Socket.IO 1.4.2 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 184375 bytes (180.1k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 97182 bytes (94.9k, 53%).

After GZIP compression these minified files vary in size:

gzip -6 (default)	25307 bytes (24.7k)	local copy
gzip -9	25217 bytes (24.6k)	local copy
Boot	25046 bytes (24.5k)	CDN
libdeflate -12	24347 bytes (23.8k)	local copy
zultra	24326 bytes (23.8k)	local copy
kzip -s0 -rn -b1	24291 bytes (23.7k)	local copy
7zip -mx=9 -tgzip	24286 bytes (23.7k)	local copy
pigz -11 -n	24273 bytes (23.7k)	local copy
Zopfli	24250 bytes (23.7k)	local copy
cdnjs	21479 bytes (21.0k)	CDN

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/socketio/socket.io-1.4.2.min.js (or via HTTPS)

You will automatically get the smallest Socket.IO 1.4.2 file, ETag caching is available and
if your browser doesn't support GZIP decompression then the uncompressed version will be sent.

Currently best Zopfli settings

You can use my super-compressed files for whatever purpose you like as long as you respect the library's original license agreement.
There are no restrictions from my side - but please avoid hot-linking if you run a high-traffic website.

These command-line settings yielded the best compression ratio so far (Linux version of zopfli-krzymod):
zopfli --i100000 --mb8 --mls2048 --bsr30 --lazy --ohh

(found June 30, 2016)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	2048	--mls2048
block splitting recursion	30	--bsr30
lazy matching in LZ77	yes	--lazy
optimized Huffman headers	yes	--ohh
initial random W for iterations	1	--rw1
initial random Z for iterations	2	--rz2

Verify file integrity

After decompression, my uncompressed files are identical to the original ones:

MD5:
curl --silent --compressed https://raw.githubusercontent.com/socketio/socket.io-client/1.4.2/socket.io.min.js --location | md5sum
e02b1773fad2bd6ff801661d458dcd53 -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-1.4.2.min.zopfli.js.gz | md5sum
e02b1773fad2bd6ff801661d458dcd53 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/socketio/socket.io-client/1.4.2/socket.io.min.js --location | sha1sum
dc3af739bd3b040fac3c8c78030d0fae756a0550 -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-1.4.2.min.zopfli.js.gz | sha1sum
dc3af739bd3b040fac3c8c78030d0fae756a0550 -

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Boot	25046 bytes	be4c474fc5fd31b49346f10366104bc6	< (function(f){if(typeof exports==="object"&&typeof module!= [...] < this.once("close",onclose);this.once("upgrading",onupgrade [...] < for(var i=0;i<lenStr.length;i++){lengthAry[i]=parseInt(len [...] < if(typeof define=="function"&&typeof define.amd=="object"& [...] > !function(t){if("object"==typeof exports&&"undefined"!=typ [...] > this.script=e;var r="undefined"!=typeof navigator&&/gecko/ [...] > }function s(){this.reconstructor=null}function a(t){var e= [...]	(invalid)
cdnjs	21479 bytes	be4c474fc5fd31b49346f10366104bc6	< (function(f){if(typeof exports==="object"&&typeof module!= [...] < this.once("close",onclose);this.once("upgrading",onupgrade [...] < for(var i=0;i<lenStr.length;i++){lengthAry[i]=parseInt(len [...] < if(typeof define=="function"&&typeof define.amd=="object"& [...] > !function(t){if("object"==typeof exports&&"undefined"!=typ [...] > this.script=e;var r="undefined"!=typeof navigator&&/gecko/ [...] > }function s(){this.reconstructor=null}function a(t){var e= [...]	(invalid)

Note: only the MD5 hashes are shown to keep things simple.

