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>

4 files changed, 89 insertions, 112 deletions

diff --git a/src/syscall/fs_wasip1.go b/src/syscall/fs_wasip1.go
index 25cabf8234..d60ab0b53e 100644
--- a/src/syscall/fs_wasip1.go
+++ b/src/syscall/fs_wasip1.go
@@ -279,6 +279,12 @@ func fd_fdstat_get_flags(fd int) (uint32, error) {
 	return uint32(stat.fdflags), errnoErr(errno)
 }
 
+func fd_fdstat_get_type(fd int) (uint8, error) {
+	var stat fdstat
+	errno := fd_fdstat_get(int32(fd), unsafe.Pointer(&stat))
+	return stat.filetype, errnoErr(errno)
+}
+
 type preopentype = uint8
 
 const (
@@ -331,12 +337,12 @@ func init() {
 		if errno == EBADF {
 			break
 		}
+		if errno == ENOTDIR || prestat.typ != preopentypeDir {
+			continue
+		}
 		if errno != 0 {
 			panic("fd_prestat: " + errno.Error())
 		}
-		if prestat.typ != preopentypeDir {
-			continue
-		}
 		if int(prestat.dir.prNameLen) > len(dirNameBuf) {
 			dirNameBuf = make([]byte, prestat.dir.prNameLen)
 		}
diff --git a/src/syscall/net_fake.go b/src/syscall/net_fake.go
new file mode 100644
index 0000000000..689f6f8812
--- /dev/null
+++ b/src/syscall/net_fake.go
@@ -0,0 +1,63 @@
+// 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.
+
+// Fake networking for js/wasm and wasip1/wasm.
+// This file only exists to make the compiler happy.
+
+//go:build (js && wasm) || wasip1
+
+package syscall
+
+const (
+	AF_UNSPEC = iota
+	AF_UNIX
+	AF_INET
+	AF_INET6
+)
+
+const (
+	SOCK_STREAM = 1 + iota
+	SOCK_DGRAM
+	SOCK_RAW
+	SOCK_SEQPACKET
+)
+
+const (
+	IPPROTO_IP   = 0
+	IPPROTO_IPV4 = 4
+	IPPROTO_IPV6 = 0x29
+	IPPROTO_TCP  = 6
+	IPPROTO_UDP  = 0x11
+)
+
+const (
+	_ = iota
+	IPV6_V6ONLY
+	SOMAXCONN
+	SO_ERROR
+)
+
+// Misc constants expected by package net but not supported.
+const (
+	_ = iota
+	F_DUPFD_CLOEXEC
+	SYS_FCNTL = 500 // unsupported
+)
+
+type Sockaddr any
+
+type SockaddrInet4 struct {
+	Port int
+	Addr [4]byte
+}
+
+type SockaddrInet6 struct {
+	Port   int
+	ZoneId uint32
+	Addr   [16]byte
+}
+
+type SockaddrUnix struct {
+	Name string
+}
diff --git a/src/syscall/net_js.go b/src/syscall/net_js.go
index 2ed4e191bd..cba33dfd2e 100644
--- a/src/syscall/net_js.go
+++ b/src/syscall/net_js.go
@@ -2,66 +2,10 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// js/wasm uses fake networking directly implemented in the net package.
-// This file only exists to make the compiler happy.
-
 //go:build js && wasm
 
