Zlib
PHP Manual

Predefined Constants

The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.

FORCE_GZIP (integer)
FORCE_DEFLATE (integer)
ZLIB_ENCODING_RAW (integer)
DEFLATE algorithm as per RFC 1951. Available as of PHP 7.0.0.
ZLIB_ENCODING_DEFLATE (integer)
ZLIB compression algorithm as per RFC 1950. Available as of PHP 7.0.0.
ZLIB_ENCODING_GZIP (integer)
GZIP algorithm as per RFC 1952. Available as of PHP 7.0.0.
ZLIB_FILTERED (integer)
Available as of PHP 7.0.0.
ZLIB_HUFFMAN_ONLY (integer)
Available as of PHP 7.0.0.
ZLIB_FIXED (integer)
Available as of PHP 7.0.0.
ZLIB_RLE (integer)
Available as of PHP 7.0.0.
ZLIB_DEFAULT_STRATEGY (integer)
Available as of PHP 7.0.0.
ZLIB_BLOCK (integer)
Available as of PHP 7.0.0.
ZLIB_NO_FLUSH (integer)
Available as of PHP 7.0.0.
ZLIB_PARTIAL_FLUSH (integer)
Available as of PHP 7.0.0.
ZLIB_SYNC_FLUSH (integer)
Available as of PHP 7.0.0.
ZLIB_FULL_FLUSH (integer)
Available as of PHP 7.0.0.
ZLIB_FINISH (integer)
Available as of PHP 7.0.0.

Zlib
PHP Manual