proptest/test_runner/rng.rs
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//-
// Copyright 2017, 2018, 2019, 2020 The proptest developers
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use crate::std_facade::{Arc, String, ToOwned, Vec};
use core::result::Result;
use core::{fmt, str, u8, convert::TryInto};
use rand::{self, Rng, RngCore, SeedableRng};
use rand_chacha::ChaChaRng;
use rand_xorshift::XorShiftRng;
/// Identifies a particular RNG algorithm supported by proptest.
///
/// Proptest supports dynamic configuration of algorithms to allow it to
/// continue operating with persisted regression files and to allow the
/// configuration to be expressed in the `Config` struct.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum RngAlgorithm {
/// The [XorShift](https://rust-random.github.io/rand/rand_xorshift/struct.XorShiftRng.html)
/// algorithm. This was the default up through and including Proptest 0.9.0.
///
/// It is faster than ChaCha but produces lower quality randomness and has
/// some pathological cases where it may fail to produce outputs that are
/// random even to casual observation.
///
/// The seed must be exactly 16 bytes.
XorShift,
/// The [ChaCha](https://rust-random.github.io/rand/rand_chacha/struct.ChaChaRng.html)
/// algorithm. This became the default with Proptest 0.9.1.
///
/// The seed must be exactly 32 bytes.
ChaCha,
/// This is not an actual RNG algorithm, but instead returns data directly
/// from its "seed".
///
/// This is useful when Proptest is being driven from some other entropy
/// source, such as a fuzzer.
///
/// If the seed is depleted, the RNG will return 0s forever.
///
/// Note that in cases where a new RNG is to be derived from an existing
/// one, *the data is split evenly between them*, regardless of how much
/// entropy is actually needed. This means that combinators like
/// `prop_perturb` and `prop_flat_map` can require extremely large inputs.
PassThrough,
/// This is equivalent to the `ChaCha` RNG, with the addition that it
/// records the bytes used to create a value.
///
/// This is useful when Proptest is used for fuzzing, and a corpus of
/// initial inputs need to be created. Note that in these cases, you need
/// to use the `TestRunner` API directly yourself instead of using the
/// `proptest!` macro, as otherwise there is no way to obtain the bytes
/// this captures.
Recorder,
#[allow(missing_docs)]
#[doc(hidden)]
_NonExhaustive,
}
impl Default for RngAlgorithm {
fn default() -> Self {
RngAlgorithm::ChaCha
}
}
impl RngAlgorithm {
pub(crate) fn persistence_key(self) -> &'static str {
match self {
RngAlgorithm::XorShift => "xs",
RngAlgorithm::ChaCha => "cc",
RngAlgorithm::PassThrough => "pt",
RngAlgorithm::Recorder => "rc",
RngAlgorithm::_NonExhaustive => unreachable!(),
}
}
pub(crate) fn from_persistence_key(k: &str) -> Option<Self> {
match k {
"xs" => Some(RngAlgorithm::XorShift),
"cc" => Some(RngAlgorithm::ChaCha),
"pt" => Some(RngAlgorithm::PassThrough),
"rc" => Some(RngAlgorithm::Recorder),
_ => None,
}
}
}
// These two are only used for parsing the environment variable
// PROPTEST_RNG_ALGORITHM.
impl str::FromStr for RngAlgorithm {
type Err = ();
fn from_str(s: &str) -> Result<Self, ()> {
RngAlgorithm::from_persistence_key(s).ok_or(())
}
}
impl fmt::Display for RngAlgorithm {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "{}", self.persistence_key())
}
}
/// Proptest's random number generator.