 package syscall
 
-const (
-	AF_UNSPEC = iota
-	AF_UNIX
-	AF_INET
-	AF_INET6
-)
-
-const (
-	SOCK_STREAM = 1 + iota
-	SOCK_DGRAM
-	SOCK_RAW
-	SOCK_SEQPACKET
-)
-
-const (
-	IPPROTO_IP   = 0
-	IPPROTO_IPV4 = 4
-	IPPROTO_IPV6 = 0x29
-	IPPROTO_TCP  = 6
-	IPPROTO_UDP  = 0x11
-)
-
-const (
-	_ = iota
-	IPV6_V6ONLY
-	SOMAXCONN
-	SO_ERROR
-)
-
-// Misc constants expected by package net but not supported.
-const (
-	_ = iota
-	F_DUPFD_CLOEXEC
-	SYS_FCNTL = 500 // unsupported
-)
-
-type Sockaddr any
-
-type SockaddrInet4 struct {
-	Port int
-	Addr [4]byte
-}
-
-type SockaddrInet6 struct {
-	Port   int
-	ZoneId uint32
-	Addr   [16]byte
-}
-
-type SockaddrUnix struct {
-	Name string
-}
-
 func Socket(proto, sotype, unused int) (fd int, err error) {
 	return 0, ENOSYS
 }
diff --git a/src/syscall/net_wasip1.go b/src/syscall/net_wasip1.go
index 896dd3e770..3918840a7e 100644
--- a/src/syscall/net_wasip1.go
+++ b/src/syscall/net_wasip1.go
@@ -2,66 +2,27 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// wasip1/wasm uses fake networking directly implemented in the net package.
-// This file only exists to make the compiler happy.
-
 //go:build wasip1
 
 package syscall
 
-const (
-	AF_UNSPEC = iota
-	AF_UNIX
-	AF_INET
-	AF_INET6
-)
+import "unsafe"
 
 const (
-	SOCK_STREAM = 1 + iota
-	SOCK_DGRAM
-	SOCK_RAW
-	SOCK_SEQPACKET
+	SHUT_RD   = 0x1
+	SHUT_WR   = 0x2
+	SHUT_RDWR = SHUT_RD | SHUT_WR
 )
 
-const (
-	IPPROTO_IP   = 0
-	IPPROTO_IPV4 = 4
-	IPPROTO_IPV6 = 0x29
-	IPPROTO_TCP  = 6
-	IPPROTO_UDP  = 0x11
-)
+type sdflags = uint32
 
-const (
-	_ = iota
-	IPV6_V6ONLY
-	SOMAXCONN
-	SO_ERROR
-)
+//go:wasmimport wasi_snapshot_preview1 sock_accept
+//go:noescape
+func sock_accept(fd int32, flags fdflags, newfd unsafe.Pointer) Errno
 
-// Misc constants expected by package net but not supported.
-const (
-	_ = iota
-	F_DUPFD_CLOEXEC
-	SYS_FCNTL = 500 // unsupported; same value as net_nacl.go
-)
-
-type Sockaddr interface {
-}
-
-type SockaddrInet4 struct {
-	Port int
-	Addr [4]byte
-}
-
-type SockaddrInet6 struct {
-	Port   int
-	ZoneId uint32
-	Addr   [16]byte
-}
-
-type SockaddrUnix struct {
-	Name string
-}
+//go:wasmimport wasi_snapshot_preview1 sock_shutdown
+//go:noescape
+func sock_shutdown(fd int32, flags sdflags) Errno
 
 func Socket(proto, sotype, unused int) (fd int, err error) {
 	return 0, ENOSYS
@@ -79,8 +40,10 @@ func Listen(fd int, backlog int) error {
 	return ENOSYS
 }
 
-func Accept(fd int) (newfd int, sa Sockaddr, err error) {
-	return 0, nil, ENOSYS
+func Accept(fd int) (int, Sockaddr, error) {
+	var newfd int32
+	errno := sock_accept(int32(fd), 0, unsafe.Pointer(&newfd))
+	return int(newfd), nil, errnoErr(errno)
 }
 
 func Connect(fd int, sa Sockaddr) error {
@@ -120,5 +83,6 @@ func SetWriteDeadline(fd int, t int64) error {
 }
 
 func Shutdown(fd int, how int) error {
-	return ENOSYS
+	errno := sock_shutdown(int32(fd), sdflags(how))
+	return errnoErr(errno)
 }