Download an image using node-request, and fs Promisified, with no pipe in Node.js

Question

I have been struggling to succeed in downloading an image without piping it to fs. Here's what I have accomplished:

var Promise = require('bluebird'),
    fs = Promise.promisifyAll(require('fs')),
    requestAsync = Promise.promisify(require('request'));

function downloadImage(uri, filename){
    return requestAsync(uri)
        .spread(function (response, body) {
            if (response.statusCode != 200) return Promise.resolve();
            return fs.writeFileAsync(filename, body);
        })
       .then(function () { ... })

       // ...
}

A valid input might be:

downloadImage('http://goo.gl/5FiLfb', 'c:\\thanks.jpg');

I do believe the problem is with the handling of body. I have tried casting it to a Buffer (new Buffer(body, 'binary') etc.) in several encodings, but all failed.

Thanks from ahead for any help!

Hem

Any idea how would one do that with streams? – Quatrain

Answer 1

You have to tell request that the data is binary:

requestAsync(uri, { encoding : null })

Documented here:

encoding - Encoding to be used on setEncoding of response data. If null, the body is returned as a Buffer. Anything else (including the default value of undefined) will be passed as the encoding parameter to toString() (meaning this is effectively utf8 by default).

So without that option, the body data is interpreted as UTF-8 encoded, which it isn't (and yields an invalid JPEG file).

Interosculate

Thanks! I don't know how I missed that. :) – Hem

This answer helped me finally save valid PDFs I was fetching with request-promise. I tried every encoding supported by Node.js, but the resulting file was always corrupt (and larger than it should have been). Turns out the problem was how it was coming back to begin with. Adding encoding: null fixed it, and then it saved fine no matter which encoding I used during fs.writeFile(). Thanks! – Gripe