Get length of compressed stream so far without closing stream?

I would like to get the length of the compressed stream up to now but without closing the stream or affecting continued compression. I understand most Codecs might not support this, given their internal block lengths etc, but maybe there are ways to get related/close to this behavior?

The use case is something like this:

• We have a very long string/stream which has been compressed already, C(s_long)
• We now have a set of N shorter strings S_shorts = [s1, ..., sN] and we want to calculate map(length, [C(s_long * s1), ..., C(s_long * sN)]) but without having to redo the whole C(s_long) compression for each of the shorter strings si (since calculating C(s_long) might be costly in time).
• Note that we only need the lengths of all the C(s_long * si), not their actual bytes.

Any ideas how this can be done as fast as possible? :)

Currently I basically do a Huffman coding/tree or dictionary-based compression by hand and can thus save the intermediate tree/dictionary between each consideration of the short strings, but it would be nice if there is a way to use more advanced compressors like the CodecX ones in the TranscodingStreams framework.

Start by reviewing the TranscodingStreams codec interfaces and the CodecX implementations mentioned in the issue. Check whether a supported operation can report compressed length for a prefix without closing or changing continued compression; done means documenting a feasible interface or confirming codec limitations and an example.