Socket.IO 1.3.1 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 169678 bytes (165.7k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 88884 bytes (86.8k, 52%).

After GZIP compression these minified files vary in size:

gzip -6 (default)	23251 bytes (22.7k)	local copy
Boot	23165 bytes (22.6k)	CDN
gzip -9	23164 bytes (22.6k)	local copy
libdeflate -12	22392 bytes (21.9k)	local copy
7zip -mx=9 -tgzip	22312 bytes (21.8k)	local copy
zultra	22310 bytes (21.8k)	local copy
kzip -s0 -rn -b0	22284 bytes (21.8k)	local copy
pigz -11 -n	22270 bytes (21.7k)	local copy
Zopfli	22248 bytes (21.7k)	local copy
cdnjs	19895 bytes (19.4k)	CDN

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/socketio/socket.io-1.3.1.min.js (or via HTTPS)

You will automatically get the smallest Socket.IO 1.3.1 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 --mls64 --bsr18 --lazy --ohh

(found June 30, 2016)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	64	--mls64
block splitting recursion	18	--bsr18
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/1.3.1/socket.io.min.js --location | md5sum
6583c4887c0335fad997a8470aeaaa43 -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-1.3.1.min.zopfli.js.gz | md5sum
6583c4887c0335fad997a8470aeaaa43 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/socketio/socket.io-client/1.3.1/socket.io.min.js --location | sha1sum
717e97ef9397eb2f87654883800fa8a7fa56fc3f -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-1.3.1.min.zopfli.js.gz | sha1sum
717e97ef9397eb2f87654883800fa8a7fa56fc3f -

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Boot	23165 bytes	997598ed6d5ecdb6c727e8dabf492138	< !function(e){if("object"==typeof exports&&"undefined"!=typ [...] < this.form=null;this.iframe=null}Polling.prototype.doClose. [...] < for(var key in utf8){hasOwnProperty.call(utf8,key)&&(freeE [...] > !function(t){if("object"==typeof exports&&"undefined"!=typ [...] > a("polling got data %s",t);var n=function(t){return"openin [...]	(invalid)
cdnjs	19895 bytes	997598ed6d5ecdb6c727e8dabf492138	< !function(e){if("object"==typeof exports&&"undefined"!=typ [...] < this.form=null;this.iframe=null}Polling.prototype.doClose. [...] < for(var key in utf8){hasOwnProperty.call(utf8,key)&&(freeE [...] > !function(t){if("object"==typeof exports&&"undefined"!=typ [...] > a("polling got data %s",t);var n=function(t){return"openin [...]	(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
22248 bytes	-1 byte	zopfli --i100000 --mls64 --bsr18 --lazy --ohh	June 30, 2016 @ 13:26
22249 bytes	-1 byte	zopfli --i10000 --mls64 --bsr18 --lazy --ohh	June 30, 2016 @ 07:21
22250 bytes	-2 bytes	zopfli --i10000 --mls128 --bsr20 --lazy --ohh	June 29, 2016 @ 17:43
22252 bytes	-5 bytes	zopfli --i1000 --mls128 --bsr20 --lazy --ohh	June 29, 2016 @ 15:33
22257 bytes	–	zopfli --i100 --mls128 --bsr20 --lazy --ohh	June 29, 2016 @ 13:15

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 @ 12:51.

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	22260	22260	22261	22261	22261	22260	22261	22261	22260	22275	22279	22278	22279	22275	22276
4	22280	22279	22287	22292	22258	22259	22263	22259	22261	22259	22279	22277	22274	22276	22277
6	22263	22263	22273	22280	22264	22259	22259	22257	22260	22260	22278	22278	22278	22279	22277
7	22262	22259	22259	22263	22260	22257	22258	22257	22258	22258	22278	22277	22278	22276	22280
8	22262	22286	22291	22259	22257	22263	22260	22258	22262	22280	22278	22278	22276	22278	22277
9	22280	22261	22258	22258	22263	22264	22261	22258	22258	22258	22277	22275	22277	22277	22277
10	22258	22258	22272	22261	22257	22258	22257	22259	22258	22258	22278	22275	22278	22279	22277
11	22273	22272	22272	22273	22257	22259	22258	22257	22262	22257	22277	22276	22276	22279	22277
12	22275	22273	22273	22274	22270	22273	22262	22293	22257	22258	22278	22277	22276	22277	22278
13	22257	22257	22259	22261	22257	22261	22257	22260	22258	22257	22278	22275	22276	22277	22277
14	22274	22264	22259	22261	22261	22258	22258	22258	22258	22259	22277	22277	22277	22277	22278
15	22260	22260	22258	22264	22257	22257	22257	22257	22257	22258	22278	22277	22278	22277	22279
16	22282	22280	22273	22274	22258	22258	22259	22263	22262	22258	22276	22275	22275	22277	22277
17	22266	22259	22259	22261	22257	22263	22257	22258	22258	22258	22278	22277	22276	22277	22278
18	22266	22262	22259	22261	22260	22248	22250	22261	22263	22258	22277	22275	22276	22278	22281
19	22279	22280	22272	22273	22263	22258	22259	22257	22258	22257	22275	22275	22278	22278	22279
20	22259	22259	22272	22281	22258	22259	22250	22257	22263	22258	22275	22278	22278	22277	22280
21	22266	22262	22259	22281	22270	22274	22257	22259	22258	22257	22275	22277	22278	22278	22278
22	22267	22264	22259	22265	22269	22264	22265	22258	22259	22257	22277	22277	22277	22278	22277
23	22259	22258	22260	22263	22257	22259	22258	22257	22257	22257	22278	22275	22278	22277	22277
25	22262	22280	22273	22272	22257	22275	22259	22292	22262	22260	22278	22277	22277	22279	22279
30	22265	22262	22259	22260	22257	22265	22258	22258	22258	22276	22275	22277	22276	22279	22277
40	22263	22260	22272	22281	22259	22259	22265	22258	22258	22258	22278	22278	22276	22276	22277

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	22257 bytes	–	100%
1,000	22252 bytes	-5 bytes	100%
10,000	22249 bytes	-3 bytes	100%
100,000	22248 bytes	-1 byte	0.29%
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)	22284 bytes	+36 bytes (+0.16%)	–
1	22292 bytes	+44 bytes (+0.20%)	+8 bytes
2	22285 bytes	+37 bytes (+0.17%)	+1 byte
3	22330 bytes	+82 bytes (+0.37%)	+46 bytes
4	22357 bytes	+109 bytes (+0.49%)	+73 bytes
5	22391 bytes	+143 bytes (+0.64%)	+107 bytes
6	22424 bytes	+176 bytes (+0.79%)	+140 bytes
7	22453 bytes	+205 bytes (+0.92%)	+169 bytes
8	22453 bytes	+205 bytes (+0.92%)	+169 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	18022 bytes	-4226 bytes (-18.99%)
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	18983 bytes	-3265 bytes (-14.68%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	19793 bytes	-2455 bytes (-11.03%)
Brotli (Wikipedia)	brotli	brotli -q 11	21004 bytes	-1244 bytes (-5.59%)
LZMA2 (Wikipedia)	xz	xz -9	21768 bytes	-480 bytes (-2.16%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	21922 bytes	-326 bytes (-1.47%)
Zstandard (Wikipedia)	zstd	zstd -19	22079 bytes	-169 bytes (-0.76%)

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 2024.
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.