Socket.IO 1.4.5 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 184656 bytes (180.3k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 97690 bytes (95.4k, 53%).

After GZIP compression these minified files vary in size:

Boot	30585 bytes (29.9k)	CDN
cdnjs	25680 bytes (25.1k)	CDN
gzip -6 (default)	25467 bytes (24.9k)	local copy
gzip -9	25352 bytes (24.8k)	local copy
libdeflate -12	24460 bytes (23.9k)	local copy
7zip -mx=9 -tgzip	24455 bytes (23.9k)	local copy
zultra	24425 bytes (23.9k)	local copy
kzip -s0 -rn -b2	24411 bytes (23.8k)	local copy
pigz -11 -n	24405 bytes (23.8k)	local copy
Zopfli	24381 bytes (23.8k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/socketio/socket.io-1.4.5.min.js (or via HTTPS)

You will automatically get the smallest Socket.IO 1.4.5 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 --i1000000 --mb8 --mls1024 --bsr16 --lazy --ohh

(found June 29, 2016)

Description	Value	Parameter
iterations	1000000	--i1000000
maximum blocks	8	--mb8
maximum length score	1024	--mls1024
block splitting recursion	16	--bsr16
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/1.4.5/socket.io.min.js --location | md5sum
60d95a466f90b4146189b2d49cbc48c8 -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-1.4.5.min.zopfli.js.gz | md5sum
60d95a466f90b4146189b2d49cbc48c8 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/socketio/socket.io-client/1.4.5/socket.io.min.js --location | sha1sum
137f37530457707477f252a8965a5872c1fc409e -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-1.4.5.min.zopfli.js.gz | sha1sum
137f37530457707477f252a8965a5872c1fc409e -

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Boot	30585 bytes	2fd19ba922f18342f2f7b934b79b8e6f	< socket.on("connect",function(){socket.id=self.engine.id}); [...] < }return results}abort()}return value};var update=function( [...] > socket.on("connect",function(){socket.id=self.engine.id}); [...] > }abort()}return value};var update=function(source,property [...]	(invalid)
cdnjs	25680 bytes	2fd19ba922f18342f2f7b934b79b8e6f	< socket.on("connect",function(){socket.id=self.engine.id}); [...] < }return results}abort()}return value};var update=function( [...] > socket.on("connect",function(){socket.id=self.engine.id}); [...] > }abort()}return value};var update=function(source,property [...]	(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
24381 bytes	-2 bytes	zopfli --i1000000 --mls1024 --bsr16 --lazy --ohh	June 29, 2016 @ 22:41
24383 bytes	-1 byte	zopfli --i100000 --mls1024 --bsr16 --lazy --ohh	June 29, 2016 @ 16:45
24384 bytes	-1 byte	zopfli --i10000 --mls256 --bsr13 --lazy --ohh	June 29, 2016 @ 15:32
24385 bytes	-3 bytes	zopfli --i10000 --mls1024 --bsr9 --lazy --ohh	June 29, 2016 @ 15:29
24388 bytes	-1 byte	zopfli --i1000 --mls256 --bsr13 --lazy --ohh	June 29, 2016 @ 15:28
24389 bytes	-2 bytes	zopfli --i1000 --mls512 --bsr13 --lazy --ohh	June 29, 2016 @ 15:22
24391 bytes	-1 byte	zopfli --i1000 --mls512 --bsr16 --lazy --ohh	June 29, 2016 @ 15:22
24392 bytes	-3 bytes	zopfli --i1000 --mls128 --bsr11 --lazy --ohh	June 29, 2016 @ 14:19
24395 bytes	–	zopfli --i100 --mls128 --bsr12 --lazy --ohh	June 29, 2016 @ 13:18

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 @ 12:48.

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, 100,000 or 1,000,000.

