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make rand/getrandom dependency explicit with a feature #37

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merged 3 commits into from Jan 14, 2022
Merged

make rand/getrandom dependency explicit with a feature #37

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d6c9787
make rand/getrandom dependency explicit with a feature
Oct 25, 2021
b2013e1
setting resolver "2" to fix no-std build error
Oct 27, 2021
440828c
cargo fmt
Oct 27, 2021
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15 changes: 8 additions & 7 deletions Cargo.toml
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Expand Up @@ -11,23 +11,24 @@ categories = ["cryptography"]
include = ["Cargo.toml", "src", "README.md", "LICENSE-APACHE", "LICENSE-MIT"]
license = "MIT/Apache-2.0"
edition = "2018"
resolver = "2"

[dependencies]
rand = { version = "0.8", default-features = false, features = ["std_rng"] }
rand = { version = "0.8", default-features = false, features = ["std_rng"]}
rayon = { version = "1", optional = true }
colored = { version = "2", optional = true }
num-traits = { version = "0.2", default-features = false }

[dev-dependencies]
rand = { version = "0.8", features = ["std"]}


[features]
default = [ "std" ]
std = [ "rand/std" ]
std = []
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Is there a reason to disable rand/std when std is on? That's not supported in wasm anyway, right? Or does wasm support std?

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I haven't done any in-depth research, but, while working on this wasm contract, I can tell you that many things from std are compatible with wasm.

  • std::collections like Vec or Hashmap are ok
  • Option and Result work just fine
  • So far, never hit any issue working withString and str
  • array and slices are 👌

AFAIK there isn't any particular issue using std in wasm environment, except probably IO and multi-thread stuff.

The issue with using the current version of ark-std in wasm for smart contracts is getrandom crate: there is no way a blockchain EVM can provide you with functions that generate randomness.
This change aims at making the dependency over getrandom optional. So crates that sit above ark-std like all the algebra crates, crypto-primitives , crates in curve, etc..., they can still rely on re-exported traits from ark_std::rand, while gaining wasm compatibility for free.

Side Note: all the no-std gears are dedicated more to the embedded world, rather than to wasm.

parallel = [ "rayon", "std" ]
print-trace = [ "std", "colored" ]

[profile.release]
opt-level = 3
lto = "thin"
incremental = true
getrandom = ["rand/std"]

[profile.bench]
opt-level = 3
Expand Down
28 changes: 20 additions & 8 deletions src/rand_helper.rs
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@@ -1,10 +1,10 @@
#[cfg(feature = "std")]
use rand::RngCore;
use rand::{
distributions::{Distribution, Standard},
prelude::StdRng,
Rng,
};
#[cfg(feature = "std")]
use rand::{prelude::ThreadRng, RngCore};

pub use rand;

Expand Down Expand Up @@ -41,20 +41,28 @@ pub fn test_rng() -> impl rand::Rng {
/// Should be used only for tests, not for any real world usage.
#[cfg(feature = "std")]
pub fn test_rng() -> impl rand::Rng {
let is_deterministic =
std::env::vars().any(|(key, val)| key == "DETERMINISTIC_TEST_RNG" && val == "1");
if is_deterministic {
#[cfg(any(feature = "getrandom", test))]
{
let is_deterministic =
std::env::vars().any(|(key, val)| key == "DETERMINISTIC_TEST_RNG" && val == "1");
if is_deterministic {
RngWrapper::Deterministic(test_rng_helper())
} else {
RngWrapper::Randomized(rand::thread_rng())
}
}
#[cfg(not(any(feature = "getrandom", test)))]
{
RngWrapper::Deterministic(test_rng_helper())
} else {
RngWrapper::Randomized(rand::thread_rng())
}
}

/// Helper wrapper to enable `test_rng` to return `impl::Rng`.
#[cfg(feature = "std")]
enum RngWrapper {
Deterministic(StdRng),
Randomized(ThreadRng),
#[cfg(any(feature = "getrandom", test))]
Randomized(rand::rngs::ThreadRng),
}

#[cfg(feature = "std")]
Expand All @@ -63,6 +71,7 @@ impl RngCore for RngWrapper {
fn next_u32(&mut self) -> u32 {
match self {
Self::Deterministic(rng) => rng.next_u32(),
#[cfg(any(feature = "getrandom", test))]
Self::Randomized(rng) => rng.next_u32(),
}
}
Expand All @@ -71,6 +80,7 @@ impl RngCore for RngWrapper {
fn next_u64(&mut self) -> u64 {
match self {
Self::Deterministic(rng) => rng.next_u64(),
#[cfg(any(feature = "getrandom", test))]
Self::Randomized(rng) => rng.next_u64(),
}
}
Expand All @@ -79,6 +89,7 @@ impl RngCore for RngWrapper {
fn fill_bytes(&mut self, dest: &mut [u8]) {
match self {
Self::Deterministic(rng) => rng.fill_bytes(dest),
#[cfg(any(feature = "getrandom", test))]
Self::Randomized(rng) => rng.fill_bytes(dest),
}
}
Expand All @@ -87,6 +98,7 @@ impl RngCore for RngWrapper {
fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), rand::Error> {
match self {
Self::Deterministic(rng) => rng.try_fill_bytes(dest),
#[cfg(any(feature = "getrandom", test))]
Self::Randomized(rng) => rng.try_fill_bytes(dest),
}
}
Expand Down