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diff --git a/doc/manual/filters.rst b/doc/manual/filters.rst index e8016eac7..bd73739af 100644 --- a/doc/manual/filters.rst +++ b/doc/manual/filters.rst @@ -693,48 +693,6 @@ letters for its output. You can find the declarations for these types in ``hex_filt.h`` and ``b64_filt.h``. -Compressors -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - -There are two compression algorithms supported by Botan, zlib and -bzip2. Only lossless compression algorithms are currently supported by -Botan, because they tend to be the most useful for -cryptography. However, it is very reasonable to consider supporting -something like GSM speech encoding (which is lossy), for use in -encrypted voice applications. - -You should always compress *before* you encrypt, because encryption seeks -to hide the redundancy that compression is supposed to try to find and remove. - -To test for Bzip2, check to see if ``BOTAN_HAS_COMPRESSOR_BZIP2`` is -defined. If so, you can include ``botan/bzip2.h``, which will declare -a pair of ``Filter`` objects: ``Bzip2_Compression`` and -``Bzip2_Decompression``. - -You should be prepared to take an exception when using the -decompressing filter, for if the input is not valid bzip2 data, that -is what you will receive. You can specify the desired level of -compression to ``Bzip2_Compression``'s constructor as an integer -between 1 and 9, 1 meaning worst compression, and 9 meaning the -best. The default is to use 9, since small values take the same amount -of time, just use a little less memory. - -Zlib compression works much like Bzip2 compression. The only -differences in this case are that the macro is -``BOTAN_HAS_COMPRESSOR_ZLIB``, the header you need to include is -called ``botan/zlib.h`` (remember that you shouldn't just ``#include -<zlib.h>``, or you'll get the regular zlib API, which is not what you -want). The Botan classes for zlib compression/decompression are called -``Zlib_Compression`` and ``Zlib_Decompression``. - -Like Bzip2, a ``Zlib_Decompression`` object will throw an exception if -invalid (in the sense of not being in the Zlib format) data is passed -into it. - -While the zlib compression library uses the same compression algorithm -as the gzip and zip programs, the format is different. The zlib format -is defined in RFC 1950. - Writing New Filters --------------------------------- |