Thank you for verifying - when we run it from terminal using the string you provided we get an "End of File" error. Maybe this means our systems our configured differently?

Regardless thank you for the quick responses and information!

Oh thank you for clarifying! When trying to implement this code we're getting a <WRITE> error at zUnDeflate + 7, the line "Write Compressed" - have you ever experienced that before?

Thank you! So we already have the deflated data sent to us from a client in an http header - we need to decompress it only (not compress it). It seems like this is not possible, but I appreciate you confirming! We're looking into pulling in a python library for the decompression. 

Agreed it would be nice for intersystems to add this for generic zlib compression/decmopression