add stream shutdown and support half-duplex operation

[vtjnash]

Fixes one of the issues mentioned in #24526

[vtjnash]

required for #39027

[vtjnash]

CI failures are waiting for libuv/libuv#3006

[c42f]

I like everything about this PR except for the newly exported name shutdown().

Do we really want to export such a generic verb with such a relatively obscure meaning? (Yes, it maps to the names used in the underlying system calls, but IMO that's the only thing it's got going for it.)

In #24526 it was suggested that closewrite() might be used which seems far more obvious.

[vtjnash]

Ah, I didn't see discussion of names. I am okay with it, since it dispatches on being an IO object

[c42f]

I am okay with it, since it dispatches on being an IO object

To me this seems like close() but for the writer side? So closewrite() is a completely self-evident name if someone knows what close() does? Whereas shutdown() has no analogy, except for the small number of Juila programmers who also know about man 2 shutdown.

The fact that it only applies to IO abstractions is kind of the problem — other libraries should not really overload Base.shutdown() for unrelated functionality... that would be mixing semantics for the same verb.

Is closewrite() a correct renaming? I'm happy to make a PR.

[vtjnash]

Yeah, there is also a closeread option, but generally seems pretty useless, and libuv doesn't expose it.

[notinaboat]

closeread is used in HTTP.jl: https://github.com/JuliaWeb/HTTP.jl/blob/7e4420d0733c87b3664657ac22d1bdc2fb86d789/src/IOExtras.jl#L1-L7

[c42f]

True. In HTTP, closeread(::Transaction) indicates that a transaction is done reading which unblocks the next transaction and enables it to start using the underlying TCP socket.