yourCanvas = document.getElementById('yourCanvasId');
var context = yourCanvas.getContext('2d');
var waterMarkImg = document.getElementById("waterMarkImageId");
context.drawImage(waterMarkImg, 0, 0, yourCanvas.width, yourCanvas.height);
var basse64 = yourCanvas.toDataURL();

Length of uploaded couchDB attachment always 0 Bytes

So...I'm new to all this stuff and I'm developing an app for android with AngularJS and Ionic Framework and try to upload an audiofile I have recorded with the cordova capture Plugin like this:
// gets called from scope
$scope.captureAudio = function() {
var options = { limit: 1, duration: 10 };
$cordovaCapture.captureAudio(options).then(function(audioData) {
uploadFile(documentID, audioData);
}, function(err) {
console.log('error code: ' + err);
});
};
var uploadFile = function (document, file) {
var baseUrl = 'urltomydatabase';
var name = encodeURIComponent'test.3gpp'),
type = file[0].type,
fileReader = new FileReader(),
putRequest = new XMLHttpRequest();
$http.get(baseUrl + encodeURIComponent(document))
.success(function (data) {
putRequest.open('PUT', baseUrl + encodeURIComponent(document) + '/' + name + '?rev=' + data._rev, true);
putRequest.setRequestHeader('Content-Type', type);
fileReader.readAsArrayBuffer(file[0]);
fileReader.onload = function (readerEvent) {
putRequest.send(readerEvent);
};
putRequest.onreadystatechange = function (response) {
if (putRequest.readyState == 4) {
//success - be happy
}
};
})
.error(function () {
// failure
});
};
How the file looks in the console.log:
Playing the recorded file on the device works nice.
But everytime I upload the recording and the upload has finished, the uploaded attachment inside the document has the length '0' in the couchDB.
How the created file looks in the database after the upload:
What am I doing wrong?
EDIT: I just found out, when I upload an image, passed from this function as blob, it works well:
function upload(imageURL) {
var image = new Image();
var onload = function () {
var canvas = document.createElement("canvas");
canvas.width = this.width;
canvas.height = this.height;
var ctx = canvas.getContext("2d");
ctx.drawImage(this, 0, 0);
canvas.toBlob(function (blob) {
uploadFile(documentID, blob);
});
};
image.onload = onload;
image.src = imageURL;
}
So maybe the solution is creating a blob from the audiofile? But everytime I try it, my blob has the size of 0 bytes even before uploading it and I don't find somewhere a great explanation of how to convert a MediaFile object to blob...

It looks like your code does not send the content of your file as multipart attachment. To see what is really send to couchdb, capture the traffic with wireshark (https://www.wireshark.org/) or such.

This thread brought me to the solution, PouchDB purifies it. Now my upload function looks like this and can handle every file format
// e.g capture Audio
$scope.captureAudio = function () {
var options = {limit: 1, duration: 10};
$cordovaCapture.captureAudio(options).then(function (audioData) {
uploadFile(documentID, audioData, 'audio');
}, function (err) {
console.log('error code: ' + err);
});
};
var uploadFile = function (id, file, mediatype) {
var fileName = makeID();
if (mediatype == 'image') var name = encodeURIComponent(fileName + '.jpg');
if (mediatype == 'audio') var name = encodeURIComponent(fileName + '.3gpp');
if (mediatype == 'video') var name = encodeURIComponent(fileName + '.3gp');
db.get(id).then(function (doc) {
var path = file.fullPath;
window.resolveLocalFileSystemURL(path, function (fileEntry) {
return fileEntry.file(function (data) {
var reader = new FileReader();
reader.onloadend = function (e) {
var blob = b64toBlobAlt(e.target.result, file.type);
if (blob) {
db.putAttachment(id, name, doc._rev, blob, file.type).then(function () {
if (mediatype == 'video' || mediatype == 'image') getMedia();
if (mediatype == 'audio') $scope.audios.push(source);
});
}
};
return reader.readAsDataURL(data);
});
});
});
};
// creating the blob from the base64 string
function b64toBlobAlt(dataURI, contentType) {
var ab, byteString, i, ia;
byteString = atob(dataURI.split(',')[1]);
ab = new ArrayBuffer(byteString.length);
ia = new Uint8Array(ab);
i = 0;
while (i < byteString.length) {
ia[i] = byteString.charCodeAt(i);
i++;
}
return new Blob([ab], {
type: contentType
});
}