#[derive(Clone, Debug)]
pub struct TestRng {
rng: TestRngImpl,
}
#[derive(Clone, Debug)]
enum TestRngImpl {
XorShift(XorShiftRng),
ChaCha(ChaChaRng),
PassThrough {
off: usize,
end: usize,
data: Arc<[u8]>,
},
Recorder {
rng: ChaChaRng,
record: Vec<u8>,
},
}
impl RngCore for TestRng {
fn next_u32(&mut self) -> u32 {
match &mut self.rng {
&mut TestRngImpl::XorShift(ref mut rng) => rng.next_u32(),
&mut TestRngImpl::ChaCha(ref mut rng) => rng.next_u32(),
&mut TestRngImpl::PassThrough { .. } => {
let mut buf = [0; 4];
self.fill_bytes(&mut buf[..]);
u32::from_le_bytes(buf)
}
&mut TestRngImpl::Recorder {
ref mut rng,
ref mut record,
} => {
let read = rng.next_u32();
record.extend_from_slice(&read.to_le_bytes());
read
}
}
}
fn next_u64(&mut self) -> u64 {
match &mut self.rng {
&mut TestRngImpl::XorShift(ref mut rng) => rng.next_u64(),
&mut TestRngImpl::ChaCha(ref mut rng) => rng.next_u64(),
&mut TestRngImpl::PassThrough { .. } => {
let mut buf = [0; 8];
self.fill_bytes(&mut buf[..]);
u64::from_le_bytes(buf)
}
&mut TestRngImpl::Recorder {
ref mut rng,
ref mut record,
} => {
let read = rng.next_u64();
record.extend_from_slice(&read.to_le_bytes());
read
}
}
}
fn fill_bytes(&mut self, dest: &mut [u8]) {
match &mut self.rng {
&mut TestRngImpl::XorShift(ref mut rng) => rng.fill_bytes(dest),
&mut TestRngImpl::ChaCha(ref mut rng) => rng.fill_bytes(dest),
&mut TestRngImpl::PassThrough {
ref mut off,
end,
ref data,
} => {
let bytes_to_copy = dest.len().min(end - *off);
dest[..bytes_to_copy]
.copy_from_slice(&data[*off..*off + bytes_to_copy]);
*off += bytes_to_copy;
for i in bytes_to_copy..dest.len() {
dest[i] = 0;
}
}
&mut TestRngImpl::Recorder {
ref mut rng,
ref mut record,
} => {
let res = rng.fill_bytes(dest);
record.extend_from_slice(&dest);
res
}
}
}
fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), rand::Error> {
match self.rng {
TestRngImpl::XorShift(ref mut rng) => rng.try_fill_bytes(dest),
TestRngImpl::ChaCha(ref mut rng) => rng.try_fill_bytes(dest),
TestRngImpl::PassThrough { .. } => {
self.fill_bytes(dest);
Ok(())
}
TestRngImpl::Recorder {
ref mut rng,
ref mut record,
} => {
let res = rng.try_fill_bytes(dest);
if res.is_ok() {
record.extend_from_slice(&dest);
}
res
}
}
}
}
#[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
pub(crate) enum Seed {
XorShift([u8; 16]),
ChaCha([u8; 32]),
PassThrough(Option<(usize, usize)>, Arc<[u8]>),
Recorder([u8; 32]),
}
impl Seed {
pub(crate) fn from_bytes(algorithm: RngAlgorithm, seed: &[u8]) -> Self {
match algorithm {
RngAlgorithm::XorShift => {
assert_eq!(16, seed.len(), "XorShift requires a 16-byte seed");
let mut buf = [0; 16];
buf.copy_from_slice(seed);
Seed::XorShift(buf)
}
RngAlgorithm::ChaCha => {
assert_eq!(32, seed.len(), "ChaCha requires a 32-byte seed");
let mut buf = [0; 32];
buf.copy_from_slice(seed);
Seed::ChaCha(buf)
}
RngAlgorithm::PassThrough => Seed::PassThrough(None, seed.into()),
RngAlgorithm::Recorder => {
assert_eq!(32, seed.len(), "Recorder requires a 32-byte seed");
let mut buf = [0; 32];
buf.copy_from_slice(seed);
Seed::Recorder(buf)
}
RngAlgorithm::_NonExhaustive => unreachable!(),
}
}
pub(crate) fn from_persistence(string: &str) -> Option<Seed> {
fn from_base16(dst: &mut [u8], src: &str) -> Option<()> {
if dst.len() * 2 != src.len() {
return None;
}
for (dst_byte, src_pair) in
dst.into_iter().zip(src.as_bytes().chunks(2))
{
*dst_byte =
u8::from_str_radix(str::from_utf8(src_pair).ok()?, 16)
.ok()?;
}
Some(())
}
let parts =
string.trim().split(char::is_whitespace).collect::<Vec<_>>();
RngAlgorithm::from_persistence_key(&parts[0]).and_then(
|alg| match alg {
RngAlgorithm::XorShift => {
if 5 != parts.len() {
return None;
}
let mut dwords = [0u32; 4];
for (dword, part) in
(&mut dwords[..]).into_iter().zip(&parts[1..])
