Implement sock_accept

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)` on a socket.

Signed-off-by: Harald Hoyer <harald@profian.com>

crates/wasi-common/cap-std-sync/src/stdio.rs

@@ -8,6 +8,8 @@ use std::io;
 use std::io::{Read, Write};
 use system_interface::io::ReadReady;
 
+#[cfg(windows)]
+use io_extras::os::windows::{AsRawHandleOrSocket, RawHandleOrSocket};
 #[cfg(unix)]
 use io_lifetimes::{AsFd, BorrowedFd};
 #[cfg(windows)]
@@ -124,6 +126,10 @@ impl WasiFile for Stdin {
     async fn writable(&self) -> Result<(), Error> {
         Err(Error::badf())
     }
+
+    async fn sock_accept(&mut self, _fdflags: FdFlags) -> Result<Box<dyn WasiFile>, Error> {
+        Err(Error::badf())
+    }
 }
 #[cfg(windows)]
 impl AsHandle for Stdin {
@@ -131,6 +137,13 @@ impl AsHandle for Stdin {
         self.0.as_handle()
     }
 }
+#[cfg(windows)]
+impl AsRawHandleOrSocket for Stdin {
+    #[inline]
+    fn as_raw_handle_or_socket(&self) -> RawHandleOrSocket {
+        self.0.as_raw_handle_or_socket()
+    }
+}
 #[cfg(unix)]
 impl AsFd for Stdin {
     fn as_fd(&self) -> BorrowedFd<'_> {
@@ -244,6 +257,9 @@ macro_rules! wasi_file_write_impl {
             async fn writable(&self) -> Result<(), Error> {
                 Err(Error::badf())
             }
+            async fn sock_accept(&mut self, _fdflags: FdFlags) -> Result<Box<dyn WasiFile>, Error> {
+                Err(Error::badf())
+            }
         }
         #[cfg(windows)]
         impl AsHandle for $ty {
@@ -257,6 +273,13 @@ macro_rules! wasi_file_write_impl {
                 self.0.as_fd()
             }
         }
+        #[cfg(windows)]
+        impl AsRawHandleOrSocket for $ty {
+            #[inline]
+            fn as_raw_handle_or_socket(&self) -> RawHandleOrSocket {
+                self.0.as_raw_handle_or_socket()
+            }
+        }
     };
 }