GetDecompressedSize reports wrong size from stream compressed array.

[mateli]

When using CompressorStream to create a compressed byte array running GetCompressedSize returns the wrong number.
However compressing the same source data using Compressor.Wrap produces the correct size.
Is the storage format different?

[oleg-st]

GetDecompressedSize returns the upper bound for the decompressed size, see ZSTD_decompressBound. You can use SetPledgedSrcSize to specify the source size in streaming mode, in which case GetDecompressedSize will return the exact value.

Is the storage format different?

https://facebook.github.io/zstd/zstd_manual.html#Chapter15:

Decompressed size is an optional field, that may not be present, especially in streaming mode

[mateli]

So I manually keep track of written bytes and call this before closing the stream/file? Is it possible to update files that has already been written with a correct size?

[oleg-st]

SetPledgedSrcSize can be called before the frame header is written.

Is it possible to update files that has already been written with a correct size?

I don't think there's an API for something like this. You can forward your question to the authors of zstd.