Source file src/crypto/rand/rand_batched.go
Documentation: crypto/rand
1 // Copyright 2014 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 linux || freebsd || dragonfly || solaris 6 // +build linux freebsd dragonfly solaris 7 8 package rand 9 10 import ( 11 "internal/syscall/unix" 12 ) 13 14 // maxGetRandomRead is platform dependent. 15 func init() { 16 altGetRandom = batched(getRandomBatch, maxGetRandomRead) 17 } 18 19 // batched returns a function that calls f to populate a []byte by chunking it 20 // into subslices of, at most, readMax bytes. 21 func batched(f func([]byte) bool, readMax int) func([]byte) bool { 22 return func(buf []byte) bool { 23 for len(buf) > readMax { 24 if !f(buf[:readMax]) { 25 return false 26 } 27 buf = buf[readMax:] 28 } 29 return len(buf) == 0 || f(buf) 30 } 31 } 32 33 // If the kernel is too old to support the getrandom syscall(), 34 // unix.GetRandom will immediately return ENOSYS and we will then fall back to 35 // reading from /dev/urandom in rand_unix.go. unix.GetRandom caches the ENOSYS 36 // result so we only suffer the syscall overhead once in this case. 37 // If the kernel supports the getrandom() syscall, unix.GetRandom will block 38 // until the kernel has sufficient randomness (as we don't use GRND_NONBLOCK). 39 // In this case, unix.GetRandom will not return an error. 40 func getRandomBatch(p []byte) (ok bool) { 41 n, err := unix.GetRandom(p, 0) 42 return n == len(p) && err == nil 43 } 44