{
*dword = part.parse().ok()?;
}
let mut seed = [0u8; 16];
for (chunk, dword) in seed.chunks_mut(4).zip(dwords) {
chunk.copy_from_slice(&dword.to_le_bytes());
}
Some(Seed::XorShift(seed))
}
RngAlgorithm::ChaCha => {
if 2 != parts.len() {
return None;
}
let mut seed = [0u8; 32];
from_base16(&mut seed, &parts[1])?;
Some(Seed::ChaCha(seed))
}
RngAlgorithm::PassThrough => {
if 1 == parts.len() {
return Some(Seed::PassThrough(None, vec![].into()));
}
if 2 != parts.len() {
return None;
}
let mut seed = vec![0u8; parts[1].len() / 2];
from_base16(&mut seed, &parts[1])?;
Some(Seed::PassThrough(None, seed.into()))
}
RngAlgorithm::Recorder => {
if 2 != parts.len() {
return None;
}
let mut seed = [0u8; 32];
from_base16(&mut seed, &parts[1])?;
Some(Seed::Recorder(seed))
}
RngAlgorithm::_NonExhaustive => unreachable!(),
},
)
}
pub(crate) fn to_persistence(&self) -> String {
fn to_base16(dst: &mut String, src: &[u8]) {
for byte in src {
dst.push_str(&format!("{:02x}", byte));
}
}
match *self {
Seed::XorShift(ref seed) => {
let dwords = [
u32::from_le_bytes(seed[0..4].try_into().unwrap()),
u32::from_le_bytes(seed[4..8].try_into().unwrap()),
u32::from_le_bytes(seed[8..12].try_into().unwrap()),
u32::from_le_bytes(seed[12..16].try_into().unwrap()),
];
format!(
"{} {} {} {} {}",
RngAlgorithm::XorShift.persistence_key(),
dwords[0],
dwords[1],
dwords[2],
dwords[3]
)
}
Seed::ChaCha(ref seed) => {
let mut string =
RngAlgorithm::ChaCha.persistence_key().to_owned();
string.push(' ');
to_base16(&mut string, seed);
string
}
Seed::PassThrough(bounds, ref data) => {
let data =
bounds.map_or(&data[..], |(start, end)| &data[start..end]);
let mut string =
RngAlgorithm::PassThrough.persistence_key().to_owned();
string.push(' ');
to_base16(&mut string, data);
string
}
Seed::Recorder(ref seed) => {
let mut string =
RngAlgorithm::Recorder.persistence_key().to_owned();
string.push(' ');
to_base16(&mut string, seed);
string
}
}
}
}
impl TestRng {
/// Create a new RNG with the given algorithm and seed.
///
/// Any RNG created with the same algorithm-seed pair will produce the same
/// sequence of values on all systems and all supporting versions of
/// proptest.
///
/// ## Panics
///
/// Panics if `seed` is not an appropriate length for `algorithm`.
pub fn from_seed(algorithm: RngAlgorithm, seed: &[u8]) -> Self {
TestRng::from_seed_internal(Seed::from_bytes(algorithm, seed))
}
/// Dumps the bytes obtained from the RNG so far (only works if the RNG is
/// set to `Recorder`).
///
/// ## Panics
///
/// Panics if this RNG does not capture generated data.
pub fn bytes_used(&self) -> Vec<u8> {
match self.rng {
TestRngImpl::Recorder { ref record, .. } => record.clone(),
_ => panic!("bytes_used() called on non-Recorder RNG"),
}
}
/// Construct a default TestRng from entropy.
pub(crate) fn default_rng(algorithm: RngAlgorithm) -> Self {
#[cfg(feature = "std")]
{
Self {
rng: match algorithm {
RngAlgorithm::XorShift => {
TestRngImpl::XorShift(XorShiftRng::from_entropy())
}
RngAlgorithm::ChaCha => {
TestRngImpl::ChaCha(ChaChaRng::from_entropy())
}
RngAlgorithm::PassThrough => {
panic!("cannot create default instance of PassThrough")
}
RngAlgorithm::Recorder => TestRngImpl::Recorder {
rng: ChaChaRng::from_entropy(),
record: Vec::new(),
},
RngAlgorithm::_NonExhaustive => unreachable!(),
},
}
}
#[cfg(all(
not(feature = "std"),
any(target_arch = "x86", target_arch = "x86_64"),
feature = "hardware-rng"
))]
{
return Self::hardware_rng(algorithm);
}
#[cfg(not(feature = "std"))]
{
return Self::deterministic_rng(algorithm);
}
}
const SEED_FOR_XOR_SHIFT: [u8; 16] = [
0xf4, 0x16, 0x16, 0x48, 0xc3, 0xac, 0x77, 0xac, 0x72, 0x20, 0x0b, 0xea,
0x99, 0x67, 0x2d, 0x6d,
];
const SEED_FOR_CHA_CHA: [u8; 32] = [
0xf4, 0x16, 0x16, 0x48, 0xc3, 0xac, 0x77, 0xac, 0x72, 0x20, 0x0b, 0xea,
0x99, 0x67, 0x2d, 0x6d, 0xca, 0x9f, 0x76, 0xaf, 0x1b, 0x09, 0x73, 0xa0,
0x59, 0x22, 0x6d, 0xc5, 0x46, 0x39, 0x1c, 0x4a,
];
/// Returns a `TestRng` with a seed generated with the
/// RdRand instruction on x86 machines.
