nimbus-eth2/beacon_chain/block_pool.nim

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import
bitops, chronicles, options, sequtils, tables,
ssz, beacon_chain_db, state_transition, extras,
beacon_node_types,
spec/[crypto, datatypes, digest, helpers]
proc link(parent, child: BlockRef) =
doAssert (not (parent.root == Eth2Digest() or child.root == Eth2Digest())),
"blocks missing root!"
doAssert parent.root != child.root, "self-references not allowed"
child.parent = parent
parent.children.add(child)
proc init*(T: type BlockRef, root: Eth2Digest, slot: Slot): BlockRef =
BlockRef(
root: root,
slot: slot
)
proc init*(T: type BlockRef, root: Eth2Digest, blck: BeaconBlock): BlockRef =
BlockRef.init(root, blck.slot)
proc findAncestorBySlot*(blck: BlockRef, slot: Slot): BlockRef =
## Find the first ancestor that has a slot number less than or equal to `slot`
assert(not blck.isNil)
result = blck
while result.parent != nil and result.slot > slot:
result = result.parent
assert(not result.isNil)
proc init*(T: type BlockPool, db: BeaconChainDB): BlockPool =
# TODO we require that the db contains both a head and a tail block -
# asserting here doesn't seem like the right way to go about it however..
let
tail = db.getTailBlock()
head = db.getHeadBlock()
doAssert tail.isSome(), "Missing tail block, database corrupt?"
doAssert head.isSome(), "Missing head block, database corrupt?"
let
tailRoot = tail.get()
tailBlock = db.getBlock(tailRoot).get()
tailRef = BlockRef.init(tailRoot, tailBlock)
headRoot = head.get()
var
blocks = {tailRef.root: tailRef}.toTable()
latestStateRoot = Option[Eth2Digest]()
headStateBlock = tailRef
headRef: BlockRef
if headRoot != tailRoot:
var curRef: BlockRef
for root, blck in db.getAncestors(headRoot):
if root == tailRef.root:
2019-03-13 23:04:43 +00:00
doAssert(not curRef.isNil)
link(tailRef, curRef)
curRef = curRef.parent
break
let newRef = BlockRef.init(root, blck)
if curRef == nil:
curRef = newRef
headRef = newRef
else:
link(newRef, curRef)
curRef = curRef.parent
blocks[curRef.root] = curRef
if latestStateRoot.isNone() and db.containsState(blck.state_root):
latestStateRoot = some(blck.state_root)
doAssert curRef == tailRef,
"head block does not lead to tail, database corrupt?"
else:
headRef = tailRef
var blocksBySlot = initTable[uint64, seq[BlockRef]]()
for _, b in tables.pairs(blocks):
let slot = db.getBlock(b.root).get().slot
blocksBySlot.mgetOrPut(slot.uint64, @[]).add(b)
let
# The head state is necessary to find out what we considered to be the
# finalized epoch last time we saved something.
headStateRoot =
if latestStateRoot.isSome():
latestStateRoot.get()
else:
db.getBlock(tailRef.root).get().state_root
# TODO right now, because we save a state at every epoch, this *should*
# be the latest justified state or newer, meaning it's enough for
# establishing what we consider to be the finalized head. This logic
# will need revisiting however
headState = db.getState(headStateRoot).get()
finalizedHead =
headRef.findAncestorBySlot(headState.finalized_epoch.get_epoch_start_slot())
justifiedHead =
headRef.findAncestorBySlot(headState.current_justified_epoch.get_epoch_start_slot())
doAssert justifiedHead.slot >= finalizedHead.slot,
"justified head comes before finalized head - database corrupt?"
