os: move file logic to file.v (#6013)

vlib/os/file.v

@@ -0,0 +1,89 @@
+module os
+
+pub struct File {
+	cfile  voidptr // Using void* instead of FILE*
+pub:
+	fd     int
+pub mut:
+	is_opened bool
+}
+
+struct FileInfo {
+	name string
+	size int
+}
+
+[deprecated]
+pub fn (f File) is_opened() bool {
+	eprintln('warning: `file.is_opened()` has been deprecated, use `file.is_opened` instead')
+	return f.is_opened
+}
+
+// **************************** Write ops  ***************************
+pub fn (mut f File) write(s string) {
+	if !f.is_opened {
+		return
+	}
+	/*
+	$if linux {
+		$if !android {
+			C.syscall(sys_write, f.fd, s.str, s.len)
+			return
+		}
+	}
+	*/
+	C.fwrite(s.str, s.len, 1, f.cfile)
+}
+
+pub fn (mut f File) writeln(s string) {
+	if !f.is_opened {
+		return
+	}
+	/*
+	$if linux {
+		$if !android {
+			snl := s + '\n'
+			C.syscall(sys_write, f.fd, snl.str, snl.len)
+			return
+		}
+	}
+	*/
+	// TODO perf
+	C.fwrite(s.str, s.len, 1, f.cfile)
+	C.fputs('\n', f.cfile)
+}
+
+pub fn (mut f File) write_bytes(data voidptr, size int) int {
+	return C.fwrite(data, 1, size, f.cfile)
+}
+
+pub fn (mut f File) write_bytes_at(data voidptr, size, pos int) int {
+	C.fseek(f.cfile, pos, C.SEEK_SET)
+	res := C.fwrite(data, 1, size, f.cfile)
+	C.fseek(f.cfile, 0, C.SEEK_END)
+	return res
+}
+
+// **************************** Read ops  ***************************
+// read_bytes reads an amount of bytes from the beginning of the file
+pub fn (f &File) read_bytes(size int) []byte {
+	return f.read_bytes_at(size, 0)
+}
+
+// read_bytes_at reads an amount of bytes at the given position in the file
+pub fn (f &File) read_bytes_at(size, pos int) []byte {
+	mut arr := [`0`].repeat(size)
+	C.fseek(f.cfile, pos, C.SEEK_SET)
+	nreadbytes := C.fread(arr.data, 1, size, f.cfile)
+	C.fseek(f.cfile, 0, C.SEEK_SET)
+	return arr[0..nreadbytes]
+}
+
+// **************************** Utility  ops ***********************
+// write any unwritten data in stream's buffer
+pub fn (mut f File) flush() {
+	if !f.is_opened {
+		return
+	}
+	C.fflush(f.cfile)
+}