Source File
rand_getrandom.go
Belonging Package
crypto/internal/sysrand
// Copyright 2014 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.
//go:build dragonfly || freebsd || linux || solaris
package sysrand
import (
)
func read( []byte) error {
// Linux, DragonFly, and illumos don't have a limit on the buffer size.
// FreeBSD has a limit of IOSIZE_MAX, which seems to be either INT_MAX or
// SSIZE_MAX. 2^31-1 is a safe and high enough value to use for all of them.
//
// Note that Linux returns "a maximum of 32Mi-1 bytes", but that will only
// result in a short read, not an error. Short reads can also happen above
// 256 bytes due to signals. Reads up to 256 bytes are guaranteed not to
// return short (and not to return an error IF THE POOL IS INITIALIZED) on
// at least Linux, FreeBSD, DragonFly, and Oracle Solaris, but we don't make
// use of that.
:= math.MaxInt32
// Oracle Solaris has a limit of 133120 bytes. Very specific.
//
// The getrandom() and getentropy() functions fail if: [...]
//
// - bufsz is <= 0 or > 133120, when GRND_RANDOM is not set
//
// https://docs.oracle.com/cd/E88353_01/html/E37841/getrandom-2.html
if runtime.GOOS == "solaris" {
= 133120
}
for len() > 0 {
:= len()
if > {
=
}
, := unix.GetRandom([:], 0)
if errors.Is(, syscall.ENOSYS) {
// If getrandom(2) is not available, presumably on Linux versions
// earlier than 3.17, fall back to reading from /dev/urandom.
return urandomRead()
}
if errors.Is(, syscall.EINTR) {
// If getrandom(2) is blocking, either because it is waiting for the
// entropy pool to become initialized or because we requested more
// than 256 bytes, it might get interrupted by a signal.
continue
}
if != nil {
return
}
= [:]
}
return nil
}
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