WASI & darwin: support basic file io based on libc

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

src/syscall/syscall_libc.go

@@ -13,12 +13,15 @@ type sliceHeader struct {
 }
 
 func Close(fd int) (err error) {
-	return ENOSYS // TODO
+	if libc_close(fd) < 0 {
+		err = getErrno()
+	}
+	return
 }
 
 func Write(fd int, p []byte) (n int, err error) {
 	buf, count := splitSlice(p)
-	n = libc_write(int32(fd), buf, uint(count))
+	n = libc_write(fd, buf, uint(count))
 	if n < 0 {
 		err = getErrno()
 	}
@@ -26,15 +29,25 @@ func Write(fd int, p []byte) (n int, err error) {
 }
 
 func Read(fd int, p []byte) (n int, err error) {
-	return 0, ENOSYS // TODO
+	buf, count := splitSlice(p)
+	n = libc_read(fd, buf, uint(count))
+	if n < 0 {
+		err = getErrno()
+	}
+	return
 }
 
 func Seek(fd int, offset int64, whence int) (off int64, err error) {
 	return 0, ENOSYS // TODO
 }
 
-func Open(path string, mode int, perm uint32) (fd int, err error) {
-	return 0, ENOSYS // TODO
+func Open(path string, flag int, mode uint32) (fd int, err error) {
+	data := append([]byte(path), 0)
+	fd = libc_open(&data[0], flag, mode)
+	if fd < 0 {
+		err = getErrno()
+	}
+	return
 }
 
 func Mkdir(path string, mode uint32) (err error) {
@@ -78,8 +91,20 @@ func splitSlice(p []byte) (buf *byte, len uintptr) {
 
 // ssize_t write(int fd, const void *buf, size_t count)
 //export write
-func libc_write(fd int32, buf *byte, count uint) int
+func libc_write(fd int, buf *byte, count uint) int
 
 // char *getenv(const char *name);
 //export getenv
 func libc_getenv(name *byte) *byte
+
+// ssize_t read(int fd, void *buf, size_t count);
+//export read
+func libc_read(fd int, buf *byte, count uint) int
+
+// int open(const char *pathname, int flags, mode_t mode);
+//export open
+func libc_open(pathname *byte, flags int, mode uint32) int
+
+// int close(int fd)
+//export close
+func libc_close(fd int) int