Socket.IO 1.4.1 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 183798 bytes (179.5k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 96693 bytes (94.4k, 53%).

After GZIP compression these minified files vary in size:

gzip -6 (default)	25298 bytes (24.7k)	local copy
gzip -9	25207 bytes (24.6k)	local copy
Boot	25045 bytes (24.5k)	CDN
libdeflate -12	24336 bytes (23.8k)	local copy
zultra	24319 bytes (23.7k)	local copy
kzip -s0 -rn -b1	24278 bytes (23.7k)	local copy
7zip -mx=9 -tgzip	24277 bytes (23.7k)	local copy
pigz -11 -n	24268 bytes (23.7k)	local copy
Zopfli	24244 bytes (23.7k)	local copy
cdnjs	21485 bytes (21.0k)	CDN

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/socketio/socket.io-1.4.1.min.js (or via HTTPS)

You will automatically get the smallest Socket.IO 1.4.1 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 --bsr21 --lazy --ohh

(found July 1, 2016)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	64	--mls64
block splitting recursion	21	--bsr21
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/1.4.1/socket.io.min.js --location | md5sum
0cb0cc24006d786154e7ab27c4993045 -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-1.4.1.min.zopfli.js.gz | md5sum
0cb0cc24006d786154e7ab27c4993045 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/socketio/socket.io-client/1.4.1/socket.io.min.js --location | sha1sum
faedab4666c42cab275a674a84b15c0a48e7ef96 -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-1.4.1.min.zopfli.js.gz | sha1sum
faedab4666c42cab275a674a84b15c0a48e7ef96 -

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Boot	25045 bytes	95b0bc321cb310e084ca5c35a291f26c	< (function(f){if(typeof exports==="object"&&typeof module!= [...] < this.once("close",onclose);this.once("upgrading",onupgrade [...] < }})}map(packets,encodeOne,function(err,results){return cal [...] < },{}],47:[function(_dereq_,module,exports){"use strict";va [...] > !function(t){if("object"==typeof exports&&"undefined"!=typ [...] > var t=document.createElement("iframe");document.body.appen [...] > if(e.nsp+=i,r==t.length)break}else e.nsp="/";var s=t.charA [...]	(invalid)
cdnjs	21485 bytes	95b0bc321cb310e084ca5c35a291f26c	< (function(f){if(typeof exports==="object"&&typeof module!= [...] < this.once("close",onclose);this.once("upgrading",onupgrade [...] < }})}map(packets,encodeOne,function(err,results){return cal [...] < },{}],47:[function(_dereq_,module,exports){"use strict";va [...] > !function(t){if("object"==typeof exports&&"undefined"!=typ [...] > var t=document.createElement("iframe");document.body.appen [...] > if(e.nsp+=i,r==t.length)break}else e.nsp="/";var s=t.charA [...]	(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
24244 bytes	-1 byte	zopfli --i100000 --mls64 --bsr21 --lazy --ohh	July 1, 2016 @ 11:54
24245 bytes	-2 bytes	zopfli --i10000 --mls64 --bsr10 --lazy --ohh	June 29, 2016 @ 15:32
24247 bytes	-3 bytes	zopfli --i1000 --mls64 --bsr10 --lazy --ohh	June 29, 2016 @ 15:24
24250 bytes	–	zopfli --i100 --mls64 --bsr10 --lazy --ohh	June 29, 2016 @ 13:32

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 @ 12:49.

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	24250	24251	24253	24253	24253	24257	24257	24258	24254	24252	24258	24259	24257	24255	24257
4	24260	24257	24258	24261	24260	24267	24261	24259	24261	24263	24263	24257	24252	24256	24257
6	24251	24252	24252	24251	24247	24256	24253	24249	24252	24249	24251	24254	24254	24255	24255
7	24259	24259	24262	24258	24260	24259	24267	24261	24258	24253	24255	24256	24257	24258	24255
8	24260	24262	24260	24260	24257	24257	24258	24266	24261	24261	24257	24257	24253	24255	24255
9	24250	24252	24250	24247	24247	24253	24255	24252	24257	24250	24252	24258	24253	24256	24256
10	24259	24261	24259	24256	24249	24244	24257	24250	24251	24262	24249	24258	24250	24255	24255
11	24258	24261	24261	24262	24260	24260	24258	24260	24262	24258	24262	24257	24251	24255	24255
12	24259	24259	24259	24260	24251	24256	24257	24248	24250	24257	24261	24257	24250	24258	24255
13	24251	24251	24253	24250	24251	24255	24255	24252	24251	24247	24260	24257	24252	24254	24255
14	24259	24261	24260	24260	24260	24261	24258	24258	24257	24258	24256	24256	24253	24255	24255
15	24250	24250	24252	24251	24247	24255	24252	24255	24250	24248	24250	24249	24253	24258	24255
16	24259	24263	24261	24259	24260	24260	24266	24267	24258	24252	24260	24256	24251	24255	24255
17	24261	24262	24261	24260	24260	24259	24267	24251	24260	24258	24261	24253	24251	24255	24255
18	24257	24259	24259	24251	24260	24261	24267	24248	24262	24248	24259	24258	24251	24256	24256
19	24260	24260	24252	24258	24248	24246	24251	24248	24258	24251	24261	24258	24259	24259	24256
20	24259	24249	24251	24249	24246	24255	24244	24250	24250	24250	24249	24257	24252	24258	24256
21	24251	24261	24253	24249	24246	24244	24244	24255	24257	24250	24260	24253	24251	24256	24255
22	24259	24260	24260	24259	24260	24260	24266	24250	24257	24248	24259	24257	24249	24255	24255
23	24260	24263	24261	24260	24259	24261	24267	24261	24260	24258	24262	24260	24250	24256	24255
25	24256	24260	24260	24259	24257	24253	24258	24254	24256	24248	24260	24256	24259	24258	24255
30	24250	24262	24261	24259	24260	24260	24251	24252	24258	24249	24260	24256	24251	24255	24255
40	24257	24261	24261	24260	24261	24259	24258	24255	24256	24251	24255	24256	24257	24258	24256

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	24250 bytes	–	100%
1,000	24247 bytes	-3 bytes	100%
10,000	24245 bytes	-2 bytes	100%
100,000	24244 bytes	-1 byte	1.16%
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)	24285 bytes	+41 bytes (+0.17%)	+7 bytes
1	24278 bytes	+34 bytes (+0.14%)	–
2	24285 bytes	+41 bytes (+0.17%)	+7 bytes
3	24323 bytes	+79 bytes (+0.33%)	+45 bytes
4	24297 bytes	+53 bytes (+0.22%)	+19 bytes
5	24317 bytes	+73 bytes (+0.30%)	+39 bytes
6	24348 bytes	+104 bytes (+0.43%)	+70 bytes
7	24383 bytes	+139 bytes (+0.57%)	+105 bytes
8	24416 bytes	+172 bytes (+0.71%)	+138 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	19158 bytes	-5086 bytes (-20.98%)
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	20322 bytes	-3922 bytes (-16.18%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	22199 bytes	-2045 bytes (-8.44%)
Brotli (Wikipedia)	brotli	brotli -q 11	22432 bytes	-1812 bytes (-7.47%)
LZMA2 (Wikipedia)	xz	xz -9	23172 bytes	-1072 bytes (-4.42%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	23485 bytes	-759 bytes (-3.13%)
Zstandard (Wikipedia)	zstd	zstd -19	23541 bytes	-703 bytes (-2.90%)

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.