///
/// This is useful in `no_std` scenarios on x86 where we don't
/// have a random number infrastructure but the `rdrand` instruction is
/// available.
#[cfg(all(
not(feature = "std"),
any(target_arch = "x86", target_arch = "x86_64"),
feature = "hardware-rng"
))]
pub fn hardware_rng(algorithm: RngAlgorithm) -> Self {
use x86::random::{rdrand_slice, RdRand};
Self::from_seed_internal(match algorithm {
RngAlgorithm::XorShift => {
// Initialize to a sane seed just in case
let mut seed: [u8; 16] = TestRng::SEED_FOR_XOR_SHIFT;
unsafe {
let r = rdrand_slice(&mut seed);
debug_assert!(r, "hardware_rng should only be called on machines with support for rdrand");
}
Seed::XorShift(seed)
}
RngAlgorithm::ChaCha => {
// Initialize to a sane seed just in case
let mut seed: [u8; 32] = TestRng::SEED_FOR_CHA_CHA;
unsafe {
let r = rdrand_slice(&mut seed);
debug_assert!(r, "hardware_rng should only be called on machines with support for rdrand");
}
Seed::ChaCha(seed)
}
RngAlgorithm::PassThrough => {
panic!("deterministic RNG not available for PassThrough")
}
RngAlgorithm::Recorder => {
// Initialize to a sane seed just in case
let mut seed: [u8; 32] = TestRng::SEED_FOR_CHA_CHA;
unsafe {
let r = rdrand_slice(&mut seed);
debug_assert!(r, "hardware_rng should only be called on machines with support for rdrand");
}
Seed::Recorder(seed)
}
RngAlgorithm::_NonExhaustive => unreachable!(),
})
}
/// Returns a `TestRng` with a particular hard-coded seed.
///
/// The seed value will always be the same for a particular version of
/// Proptest and algorithm, but may change across releases.
///
/// This is useful for testing things like strategy implementations without
/// risking getting "unlucky" RNGs which deviate from average behaviour
/// enough to cause spurious failures. For example, a strategy for `bool`
/// which is supposed to produce `true` 50% of the time might have a test
/// which checks that the distribution is "close enough" to 50%. If every
/// test run starts with a different RNG, occasionally there will be
/// spurious test failures when the RNG happens to produce a very skewed
/// distribution. Using this or `TestRunner::deterministic()` avoids such
/// issues.
pub fn deterministic_rng(algorithm: RngAlgorithm) -> Self {
Self::from_seed_internal(match algorithm {
RngAlgorithm::XorShift => {
Seed::XorShift(TestRng::SEED_FOR_XOR_SHIFT)
}
RngAlgorithm::ChaCha => Seed::ChaCha(TestRng::SEED_FOR_CHA_CHA),
RngAlgorithm::PassThrough => {
panic!("deterministic RNG not available for PassThrough")
}
RngAlgorithm::Recorder => Seed::Recorder(TestRng::SEED_FOR_CHA_CHA),
RngAlgorithm::_NonExhaustive => unreachable!(),
})
}
/// Construct a TestRng by the perturbed randomized seed
/// from an existing TestRng.
pub(crate) fn gen_rng(&mut self) -> Self {
Self::from_seed_internal(self.new_rng_seed())
}
/// Overwrite the given TestRng with the provided seed.
pub(crate) fn set_seed(&mut self, seed: Seed) {
*self = Self::from_seed_internal(seed);
}
/// Generate a new randomized seed, set it to this TestRng,
/// and return the seed.
pub(crate) fn gen_get_seed(&mut self) -> Seed {
let seed = self.new_rng_seed();
self.set_seed(seed.clone());
seed
}
/// Randomize a perturbed randomized seed from the given TestRng.
pub(crate) fn new_rng_seed(&mut self) -> Seed {
match self.rng {
TestRngImpl::XorShift(ref mut rng) => {
let mut seed = rng.gen::<[u8; 16]>();
// Directly using XorShiftRng::from_seed() at this point would
// result in rng and the returned value being exactly the same.
