zopen(+Stream,
-ZStream, +Options)Creates ZStream, providing compressed access to Stream.
If an input stream is wrapped, it recognises a gzip or deflate header.
If an output stream is wrapped, Options define the desired
wrapper and compression level. The new ZStream inherits its
encoding from Stream. In other words, if Stream
is a text-stream, so is ZStream. The original Stream
is switched to binary mode while it is wrapped. The original encoding of
Stream is restored if ZStream is closed. Note that zopen/3
does not actually process any data and therefore succeeds on input
streams that do not contain valid data. Errors may be generated by read
operations performed on the stream.
Defined options on output streams are:
- format(+Format)
- Either
deflate (default), raw_deflate or gzip.
The deflate envelope is simple and short and is typically
used for compressed (network) communication. The raw_deflate
does not include an envelope and is often used as a step in crypographic
encodings. The gzip envelope is compatible to the gzip
program and intended to read/write compressed files.
- level(+Level)
- Number between 0 and 9, specifying the compression level, Higher levels
use more resources. Default is 6, generally believed to be a good
compromise between speed, memory requirement and compression.
- multi_part(+Boolean)
- If
true, restart reading if the input is not at
end-of-file. The default is true for gzip streams.
Generic options are:
- close_parent(Bool)
- If
true (default), closing the compressed stream also
closes (and thus invalidates) the wrapped stream. If false,
the wrapped stream is not closed. This can be used to
read/write a compressed data block as partial input/output on a stream.