WASI & darwin: support basic file io based on libc

Signed-off-by: Takeshi Yoneda <takeshi@tetrate.io>

src/os/errors.go

@@ -2,6 +2,7 @@ package os
 
 import (
 	"errors"
+	"syscall"
 )
 
 var (
@@ -17,9 +18,8 @@ var (
 	ErrExist          = errors.New("file exists")
 )
 
-func IsPermission(err error) bool {
-	return err == ErrPermission
-}
+// The following code is copied from the official implementation.
+// https://github.com/golang/go/blob/4ce6a8e89668b87dce67e2f55802903d6eb9110a/src/os/error.go#L65-L104
 
 func NewSyscallError(syscall string, err error) error {
 	if err == nil {
@@ -37,3 +37,39 @@ type SyscallError struct {
 func (e *SyscallError) Error() string { return e.Syscall + ": " + e.Err.Error() }
 
 func (e *SyscallError) Unwrap() error { return e.Err }
+
+func IsExist(err error) bool {
+	return underlyingErrorIs(err, ErrExist)
+}
+
+func IsNotExist(err error) bool {
+	return underlyingErrorIs(err, ErrNotExist)
+}
+
+func IsPermission(err error) bool {
+	return underlyingErrorIs(err, ErrPermission)
+}
+
+func underlyingErrorIs(err, target error) bool {
+	// Note that this function is not errors.Is:
+	// underlyingError only unwraps the specific error-wrapping types
+	// that it historically did, not all errors implementing Unwrap().
+	err = underlyingError(err)
+	if err == target {
+		return true
+	}
+	// To preserve prior behavior, only examine syscall errors.
+	e, ok := err.(syscall.Errno)
+	return ok && e.Is(target)
+}
+
+// underlyingError returns the underlying error for known os error types.
+func underlyingError(err error) error {
+	switch err := err.(type) {
+	case *PathError:
+		return err.Err
+	case *SyscallError:
+		return err.Err
+	}
+	return err
+}

src/os/file.go

@@ -6,6 +6,7 @@
 package os
 
 import (
+	"io"
 	"syscall"
 )
 
@@ -76,7 +77,7 @@ func Create(name string) (*File, error) {
 // read and any error encountered. At end of file, Read returns 0, io.EOF.
 func (f *File) Read(b []byte) (n int, err error) {
 	n, err = f.handle.Read(b)
-	if err != nil {
+	if err != nil && err != io.EOF {
 		err = &PathError{"read", f.name, err}
 	}
 	return
@@ -155,59 +156,17 @@ func (e *PathError) Error() string {
 	return e.Op + " " + e.Path + ": " + e.Err.Error()
 }
 
-type FileMode uint32
-
-// Mode constants, copied from the mainline Go source
-// https://github.com/golang/go/blob/4ce6a8e89668b87dce67e2f55802903d6eb9110a/src/os/types.go#L35-L63
 const (
-	// The single letters are the abbreviations used by the String method's formatting.
-	ModeDir        FileMode = 1 << (32 - 1 - iota) // d: is a directory
-	ModeAppend                                     // a: append-only
-	ModeExclusive                                  // l: exclusive use
-	ModeTemporary                                  // T: temporary file; Plan 9 only
-	ModeSymlink                                    // L: symbolic link
-	ModeDevice                                     // D: device file
-	ModeNamedPipe                                  // p: named pipe (FIFO)
-	ModeSocket                                     // S: Unix domain socket
-	ModeSetuid                                     // u: setuid
-	ModeSetgid                                     // g: setgid
-	ModeCharDevice                                 // c: Unix character device, when ModeDevice is set
-	ModeSticky                                     // t: sticky
-	ModeIrregular                                  // ?: non-regular file; nothing else is known about this file
-
-	// Mask for the type bits. For regular files, none will be set.
-	ModeType = ModeDir | ModeSymlink | ModeNamedPipe | ModeSocket | ModeDevice | ModeCharDevice | ModeIrregular
-
-	ModePerm FileMode = 0777 // Unix permission bits
+	O_RDONLY int = syscall.O_RDONLY
+	O_WRONLY int = syscall.O_WRONLY
+	O_RDWR   int = syscall.O_RDWR
+	O_APPEND int = syscall.O_APPEND
+	O_CREATE int = syscall.O_CREAT
+	O_EXCL   int = syscall.O_EXCL
+	O_SYNC   int = syscall.O_SYNC
+	O_TRUNC  int = syscall.O_TRUNC
 )
 
-// IsDir is a stub, always returning false
-func (m FileMode) IsDir() bool {
-	return false
-}
-
-// Stub constants
-const (
-	O_RDONLY int = 1
-	O_WRONLY int = 2
-	O_RDWR   int = 4
-	O_APPEND int = 8
-	O_CREATE int = 16
-	O_EXCL   int = 32
-	O_SYNC   int = 64
-	O_TRUNC  int = 128
-)
-
-// A FileInfo describes a file and is returned by Stat and Lstat.
-type FileInfo interface {
-	Name() string   // base name of the file
-	Size() int64    // length in bytes for regular files; system-dependent for others
-	Mode() FileMode // file mode bits
-	// TODO ModTime() time.Time // modification time
-	IsDir() bool      // abbreviation for Mode().IsDir()
-	Sys() interface{} // underlying data source (can return nil)
-}
-
 // Stat is a stub, not yet implemented
 func Stat(name string) (FileInfo, error) {
 	return nil, &PathError{"stat", name, ErrNotImplemented}
@@ -233,16 +192,6 @@ func TempDir() string {
 	return "/tmp"
 }
 
