multipart-form-parser

A javascript/nodejs multipart/form-data parser which operates on raw data.

Author

David McGinnis ([e-mail])

Background

Sometimes you only have access to the raw multipart payload and it needs to be parsed in order to extract the files or data contained on it. As an example: the Amazon AWS ApiGateway, which will operate as a facade between the http client and your component (the one written by you designed to extract the uploaded files or data).

The raw payload formatted as multipart/form-data will looks like this one:

------WebKitFormBoundaryDtbT5UpPj83kllfw
Content-Disposition: form-data; name="uploads[]"; filename="somebinary.dat"
Content-Type: application/octet-stream

some binary data...maybe the bits of a image..
------WebKitFormBoundaryDtbT5UpPj83kllfw
Content-Disposition: form-data; name="uploads[]"; filename="sometext.txt"
Content-Type: text/plain

hello how are you
------WebKitFormBoundaryDtbT5UpPj83kllfw--

The lines above represents a raw multipart/form-data payload sent by some HTTP client via form submission containing two files. We need to extract the all files contained inside it. The multipart format allows you to send more than one file in the same payload, that's why it is called: multipart.

Usage

In the next lines you can see a implementation. In this case two key values needs to be present:

• body, which can be:

------WebKitFormBoundaryDtbT5UpPj83kllfw
Content-Disposition: form-data; name="uploads[]"; filename="sometext.txt"
Content-Type: application/octet-stream

hello how are you
------WebKitFormBoundaryDtbT5UpPj83kllfw--

• boundary, the string which serve as a 'separator' between parts, it normally comes to you via headers. In this case, the boundary is:

    ----WebKitFormBoundaryDtbT5UpPj83kllfw

Now, having this two key values then you can implement it:

    var multipart = require('parse-multipart');
    var body = "..the multipart raw body..";
    var boundary = "----WebKitFormBoundaryDtbT5UpPj83kllfw";
    var parts = multipart.Parse(body,boundary);
    
    for(var i=0;i<parts.length;i++){
        var part = parts[i];
        // will be:
        // { filename: 'A.txt', type: 'text/plain', 
        //		data: <Buffer 41 41 41 41 42 42 42 42> }
    }

The returned data is an array of parts, each one described by a filename, a type and a data, this last one is a Buffer (see also Node Buffer).