How to write binary data to a file using node.js?

Question

I am trying to make toDataUrl() canvas and it gives base64 data. I want to save it as png . I can get the converted binary data from base64, but I can not write it to a file using the NodeJs service.

If I write base64 data directly to a file, all the data can be written, but it cannot be png right ?. I want to save the stored binary data. How to do it?

Code snippet:

 var strData = this.drawingCanvas.getContext().canvas.toDataURL(); var data = strData.replace(/^data:image\/\w+;base64,/, ""); var imgData = this.decode(data); // decode(data) is DEFINED BELOW this.call({filePath:'<path>/image.png', data: imgData}, {method:"writeFile"});` `utf8decode : function (utftext) { var string = ""; var i = 0; var c = c1 = c2 = 0; while ( i < utftext.length ) { c = utftext.charCodeAt(i); if (c < 128) { string += String.fromCharCode(c); i++; } else if((c > 191) && (c < 224)) { c2 = utftext.charCodeAt(i+1); string += String.fromCharCode(((c & 31) << 6) | (c2 & 63)); i += 2; } else { c2 = utftext.charCodeAt(i+1); c3 = utftext.charCodeAt(i+2); string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63)); i += 3; } } return string; },` `_keyStr : "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=", decode : function (input) { var output = ""; var chr1, chr2, chr3; var enc1, enc2, enc3, enc4; var i = 0; input = input.replace(/[^A-Za-z0-9\+\/\=]/g, ""); while (i < input.length) { enc1 = this._keyStr.indexOf(input.charAt(i++)); enc2 = this._keyStr.indexOf(input.charAt(i++)); enc3 = this._keyStr.indexOf(input.charAt(i++)); enc4 = this._keyStr.indexOf(input.charAt(i++)); chr1 = (enc1 << 2) | (enc2 >> 4); chr2 = ((enc2 & 15) << 4) | (enc3 >> 2); chr3 = ((enc3 & 3) << 6) | enc4; output = output + String.fromCharCode(chr1); if (enc3 != 64) { output = output + String.fromCharCode(chr2); } if (enc4 != 64) { output = output + String.fromCharCode(chr3); } } output = this.utf8decode(output); return output; },` /************************************************** wRITEfILEaaSSISTANT.JS ***************************************************/ var WriteFileAssistant = function(){}; WriteFileAssistant.prototype.run = function(future, subscription) { var fs = IMPORTS.require('fs'); var filePath = this.controller.args.filePath; var f = subscription.get(); f.result = {reply: data}; var fd = fs.openSync('<path>/image.png', 'a+'); //var data = fs.writeSync(fd, g, null, encoding='utf8'); //this.controller.args.data - Image data (binary) var buff = new Buffer(this.controller.args.data, 'binary'); //tried also with 'base64' fs.write(fd, buff, 0, buff.length, 0, function(err,written){ }); var f = subscription.get(); f.result = {reply: data}; 

Answer 1

You make things a lot harder than they should be. The node buffer object accepts base64 as input and does all this for you.

You can simply delete the data: image ... from the base64 string and pass that data to your WriteFileAssistant.

 var strData = this.drawingCanvas.getContext().canvas.toDataURL(); var imgData = strData.replace(/^data:image\/\w+;base64,/, ""); this.call( { filePath:'/media/internal/Collage/image.png', data: imgData }, { method:"writeFile" } ); 

WriteFileAssistant just has to take a base64 string and pass this as an argument to the Buffer constructor. In addition, having a “+” in an openSync call will also break.

 var WriteFileAssistant = function(){}; WriteFileAssistant.prototype.run = function(future, subscription) { var fs = IMPORTS.require('fs'); var filePath = this.controller.args.filePath; var fd = fs.openSync('<path>/image.png', 'w'); var buff = new Buffer(this.controller.args.data, 'base64'); fs.write(fd, buff, 0, buff.length, 0, function(err,written){ }); } 

The buffer takes a string and an encoding, and then uses the encoding value to process the string into a series of bytes, so when you report that the string is base64, it will decode base64 for you and create a proper decoded array of bytes to write to the file.