src/crypto/rand/rand.go

// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package rand implements a cryptographically secure
// random number generator.
package rand

import "io"

// Reader is a global, shared instance of a cryptographically
// secure random number generator.
//
//   - On Linux, FreeBSD, Dragonfly, and Solaris, Reader uses getrandom(2)
//     if available, and /dev/urandom otherwise.
//   - On macOS and iOS, Reader uses arc4random_buf(3).
//   - On OpenBSD and NetBSD, Reader uses getentropy(2).
//   - On other Unix-like systems, Reader reads from /dev/urandom.
//   - On Windows, Reader uses the ProcessPrng API.
//   - On js/wasm, Reader uses the Web Crypto API.
//   - On wasip1/wasm, Reader uses random_get from wasi_snapshot_preview1.
var Reader io.Reader

// Read is a helper function that calls Reader.Read using io.ReadFull.
// On return, n == len(b) if and only if err == nil.
func Read(b []byte) (n int, err error) {
	return io.ReadFull(Reader, b)
}

// batched returns a function that calls f to populate a []byte by chunking it
// into subslices of, at most, readMax bytes.
func batched(f func([]byte) error, readMax int) func([]byte) error {
	return func(out []byte) error {
		for len(out) > 0 {
			read := len(out)
			if read > readMax {
				read = readMax
			}
			if err := f(out[:read]); err != nil {
				return err
			}
			out = out[read:]
		}
		return nil
	}
}