net: implement wasip1 FileListener and FileConn

Implements net.FileListener and net.FileConn for wasip1.

net.FileListener can be used with a pre-opened socket. If the WASM
module knows the file descriptor, a listener can be constructed with:

    l, err := net.FileListener(os.NewFile(fd, ""))

If the WASM module does not know the file descriptor, but knows that at
least one of the preopens is a socket, it can find the file descriptor
and construct a listener like so:

    func findListener() (net.Listener, error) {
        // We start looking for pre-opened sockets at fd=3 because 0, 1,
        // and 2 are reserved for stdio. Pre-opened directories also
        // start at fd=3, so we skip fds that aren't sockets. Once we
        // reach EBADF we know there are no more pre-opens.
        for preopenFd := uintptr(3); ; preopenFd++ {
            l, err := net.FileListener(os.NewFile(preopenFd, ""))

            var se syscall.Errno
            switch errors.As(err, &se); se {
            case syscall.ENOTSOCK:
                continue
            case syscall.EBADF:
                err = nil
            }
            return l, err
        }
    }

A similar strategy can be used with net.FileConn and pre-opened
connection sockets.

The wasmtime runtime supports pre-opening listener sockets:

    $ wasmtime --tcplisten 127.0.0.1:8080 module.wasm

Change-Id: Iec6ae4ffa84b3753cce4f56a2817e150445db643
Reviewed-on: https://go-review.googlesource.com/c/go/+/493358
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Bypass: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>
Auto-Submit: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/misc/wasm/go_wasip1_wasm_exec b/misc/wasm/go_wasip1_wasm_exec
index abcac8df36..dcec1c6392 100755
--- a/misc/wasm/go_wasip1_wasm_exec
+++ b/misc/wasm/go_wasip1_wasm_exec
@@ -11,10 +11,10 @@ case "$GOWASIRUNTIME" in
 		exec wasmer run --dir=/ --env PWD="$PWD" ${GOWASIRUNTIMEARGS:-} "$1" -- "${@:2}"
 		;;
 	"wasmtime")
-		exec wasmtime run --dir=/ --env PWD="$PWD" --max-wasm-stack 1048576 "$1" -- "${@:2}"
+		exec wasmtime run --dir=/ --env PWD="$PWD" --max-wasm-stack 1048576 ${GOWASIRUNTIMEARGS:-} "$1" -- "${@:2}"
 		;;
 	"wazero" | "")
-		exec wazero run -mount /:/ -env-inherit -cachedir "${TMPDIR:-/tmp}"/wazero "$1" "${@:2}"
+		exec wazero run -mount /:/ -env-inherit -cachedir "${TMPDIR:-/tmp}"/wazero ${GOWASIRUNTIMEARGS:-} "$1" "${@:2}"
 		;;
 	*)
 		echo "Unknown Go WASI runtime specified: $GOWASIRUNTIME"