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	24399	24401	24400	24401	24407	24404	24398	24399	24400	24400	24400	24402	24400	24400	24400
4	24397	24399	24399	24412	24398	24396	24393	24396	24398	24399	24396	24398	24395	24395	24398
6	24403	24400	24403	24391	24391	24393	24402	24396	24395	24399	24399	24399	24395	24398	24397
7	24401	24403	24391	24389	24405	24392	24398	24384	24404	24399	24399	24399	24395	24397	24403
8	24396	24390	24397	24390	24406	24393	24396	24401	24386	24399	24399	24400	24395	24398	24398
9	24403	24402	24403	24410	24404	24390	24395	24399	24388	24385	24398	24399	24396	24398	24397
10	24398	24399	24394	24398	24393	24396	24392	24392	24394	24395	24399	24396	24395	24398	24396
11	24394	24396	24396	24395	24395	24390	24391	24389	24393	24400	24390	24398	24396	24397	24396
12	24401	24400	24401	24390	24406	24390	24391	24385	24387	24386	24396	24399	24390	24396	24395
13	24391	24398	24397	24395	24405	24400	24394	24384	24385	24399	24400	24398	24395	24398	24396
14	24400	24400	24403	24400	24402	24392	24398	24396	24387	24399	24399	24400	24398	24398	24397
15	24401	24402	24403	24400	24399	24390	24395	24395	24392	24399	24395	24399	24395	24398	24397
16	24410	24403	24403	24391	24391	24397	24396	24393	24390	24381	24395	24399	24401	24398	24398
17	24401	24399	24403	24394	24392	24396	24395	24393	24391	24399	24395	24399	24395	24398	24398
18	24403	24400	24397	24390	24405	24390	24395	24400	24386	24399	24395	24398	24402	24397	24396
19	24401	24403	24400	24401	24404	24398	24399	24400	24385	24399	24396	24398	24403	24398	24398
20	24401	24402	24401	24405	24404	24401	24399	24400	24391	24386	24399	24398	24396	24398	24398
21	24401	24401	24400	24389	24405	24391	24398	24395	24386	24385	24396	24399	24396	24398	24395
22	24402	24401	24401	24394	24391	24390	24391	24400	24386	24386	24396	24396	24395	24397	24396
23	24401	24402	24401	24391	24392	24401	24388	24382	24385	24382	24396	24398	24396	24398	24396
25	24401	24400	24400	24404	24404	24395	24393	24382	24387	24385	24399	24398	24395	24398	24395
30	24401	24403	24403	24387	24401	24389	24394	24399	24403	24399	24396	24399	24395	24398	24398
40	24399	24399	24399	24403	24404	24391	24395	24384	24385	24385	24395	24400	24395	24397	24395

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	24395 bytes	–	100%
1,000	24386 bytes	-9 bytes	100%
10,000	24384 bytes	-2 bytes	100%
100,000	24383 bytes	-1 byte	2.03%
1,000,000	24381 bytes	-2 bytes	1.16%
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)	24421 bytes	+40 bytes (+0.16%)	+10 bytes
1	24423 bytes	+42 bytes (+0.17%)	+12 bytes
2	24411 bytes	+30 bytes (+0.12%)	–
3	24442 bytes	+61 bytes (+0.25%)	+31 bytes
4	24468 bytes	+87 bytes (+0.36%)	+57 bytes
5	24503 bytes	+122 bytes (+0.50%)	+92 bytes
6	24531 bytes	+150 bytes (+0.62%)	+120 bytes
7	24569 bytes	+188 bytes (+0.77%)	+158 bytes
8	24603 bytes	+222 bytes (+0.91%)	+192 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	19205 bytes	-5176 bytes (-21.23%)
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	20400 bytes	-3981 bytes (-16.33%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	22098 bytes	-2283 bytes (-9.36%)
Brotli (Wikipedia)	brotli	brotli -q 11	22565 bytes	-1816 bytes (-7.45%)
LZMA2 (Wikipedia)	xz	xz -9	23292 bytes	-1089 bytes (-4.47%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	23487 bytes	-894 bytes (-3.67%)
Zstandard (Wikipedia)	zstd	zstd -19	23693 bytes	-688 bytes (-2.82%)

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.