Implement sock_accept and basic networking

[haraldh]

Together with rust-lang/rust#93158 this enables basic networking in rust.

See #3730 for the tracking issue.

With the addition of sock_accept() in wasi-0.11.0, wasmtime can now implement basic networking for pre-opened sockets.

For Windows AsHandle was replaced with AsRawHandleOrSocket to cope with the duality of Handles and Sockets.

For Unix a wasi_cap_std_sync::net::Socket enum was created to handle the {Tcp,Unix}{Listener,Stream} more efficiently in
WasiCtxBuilder::preopened_socket().

The addition of that many WasiFile implementors was mainly necessary, because of the difference in the num_ready_bytes() function.

A known issue is Windows now busy polling on sockets, because except for stdin, nothing is querying the status of windows handles/sockets.

Another know issue on Windows, is that there is no crate providing support for fcntl(fd, F_GETFL, 0) for sockets, so WasiFile::get_fdflags() always returns 0.

Todo

• Test cases

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[npmccallum]

@haraldh Is this still a draft?

[haraldh]

@npmccallum now it's ready for a review :)

[sunfishcode]

Looks good to me! Just one potential question:

[sunfishcode]

Another option here would be to make Socket be a simple struct that holds an OwnedFd, and uses rustix::net calls to implement the functions rather than cap_std::net/std::net. Rustix even supports the socket APIs on Windows, so this ought to work. And you could probably unify the "stream" vs. "listener" implementations below. That said, either way seems fine for now, so feel free to make a judgement call here.

[haraldh]

Yeah, I didn't want to change all the other parts too much.

What you are proposing can be done in a separate PR, which will change much more, I guess.

With the Socket abstraction, I think I didn't make the "user" facing API incompatible with your proposal.

[haraldh]

Changed one more thing to make fd_fdstat_get() work on the sockets.

             async fn get_fdflags(&self) -> Result<FdFlags, Error> {
-                Err(Error::badf())
+                let fdflags = self.0.as_filelike().get_fd_flags()?;
+                Ok(from_sysif_fdflags(fdflags))
             }

[haraldh]

All right.. rust-lang PR merged 🥳

[npmccallum]

@sunfishcode Is this ready for merge?

[sunfishcode]

Yes, looks good to me!