base64 encoded image is corrupted when saved to disk

I am posting the base64 clipboard image to server (node) and I am saving the base64 to disk. For some reason the image is corrupted.
Client side logic of posting:
function sendData($http, clipboardImage) {
// $http.defaults.headers.post["Content-Type"] = "application/x-www-form-urlencoded";
// var imgData = JSON.stringify(clipboardImage);
//var data = {"imgdata" : clipboardImage};
var url = "http://localhost:3000/pad/img/";
$http({
method: 'POST',
url: url,
data: "data=" + clipboardImage
});
}
$("[ng-model='html']").delegate("p", "paste", function(event) {
var items = (event.clipboardData || event.originalEvent.clipboardData).items;
console.log(JSON.stringify(items)); // will give you the mime types
// find pasted image among pasted items
var blob = null;
for (var i = 0; i < items.length; i++) {
if (items[i].type.indexOf("image") === 0) {
blob = items[i].getAsFile();
}
}
// load image if there is a pasted image
if (blob !== null) {
var reader = new FileReader();
reader.onload = function(e) {
sendData($http, e.target.result);
};
reader.readAsDataURL(blob);
}
});
Server logic:
app.post("/pad/img/", function(req, res) {
var imgB64Data = req.body.data;
var decodedImg = decodeBase64Image(imgB64Data);
var imageBuffer = decodedImg.data;
var type = decodedImg.type;
var extension = mime.extension(type);
var fileName = "image." + extension;
try {
fs.writeFile(fileName, imageBuffer, function(err) {
console.log(err);
});
} catch (err) {
console.error(err);
}
});
function decodeBase64Image(dataString) {
var matches = dataString.match(/^data:([A-Za-z-+\/]+);base64,(.+)$/),
response = {};
if (matches.length !== 3) {
return new Error('Invalid input string');
}
response.type = matches[1];
response.data = new Buffer(matches[2], 'base64');
return response;
}
The image is being saved successfully but it seems to be corrupted. Can you please point out what may be missing?

Have you tried explicitly setting the file encoding when calling fs.writeFile?
try {
fs.writeFile(fileName, imageBuffer, {encoding:'utf8'}, function(err) {
console.log(err);
});
} catch (err) {
console.error(err);
}
NodeJS Docs: fs.writeFile(filename, data\[, options\], callback)

Converting image dataUrl to Blob image for AJAX POST with javascript

I have the following code which will take an image, allow the user to crop (with other code not shown or necessary for this question), and then render the image in base64 from canvas.
I need to be able to convert the image to binary, as the API endpoint its being submitted to can't take base64. I have functionality to convert to a Blob, but I'm not sure how to implement it correctly:
$(function () {
var fileInput = document.getElementById("file"),
renderButton = $("#renderButton"),
submit = $(".submit"),
imgly = new ImglyKit({
container: "#container",
ratio: 1 / 1
});
// As soon as the user selects a file...
fileInput.addEventListener("change", function (event) {
var file;
var fileToBlob = event.target.files[0];
var blob = new Blob([fileToBlob], {
"type": fileToBlob.type
});
// do stuff with blob
console.log(blob);
// Find the selected file
if (event.target.files) {
file = event.target.files[0];
} else {
file = event.target.value;
}
// Use FileReader to turn the selected
// file into a data url. ImglyKit needs
// a data url or an image
var reader = new FileReader();
reader.onload = (function (file) {
return function (e) {
data = e.target.result;
// Run ImglyKit with the selected file
try {
imgly.run(data);
} catch (e) {
if (e.name == "NoSupportError") {
alert("Your browser does not support canvas.");
} else if (e.name == "InvalidError") {
alert("The given file is not an image");
}
}
};
})(file);
reader.readAsDataURL(file);
});
// As soon as the user clicks the render button...
// Listen for "Render final image" click
renderButton.click(function (event) {
var dataUrl;
imgly.renderToDataURL("image/jpeg", {
size: "1200"
}, function (err, dataUrl) {
// `dataUrl` now contains a resized rendered image
//Convert DataURL to Blob to send over Ajax
function dataURItoBlob(dataUrl) {
// convert base64 to raw binary data held in a string
var byteString = atob(dataUrl.split(',')[1]);
// separate out the mime component
var mimeString = dataUrl.split(',')[0].split(':')[1].split(';')[0];
// write the bytes of the string to an ArrayBuffer
var ab = new ArrayBuffer(byteString.length);
var ia = new Uint8Array(ab);
for (var i = 0; i < byteString.length; i++) {
ia[i] = byteString.charCodeAt(i);
}
// write the ArrayBuffer to a blob, and you're done
//var bb = new BlobBuilder();
//bb.append(ab);
//return bb.getBlob(mimeString);
return new Blob([ab], {
type: 'image/jpeg'
});
}
var blob = dataURItoBlob(dataUrl);
//console.log("var blob: " + blob);
//var fd = new FormData(document.forms[0]);
var image = $("<img><br>").attr({
src: dataUrl
});
image.appendTo($(".result"))
$removeButton = $('<button class="btn btn-default remove">')
.text('Remove ' + imageid.value).appendTo($(".result"))
.on('click', function () {
panel.remove();
$(this).remove();
return false;
});
$submitButton = $('<div class="btn btn-default submit"></div>')
.text('Submit ' + imageid.value).appendTo($(".result"))
.on('click', function () {
var fd = new FormData;
fd.append('file', blob, 'image.png');
//console.log("var fd: " + fd);
var xhr = new XMLHttpRequest();
var saveImage = encodeURIComponent(dataUrl);
//console.log("SAVE IMAGE: " + saveImage);
//console.log(saveImage);
fd.append("myFile", blob);
xhr.open('POST', 'http://url.com/rest/v1/utils/guid/encode?' + saveImage + '&imageid=' + imageid.value, true);
xhr.send(fd);
});
});
});
});
On Submit, I get the following in the console:
http://url.com/rest/v1/utils/guid/encode?data%3Aimage%2Fjpeg%3Bbase64%2C%2F…CiiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKAP%2FZ
The current version in jsFiddle: LINK