multipartform data - parsing a formdata object with javascript

Question

My company uses a propitiatory application server in which the server side programs are written in javascript (not node.js) . This is a very initial thing and support isn't that good

Now here is my problem :

I am having to process an uploaded csv on the server side .. I am using the super answer at How can I upload files asynchronously? (passing the formdata object with jquery) and i am able to access the sent file on the server side . But how do i parse it out ?

It looks like this

------WebKitFormBoundaryU5rJUDxGnj15hIGW
Content-Disposition: form-data; name="fileToUpload"; filename="test.csv"
Content-Type: application/vnd.ms-excel

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------WebKitFormBoundaryU5rJUDxGnj15hIGW--

I'm really confused how to handle this file with plain javascript on the server side.

Please help.

Answer 1

Best would be to use node-formidable, browserify and polyfill it. Here is a standalone parser, works both with string and raw responses. Make sure you use a modern browser for the raw-stuff.

/* 
 * MultiPart_parse decodes a multipart/form-data encoded response into a named-part-map.
 * The response can be a string or raw bytes.
 *
 * Usage for string response:
 *      var map = MultiPart_parse(xhr.responseText, xhr.getResponseHeader('Content-Type'));
 *
 * Usage for raw bytes:
 *      xhr.open(..);     
 *      xhr.responseType = "arraybuffer";
 *      ...
 *      var map = MultiPart_parse(xhr.response, xhr.getResponseHeader('Content-Type'));
 *
 * TODO: Can we use https://github.com/felixge/node-formidable
 * See http://stackoverflow.com/questions/6965107/converting-between-strings-and-arraybuffers
 * See http://www.w3.org/Protocols/rfc1341/7_2_Multipart.html
 *
 * Copyright@ 2013-2014 Wolfgang Kuehn, released under the MIT license.
*/
function MultiPart_parse(body, contentType) {
    // Examples for content types:
    //      multipart/form-data; boundary="----7dd322351017c"; ...
    //      multipart/form-data; boundary=----7dd322351017c; ...
    var m = contentType.match(/boundary=(?:"([^"]+)"|([^;]+))/i);

    if ( !m ) {
        throw new Error('Bad content-type header, no multipart boundary');
    }

    var boundary = m[1] || m[2];

    function Header_parse(header) {
        var headerFields = {};
        var matchResult = header.match(/^.*name="([^"]*)"$/);
        if ( matchResult ) headerFields.name = matchResult[1];
        return headerFields;
    }

    function rawStringToBuffer( str ) {
        var idx, len = str.length, arr = new Array( len );
        for ( idx = 0 ; idx < len ; ++idx ) {
            arr[ idx ] = str.charCodeAt(idx) & 0xFF;
        }
        return new Uint8Array( arr ).buffer;
    }

    // 
 is part of the boundary.
    var boundary = '
--' + boundary;

    var isRaw = typeof(body) !== 'string';

    if ( isRaw ) {
        var view = new Uint8Array( body );
        s = String.fromCharCode.apply(null, view);
    } else {
        s = body;
    }

    // Prepend what has been stripped by the body parsing mechanism.
    s = '
' + s;

    var parts = s.split(new RegExp(boundary)),
        partsByName = {};

    // First part is a preamble, last part is closing '--'
    for (var i=1; i<parts.length-1; i++) {
      var subparts = parts[i].split('

');
      var headers = subparts[0].split('
');
      for (var j=1; j<headers.length; j++) {
        var headerFields = Header_parse(headers[j]);
        if ( headerFields.name ) {
            fieldName = headerFields.name;
        }
      }

      partsByName[fieldName] = isRaw?rawStringToBuffer(subparts[1]):subparts[1];
    }

    return partsByName;
}