[2/3] Proper path resolution: add readlinkat functionality

internal/fsapi/file.go

@@ -1,6 +1,10 @@
 package fsapi
 
-import experimentalsys "github.com/tetratelabs/wazero/experimental/sys"
+import (
+	"io/fs"
+
+	experimentalsys "github.com/tetratelabs/wazero/experimental/sys"
+)
 
 // File includes methods not yet ready to document for end users, notably
 // non-blocking functionality.
@@ -66,4 +70,22 @@ type File interface {
 	//     immediately true, as data will never become available.
 	//   - See /RATIONALE.md for detailed notes including impact of blocking.
 	Poll(flag Pflag, timeoutMillis int32) (ready bool, errno experimentalsys.Errno)
+
+	// OpenAt opens a file with a path relative to this directory.
+	//
+	// # Parameters
+	//
+	// The `path` parameter must be a relative path. The `flag` and `mode`
+	// parameters have the same semantics as [internal/sysfs.OpenFileAt].
+	//
+	// # Notes
+	//
+	//   - This is like `openat` in POSIX.
+	//     See https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html
+	OpenAt(
+		fs experimentalsys.FS,
+		path string,
+		flag experimentalsys.Oflag,
+		mode fs.FileMode,
+	) (experimentalsys.File, experimentalsys.Errno)
 }

internal/fsapi/unimplemented.go

@@ -1,11 +1,18 @@
 package fsapi
 
-import experimentalsys "github.com/tetratelabs/wazero/experimental/sys"
+import (
+	"fmt"
+	"io/fs"
+
+	"github.com/tetratelabs/wazero/experimental/sys"
+	experimentalsys "github.com/tetratelabs/wazero/experimental/sys"
+)
 
 func Adapt(f experimentalsys.File) File {
 	if f, ok := f.(File); ok {
 		return f
 	}
+	fmt.Printf("unimplmented %T\n", f)
 	return unimplementedFile{f}
 }
 
@@ -25,3 +32,13 @@ func (unimplementedFile) SetNonblock(bool) experimentalsys.Errno {
 func (unimplementedFile) Poll(Pflag, int32) (ready bool, errno experimentalsys.Errno) {
 	return false, experimentalsys.ENOSYS
 }
+
+// OpenAt implements File.OpenAt
+func (unimplementedFile) OpenAt(
+	fs experimentalsys.FS,
+	path string,
+	flag experimentalsys.Oflag,
+	mode fs.FileMode,
+) (sys.File, experimentalsys.Errno) {
+	return nil, experimentalsys.ENOSYS
+}

internal/sys/lazy.go

@@ -1,6 +1,8 @@
 package sys
 
 import (
+	"io/fs"
+
 	experimentalsys "github.com/tetratelabs/wazero/experimental/sys"
 	"github.com/tetratelabs/wazero/internal/fsapi"
 	"github.com/tetratelabs/wazero/sys"
@@ -149,3 +151,22 @@ func (d *lazyDir) SetNonblock(bool) experimentalsys.Errno {
 func (d *lazyDir) Poll(fsapi.Pflag, int32) (ready bool, errno experimentalsys.Errno) {
 	return false, experimentalsys.ENOSYS
 }
+
+func (d *lazyDir) OpenAt(
+	fs experimentalsys.FS,
+	path string,
+	flag experimentalsys.Oflag,
+	mode fs.FileMode,
+) (experimentalsys.File, experimentalsys.Errno) {
+	f, ok := d.file()
+	if !ok {
+		return nil, experimentalsys.EBADF
+	}
+
+	dir, ok := f.(fsapi.File)
+	if !ok {
+		return nil, experimentalsys.EBADF
+	}
+
+	return dir.OpenAt(fs, path, flag, mode)
+}

internal/sys/stdio.go

@@ -2,6 +2,7 @@ package sys
 
 import (
 	"io"
+	"io/fs"
 	"os"
 
 	experimentalsys "github.com/tetratelabs/wazero/experimental/sys"
@@ -99,6 +100,16 @@ func (noopStdioFile) Poll(fsapi.Pflag, int32) (ready bool, errno experimentalsys
 	return false, experimentalsys.ENOSYS
 }
 
+// OpenAt implements the same method as documented on fsapi.File
+func (noopStdioFile) OpenAt(
+	fs experimentalsys.FS,
+	path string,
+	flag experimentalsys.Oflag,
+	mode fs.FileMode,
+) (experimentalsys.File, experimentalsys.Errno) {
+	return nil, experimentalsys.EBADF
+}
+
 func stdinFileEntry(r io.Reader) (*FileEntry, error) {
 	if r == nil {
 		return &FileEntry{Name: "stdin", IsPreopen: true, File: &noopStdinFile{}}, nil

internal/sysfs/file.go

@@ -41,11 +41,44 @@ func OpenFile(path string, flag experimentalsys.Oflag, perm fs.FileMode) (*os.Fi
 	return openFile(path, flag, perm)
 }
 
