Bug in predicate - is_within_trust_period

[Shivani912]

Context: is_within_trust_period predicate is intended to check if the latest trusted header is still within trusting period while we verify a new, untrusted header.

We also need to perform another check for header time that it's "header from future", that means, the untrusted header that we're verifying must not have a time that is beyond our current time (= now + clock_drift)

Problem: Code below for the is_within_trust_period predicate includes the "header from future" check.

This is a bug because the header we have there is the trusted one instead of the untrusted one and so the condition will always evaluate to true.

tendermint-rs/light-client/src/predicates.rs

Lines 99 to 121 in 548d76d

	fn is_within_trust_period(
	&self,
	header: &Header,
	trusting_period: Duration,
	clock_drift: Duration,
	now: Time,
	) -> Result<(), VerificationError> {
	ensure!(
	header.time < now + clock_drift,
	VerificationError::HeaderFromTheFuture {
	header_time: header.time,
	now
	}
	);
	let expires_at = header.time + trusting_period;
	ensure!(
	expires_at > now,
	VerificationError::NotWithinTrustPeriod { expires_at, now }
	);
	Ok(())
	}

Fix: Will be clearer if we have a separate predicate for "header from future" check.

[Shivani912]

Should I submit a PR for this?

[romac]

Yes please! Great catch