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>

Author: chriso

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"

src/internal/poll/fd_unix.go

@@ -52,6 +52,8 @@ type FD struct {
 // or "file".
 // Set pollable to true if fd should be managed by runtime netpoll.
 func (fd *FD) Init(net string, pollable bool) error {
+	fd.SysFile.init()
+
 	// We don't actually care about the various network types.
 	if net == "file" {
 		fd.isFile = true
@@ -76,12 +78,7 @@ func (fd *FD) destroy() error {
 	// so this must be executed before CloseFunc.
 	fd.pd.close()
 
-	// We don't use ignoringEINTR here because POSIX does not define
-	// whether the descriptor is closed if close returns EINTR.
-	// If the descriptor is indeed closed, using a loop would race
-	// with some other goroutine opening a new descriptor.
-	// (The Linux kernel guarantees that it is closed on an EINTR error.)
-	err := CloseFunc(fd.Sysfd)
+	err := fd.SysFile.destroy(fd.Sysfd)
 
 	fd.Sysfd = -1
 	runtime_Semrelease(&fd.csema)

src/internal/poll/fd_unixjs.go

@@ -13,6 +13,17 @@ type SysFile struct {
 	iovecs *[]syscall.Iovec
 }
 
+func (s *SysFile) init() {}
+
+func (s *SysFile) destroy(fd int) error {
+	// We don't use ignoringEINTR here because POSIX does not define
+	// whether the descriptor is closed if close returns EINTR.
+	// If the descriptor is indeed closed, using a loop would race
+	// with some other goroutine opening a new descriptor.
+	// (The Linux kernel guarantees that it is closed on an EINTR error.)
+	return CloseFunc(fd)
+}
+
 // dupCloseOnExecOld is the traditional way to dup an fd and
 // set its O_CLOEXEC bit, using two system calls.
 func dupCloseOnExecOld(fd int) (int, string, error) {

src/internal/poll/fd_wasip1.go

@@ -11,6 +11,18 @@ import (
 )
 
 type SysFile struct {
+	// RefCountPtr is a pointer to the reference count of Sysfd.
+	//
+	// WASI preview 1 lacks a dup(2) system call. When the os and net packages
+	// need to share a file/socket, instead of duplicating the underlying file
+	// descriptor, we instead provide a way to copy FD instances and manage the
+	// underlying file descriptor with reference counting.
+	RefCountPtr *int32
+
+	// RefCount is the reference count of Sysfd. When a copy of an FD is made,
+	// it points to the reference count of the original FD instance.
+	RefCount int32
+
 	// Cache for the file type, lazily initialized when Seek is called.
 	Filetype uint32
 
@@ -29,6 +41,47 @@ type SysFile struct {
 	// always set instead of being lazily initialized.
 }
 
+func (s *SysFile) init() {
+	if s.RefCountPtr == nil {
+		s.RefCount = 1
+		s.RefCountPtr = &s.RefCount
+	}
+}
+
+func (s *SysFile) ref() SysFile {
+	atomic.AddInt32(s.RefCountPtr, +1)
+	return SysFile{RefCountPtr: s.RefCountPtr}
+}
+
+func (s *SysFile) destroy(fd int) error {
+	if s.RefCountPtr != nil && atomic.AddInt32(s.RefCountPtr, -1) > 0 {
+		return nil
+	}
+
+	// We don't use ignoringEINTR here because POSIX does not define
+	// whether the descriptor is closed if close returns EINTR.
+	// If the descriptor is indeed closed, using a loop would race
+	// with some other goroutine opening a new descriptor.
+	// (The Linux kernel guarantees that it is closed on an EINTR error.)
+	return CloseFunc(fd)
+}
+
+// Copy creates a copy of the FD.
+//
+// The FD instance points to the same underlying file descriptor. The file
+// descriptor isn't closed until all FD instances that refer to it have been
+// closed/destroyed.
+func (fd *FD) Copy() FD {
+	return FD{
+		Sysfd:         fd.Sysfd,
+		SysFile:       fd.SysFile.ref(),
+		IsStream:      fd.IsStream,
+		ZeroReadIsEOF: fd.ZeroReadIsEOF,
+		isBlocking:    fd.isBlocking,
+		isFile:        fd.isFile,
+	}
+}
+
 // dupCloseOnExecOld always errors on wasip1 because there is no mechanism to
 // duplicate file descriptors.
 func dupCloseOnExecOld(fd int) (int, string, error) {