Other Versions

Available Socket.IO versions at minime.stephan-brumme.com:

4.5.4, 4.5.3, 4.5.2, 4.5.1, 4.5.0, 4.4.1, 4.4.0, 4.3.2, 4.3.1, 4.3.0, 4.2.0, 4.1.3, 4.1.2, 4.1.1, 4.1.0, 4.0.2, 4.0.1, 4.0.0,
3.1.2, 3.1.1, 3.1.0, 3.0.5, 3.0.4, 3.0.3, 3.0.2, 3.0.1, 3.0.0,
2.4.0, 2.3.1, 2.3.0, 2.2.0, 2.1.1, 2.1.0, 2.0.4, 2.0.3, 2.0.2, 2.0.1, 2.0.0,
1.7.4, 1.7.2, 1.7.1, 1.7.0, 1.6.0, 1.5.0, 1.4.5, 1.4.4, 1.4.3, 1.4.2, 1.4.1, 1.4.0, 1.3.7, 1.3.6, 1.3.5, 1.3.4, 1.3.3, 1.3.2, 1.3.1, 1.3.0, 1.2.1, 1.2.0, 1.1.0, 1.0.6, 1.0.5, 1.0.4, 1.0.3, 1.0.2, 1.0.1, 1.0.0

The project site contains an overview how well these versions were compressed.
Other interesting projects are AngularJS, BackboneJS, Bootstrap, D3, Dojo, Ember, jQuery, Knockout, lodash, React, ThreeJS, UnderscoreJS and Vue.

Changelog

Best Zopfli parameters so far:

Size	Improvement	Parameters	Found
24250 bytes	-1 byte	zopfli --i100000 --mls2048 --bsr30 --lazy --ohh	June 30, 2016 @ 11:14
24251 bytes	-1 byte	zopfli --i10000 --mls2048 --bsr30 --lazy --ohh	June 30, 2016 @ 09:46
24252 bytes	-2 bytes	zopfli --i1000 --mls2048 --bsr30 --lazy --ohh	June 29, 2016 @ 17:23
24254 bytes	-1 byte	zopfli --i1000 --mls2048 --bsr21 --lazy --ohh	June 29, 2016 @ 15:42
24255 bytes	–	zopfli --i100 --mls2048 --bsr23 --lazy --ohh	June 29, 2016 @ 13:57

If there are multiple parameter sets yielding the same compressed size, only the first one found is shown.

Most recent activity on July 20, 2020 @ 12:50.

Heatmaps

This Zopfli heatmap visualizes how compression changes when modifying the --bsr and --mls parameter.
Cell's contents is the best filesize achieved (in bytes, hover with mouse over cells to see number of iterations).

Good parameters are green, bad are red. The best and worst are bold as well.
The brightness of the blue background color indicates how many iterations were processed:
10,000 or 100,000.

bsr \ mls	2	4	8	16	32	64	128	256	512	1024	2048	4096	8192	16384	32768
bsr \ mls	2	4	8	16	32	64	128	256	512	1024	2048	4096	8192	16384	32768
2	24259	24261	24261	24261	24262	24267	24260	24262	24266	24265	24264	24265	24264	24264	24270
4	24266	24263	24265	24264	24266	24254	24272	24273	24273	24274	24261	24262	24259	24269	24262
6	24258	24259	24259	24257	24258	24257	24256	24258	24258	24258	24261	24259	24258	24266	24257
7	24264	24267	24261	24261	24259	24259	24261	24257	24260	24263	24260	24258	24256	24269	24259
8	24266	24267	24261	24271	24267	24259	24268	24273	24262	24269	24268	24269	24258	24266	24257
9	24257	24257	24259	24262	24252	24258	24258	24262	24261	24262	24256	24262	24259	24267	24259
10	24264	24253	24260	24257	24255	24258	24256	24257	24260	24262	24252	24263	24256	24266	24259
11	24265	24263	24263	24262	24264	24262	24269	24271	24271	24272	24271	24263	24260	24266	24258
12	24266	24257	24257	24260	24261	24250	24256	24257	24258	24260	24258	24261	24255	24269	24258
13	24262	24259	24257	24258	24255	24257	24256	24260	24259	24260	24252	24267	24259	24258	24259
14	24265	24264	24262	24264	24260	24261	24269	24270	24262	24262	24260	24269	24253	24267	24257
15	24258	24260	24258	24260	24257	24258	24258	24260	24264	24257	24258	24258	24255	24268	24259
16	24258	24258	24261	24261	24261	24258	24257	24258	24259	24257	24257	24263	24256	24256	24260
17	24266	24257	24262	24262	24255	24257	24256	24258	24259	24258	24258	24259	24258	24256	24257
18	24257	24258	24259	24263	24258	24255	24269	24258	24259	24262	24251	24259	24257	24257	24256
19	24256	24256	24258	24258	24253	24261	24259	24258	24260	24257	24252	24259	24257	24268	24257
20	24258	24252	24258	24258	24252	24256	24258	24258	24258	24255	24250	24265	24254	24267	24257
21	24256	24257	24257	24258	24254	24257	24255	24263	24260	24263	24253	24263	24263	24257	24257
22	24263	24262	24262	24261	24255	24260	24256	24263	24259	24258	24252	24256	24254	24268	24258
23	24267	24253	24262	24261	24263	24264	24259	24262	24257	24259	24251	24267	24256	24256	24258
25	24264	24258	24257	24259	24257	24264	24256	24260	24260	24260	24258	24263	24257	24268	24258
30	24257	24257	24258	24258	24253	24260	24257	24261	24258	24258	24250	24263	24257	24256	24257
40	24263	24259	24261	24259	24253	24258	24270	24259	24259	24258	24253	24264	24256	24269	24258

