How to POST base64 encoded in-memory image as file parameter

Question

How to POST base64 encoded in-memory image as file parameter

I have an image encoded as a base64 String and I'm trying to POST it as a parameter to another REST API (http://ocrapiservice.com/documentation/).

I don't want to have to store the file on disk - I want to keep the file in memory because eventually I want to create the image using getUserMedia on the client and I'll likely use a hosted service that doesn't allow direct file IO.

The problem I have is that most examples I can find post images from disk using fs.createReadStream(somePath); e.g. https://github.com/mikeal/request/blob/master/README.md#forms

I'd prefer to use a library such as the request library but maybe that won't be possible.

The code I have right now is:

var fs = require( 'fs' );
var path = require( 'path' );

var request = require( 'request' );
var WS_URL = 'http://api.ocrapiservice.com/1.0/rest/ocr';

function ocr( postData ) {
    var r = request.post(WS_URL, completed);
    var form = r.form();

    form.append('apikey', 'REMOVED');
    form.append('language', 'en' );
    form.append('image', postData );

    function completed(error, response, body) {
        console.log( body );
    }
}

// This works
ocr( fs.createReadStream(path.join(__dirname, 'example.png' ) ) );

// This does not work
// ignore that it's being read from a file (the next line)
var base64Str = fs.readFileSync( 'example.png' ).toString('base64'); 

var buffer = new Buffer(base64Str, 'base64');
ocr( buffer.toString( 'binary' ) );

form.append does allow additional parameter to be sent so if additional headers need to be set then that is possible.

Is there a Stream wrapper of some kind that I can use? I've tried using this StringReader example and it is possible to modify it to at least send a filename and the correct Content-Type.

How do I achieve this posting of an in memory file as a parameter to a web service?

Update:

I've fixed/updated the code above.

The response I get from the REST API listed above is:

HTTP/1.1 400 Bad Request

No file provided

Here's the actual code that I'm running: https://gist.github.com/leggetter/4968764

node.js
encoding
base64

Answer 1

In the stream version you are working with pieces of the file, but in the base64Image version you are working with a base64 string. Since the stream version works, the ocr API obviously expects the form to simply contain binary data, so you need to decode the base64 data before sending it.

// Reading straight from a Buffer.
var imageData = fs.readFileSync('example.png');
ocr( imageData );

// Reading from a new Buffer created from a base64 string.
var base64Image = '...';
ocr(new Buffer(base64Image, 'base64'));

Also note, in your example code:

// This line:
var base64Image = new Buffer(imageData, 'binary').toString('base64');

// does the same thing as this, because 'imageData' is alreadya  Buffer
var base64Image = imageData.toString('base64');

Answer 2

I am sure you can use Buffer directly for request, without having to wrap it into a Stream.

Its not working because you are using incorrect encoding. readFileSync returns Buffer by default, if encoding is absent. Buffer uses utf-8 by default as its encoding. But you have used the encoding as binary in between, which is not consistent with what you have in the buffer.

var imageData = fs.readFileSync('example.png');//After you get imageData 
var base64Image = imageData.toString('base64');    //base64 encoded string
var decodedImage = new Buffer(base64Image, 'base64');  //base64 encoded buffer
ocr (imageData);  //You can use the file directly
ocr (base64Image); //Or you can use either the base-64 string or the base64-buffer

Look here for more encoding/decoding details NodeJS base64 image encoding/decoding not quite working