Allow pub access to underlying 'Read' member of Take or Chain

[peter-bertok]

I asked this as a question on StackOverflow, and it was suggested that I raise an issue.

I'm writing a Rust implementation of the Google Brotli decompression algorithm, which uses a fixed number of "implicit zeroes" at the end of the stream to enable certain optimisations.

The Google C implementation does this using a spaghetti code of various counters, but I'd like to use the adaptors in the Rust std::io library instead. Something like:

pub struct StreamBitReader<R> {
    reader: Chain<R,Take<Repeat>>,
    ...
}

where 'R' is the underlying Read that the bit reader struct is wrapping. However, there are a number of cases where the decompression algorithm checks to see if it has "overrun" the stream, and it does this by checking the number of implicit zero bytes that have been read. This appears to be impossible in safe Rust, as there is no way to obtain a reference to the underlying components of Chain, unless I'm missing something.

When Chain is constructed, it takes ownership of (moves) the two Read structs, which then are hidden in private members.

Is there any way to construct the Take<Repeat> part such that I can continue to access the limit() fn of Take even after the Chain adaptor takes ownership?

If not, then there ought to be either public members or functions that allow access to the base Read members of all such adaptors, to allow this type of code.

[sfackler]

That seems pretty reasonable. We already have those kinds of accessors on other adaptors like BufferedReader and BufferedWriter.

[brson]

Does libs team care about this for completeness?

[alexcrichton]

Yes seems fine to implement to me

[aturon]

Libs team is 👍 on this, please send a PR!

[SergioBenitez]

I've started working on this and will have an implementation soon!