Due to the Monte Carlo design of my search algorithm, not all parameters have reached the same number of iterations yet:

Iterations	Min. Bytes	Reduction	Coverage
100	24255 bytes	–	100%
1,000	24252 bytes	-3 bytes	100%
10,000	24250 bytes	-2 bytes	100%
100,000	24250 bytes	–	0.87%
1,000,000	–	–	–
10,000,000	–	–	–

KZIP has far less options available for tuning/optimization. I only played around with the number of blocks (parameter -n):

Blocks	Min. Bytes	Compared To Best Zopfli	Compared To Best KZIP
(any)	24296 bytes	+46 bytes (+0.19%)	+5 bytes
1	24291 bytes	+41 bytes (+0.17%)	–
2	24294 bytes	+44 bytes (+0.18%)	+3 bytes
3	24333 bytes	+83 bytes (+0.34%)	+42 bytes
4	24304 bytes	+54 bytes (+0.22%)	+13 bytes
5	24323 bytes	+73 bytes (+0.30%)	+32 bytes
6	24357 bytes	+107 bytes (+0.44%)	+66 bytes
7	24392 bytes	+142 bytes (+0.59%)	+101 bytes
8	24419 bytes	+169 bytes (+0.70%)	+128 bytes

Non-DEFLATE Algorithms

Archivers based on completely different compression algorithms often produce superior results.
Unfortunately, browsers only support gzip compression at the moment.
However, support for Brotli is constantly growing - for example, your browser actually supports it !

Algorithm	Program	Parameters	Size	Compared To Best Zopfli
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	19166 bytes	-5084 bytes (-20.96%)
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	20328 bytes	-3922 bytes (-16.17%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	22194 bytes	-2056 bytes (-8.48%)
Brotli (Wikipedia)	brotli	brotli -q 11	22438 bytes	-1812 bytes (-7.47%)
LZMA2 (Wikipedia)	xz	xz -9	23180 bytes	-1070 bytes (-4.41%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	23483 bytes	-767 bytes (-3.16%)
Zstandard (Wikipedia)	zstd	zstd -19	23549 bytes	-701 bytes (-2.89%)

Detailled Analysis

I wrote a DEFLATE decoder in Javascript. Click the button below to start a client-side analysis of the smallest gzipped files (may take a second):

Load and Parse Data

Notes: pigz is a fast open source multi-threaded implementation of gzip written by one of the original authors of gzip.
However, when using compression level 11, pigz actually switches to the slower Zopfli algorithm and isn't multi-threaded anymore.
KrzyMOD's extensions to Zopfli offer the highest level of configuration and is therefore used for my brute-force search.
Ken Silverman wrote the closed-source KZIP compression program and Jonathon Fowler ported it to Linux.
Defluff was created by Joachim Henke; DeflOpt is a tool by Ben Jos Walbeehm.

website made by Stephan Brumme in 2015 and still improving in 2026.
all timestamps are displayed in central european time. see my changelog.
no flash, not even images or external css files - and everything squeezed into a single html file.
which was handsomely compressed before releasing it into the wild internet - obviously.

please visit my homepage and my blog, too.
email: minime (at) stephan-brumme.com

All trademarks are property of their respective owners. You know, the boring legal stuff.