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Pre- and Post-Processing

As with an origin server, it may be necessary to preprocess data before the main content-transforming filter, and/or postprocess afterwards. For example, when dealing with gzipped content we need to uncompress it for processing and re-compress the processed data. Similarly in an image-processing filter, we need to decode the original image format and re-encode the processed data.

This may involve more than one phase. For example, when filtering text, we may need to both to uncompress gzipped data and transcode the character set before the main filter.

So, potentially we have a large multiplicity of filters: transformation filters, together with pre- and post-processing for different content types and encodings. To repeat the hack of having each filter inserted and determining whether to run or remove itself in such a setup goes beyond simple inelegance and into the absurd. An alternative architecture is required.