# TODO what about ancestors? only some special blocks are
# finalized / justified but to find out exactly which ones, we would have
# to replay state transitions from tail to head and note each one...
finalizedHead.finalized = true
justifiedHead.justified = true
BlockPool(
pending: initTable[Eth2Digest, BeaconBlock](),
unresolved: initTable[Eth2Digest, UnresolvedBlock](),
blocks: blocks,
blocksBySlot: blocksBySlot,
tail: tailRef,
head: headRef,
finalizedHead: finalizedHead,
db: db
)
proc addSlotMapping(pool: BlockPool, slot: uint64, br: BlockRef) =
proc addIfMissing(s: var seq[BlockRef], v: BlockRef) =
if v notin s:
s.add(v)
pool.blocksBySlot.mgetOrPut(slot, @[]).addIfMissing(br)
proc updateState*(
pool: BlockPool, state: var StateData, blck: BlockRef, slot: Slot) {.gcsafe.}
proc add*(
pool: var BlockPool, state: var StateData, blockRoot: Eth2Digest,
blck: BeaconBlock): BlockRef {.gcsafe.} =
## return the block, if resolved...
## the state parameter may be updated to include the given block, if
## everything checks out
# TODO reevaluate passing the state in like this
doAssert blockRoot == signed_root(blck)
# Already seen this block??
if blockRoot in pool.blocks:
debug "Block already exists",
blck = shortLog(blck),
blockRoot = shortLog(blockRoot)
return pool.blocks[blockRoot]
# If the block we get is older than what we finalized already, we drop it.
# One way this can happen is that we start resolving a block and finalization
# happens in the meantime - the block we requested will then be stale
# by the time it gets here.
if blck.slot <= pool.finalizedHead.slot:
debug "Old block, dropping",
blck = shortLog(blck),
tailSlot = humaneSlotNum(pool.tail.slot),
blockRoot = shortLog(blockRoot)
return
let parent = pool.blocks.getOrDefault(blck.previous_block_root)
if parent != nil:
# The block might have been in either of these - we don't want any more
# work done on its behalf
pool.unresolved.del(blockRoot)
pool.pending.del(blockRoot)
# The block is resolved, now it's time to validate it to ensure that the
# blocks we add to the database are clean for the given state
# TODO if the block is from the future, we should not be resolving it (yet),
# but maybe we should use it as a hint that our clock is wrong?
updateState(pool, state, parent, blck.slot - 1)
if not updateState(state.data, blck, {}):
# TODO find a better way to log all this block data
notice "Invalid block",
blck = shortLog(blck),
blockRoot = shortLog(blockRoot)
return
let blockRef = BlockRef.init(blockRoot, blck)
link(parent, blockRef)
pool.blocks[blockRoot] = blockRef
pool.addSlotMapping(blck.slot.uint64, blockRef)
# Resolved blocks should be stored in database
pool.db.putBlock(blockRoot, blck)
# This block *might* have caused a justification - make sure we stow away
# that information:
let
justifiedBlock =
blockRef.findAncestorBySlot(
state.data.current_justified_epoch.get_epoch_start_slot())
if not justifiedBlock.justified:
info "Justified block",
justifiedBlockRoot = shortLog(justifiedBlock.root),
justifiedBlockRoot = humaneSlotnum(justifiedBlock.slot),
headBlockRoot = shortLog(blockRoot),
headBlockSlot = humaneSlotnum(blck.slot)
justifiedBlock.justified = true
info "Block resolved",
blck = shortLog(blck),
blockRoot = shortLog(blockRoot)
# Now that we have the new block, we should see if any of the previously
# unresolved blocks magically become resolved
# TODO there are more efficient ways of doing this, that also don't risk
# running out of stack etc
let retries = pool.pending
for k, v in retries:
discard pool.add(state, k, v)
return blockRef
# TODO possibly, it makes sense to check the database - that would allow sync
# to simply fill up the database with random blocks the other clients
# think are useful - but, it would also risk filling the database with
# junk that's not part of the block graph
if blck.previous_block_root in pool.unresolved:
return
# This is an unresolved block - put it on the unresolved list for now...
# TODO if we receive spam blocks, one heurestic to implement might be to wait
# for a couple of attestations to appear before fetching parents - this
# would help prevent using up network resources for spam - this serves
# two purposes: one is that attestations are likely to appear for the
# block only if it's valid / not spam - the other is that malicious
# validators that are not proposers can sign invalid blocks and send
# them out without penalty - but signing invalid attestations carries
# a risk of being slashed, making attestations a more valuable spam
# filter.
debug "Unresolved block",
blck = shortLog(blck),
blockRoot = shortLog(blockRoot)
pool.unresolved[blck.previous_block_root] = UnresolvedBlock()
pool.pending[blockRoot] = blck
proc get*(pool: BlockPool, blck: BlockRef): BlockData =
## Retrieve the associated block body of a block reference
doAssert (not blck.isNil), "Trying to get nil BlockRef"
let data = pool.db.getBlock(blck.root)
doAssert data.isSome, "BlockRef without backing data, database corrupt?"
BlockData(data: data.get(), refs: blck)
proc get*(pool: BlockPool, root: Eth2Digest): Option[BlockData] =
## Retrieve a resolved block reference and its associated body, if available
let refs = pool.blocks.getOrDefault(root)
if not refs.isNil:
some(pool.get(refs))
else:
none(BlockData)
proc getOrResolve*(pool: var BlockPool, root: Eth2Digest): BlockRef =
## Fetch a block ref, or nil if not found (will be added to list of
## blocks-to-resolve)
result = pool.blocks.getOrDefault(root)
if result.isNil:
pool.unresolved[root] = UnresolvedBlock()
iterator blockRootsForSlot*(pool: BlockPool, slot: uint64|Slot): Eth2Digest =
for br in pool.blocksBySlot.getOrDefault(slot.uint64, @[]):
yield br.root
proc checkUnresolved*(pool: var BlockPool): seq[Eth2Digest] =
## Return a list of blocks that we should try to resolve from other client -
## to be called periodically but not too often (once per slot?)
var done: seq[Eth2Digest]
for k, v in pool.unresolved.mpairs():
if v.tries > 8:
done.add(k)
else:
inc v.tries
for k in done:
# TODO Need to potentially remove from pool.pending - this is currently a
# memory leak here!
pool.unresolved.del(k)
# simple (simplistic?) exponential backoff for retries..
for k, v in pool.unresolved.pairs():
if v.tries.popcount() == 1:
result.add(k)
proc skipAndUpdateState(
state: var BeaconState, blck: BeaconBlock, flags: UpdateFlags,
afterUpdate: proc (state: BeaconState)): bool =
skipSlots(state, blck.slot - 1, afterUpdate)
let ok = updateState(state, blck, flags)
afterUpdate(state)
ok
proc maybePutState(pool: BlockPool, state: BeaconState) =
# TODO we save state at every epoch start but never remove them - we also
# potentially save multiple states per slot if reorgs happen, meaning
# we could easily see a state explosion
if state.slot mod SLOTS_PER_EPOCH == 0:
let root = hash_tree_root(state)
if not pool.db.containsState(root):
info "Storing state",
stateSlot = humaneSlotNum(state.slot),
stateRoot = shortLog(root)
pool.db.putState(root, state)
proc updateState*(
pool: BlockPool, state: var StateData, blck: BlockRef, slot: Slot) =
## Rewind or advance state such that it matches the given block and slot -
## this may include replaying from an earlier snapshot if blck is on a
## different branch or has advanced to a higher slot number than slot
## If slot is higher than blck.slot, replay will fill in with empty/non-block
## slots, else it is ignored
# We need to check the slot because the state might have moved forwards
# without blocks
if state.blck.root == blck.root and state.data.slot == slot:
return # State already at the right spot
var ancestors = @[pool.get(blck)]
# Common case: the last thing that was applied to the state was the parent
# of blck
if state.blck.root == ancestors[0].data.previous_block_root and
state.data.slot < blck.slot:
let ok = skipAndUpdateState(
state.data, ancestors[0].data, {skipValidation}) do (state: BeaconState):
pool.maybePutState(state)
doAssert ok, "Blocks in database should never fail to apply.."