// Perturb the seed with some arbitrary values to prevent this.
for word in seed.chunks_mut(4) {
word[3] ^= 0xde;
word[2] ^= 0xad;
word[1] ^= 0xbe;
word[0] ^= 0xef;
}
Seed::XorShift(seed)
}
TestRngImpl::ChaCha(ref mut rng) => Seed::ChaCha(rng.gen()),
TestRngImpl::PassThrough {
ref mut off,
ref mut end,
ref data,
} => {
let len = *end - *off;
let child_start = *off + len / 2;
let child_end = *off + len;
*end = child_start;
Seed::PassThrough(
Some((child_start, child_end)),
Arc::clone(data),
)
}
TestRngImpl::Recorder { ref mut rng, .. } => {
Seed::Recorder(rng.gen())
}
}
}
/// Construct a TestRng from a given seed.
fn from_seed_internal(seed: Seed) -> Self {
Self {
rng: match seed {
Seed::XorShift(seed) => {
TestRngImpl::XorShift(XorShiftRng::from_seed(seed))
}
Seed::ChaCha(seed) => {
TestRngImpl::ChaCha(ChaChaRng::from_seed(seed))
}
Seed::PassThrough(bounds, data) => {
let (start, end) = bounds.unwrap_or((0, data.len()));
TestRngImpl::PassThrough {
off: start,
end,
data,
}
}
Seed::Recorder(seed) => TestRngImpl::Recorder {
rng: ChaChaRng::from_seed(seed),
record: Vec::new(),
},
},
}
}
}
#[cfg(test)]
mod test {
use crate::std_facade::Vec;
use rand::{Rng, RngCore};
use super::{RngAlgorithm, Seed, TestRng};
use crate::arbitrary::any;
use crate::strategy::*;
proptest! {
#[test]
fn gen_parse_seeds(
seed in prop_oneof![
any::<[u8;16]>().prop_map(Seed::XorShift),
any::<[u8;32]>().prop_map(Seed::ChaCha),
any::<Vec<u8>>().prop_map(|data| Seed::PassThrough(None, data.into())),
any::<[u8;32]>().prop_map(Seed::Recorder),
])
{
assert_eq!(seed, Seed::from_persistence(&seed.to_persistence()).unwrap());
}
#[test]
fn rngs_dont_clone_self_on_genrng(
seed in prop_oneof![
any::<[u8;16]>().prop_map(Seed::XorShift),
any::<[u8;32]>().prop_map(Seed::ChaCha),
Just(()).prop_perturb(|_, mut rng| {
let mut buf = vec![0u8; 2048];
rng.fill_bytes(&mut buf);
Seed::PassThrough(None, buf.into())
}),
any::<[u8;32]>().prop_map(Seed::Recorder),
])
{
type Value = [u8;32];
let orig = TestRng::from_seed_internal(seed);
{
let mut rng1 = orig.clone();
let mut rng2 = rng1.gen_rng();
assert_ne!(rng1.gen::<Value>(), rng2.gen::<Value>());
}
{
let mut rng1 = orig.clone();
let mut rng2 = rng1.gen_rng();
let mut rng3 = rng1.gen_rng();
let mut rng4 = rng2.gen_rng();
let a = rng1.gen::<Value>();
let b = rng2.gen::<Value>();
let c = rng3.gen::<Value>();
let d = rng4.gen::<Value>();
assert_ne!(a, b);
assert_ne!(a, c);
assert_ne!(a, d);
assert_ne!(b, c);
assert_ne!(b, d);
assert_ne!(c, d);
}
}
}
#[test]
fn passthrough_rng_behaves_properly() {
let mut rng = TestRng::from_seed(
RngAlgorithm::PassThrough,
&[
0xDE, 0xC0, 0x12, 0x34, 0x56, 0x78, 0xFE, 0xCA, 0xEF, 0xBE,
0xAD, 0xDE, 0x01, 0x02, 0x03,
],
);
assert_eq!(0x3412C0DE, rng.next_u32());
assert_eq!(0xDEADBEEFCAFE7856, rng.next_u64());
let mut buf = [0u8; 4];
rng.try_fill_bytes(&mut buf[0..4]).unwrap();
assert_eq!([1, 2, 3, 0], buf);
rng.try_fill_bytes(&mut buf[0..4]).unwrap();
assert_eq!([0, 0, 0, 0], buf);
}
}