First crack at adding dataset read adapter in DS read for deflate

[naterichman]

No description provided.

[Enet4]

I had another try at this. Last time we talked about deflate TS support, the main problem was that the data RW adapter would not allow us to bind the lifetime of the adapted reader/writer to the lifetime of the input reader/writer. With the current signature, this is simply impossible.

So we had to change the trait DataRWAdapter. One way that we can do in modern Rust thanks to GATs is something the likes of this:

pub trait DataRWAdapter {
    type Reader<'r, R: 'r>: Read
        where Self: 'r;
    type Writer<'w, W: 'w>: Write
        where Self: 'w;

    /// Adapt a byte reader.
    fn adapt_reader<R>(&self, reader: R) -> Self::Reader<R>;

    /// Adapt a byte writer.
    fn adapt_reader<W>(&self, writer: W) -> Self::Writer<W>;
}

As delightful as this trait is, it is not dyn-compatible (the new nomenclature for what was previously known as object-safe), so we could not have a registry for any adapter of this kind.

Ultimately, we have to go for a fully dynamic approach with an added lifetime parameter at each method.

pub trait DataRWAdapter {
    /// Adapt a byte reader.
    fn adapt_reader<'r>(&self, reader: Box<dyn Read + 'r>) -> Box<dyn Read + 'r>;

    /// Adapt a byte writer.
    fn adapt_writer<'w>(&self, writer: Box<dyn Write + 'w>) -> Box<dyn Write + 'w>;
}

After propagating the changes to the rest of the code, we thus bring support for deflated DICOM data sets in dicom-dump, dicom-toimage, and many other tools.

---

This is not yet ready though.

• dicom-transcode needs a few more tweaks in order to enable reading and writing deflated DICOM files. I can work on this soon-ish. Done
• Two of the new tests need to be changed. A round trip from deflated DICOM data and back to deflated DICOM data does not guarantee a file with the same size, since it could be done using a different deflate encoder implementation with different compression parameters.