-// IsExist is a stub (for now), always returning false
-func IsExist(err error) bool {
-	return false
-}
-
-// IsNotExist is a stub (for now), always returning false
-func IsNotExist(err error) bool {
-	return false
-}
-
 // Getpid is a stub (for now), always returning 1
 func Getpid() int {
 	return 1

src/os/file_go_116.go

@@ -0,0 +1,81 @@
+// +build go1.16
+
+package os
+
+import (
+	"io"
+	"io/fs"
+)
+
+type (
+	DirEntry = fs.DirEntry
+	FileMode = fs.FileMode
+	FileInfo = fs.FileInfo
+)
+
+func (f *File) ReadDir(n int) ([]DirEntry, error) {
+	return nil, &PathError{"ReadDir", f.name, ErrNotImplemented}
+}
+
+// The followings are copied from Go 1.16 official implementation:
+// https://github.com/golang/go/blob/go1.16/src/os/file.go
+
+// ReadFile reads the named file and returns the contents.
+// A successful call returns err == nil, not err == EOF.
+// Because ReadFile reads the whole file, it does not treat an EOF from Read
+// as an error to be reported.
+func ReadFile(name string) ([]byte, error) {
+	f, err := Open(name)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	var size int
+	if info, err := f.Stat(); err == nil {
+		size64 := info.Size()
+		if int64(int(size64)) == size64 {
+			size = int(size64)
+		}
+	}
+	size++ // one byte for final read at EOF
+
+	// If a file claims a small size, read at least 512 bytes.
+	// In particular, files in Linux's /proc claim size 0 but
+	// then do not work right if read in small pieces,
+	// so an initial read of 1 byte would not work correctly.
+	if size < 512 {
+		size = 512
+	}
+
+	data := make([]byte, 0, size)
+	for {
+		if len(data) >= cap(data) {
+			d := append(data[:cap(data)], 0)
+			data = d[:len(data)]
+		}
+		n, err := f.Read(data[len(data):cap(data)])
+		data = data[:len(data)+n]
+		if err != nil {
+			if err == io.EOF {
+				err = nil
+			}
+			return data, err
+		}
+	}
+}
+
+// WriteFile writes data to the named file, creating it if necessary.
+// If the file does not exist, WriteFile creates it with permissions perm (before umask);
+// otherwise WriteFile truncates it before writing, without changing permissions.
+func WriteFile(name string, data []byte, perm FileMode) error {
+	f, err := OpenFile(name, O_WRONLY|O_CREATE|O_TRUNC, perm)
+	if err != nil {
+		return err
+	}
+	_, err = f.Write(data)
+	if err1 := f.Close(); err1 != nil && err == nil {
+		err = err1
+	}
+	return err
+}

src/os/file_go_other.go

@@ -0,0 +1,46 @@
+// +build !go1.16
+
+package os
+
+import "time"
+
+// A FileInfo describes a file and is returned by Stat and Lstat.
+type FileInfo interface {
+	Name() string       // base name of the file
+	Size() int64        // length in bytes for regular files; system-dependent for others
+	Mode() FileMode     // file mode bits
+	ModTime() time.Time // modification time
+	IsDir() bool        // abbreviation for Mode().IsDir()
+	Sys() interface{}   // underlying data source (can return nil)
+}
+
+type FileMode uint32
+
+// Mode constants, copied from the mainline Go source
+// https://github.com/golang/go/blob/4ce6a8e89668b87dce67e2f55802903d6eb9110a/src/os/types.go#L35-L63
+const (
+	// The single letters are the abbreviations used by the String method's formatting.
+	ModeDir        FileMode = 1 << (32 - 1 - iota) // d: is a directory
+	ModeAppend                                     // a: append-only
+	ModeExclusive                                  // l: exclusive use
+	ModeTemporary                                  // T: temporary file; Plan 9 only
+	ModeSymlink                                    // L: symbolic link
+	ModeDevice                                     // D: device file
+	ModeNamedPipe                                  // p: named pipe (FIFO)
+	ModeSocket                                     // S: Unix domain socket
+	ModeSetuid                                     // u: setuid
+	ModeSetgid                                     // g: setgid
+	ModeCharDevice                                 // c: Unix character device, when ModeDevice is set
+	ModeSticky                                     // t: sticky
+	ModeIrregular                                  // ?: non-regular file; nothing else is known about this file
+
+	// Mask for the type bits. For regular files, none will be set.
+	ModeType = ModeDir | ModeSymlink | ModeNamedPipe | ModeSocket | ModeDevice | ModeCharDevice | ModeIrregular
+
+	ModePerm FileMode = 0777 // Unix permission bits
+)
+
+// IsDir is a stub, always returning false
+func (m FileMode) IsDir() bool {
+	return false
+}

src/os/file_other.go

@@ -1,4 +1,4 @@
-// +build baremetal wasm
+// +build baremetal wasm,!wasi
 
 package os
 

src/os/file_unix.go

@@ -1,8 +1,9 @@
-// +build darwin linux,!baremetal,!wasi freebsd,!baremetal
+// +build darwin linux,!baremetal freebsd,!baremetal
 
 package os
 
 import (
+	"io"
 	"syscall"
 )
 
@@ -77,6 +78,9 @@ type unixFileHandle uintptr
 func (f unixFileHandle) Read(b []byte) (n int, err error) {
 	n, err = syscall.Read(int(f), b)
 	err = handleSyscallError(err)
+	if n == 0 && err == nil {
+		err = io.EOF
+	}
 	return
 }