0000ea3265 test: Add test for GetRandMillis and GetRandMicros (MarcoFalke)
fa0e5b89cf Add templated GetRandomDuration<> (MarcoFalke)
Pull request description:
A naive implementation of this template is dangerous, because the call site might accidentally omit the template parameter:
```cpp
template <typename D>
D GetRandDur(const D& duration_max)
{
return D{GetRand(duration_max.count())};
}
BOOST_AUTO_TEST_CASE(util_time_GetRandTime)
{
std::chrono::seconds rand_hour = GetRandDur(std::chrono::hours{1});
// Want seconds to be in range [0..1hour), but always get zero :((((
BOOST_CHECK_EQUAL(rand_hour.count(), 0);
}
```
Luckily `std::common_type` is already specialised in the standard lib for `std::chrono::duration` (https://en.cppreference.com/w/cpp/chrono/duration/common_type). And its effect seem to be that the call site must always specify the template argument explicitly.
So instead of implementing the function for each duration type by hand, replace it with a templated version that is safe to use.
ACKs for top commit:
laanwj:
Code review ACK 0000ea3265
promag:
Code review ACK 0000ea3265.
jonatack:
ACK 0000ea3 thanks for the improved documentation. Code review, built, ran `src/test/test_bitcoin -t random_tests -l test_suite` for the new unit tests, `git diff fa05a4c 0000ea3` since previous review:
hebasto:
ACK 0000ea3265 with non-blocking [nit](https://github.com/bitcoin/bitcoin/pull/18781#discussion_r424924671).
Tree-SHA512: e89d46e31452be6ea14269ecbbb2cdd9ae83b4412cd14dff7d1084283092722a2f847cb501e8054394e4a3eff852f9c87f6d694fd008b3f7e8458cb5a3068af7
Move the OS random test to a sanity check function that is called every
time bitcoind is initialized.
Keep `src/test/random_tests.cpp` for the case that later random tests
are added, and keep a rudimentary test that just calls the sanity check.
These are available in sandboxes without access to files or
devices. Also [they are safer and more straightforward](https://en.wikipedia.org/wiki/Entropy-supplying_system_calls)
to use than `/dev/urandom` as reading from a file has quite a few edge
cases:
- Linux: `getrandom(buf, buflen, 0)`. [getrandom(2)](http://man7.org/linux/man-pages/man2/getrandom.2.html)
was introduced in version 3.17 of the Linux kernel.
- OpenBSD: `getentropy(buf, buflen)`. The [getentropy(2)](http://man.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man2/getentropy.2)
function appeared in OpenBSD 5.6.
- FreeBSD and NetBSD: `sysctl(KERN_ARND)`. Not sure when this was added
but it has existed for quite a while.
Alternatives:
- Linux has sysctl `CTL_KERN` / `KERN_RANDOM` / `RANDOM_UUID`
which gives 16 bytes of randomness. This may be available
on older kernels, however [sysctl is deprecated on Linux](https://lwn.net/Articles/605392/)
and even removed in some distros so we shouldn't use it.
Add tests for `GetOSRand()`:
- Test that no error happens (otherwise `RandFailure()` which aborts)
- Test that all 32 bytes are overwritten (initialize with zeros, try multiple times)
Discussion:
- When to use these? Currently they are always used when available.
Another option would be to use them only when `/dev/urandom` is not
available. But this would mean these code paths receive less testing,
and I'm not sure there is any reason to prefer `/dev/urandom`.
Closes: #9676