+func OpenFileAt(
+	dir *os.File,
+	path string,
+	flag experimentalsys.Oflag,
+	perm fs.FileMode,
+) (*os.File, experimentalsys.Errno) {
+	return openFileAt(dir, path, flag, perm)
+}
+
 func OpenOSFile(path string, flag experimentalsys.Oflag, perm fs.FileMode) (experimentalsys.File, experimentalsys.Errno) {
 	f, errno := OpenFile(path, flag, perm)
 	if errno != 0 {
 		return nil, errno
 	}
+
+	return newOsFile(path, flag, perm, f), 0
+}
+
+func OpenOSFileAt(
+	dir experimentalsys.File,
+	path string,
+	flag experimentalsys.Oflag,
+	perm fs.FileMode,
+) (experimentalsys.File, experimentalsys.Errno) {
+	if len(path) == 0 {
+		return nil, experimentalsys.EINVAL
+	}
+
+	dirOsFile, ok := dir.(*osFile)
+	if !ok {
+		return nil, experimentalsys.EBADF
+	}
+
+	f, errno := OpenFileAt(dirOsFile.file, path, flag, perm)
+	if errno != 0 {
+		return nil, errno
+	}
+
 	return newOsFile(path, flag, perm, f), 0
 }
 
@@ -356,6 +389,15 @@ func (f *fsFile) Poll(fsapi.Pflag, int32) (ready bool, errno experimentalsys.Err
 	return false, experimentalsys.ENOSYS
 }
 
+func (f *fsFile) OpenAt(
+	fs experimentalsys.FS,
+	path string,
+	oflags experimentalsys.Oflag,
+	mode fs.FileMode,
+) (experimentalsys.File, experimentalsys.Errno) {
+	return nil, experimentalsys.ENOSYS
+}
+
 // dirError is used for commands that work against a directory, but not a file.
 func dirError(f experimentalsys.File, isClosed bool, errno experimentalsys.Errno) experimentalsys.Errno {
 	if vErrno := validate(f, isClosed, false, true); vErrno != 0 {

internal/sysfs/file_windows.go

@@ -8,23 +8,47 @@ import (
 	"github.com/tetratelabs/wazero/experimental/sys"
 )
 
+// NTStatus corresponds with NTSTATUS, error values returned by ntdll.dll and
+// other native functions.
+type NTStatus uint32
+
+func rtlNtStatusToDosErrorNoTeb(ntstatus NTStatus) syscall.Errno {
+	r0, _, _ := syscall.SyscallN(procRtlNtStatusToDosErrorNoTeb.Addr(), uintptr(ntstatus))
+
+	return syscall.Errno(r0)
+}
+
+func (s NTStatus) Errno() syscall.Errno {
+	return rtlNtStatusToDosErrorNoTeb(s)
+}
+
 const (
 	nonBlockingFileReadSupported  = true
 	nonBlockingFileWriteSupported = false
 
 	_ERROR_IO_INCOMPLETE = syscall.Errno(996)
 )
 
-var kernel32 = syscall.NewLazyDLL("kernel32.dll")
+var (
+	kernel32 = syscall.NewLazyDLL("kernel32.dll")
+	ntdll    = syscall.NewLazyDLL("ntdll.dll")
+)
 
-// procPeekNamedPipe is the syscall.LazyProc in kernel32 for PeekNamedPipe
 var (
+	// procFormatMessageW is the syscall.LazyProc in kernel32 for FormatMessageW
+	procFormatMessageW = kernel32.NewProc("FormatMessageW")
 	// procPeekNamedPipe is the syscall.LazyProc in kernel32 for PeekNamedPipe
 	procPeekNamedPipe = kernel32.NewProc("PeekNamedPipe")
 	// procGetOverlappedResult is the syscall.LazyProc in kernel32 for GetOverlappedResult
 	procGetOverlappedResult = kernel32.NewProc("GetOverlappedResult")
 	// procCreateEventW is the syscall.LazyProc in kernel32 for CreateEventW
 	procCreateEventW = kernel32.NewProc("CreateEventW")
+	// procNtCreateFile is the syscall.LazyProc in ntdll for NtCreateFile
+	procNtCreateFile = ntdll.NewProc("NtCreateFile")
+	// procRtlInitUnicodeString is the syscall.LazyProc in ntdll for RtlInitUnicodeString
+	procRtlInitUnicodeString = ntdll.NewProc("RtlInitUnicodeString")
+	// procRtlNtStatusToDosErrorNoTeb is the syscall.LazyProc in ntdll for RtlNtStatusToDosErrorNoTeb
+	procRtlNtStatusToDosErrorNoTeb = ntdll.NewProc("RtlNtStatusToDosErrorNoTeb")
 )
 
 // readFd returns ENOSYS on unsupported platforms.