* BlockId reform
Introduce `BlockId` that helps track a root/slot pair - this prepares
the codebase for backfilling and handling out-of-dag blocks
* move block dag code to separate module
* fix finalised state root in REST event stream
* fix finalised head computation on head update, when starting from
checkpoint
* clean up chaindag init
* revert `epochAncestor` change in introduced in #3144 that would return
an epoch ancestor from the canoncial history instead of the given
history, causing `EpochRef` keys to point to the wrong block
* Introduce slot->BlockRef mapping for finalized chain
The finalized chain is linear, thus we can use a seq to lookup blocks by
slot number.
Here, we introduce such a seq, even though in the future, it should
likely be backed by a database structure instead, or, more likely, a
flat era file with a flat lookup index.
This dramatically speeds up requests by slot, such as those coming from
the REST interface or GetBlocksByRange, as these are currently served by
a linear iteration from head.
* fix REST block requests to not return blocks from an earlier slot when
the given slot is empty
* fix StateId interpretation such that it doesn't treat state roots as
block roots
* don't load full block from database just to return its root
* move quarantine outside of chaindag
The quarantine has been part of the ChainDAG for the longest time, but
this design has a few issues:
* the function in which blocks are verified and added to the dag becomes
reentrant and therefore difficult to reason about - we're currently
using a stateful flag to work around it
* quarantined blocks bypass the processing queue leading to a processing
stampede
* the quarantine flow is unsuitable for orphaned attestations - these
should also should be quarantined eventually
Instead of processing the quarantine inside ChainDAG, this PR moves
re-queueing to `block_processor` which already is responsible for
dealing with follow-up work when a block is added to the dag
This sets the stage for keeping attestations in the quarantine as well.
Also:
* make `BlockError` `{.pure.}`
* avoid use of `ValidationResult` in block clearance (that's for gossip)
Jacek Sieka