1.0.0 • Public • Published


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    Zipline attempts to discover what content encoding is supported for a given HTTP request. As research from Yahoo has shown you cannot trust the contents of the Accept-Encoding header and just "roll" with that. In zipline we:

    1. Implements the detection algorithm as discussed in Yahoo's article.
    2. Detect broken gzip implementations in Internet Explorer 6.
    3. Provide a way to forcefully detect gzip as suggested at the velocity conference. We store the result in cookie, localStorage and sessionStorage.


    The module is released in the public npm registry and can be installed using

    npm install --save zipline

    The --save instructs npm to store the dependency in your package.json file.


    In all examples we assume that you've already required an initialized your Zipline instance as following:

    'use strict';
    var Zipline = require('zipline')
      , zipline = new Zipline();

    The constructor accepts one optional argument which is an option object that can contain the following keys:

    • pathname The pathname on which our middleware should trigger and serve our gzipped payload for forcefully detecting gzip. Defaults to /zipline.js.
    • name Name of the cookie, property and localStorage/sessionStorage on which we save our gzip information. Defaults to zipline.

    Now that we know the options we can look at the various of API methods that we expose.


    Return a middleware layer which automatically parsers the encoding headers using the Zipline.accepts method and serves our forced gzip payload if the request matches the supplied pathname option.


    So please note that you need to execute the middleware function in order to return the configured middleware layer.


    Clean up the created zipline instance and release all references.



    Please note that this method is exposed on the constructor, not the instance

    Search and parse the accept-encoding headers. If no accept-encoding header is found it will search for potential obfuscated headers to force gzip,deflate for them according to the YDN article. The method accepts 2 arguments:

    1. req Which is an incoming HTTP request so we can extract the headers, rawHeaders and potentially the query object in search for encoding information.
    2. name The name of the cookie or query param which contains gzip overriding information. Defaults to zipline.

    The method will return an array containing the encoding algorithms that can be used for the response. If no algorithms are detected we will return an empty array.

    require('http').createServer(function (req, res) {
      var encoding = Zipline.accepts(req);
      console.log(encoding); // ['gzip', 'deflate']

    Loading the /zipline.js

    The /zipline.js contains a JavaScript payload which will set a zipline cookie as well as add zipline keys to the sessionStorage and localStorage. There are a couple of ways of loading this. You can check if the req.zipline property (when using the middleware) and check if the array contains somethings. When it's empty you could trigger the following script on the page and load the /zipline.js:

      var iframe = d.body.appendChild(d.createElement('iframe')),
      doc = iframe.contentWindow.document;
  '<body onload="' +
      'var d = document;d.getElementsByTagName(\'head\')[0].' +
      'appendChild(d.createElement(\'script\')).src' +

    The reason why we load it in an iframe is so errors that might be caused because the browser doesn't support gzip do not bubble up to the main page. It would only be triggered in the iframe.




    npm i zipline

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