Slides of the talk at the deSymfonyDay unconference

1. How GZIP Compression Works
Raul Fraile …in 10 minutes

2. About me
• PHP/Symfony2 developer at
• PHP 5.3 Zend Certified Engineer
• Symfony Certified Developer
• BS in Computer Science. Ms(Res) student in
Computing Technologies.
• Open source: LadybugPHP

3. What is GZIP?
• GZIP is a lossless compression method,
we can recover the original data once
decompressed.
• It has become the de-facto lossless
compression method for compressing
textual data in websites.

4. What is GZIP?
Web server
GET index.html
Accept-Encoding: gzip

5. How it works?
• It is based on the DEFLATE algorithm,
which is a combination of LZ77 and
Huffman coding.
• First, the LZ77 algorithm replaces repeated
occurrences of data with references.
• Second, Huffman coding assigns shorter
codes to more frequent “characters”.

6. How it works?
This file is huge! That's because the file is not compressed
<33, 9>
LZ77

7. How it works?
“compressed”
Huffman coding
c: 1
o: 1
m: 1
p: 1
r: 1
e: 2
s: 2
d: 1
01100011 01101111 01101101 01110000 01110010 01100101 01110011 01110011 01100101 01100100
1100 011 010 000 001 111 10 10 111 1101

8. Why GZIP?
• GZIP is not the best compression method,
but there are a few good reasons to use it.
• Provides a good tradeoff between speed
and ratio.
• Difficulty to add newer compression
methods.

9. Implementations
GNU
GZIP
7-zip Zopfli
Different implementations, different results

10. GZIP + PHP
$originalFile = __DIR__ . '/jquery-1.11.0.min.js';
$gzipFile = __DIR__ . '/jquery-1.11.0.min.js.gz';
$originalData = file_get_contents($originalFile);
$gzipData = gzencode($originalData, 9);
file_put_contents($gzipFile, $gzipData);
var_dump(filesize($originalFile)); // int(96380)
var_dump(filesize($gzipFile)); // int(33305)

11. Beyond GZIP
• Preprocessing the text can have an
impact on the compression ratio.
• How? Optimizing matches.

12. Beyond GZIP

13. Beyond GZIP
{
"name": "Raul",
"country": "Spain"
},
{
"name": "Pablo",
"country": "USA"
},
{
"name": "Pedro",
"country": "Spain"
}
Transposing JSON
{
"name": [
"Raul",
"Pablo",
"Pedro"
],
"country": [
"Spain",
"USA",
"Spain"
]
}

14. Beyond GZIP
Ordering XML/HTML attributes
<input id='f1' class='field' name="f1" type="text" />
<input class="field" id="f2" type="text" name="f2" />
<input id="f1" class="field" name="f1" type="text" />
<input class="field" id="f2" type="text" name="f2" />
<input id="f1" class="field" name="f1" type="text" />
<input id="f2" class="field" name="f2" type="text" />
17,76 %
27,10 %
38,32 %
<input type="text" class="field" id="f1" name="f1" />
<input type="text" class="field" id="f2" name="f2" />
38,32 %

15. Thank you!