1// Copyright 2023 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5//go:build wasip1
6
7package rand
8
9import "syscall"
10
11func init() {
12	Reader = &reader{}
13}
14
15type reader struct{}
16
17func (r *reader) Read(b []byte) (int, error) {
18	// This uses the wasi_snapshot_preview1 random_get syscall defined in
19	// https://github.com/WebAssembly/WASI/blob/23a52736049f4327dd335434851d5dc40ab7cad1/legacy/preview1/docs.md#-random_getbuf-pointeru8-buf_len-size---result-errno.
20	// The definition does not explicitly guarantee that the entire buffer will
21	// be filled, but this appears to be the case in all runtimes tested.
22	err := syscall.RandomGet(b)
23	if err != nil {
24		return 0, err
25	}
26	return len(b), nil
27}
28