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v/vlib/crypto/rand/rand_linux.c.v

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// Copyright (c) 2019-2021 Alexander Medvednikov. All rights reserved.
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// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
module rand
#include <sys/syscall.h>
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const (
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read_batch_size = 256
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)
// read returns an array of `bytes_needed` random bytes read from the OS.
pub fn read(bytes_needed int) ?[]byte {
mut buffer := unsafe { vcalloc_noscan(bytes_needed) }
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mut bytes_read := 0
mut remaining_bytes := bytes_needed
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// getrandom syscall wont block if requesting <= 256 bytes
for bytes_read < bytes_needed {
batch_size := if remaining_bytes > rand.read_batch_size {
rand.read_batch_size
} else {
remaining_bytes
}
rbytes := unsafe { getrandom(batch_size, buffer + bytes_read) }
if rbytes == -1 {
unsafe { free(buffer) }
return IError(&ReadError{})
}
bytes_read += rbytes
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}
return unsafe { buffer.vbytes(bytes_needed) }
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}
fn getrandom(bytes_needed int, buffer voidptr) int {
if bytes_needed > rand.read_batch_size {
panic('getrandom() dont request more than $rand.read_batch_size bytes at once.')
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}
return unsafe { C.syscall(C.SYS_getrandom, buffer, bytes_needed, 0) }
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}