Creating a JPG file with Node.JS - node.js

Question

In my node.js server I am downloading a file from another server. The downloaded file is a JPG image data encoded with Base64 two times, that means I have to decode it 2 times. Given is my code.
var base64DecodedFileData = new Buffer(file_data, 'base64').toString('binary');
var tmp = base64DecodedFileData.split("base64,");
var base64DecodedFileData = new Buffer(tmp[1], 'base64').toString('binary');
var file = fs.createWriteStream(file_path, stream_options);
file.write(base64DecodedFileData);
file.end();
I know my image data is valid the first time I have decoded it ( I have verified that data in online base64 decoders by decoding it second time and I have got the proper image), but when I decode it second time and create a file with this data. I am not getting a valid JPG file.
I have compared it with the actual image, start and ends of both files seems fine but something is not right in my constructed file. The constructed file is also of bigger in size than the original one.
PS: I am doing the split before decoding second time because the data after the first decoding starts with
data:; base64, DATASTARTS
Any thoughts.
Farrukh Arshad.

Answer 1

I have solve My problem. The problem seems to be in the decoding from the node.js so I have written a C++ addon to do the job. Here is the code. I am pretty much sure the problem will remain if we have image file encoded only once.
.js file
ModUtils.generateImageFromData(file_data, file_path);
c++ addon: This uses the base64 C++ encoder/decoder from
http://www.adp-gmbh.ch/cpp/common/base64.html
#define BUILDING_NODE_EXTENSION
#include <node.h>
#include <iostream>
#include <fstream>
#include "base64.h"
using namespace std;
using namespace v8;
static const std::string decoding_prefix =
"data:;base64,";
// --------------------------------------------------------
// Decode the image data and save it as image
// --------------------------------------------------------
Handle<Value> GenerateImageFromData(const Arguments& args) {
HandleScope scope;
// FIXME: Improve argument checking here.
// FIXME: Add error handling here.
if ( args.Length() < 2) return v8::Undefined();
Handle<Value> fileDataArg = args[0];
Handle<Value> filePathArg = args[1];
String::Utf8Value encodedData(fileDataArg);
String::Utf8Value filePath(filePathArg);
std::string std_FilePath = std::string(*filePath);
// We have received image data which is encoded with Base64 two times
// so we have to decode it twice.
std::string decoderParam = std::string(*encodedData);
std::string decodedString = base64_decode(decoderParam);
// After first decoding the data will also contains a encoding prefix like
// data:;base64,
// We have to remove this prefix to get actual encoded image data.
std::string second_pass = decodedString.substr(decoding_prefix.length(), (decodedString.length() - decoding_prefix.length()));
std::string imageData = base64_decode(second_pass);
// Write image to file
ofstream image;
image.open(std_FilePath.c_str());
image << imageData;
image.close();
return scope.Close(String::New(" "));
//return scope.Close(decoded);
}
void Init(Handle<Object> target) {
// Register all functions here
target->Set(String::NewSymbol("generateImageFromData"),
FunctionTemplate::New(GenerateImageFromData)->GetFunction());
}
NODE_MODULE(modutils, Init);
Hope it will help for someone else.