wasi: add nonblock_test.go from gotip, fix nonblock read on Unix-like (#1517)

Signed-off-by: Edoardo Vacchi <evacchi@users.noreply.github.com>

internal/sysfs/file_test.go

@@ -28,7 +28,7 @@ var (
 	emptyFile  = "empty.txt"
 )
 
-func TestFileSetNonblock(t *testing.T) {
+func TestStdioFileSetNonblock(t *testing.T) {
 	// Test using os.Pipe as it is known to support non-blocking reads.
 	r, w, err := os.Pipe()
 	require.NoError(t, err)
@@ -47,6 +47,54 @@ func TestFileSetNonblock(t *testing.T) {
 	require.False(t, rF.IsNonblock())
 }
 
+func TestRegularFileSetNonblock(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("Nonblock on regular files is not supported on Windows")
+	}
+
+	// Test using os.Pipe as it is known to support non-blocking reads.
+	r, w, err := os.Pipe()
+	require.NoError(t, err)
+	defer r.Close()
+	defer w.Close()
+
+	rF := newOsFile("", syscall.O_RDONLY, 0, r)
+
+	errno := rF.SetNonblock(true)
+	require.EqualErrno(t, 0, errno)
+	require.True(t, rF.IsNonblock())
+
+	// Read from the file without ever writing to it should not block.
+	buf := make([]byte, 8)
+	_, e := rF.Read(buf)
+	require.EqualErrno(t, syscall.EAGAIN, e)
+
+	errno = rF.SetNonblock(false)
+	require.EqualErrno(t, 0, errno)
+	require.False(t, rF.IsNonblock())
+}
+
+func TestReadFdNonblock(t *testing.T) {
+	// Test using os.Pipe as it is known to support non-blocking reads.
+	r, w, err := os.Pipe()
+	require.NoError(t, err)
+	defer r.Close()
+	defer w.Close()
+
+	fd := r.Fd()
+	err = setNonblock(fd, true)
+	require.NoError(t, err)
+
+	// Read from the file without ever writing to it should not block.
+	buf := make([]byte, 8)
+	_, e := readFd(fd, buf)
+	if runtime.GOOS == "windows" {
+		require.EqualErrno(t, syscall.ENOSYS, e)
+	} else {
+		require.EqualErrno(t, syscall.EAGAIN, e)
+	}
+}
+
 func TestFileSetAppend(t *testing.T) {
 	tmpDir := t.TempDir()
 

internal/sysfs/file_unix.go

@@ -0,0 +1,21 @@
+//go:build unix || darwin || linux
+
+package sysfs
+
+import (
+	"syscall"
+
+	"github.com/tetratelabs/wazero/internal/platform"
+)
+
+const NonBlockingFileIoSupported = true
+
+// readFd exposes syscall.Read.
+func readFd(fd uintptr, buf []byte) (int, syscall.Errno) {
+	if len(buf) == 0 {
+		return 0, 0 // Short-circuit 0-len reads.
+	}
+	n, err := syscall.Read(int(fd), buf)
+	errno := platform.UnwrapOSError(err)
+	return n, errno
+}

internal/sysfs/file_unsupported.go

@@ -0,0 +1,12 @@
+//go:build !unix && !linux && !darwin
+
+package sysfs
+
+import "syscall"
+
+const NonBlockingFileIoSupported = false
+
+// readFd returns ENOSYS on unsupported platforms.
+func readFd(fd uintptr, buf []byte) (int, syscall.Errno) {
+	return -1, syscall.ENOSYS
+}

internal/sysfs/open_file_windows.go

@@ -13,7 +13,7 @@ import (
 
 func newOsFile(openPath string, openFlag int, openPerm fs.FileMode, f *os.File) fsapi.File {
 	return &windowsOsFile{
-		osFile: osFile{path: openPath, flag: openFlag, perm: openPerm, file: f},
+		osFile: osFile{path: openPath, flag: openFlag, perm: openPerm, file: f, fd: f.Fd()},
 	}
 }
 

internal/sysfs/osfile.go

@@ -12,7 +12,7 @@ import (
 )
 
 func newDefaultOsFile(openPath string, openFlag int, openPerm fs.FileMode, f *os.File) fsapi.File {
-	return &osFile{path: openPath, flag: openFlag, perm: openPerm, file: f}
+	return &osFile{path: openPath, flag: openFlag, perm: openPerm, file: f, fd: f.Fd()}
 }
 
 // osFile is a file opened with this package, and uses os.File or syscalls to
@@ -22,6 +22,7 @@ type osFile struct {
 	flag int
 	perm fs.FileMode
 	file *os.File
+	fd   uintptr
 
 	// closed is true when closed was called. This ensures proper syscall.EBADF
 	closed bool
@@ -92,7 +93,7 @@ func (f *osFile) SetNonblock(enable bool) (errno syscall.Errno) {
 	} else {
 		f.flag &= ^fsapi.O_NONBLOCK
 	}
-	if err := setNonblock(f.file.Fd(), enable); err != nil {
+	if err := setNonblock(f.fd, enable); err != nil {
 		return fileError(f, f.closed, platform.UnwrapOSError(err))
 	}
 	return 0
@@ -126,7 +127,15 @@ func (f *osFile) Stat() (fsapi.Stat_t, syscall.Errno) {
 
 // Read implements the same method as documented on fsapi.File
 func (f *osFile) Read(buf []byte) (n int, errno syscall.Errno) {
-	if n, errno = read(f.file, buf); errno != 0 {
+	if len(buf) == 0 {
+		return 0, 0 // Short-circuit 0-len reads.
+	}
+	if NonBlockingFileIoSupported && f.IsNonblock() {
+		n, errno = readFd(f.fd, buf)
+	} else {
+		n, errno = read(f.file, buf)
+	}
+	if errno != 0 {
 		// Defer validation overhead until we've already had an error.
 		errno = fileError(f, f.closed, errno)
 	}
@@ -160,7 +169,7 @@ func (f *osFile) Seek(offset int64, whence int) (newOffset int64, errno syscall.
 // PollRead implements the same method as documented on fsapi.File
 func (f *osFile) PollRead(timeout *time.Duration) (ready bool, errno syscall.Errno) {
 	fdSet := platform.FdSet{}
-	fd := int(f.file.Fd())
+	fd := int(f.fd)
 	fdSet.Set(fd)
 	nfds := fd + 1 // See https://man7.org/linux/man-pages/man2/select.2.html#:~:text=condition%20has%20occurred.-,nfds,-This%20argument%20should
 	count, err := _select(nfds, &fdSet, nil, nil, timeout)
@@ -232,7 +241,7 @@ func (f *osFile) Chown(uid, gid int) syscall.Errno {
 		return syscall.EBADF
 	}
 
-	return fchown(f.file.Fd(), uid, gid)
+	return fchown(f.fd, uid, gid)
 }
 
 // Utimens implements the same method as documented on fsapi.File
@@ -241,7 +250,7 @@ func (f *osFile) Utimens(times *[2]syscall.Timespec) syscall.Errno {
 		return syscall.EBADF
 	}
 
-	err := futimens(f.file.Fd(), times)
+	err := futimens(f.fd, times)
 	return platform.UnwrapOSError(err)
 }