zlib.Deflater.Deflate

zlib.Deflater.Deflate

Method Signatures

 Function Deflate(Data As MemoryBlock, Flushing As Integer = zlib.Z_NO_FLUSH) As MemoryBlock
 Function Deflate(ReadFrom As Readable, WriteTo As Writeable, Flushing As Integer = zlib.Z_NO_FLUSH, ReadCount As Integer = -1) As Boolean

Parameters

Deflate(MemoryBlock, Integer)

Name	Type	Comment
Data	MemoryBlock	The next chunk of data to compress.
Flushing	Integer	Optional. If specified, indicates whether (and how) pending output should be flushed (see remarks.)

Deflate(Readable, Writeable, Integer, Integer)

Name	Type	Comment
ReadFrom	Readable	The stream from which to read uncompressed data.
WriteTo	Writeable	The stream to which compressed data will be written.
Flushing	Integer	Optional. If specified, indicates whether (and how) pending output should be flushed (see remarks.)
ReadCount	Integer	Optional. If specified, the number of uncompressed bytes to read.

Remarks

There are two versions of this method:

Deflate(MemoryBlock, Integer) As MemoryBlock

Processes uncompressed bytes in Data into the compressor, and returns any compressed bytes that were emitted. If there was no output then a zero-length MemoryBlock is returned.

Deflate(Readable, Writeable, Integer, Integer) As Boolean

Processes uncompressed bytes from ReadFrom into the compressor, and writes any compressed bytes that were emitted to WriteTo. If ReadCount is specified then exactly ReadCount uncompressed bytes are read; otherwise uncompressed bytes will continue to be read until ReadFrom.EOF=True.

In both versions the unprocessed portion of the input is retained by the compressor until a subsequent call to this method.

Deflate does not necessarily consume uncompressed data immediately. The "sliding window" determines the size of the compression buffer, and the size of the compression buffer determines how many uncompressed bytes have to be consumed in order to emit one or more compressed bytes.

If the compressor needed more uncompressed bytes than were provided then zero bytes will be emitted and Avail_Out will be >0. Call Deflate again with more uncompressed bytes until Avail_Out=0. If there are no more uncompressed bytes then call Deflate with zero uncompressed bytes (or specify Nil as the ReadFrom parameter) and Z_FINISH as the Flushing parameter.

Flushing

The Flushing parameter may be one of the following constants

Name	Comment
Z_NO_FLUSH	The default, this allows deflate to decide how much data to accumulate before producing output.
Z_SYNC_FLUSH	All pending output is flushed to the output buffer and the output is aligned on a byte boundary.
Z_PARTIAL_FLUSH	All pending output is flushed to the output buffer, but the output is not aligned to a byte boundary.
Z_BLOCK	A deflate block is completed and emitted, but the output is not aligned on a byte boundary.
Z_FULL_FLUSH	Like Z_SYNC_FLUSH, and the compression state is reset so that decompression can restart from this point.
Z_FINISH	All remaining output is aligned on a byte boundary and written to the output buffer.