Feature request: access to the underlying writer

[kristoff3r]

This is a straight up duplicate of #660, which was closed and I don't have permission to reopen.

I have a use case where the accepted solution of using a mutable reference doesn't work. I would like to store the partially written data inside the Writer as a std::io::Cursor<Vec<u8>>, so I can keep the Writer around without dealing with lifetimes or file handles, but since there's no way to access the inner writer at all this isn't currently possible.

My suggestion would be for Writer::finish to simply return the writer, but a getter would also work.

[197g]

PRs can be filed anytime. We have Writer<W>: Drop so we can't destructure into the writer field. And having unsafe for that does not seem worth it. We can wait on Rust to stabilize private destructuring through a ManuallyDrop<_>: rust-lang/rfcs#713, rust-lang/rfcs#3738

[kristoff3r]

PRs can be filed anytime. We have Writer<W>: Drop so we can't destructure into the writer field. And having unsafe for that does not seem worth it. We can wait on Rust to stabilize private destructuring through a ManuallyDrop<_>: rust-lang/rfcs#713, rust-lang/rfcs#3738

Ah, I didn't notice the Drop impl, well that explains why finish() didn't already return the writer.

Are you open to adding something like one of these? Or do you have another solution you'd prefer? I'd be happy to do the PR in any case.

pub fn writer(&self) -> &W {
    &self.w
}

pub fn finish_with_writer(&mut self) -> Result<&mut W> {
    self.validate_sequence_done()?;
    self.write_iend()?;
    self.w.flush()?;

    Ok(&mut self.w)
}