Socket.IO 1.0.0 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 151203 bytes (147.7k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 78470 bytes (76.6k, 52%).

After GZIP compression these minified files vary in size:

gzip -6 (default)	20512 bytes (20.0k)	local copy
gzip -9	20437 bytes (20.0k)	local copy
Boot	20354 bytes (19.9k)	CDN
libdeflate -12	19756 bytes (19.3k)	local copy
7zip -mx=9 -tgzip	19712 bytes (19.3k)	local copy
zultra	19693 bytes (19.2k)	local copy
pigz -11 -n	19683 bytes (19.2k)	local copy
kzip -s0 -rn -b2	19668 bytes (19.2k)	local copy
Zopfli	19648 bytes (19.2k)	local copy
cdnjs	17436 bytes (17.0k)	CDN

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/socketio/socket.io-1.0.0.min.js (or via HTTPS)

You will automatically get the smallest Socket.IO 1.0.0 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 --mls128 --bsr15 --lazy --ohh

(found July 1, 2016)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	128	--mls128
block splitting recursion	15	--bsr15
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/1.0.0/socket.io.min.js --location | md5sum
ba27831af5d11750796d29641295dd75 -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-1.0.0.min.zopfli.js.gz | md5sum
ba27831af5d11750796d29641295dd75 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/socketio/socket.io-client/1.0.0/socket.io.min.js --location | sha1sum
ed4365e569ab87c7f82effee7e9ef7c35dbc2965 -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-1.0.0.min.zopfli.js.gz | sha1sum
ed4365e569ab87c7f82effee7e9ef7c35dbc2965 -

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Boot	20354 bytes	663baf9b8d329f17880530d6ecd44f99	< !function(e){"object"==typeof exports?module.exports=e():" [...] < var self=this;try{debug("xhr open %s: %s",this.method,this [...] < }};function BinaryReconstructor(packet){this.reconPack=pac [...] > !function(t){"object"==typeof exports?module.exports=t():" [...] > var s=new m([i.buffer,t.data]);return r(s)}function s(t,e, [...]	(invalid)
cdnjs	17436 bytes	663baf9b8d329f17880530d6ecd44f99	< !function(e){"object"==typeof exports?module.exports=e():" [...] < var self=this;try{debug("xhr open %s: %s",this.method,this [...] < }};function BinaryReconstructor(packet){this.reconPack=pac [...] > !function(t){"object"==typeof exports?module.exports=t():" [...] > var s=new m([i.buffer,t.data]);return r(s)}function s(t,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
19648 bytes	-1 byte	zopfli --i100000 --mls128 --bsr15 --lazy --ohh	July 1, 2016 @ 13:39
19649 bytes	-2 bytes	zopfli --i100000 --mls128 --bsr23 --lazy --ohh	June 30, 2016 @ 12:01
19651 bytes	-1 byte	zopfli --i10000 --mls64 --bsr23 --lazy --ohh	June 30, 2016 @ 08:58
19652 bytes	-1 byte	zopfli --i10000 --mls32768 --bsr20 --lazy --ohh	June 30, 2016 @ 07:38
19653 bytes	-4 bytes	zopfli --i1000 --mls64 --bsr15 --lazy --ohh	June 29, 2016 @ 15:38
19657 bytes	–	zopfli --i100 --mls128 --bsr15 --lazy --ohh	June 29, 2016 @ 11:37

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 @ 12:52.

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	19660	19660	19660	19660	19660	19661	19671	19661	19671	19672	19673	19673	19672	19667	19667
4	19660	19659	19660	19660	19661	19661	19675	19674	19675	19675	19673	19670	19681	19666	19667
6	19662	19662	19663	19662	19661	19659	19661	19676	19666	19674	19672	19666	19667	19666	19667
7	19662	19660	19661	19665	19663	19665	19662	19661	19672	19666	19673	19669	19667	19667	19669
8	19661	19660	19661	19658	19662	19660	19675	19661	19673	19673	19674	19673	19667	19666	19654
9	19661	19662	19666	19665	19672	19674	19673	19674	19672	19672	19682	19674	19666	19666	19653
10	19661	19661	19666	19665	19662	19666	19673	19659	19667	19667	19668	19667	19669	19666	19652
11	19661	19660	19661	19660	19661	19674	19659	19677	19674	19673	19673	19667	19666	19666	19666
12	19661	19660	19662	19660	19659	19659	19675	19676	19674	19674	19674	19674	19667	19671	19652
13	19661	19660	19661	19660	19659	19659	19675	19659	19673	19672	19675	19667	19658	19666	19661
14	19661	19665	19661	19659	19664	19659	19673	19676	19667	19672	19673	19666	19666	19666	19652
15	19661	19662	19661	19665	19661	19651	19648	19676	19667	19669	19666	19666	19666	19669	19669
16	19661	19660	19661	19665	19661	19659	19675	19661	19672	19672	19673	19676	19666	19666	19652
17	19661	19660	19662	19658	19665	19660	19676	19677	19674	19673	19675	19670	19669	19669	19673
18	19661	19661	19662	19660	19662	19659	19660	19674	19674	19674	19674	19672	19671	19671	19653
19	19662	19661	19661	19660	19659	19659	19657	19676	19666	19674	19672	19671	19667	19669	19652
20	19662	19663	19662	19660	19664	19661	19660	19661	19673	19674	19673	19667	19666	19669	19652
21	19662	19660	19660	19659	19665	19658	19658	19676	19673	19674	19673	19674	19669	19666	19654
22	19662	19664	19661	19659	19662	19659	19674	19676	19674	19672	19673	19667	19666	19669	19653
23	19661	19660	19662	19660	19668	19651	19649	19676	19667	19674	19674	19666	19667	19666	19652
25	19661	19661	19662	19659	19661	19662	19660	19676	19673	19674	19673	19673	19669	19666	19653
30	19661	19660	19661	19658	19664	19660	19675	19661	19673	19672	19674	19673	19666	19666	19652
40	19662	19660	19662	19661	19658	19659	19675	19676	19674	19674	19674	19673	19666	19666	19666

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	19657 bytes	–	100%
1,000	19653 bytes	-4 bytes	100%
10,000	19650 bytes	-3 bytes	100%
100,000	19648 bytes	-2 bytes	0.58%
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)	19669 bytes	+21 bytes (+0.11%)	+1 byte
1	19695 bytes	+47 bytes (+0.24%)	+27 bytes
2	19668 bytes	+20 bytes (+0.10%)	–
3	19715 bytes	+67 bytes (+0.34%)	+47 bytes
4	19741 bytes	+93 bytes (+0.47%)	+73 bytes
5	19776 bytes	+128 bytes (+0.65%)	+108 bytes
6	19811 bytes	+163 bytes (+0.83%)	+143 bytes
7	19809 bytes	+161 bytes (+0.82%)	+141 bytes
8	19849 bytes	+201 bytes (+1.02%)	+181 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	16079 bytes	-3569 bytes (-18.16%)
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	16796 bytes	-2852 bytes (-14.52%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	17539 bytes	-2109 bytes (-10.73%)
Brotli (Wikipedia)	brotli	brotli -q 11	18593 bytes	-1055 bytes (-5.37%)
LZMA2 (Wikipedia)	xz	xz -9	19272 bytes	-376 bytes (-1.91%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	19328 bytes	-320 bytes (-1.63%)
Zstandard (Wikipedia)	zstd	zstd -19	19548 bytes	-100 bytes (-0.51%)

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.