getrandom 0.1.1

A small cross-platform library for retrieving random data from system source
Documentation 
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// Copyright 2018 Developers of the Rand project.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! Implementation for WASM via stdweb
use core::cell::RefCell;
use core::mem;
use core::num::NonZeroU32;
use std::thread_local;

use stdweb::{js, _js_impl};
use stdweb::unstable::TryInto;
use stdweb::web::error::Error as WebError;

use crate::Error;
use crate::utils::use_init;

#[derive(Clone, Debug)]
enum RngSource {
    Browser,
    Node
}

thread_local!(
    static RNG_SOURCE: RefCell<Option<RngSource>> = RefCell::new(None);
);

pub fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
    assert_eq!(mem::size_of::<usize>(), 4);

    RNG_SOURCE.with(|f| {
        use_init(f, getrandom_init, |source| getrandom_fill(source, dest))
    })

}

fn getrandom_init() -> Result<RngSource, Error> {
    let result = js! {
        try {
            if (
                typeof self === "object" &&
                typeof self.crypto === "object" &&
                typeof self.crypto.getRandomValues === "function"
            ) {
                return { success: true, ty: 1 };
            }

            if (typeof require("crypto").randomBytes === "function") {
                return { success: true, ty: 2 };
            }

            return { success: false, error: new Error("not supported") };
        } catch(err) {
            return { success: false, error: err };
        }
    };

    if js!{ return @{ result.as_ref() }.success } == true {
        let ty = js!{ return @{ result }.ty };

        if ty == 1 { Ok(RngSource::Browser) }
        else if ty == 2 { Ok(RngSource::Node) }
        else { unreachable!() }
    } else {
        let err: WebError = js!{ return @{ result }.error }.try_into().unwrap();
        error!("getrandom unavailable: {}", err);
        Err(Error::UNAVAILABLE)
    }
}

fn getrandom_fill(source: &mut RngSource, dest: &mut [u8]) -> Result<(), Error> {
    for chunk in dest.chunks_mut(65536) {
        let len = chunk.len() as u32;
        let ptr = chunk.as_mut_ptr() as i32;

        let result = match source {
            RngSource::Browser => js! {
                try {
                    let array = new Uint8Array(@{ len });
                    self.crypto.getRandomValues(array);
                    HEAPU8.set(array, @{ ptr });

                    return { success: true };
                } catch(err) {
                    return { success: false, error: err };
                }
            },
            RngSource::Node => js! {
                try {
                    let bytes = require("crypto").randomBytes(@{ len });
                    HEAPU8.set(new Uint8Array(bytes), @{ ptr });

                    return { success: true };
                } catch(err) {
                    return { success: false, error: err };
                }
            }
        };

        if js!{ return @{ result.as_ref() }.success } != true {
            let err: WebError = js!{ return @{ result }.error }.try_into().unwrap();
            error!("getrandom failed: {}", err);
            return Err(Error::UNKNOWN)
        }
    }
    Ok(())
}

#[inline(always)]
pub fn error_msg_inner(_: NonZeroU32) -> Option<&'static str> { None }