Decompress gzip and zlib string in javascript

Toan Nguyen picture Toan Nguyen · Jan 31, 2013 · Viewed 87.8k times · Source

I want to get compress layer data from tmx file . Who knows libraries for decompress gzip and zlib string in javascript ? I try zlib but it doesn't work for me . Ex , layer data in tmx file is :

  <data encoding="base64" compression="zlib">
       eJztwTEBAAAAwqD1T20JT6AAAHgaCWAAAQ==
  </data>

My javascript code is

var base64Data = "eJztwTEBAAAAwqD1T20JT6AAAHgaCWAAAQ==";
var compressData = atob(base64Data);
var inflate = new Zlib.Inflate(compressData);
var output = inflate.decompress();

It runs with displays message error "unsupported compression method" . But I try decompress with online tool as http://i-tools.org/gzip , it returns correct string.

Answer

Redsandro picture Redsandro · Mar 27, 2014

Pako is a full and modern Zlib port.

Here is a very simple example and you can work from there.

Get pako.js and you can decompress byteArray like so:

<html>
<head>
  <title>Gunzipping binary gzipped string</title>
  <script type="text/javascript" src="pako.js"></script>
  <script type="text/javascript">

    // Get datastream as Array, for example:
    var charData    = [31,139,8,0,0,0,0,0,0,3,5,193,219,13,0,16,16,4,192,86,214,151,102,52,33,110,35,66,108,226,60,218,55,147,164,238,24,173,19,143,241,18,85,27,58,203,57,46,29,25,198,34,163,193,247,106,179,134,15,50,167,173,148,48,0,0,0];

    // Turn number array into byte-array
    var binData     = new Uint8Array(charData);

    // Pako magic
    var data        = pako.inflate(binData);

    // Convert gunzipped byteArray back to ascii string:
    var strData     = String.fromCharCode.apply(null, new Uint16Array(data));

    // Output to console
    console.log(strData);

  </script>
</head>
<body>
    Open up the developer console.
</body>
</html>

Running example: http://jsfiddle.net/9yH7M/

Alternatively you can base64 encode the array before you send it over as the Array takes up a lot of overhead when sending as JSON or XML. Decode likewise:

// Get some base64 encoded binary data from the server. Imagine we got this:
var b64Data     = 'H4sIAAAAAAAAAwXB2w0AEBAEwFbWl2Y0IW4jQmziPNo3k6TuGK0Tj/ESVRs6yzkuHRnGIqPB92qzhg8yp62UMAAAAA==';

// Decode base64 (convert ascii to binary)
var strData     = atob(b64Data);

// Convert binary string to character-number array
var charData    = strData.split('').map(function(x){return x.charCodeAt(0);});

// Turn number array into byte-array
var binData     = new Uint8Array(charData);

// Pako magic
var data        = pako.inflate(binData);

// Convert gunzipped byteArray back to ascii string:
var strData     = String.fromCharCode.apply(null, new Uint16Array(data));

// Output to console
console.log(strData);

Running example: http://jsfiddle.net/9yH7M/1/

To go more advanced, here is the pako API documentation.