gzdeflate()

(PHP 4 >= 4.0.4, PHP 5, PHP 7)

Deflate a string

说明

This function compresses the given string using theDEFLATEdata format.

For details on the DEFLATE compression algorithm see the document "» DEFLATE Compressed Data Format Specification version 1.3"(RFC 1951).

参数

The data to deflate.

The level of compression. Can be given as 0 for no compression up to 9 for maximum compression. If not given, the default compression level will be the default compression level of the zlib library.

One of ZLIB_ENCODING_* constants.

返回值

The deflated string or FALSE if an error occurred.

范例

gzdeflate() example

更新日志

参见

• gzinflate()Inflate a deflated string
• gzcompress()Compress a string
• gzuncompress()Uncompress a compressed string
• gzencode()Create a gzip compressed string

Take care that that "PHP deflate" != "HTTP deflate".
The deflate encoding used in HTTP is actually zlib encoded.
This is what PHP functions return:
gzencode() == gzip
gzcompress() == zlib (aka. HTTP deflate)
gzdeflate() == *raw* deflate encoding

gzcompress produces longer data because it embeds information about the encoding onto the string. If you are compressing data that will only ever be handled on one machine, then you don't need to worry about which of these functions you use. However, if you are passing data compressed with these functions to a different machine you should use gzcompress.

running 50000 repetitions on various content, i found that gzdeflate() and gzcompress() both performed equally fast regardless content and compression level, but gzinflate() was always about twice as fast as gzuncompress().

After some searching and experimentation I found that the output from this function cannot be 'inflated' with the objective c 'zlibInflate' wrapper for 'zlib' that is available at http://cocoadev.com/wiki/NSDataCategory but the output from gzcompress() can be. Thank you "anonymous at php dot net" and "tomas at slax dot org" for the clues. I hope this saves someone else the searching.

start from php5.4.0 gzdeflate has the fastest speed and best zip rate.
http://3v4l.org/K2XAf

The HTTP deflate is quite complicated.
The RFC7230, Sec 4.2.2 (https://tools.ietf.org/html/rfc7230#section-4.2.2) says:
«The "deflate" coding is a "zlib" data format [RFC1950] containing a "deflate" compressed data stream [RFC1951] that uses a combination of the Lempel-Ziv (LZ77) compression algorithm and Huffman coding.»
and, also:
«Note: Some non-conformant implementations send the "deflate" compressed data without the zlib wrapper.»
Since this function implements the RFC1951, the compliant encoding of a $payload should be:
gzcompress(gzdeflate($payload));

gzcompress() is the same like gzdefflate(), it produces identical data and its speed is the same as well. The only difference is that gzcompress produces 6 bytes bigger result (2 extra bytes at the beginning and 4 extra bytes at the end).

if you have compressed data which is greater than 2 MB (system dependent), you will receive a buffer error by calling the function gzinflate().
be sure to to compress your data by a lower compression level, like 1.
i.e.: gzdeflate($sData, 1);

The "One of ZLIB_ENCODING_* constants." seems to be available only from PHP 5.4. 
So I guess that is you are PHP 5.3 you don't use the $encoding parameter...

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