Multi part it yourself

Question

I would like to create a HTTP response, using multipart/mixed, but I m not sure which browsers support it; and if it s as convenient as it sounds, from the client s point of view. To be honest, I do not need specifically that content type. I just want to transmit more than one file in the same response; maybe there s another content-type more used.

Answer 1

I ve tested it, with a home-made server and a simple response. Not sure if the response is well-formed because no browser understands it 100% OK. But here are the results:

Firefox 67.0.1 (64-bit): Renders only the last part, others are ignored.
IE 11.503: Saves all the content in a single file (including the boundaries), nothing is rendered.
Chrome May 2019: Saves all the content in a single file, nothing is rendered.
Safari 4: Saves all the content in a single file, nothing is rendered.
Opera 10.10: Something weird. Starts rendering the first part as plain/text, and then clears everything. The loading progress bar hangs on 31%.

Here s the complete response, if anyone finds any error, please tell me and I ll try again:

HTTP/1.1 200 OK
Date: Tue, 01 Dec 2009 23:27:30 GMT
Vary: Accept-Encoding,User-Agent
Content-Length: 681
Content-Type: Multipart/mixed; boundary="sample_boundary";

Multipart not supported :(
--sample_boundary
Content-Type: text/css; charset=utf-8
Content-Location: http://localhost:2080/file.css

body
{
 background-color: yellow;
}
--sample_boundary
Content-Type: application/x-javascript; charset=utf-8
Content-Location: http://localhost:2080/file.js

alert("Hello from a javascript!!!");

--sample_boundary
Content-Type: text/html; charset=utf-8
Content-Base: http://localhost:2080/

<html>
<head>
    <link rel="stylesheet" href="http://localhost:2080/file.css">
</head>
<body>
 Hello from a html
    <script type="text/javascript" src="http://localhost:2080/file.js"></script>
</body>
</html>
--sample_boundary--

Answer 2

In my experience, multipart responses work in Firefox but not in Internet Explorer. This was 2 years ago, using the browsers of the time.

I have had HTTP multipart responses working for a stream of JPEG images. For example, Axis IP cameras use for their motion JPEG stream for Firefox. For Internet explorer, Axis require the use of a plugin.

If Firefox-only support meets your requirements, then I recommend setting the content-length header in each part of the multi-part response. It might help to make the boundary string identical in the original HTTP header and the multi-part response (the -- is missing in the HTTP header).

Answer 3

Two ideas:

Formatting: I think "multipart" should be in lower case, and I don t think a semicolon is expected at the end of the Content-type header (although it s doubtful that it will make a difference, it s possible that it might).
Have you tried replace mode? Just use: Content-type: multipart/x-mixed-replace -- everything else should stay the same.

Answer 4

Multi part it yourself

(A good option)

A multipart response can be made manually!

So one can write a no multipart response! Let s say in chunked mode! There it make sense!

So you are streaming the data!

Send all as blunt text!

Make your own separators! Between each part!

In the browser! Extract and parse the data! Split to get each part separately!
And parse each appart! Depending on what type of data it hold!

So if a part is json! You parse it as so!

Quick illustration! Let say we want to send a csv file! Or some other type of file! Along that we want to send too a json object!

And that by streaming it by chunk

Here a code that illustrate that in express:

const data = {
    initCapital: fileState.mappingObj.initialCapital
};

res.write(JSON.stringify(data, undefined, 0));
res.write( >>>> ); // parts separator
fileState.readStream.pipe(res); // continue streaming the file (chunk by chunk)

And in the client

export function parseBackTestFetchedData(data: string) {
    const [_data, csvData] = data.split( >>>> );
    return {
        data: JSON.parse(_data),
        backTestStatesData: parseCsv(csvData)
    };
}

That way! it doesn t matter who the client is!

Multi part it yourself

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