content negotiation in JS for ASP-classic

contentNego.js

// contentNego.js
//
// Simple content negotiation logic for ASP-classic modules.
//
// This module exposes one public function - figureDesiredContentType().
// It checks the HTTP_ACCEPT server variable (whose value is set to the
// value of the Accept request header), and sets a content-type
// mime-string accordingly.
//
// When there are multiple mime-types in the Accept header, or when the
// Accept header includes */*, this means that multiple response
// formats are acceptable.  In that case, the order of preference used
// by this function priority is hard-coded to be roughly: html, XML, JSON.
//
//
// created: Fri, 16 Mar 2012  15:27
// last saved: <2012-April-20 08:43:45>
//
// -------------------------------------------------------
//
// Example usage:
//
// <script language="javascript" runat="server" src='contentNego.js'></script>
//  ...
// function handleGet() {
//     var cnego = CNego.figureDesiredContentType(),
//         r = getResult();
//
//     header('Content-Type: ' + cnego[0]);
//
//     switch (cnego[1]) {
//         case CNego.contentFlavor.HTML:
//             Response.Write(formatAsHtml(r));
//             break;
//         case CNego.contentFlavor.XML:
//             Response.Write(formatAsXml(r));
//             break;
//         case CNego.contentFlavor.JSON:
//             Response.Write(JSON.stringify(r));
//             break;
//         case CNego.contentFlavor.Text:
//             Response.Write(formatAsText(r));
//             break;
//     }
// }
//
//
// Bugs:
//
(function() {

    // When CNego is declared as a symbol in the containing scope, as is
    // done here, it gets "exported" to the global naming scope when
    // used in an ASP-classic environment. An .asp module that includes
    // this script will be able to "see" and use this symbol.
    var flavor = {
        Unknown: 0,
        Text: 1,
        XML: 2,
        HTML: 3,
        JSON: 4
    };

    CNego = {
        contentFlavor : flavor,

        figureDesiredContentType : function() {
            // Return a 2-element tuple; the first element is the mime-type
            // string, the second is a number indicating the flavor.  The
            // mapping of mime-type to flavor is N:1. In other words, there
            // are several distinct mime-type strings corresponding to the
            // JSON "flavor", and several different mime-type strings that
            // fall under the XML "flavor".

            var accept = (Request.ServerVariables('HTTP_ACCEPT') + '').toLowerCase();

            if (accept == 'undefined') {
                return ["text/plain", flavor.Text];
            }
            if (accept.indexOf('*/*') != -1) {
                return ["text/html", flavor.HTML];
            }
            if (accept.indexOf('application/html') != -1) {
                return ["application/html", flavor.HTML];
            }
            if (accept.indexOf('text/html') != -1) {
                return ["text/html", flavor.HTML];
            }
            if (accept.indexOf("application/xml") != -1) {
                return ["application/xml", flavor.XML];
            }
            if (accept.indexOf("text/xml") != -1) {
                return ["text/xml", flavor.XML];
            }
            if (accept.indexOf("application/x-xml") != -1) {
                return ["application/x-xml", flavor.XML];
            }
            if (accept.indexOf("application/json") != -1) {
                return ["application/json", flavor.JSON];
            }
            if (accept.indexOf("text/x-json") != -1) {
                return ["text/x-json", flavor.JSON];
            }
            if (accept.indexOf("text/javascript") != -1) {
                return ["text/javascript", flavor.JSON];
            }
            if (accept.indexOf("application/javascript") != -1) {
                return ["application/javascript", flavor.JSON];
            }
            if (accept.indexOf("application/x-javascript") != -1) {
                return ["application/x-javascript",  flavor.JSON];
            }

            return ["text/plain", flavor.Text];
        }
    };

}());