src/net/fd_wasip1.go

@@ -0,0 +1,168 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build wasip1
+
+package net
+
+import (
+	"internal/poll"
+	"runtime"
+	"syscall"
+	"time"
+)
+
+const (
+	readSyscallName  = "fd_read"
+	writeSyscallName = "fd_write"
+)
+
+// Network file descriptor.
+type netFD struct {
+	pfd poll.FD
+
+	// immutable until Close
+	family      int
+	sotype      int
+	isConnected bool // handshake completed or use of association with peer
+	net         string
+	laddr       Addr
+	raddr       Addr
+
+	// The only networking available in WASI preview 1 is the ability to
+	// sock_accept on an pre-opened socket, and then fd_read, fd_write,
+	// fd_close, and sock_shutdown on the resulting connection. We
+	// intercept applicable netFD calls on this instance, and then pass
+	// the remainder of the netFD calls to fakeNetFD.
+	*fakeNetFD
+}
+
+func newFD(sysfd int) (*netFD, error) {
+	return newPollFD(poll.FD{
+		Sysfd:         sysfd,
+		IsStream:      true,
+		ZeroReadIsEOF: true,
+	})
+}
+
+func newPollFD(pfd poll.FD) (*netFD, error) {
+	ret := &netFD{
+		pfd:   pfd,
+		net:   "tcp",
+		laddr: unknownAddr{},
+		raddr: unknownAddr{},
+	}
+	return ret, nil
+}
+
+func (fd *netFD) init() error {
+	return fd.pfd.Init(fd.net, true)
+}
+
+func (fd *netFD) name() string {
+	return "unknown"
+}
+
+func (fd *netFD) accept() (netfd *netFD, err error) {
+	if fd.fakeNetFD != nil {
+		return fd.fakeNetFD.accept()
+	}
+	d, _, errcall, err := fd.pfd.Accept()
+	if err != nil {
+		if errcall != "" {
+			err = wrapSyscallError(errcall, err)
+		}
+		return nil, err
+	}
+	if netfd, err = newFD(d); err != nil {
+		poll.CloseFunc(d)
+		return nil, err
+	}
+	if err = netfd.init(); err != nil {
+		netfd.Close()
+		return nil, err
+	}
+	return netfd, nil
+}
+
+func (fd *netFD) setAddr(laddr, raddr Addr) {
+	fd.laddr = laddr
+	fd.raddr = raddr
+	runtime.SetFinalizer(fd, (*netFD).Close)
+}
+
+func (fd *netFD) Close() error {
+	if fd.fakeNetFD != nil {
+		return fd.fakeNetFD.Close()
+	}
+	runtime.SetFinalizer(fd, nil)
+	return fd.pfd.Close()
+}
+
+func (fd *netFD) shutdown(how int) error {
+	if fd.fakeNetFD != nil {
+		return nil
+	}
+	err := fd.pfd.Shutdown(how)
+	runtime.KeepAlive(fd)
+	return wrapSyscallError("shutdown", err)
+}
+
+func (fd *netFD) closeRead() error {
+	if fd.fakeNetFD != nil {
+		return fd.fakeNetFD.closeRead()
+	}
+	return fd.shutdown(syscall.SHUT_RD)
+}
+
+func (fd *netFD) closeWrite() error {
+	if fd.fakeNetFD != nil {
+		return fd.fakeNetFD.closeWrite()
+	}
+	return fd.shutdown(syscall.SHUT_WR)
+}
+
+func (fd *netFD) Read(p []byte) (n int, err error) {
+	if fd.fakeNetFD != nil {
+		return fd.fakeNetFD.Read(p)
+	}
+	n, err = fd.pfd.Read(p)
+	runtime.KeepAlive(fd)
+	return n, wrapSyscallError(readSyscallName, err)
+}
+
+func (fd *netFD) Write(p []byte) (nn int, err error) {
+	if fd.fakeNetFD != nil {
+		return fd.fakeNetFD.Write(p)
+	}
+	nn, err = fd.pfd.Write(p)
+	runtime.KeepAlive(fd)
+	return nn, wrapSyscallError(writeSyscallName, err)
+}
+
+func (fd *netFD) SetDeadline(t time.Time) error {
+	if fd.fakeNetFD != nil {
+		return fd.fakeNetFD.SetDeadline(t)
+	}
+	return fd.pfd.SetDeadline(t)
+}
+
+func (fd *netFD) SetReadDeadline(t time.Time) error {
+	if fd.fakeNetFD != nil {
+		return fd.fakeNetFD.SetReadDeadline(t)
+	}
+	return fd.pfd.SetReadDeadline(t)
+}
+
+func (fd *netFD) SetWriteDeadline(t time.Time) error {
+	if fd.fakeNetFD != nil {
+		return fd.fakeNetFD.SetWriteDeadline(t)
+	}
+	return fd.pfd.SetWriteDeadline(t)
+}
+
+type unknownAddr struct{}
+
+func (unknownAddr) Network() string { return "unknown" }
+func (unknownAddr) String() string  { return "unknown" }

src/net/file_stub.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build (js && wasm) || wasip1
+//go:build js && wasm
 
 package net
 

src/net/file_wasip1.go

@@ -0,0 +1,62 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build wasip1
+
+package net
+
+import (
+	"os"
+	"syscall"
+	_ "unsafe" // for go:linkname
+)
+
+func fileListener(f *os.File) (Listener, error) {
+	fd, err := newFileFD(f)
+	if err != nil {
+		return nil, err
+	}
+	return &TCPListener{fd: fd}, nil
+}
+
+func fileConn(f *os.File) (Conn, error) {
+	fd, err := newFileFD(f)
+	if err != nil {
+		return nil, err
+	}
+	return &TCPConn{conn{fd: fd}}, nil
+}
+
+func filePacketConn(f *os.File) (PacketConn, error) { return nil, syscall.ENOPROTOOPT }
+
+func newFileFD(f *os.File) (fd *netFD, err error) {
+	pfd := f.PollFD().Copy()
+	defer func() {
+		if err != nil {
+			pfd.Close()
+		}
+	}()
+	filetype, err := fd_fdstat_get_type(pfd.Sysfd)
+	if err != nil {
+		return nil, err
+	}
+	if filetype != syscall.FILETYPE_SOCKET_STREAM {
+		return nil, syscall.ENOTSOCK
+	}
+	fd, err = newPollFD(pfd)
+	if err != nil {
+		return nil, err
+	}
+	if err := fd.init(); err != nil {
+		return nil, err
+	}
+	return fd, nil
+}
+
+// This helper is implemented in the syscall package. It means we don't have
+// to redefine the fd_fdstat_get host import or the fdstat struct it
+// populates.
+//
+//go:linkname fd_fdstat_get_type syscall.fd_fdstat_get_type
+func fd_fdstat_get_type(fd int) (uint8, error)