One difference between pebble and leveldb is that the latter returns error when performing Get on a closed database, the former does a panic. This may be triggered during shutdown (see #27237)
This PR changes the pebble driver so we check that the db is not closed already, for several operations. It also adds tests to the db test-suite, so the previously implicit assumption of "not panic:ing at ops on closed database" is covered by tests.
This PR is a (superior) alternative to https://github.com/ethereum/go-ethereum/pull/26708, it handles deprecation, primarily two specific cases.
`rand.Seed` is typically used in two ways
- `rand.Seed(time.Now().UnixNano())` -- we seed it, just to be sure to get some random, and not always get the same thing on every run. This is not needed, with global seeding, so those are just removed.
- `rand.Seed(1)` this is typically done to ensure we have a stable test. If we rely on this, we need to fix up the tests to use a deterministic prng-source. A few occurrences like this has been replaced with a proper custom source.
`rand.Read` has been replaced by `crypto/rand`.`Read` in this PR.
- Move the existing tests from memorydb into a generalized testsuite
that can be run by any ethdb backend implementation.
- Add several more test cases to clarify some non-obvious nuances when
implementing a custom ethdb backend, such as the behaviour of
NewIteratorWithPrefix vs NewIteratorWithStart.
- Add leveldb to the testsuite using in-memory storage for fast
execution.
