Express - Return binary data from webservice

Question

I try to return some binary data with Express. In the example, it's a PDF but theorically, this can be any sort of file.

But focus on the pdf for the moment. I wrote this code :

app.get('*', function (req, res) {
    getBinaryData(req.url,
        function (answer) {
            res.type('pdf');
            res.end(new Buffer(answer, 'binary'));
        },
        function (error) {
            res.setHeader('Content-Type', 'text/plain');
            return res.end(error);
        }
    );
});

Based on what I saw here : https://github.com/strongloop/express/issues/1555

But, i get a pdf file with the right number of pages, right title.... but all the pages are blank

I'm sure concern the return of getBinaryData(), because this function asked an external Web Service and when I asked directly this service, I got the right document.

Thank you in advance for your answers

Solution 1

I found a more simple solution :

request(req.url).pipe(res);

This pipes the original response from distant Web Service directly to my response! I got the correct file regardless of the file type.

Solution 2

Here is my slightly cleaned up version of how to return binary files with Express. I assume that the data is in an object that can be declared as binary and has a length:

exports.download = function (data, filename, mimetype, res) {
    res.writeHead(200, {
        'Content-Type': mimetype,
        'Content-disposition': 'attachment;filename=' + filename,
        'Content-Length': data.length
    });
    res.end(Buffer.from(data, 'binary'));
};

Comments

[vanadium23]

Why don't use res.sendFile method?

[Varkal]

cause I don't have the file : I get this binary content from another WebService. Eventually, I can create a temp file and use sendFile...

[dark_shadow]

I tried same thing but it's not working for me. stackoverflow.com/questions/37517312/…

[Aneil Mallavarapu]

Slight typo. It should be: res.end(new Buffer(data), 'binary')

[Idan Dagan]

keep in mind that new Buffer() is deprecated and it have security issues.

[Nickolodeon]

In what library does request lib reside for request(req.url).pipe(res)?

[realtebo]

@IdanDagan: what could we use instead of new Buffer()?

[Idan Dagan]

@realtebo you can use Buffer.from() - see Node.js docs for more examples.

[Seybsen]

new Buffer() is deprecated, use Buffer.from() instead.

[Prav]

why use Buffer.from when data is binary, isn't that reserved for strings? wouldn't you have to use Buffer.alloc?

[NamedArray]

What is the significance of using .end() instead of .send() with these examples?

[Michael Shopsin]

@NamedArray .end() makes sure the connection is closed after the file is sent. .send() leaves the connection open using up a TCP socket.

[Dan Sterrett]

For everyone wondering what library request comes from, it's a built in node module, so just add const request = require('request'); before the call.