seekstart/seek/seekend leads to invalid position

[Marlin-Na]

Currently TranscodingStreams has default methods for seekstart seekend and position. position implementation is based on the bytes read from the io. However, when seekstart or seekend is called, it will lead to invalid position. For example:

# Create a gzip file
using CodecZlib
s = GzipCompressorStream(open("/tmp/test.txt.gz", "w"))
write(s, "abbccc"); close(s)

# Reading stream
s = GzipDecompressorStream(open("/tmp/test.txt.gz"))
read(s, Char); position(s) ## position is 1, correct!
seekstart(s); position(s)  ## position changes to 6, it should be 0
read(s, Char); position(s) ## position changes to 7, it should be 1
seekend(s); position(s)    ## position changes to 12, it should be 6

I think when seekstart is called, we probably need to reset the Stats of the stream. For seekend, I think it might be hard/impossible to get the right position after decompression, however at least an warning should be given. seek is not provided by default, however if a Codec implements only seek but not position, it might leads invalid position as well.

What's your thoughts on this issue? Maybe it is possible to just issue an warning when calling position after called seek/seekstart/seekend? Then a Codec might implements its specialized methods for position (e.g. for Noop).