state.blck = blck
state.root = ancestors[0].data.state_root
skipSlots(state.data, slot) do (state: BeaconState):
pool.maybePutState(state)
return
# It appears that the parent root of the proposed new block is different from
# what we expected. We will have to rewind the state to a point along the
# chain of ancestors of the new block. We will do this by loading each
# successive parent block and checking if we can find the corresponding state
# in the database.
while not ancestors[^1].refs.parent.isNil:
let parent = pool.get(ancestors[^1].refs.parent)
ancestors.add parent
if pool.db.containsState(parent.data.state_root): break
let
ancestor = ancestors[^1]
ancestorState = pool.db.getState(ancestor.data.state_root)
if ancestorState.isNone():
# TODO this should only happen if the database is corrupt - we walked the
# list of parent blocks and couldn't find a corresponding state in the
# database, which should never happen (at least we should have the
# tail state in there!)
error "Couldn't find ancestor state or block parent missing!",
blockRoot = shortLog(blck.root)
doAssert false, "Oh noes, we passed big bang!"
debug "Replaying state transitions",
stateSlot = humaneSlotNum(state.data.slot),
stateRoot = shortLog(ancestor.data.state_root),
prevStateSlot = humaneSlotNum(ancestorState.get().slot),
ancestors = ancestors.len
state.data = ancestorState.get()
# If we come this far, we found the state root. The last block on the stack
# is the one that produced this particular state, so we can pop it
# TODO it might be possible to use the latest block hashes from the state to
# do this more efficiently.. whatever!
# Time to replay all the blocks between then and now. We skip the one because
# it's the one that we found the state with, and it has already been
# applied
for i in countdown(ancestors.len - 2, 0):
let last = ancestors[i]
skipSlots(state.data, last.data.slot - 1) do(state: BeaconState):
pool.maybePutState(state)
let ok = updateState(state.data, last.data, {skipValidation})
doAssert ok,
"We only keep validated blocks in the database, should never fail"
state.blck = blck
state.root = ancestors[0].data.state_root
pool.maybePutState(state.data)
skipSlots(state.data, slot) do (state: BeaconState):
pool.maybePutState(state)
proc loadTailState*(pool: BlockPool): StateData =
## Load the state associated with the current tail in the pool
let stateRoot = pool.db.getBlock(pool.tail.root).get().state_root
StateData(
data: pool.db.getState(stateRoot).get(),
root: stateRoot,
blck: pool.tail
)
proc updateHead*(pool: BlockPool, state: var StateData, blck: BlockRef) =
## Update what we consider to be the current head, as given by the fork
## choice.
## The choice of head affects the choice of finalization point - the order
## of operations naturally becomes important here - after updating the head,
## blocks that were once considered potential candidates for a tree will
## now fall from grace, or no longer be considered resolved.
if pool.head == blck:
debug "No head update this time",
headBlockRoot = shortLog(blck.root),
headBlockSlot = humaneSlotNum(blck.slot)
return
let
lastHead = pool.head
pool.head = blck
# Start off by making sure we have the right state
updateState(pool, state, blck, blck.slot)
if lastHead != blck.parent:
notice "Updated head with new parent",
lastHeadRoot = shortLog(lastHead.root),
parentRoot = shortLog(blck.parent.root),
stateRoot = shortLog(state.root),
headBlockRoot = shortLog(state.blck.root),
stateSlot = humaneSlotNum(state.data.slot),
justifiedEpoch = humaneEpochNum(state.data.current_justified_epoch),
finalizedEpoch = humaneEpochNum(state.data.finalized_epoch)
else:
info "Updated head",
stateRoot = shortLog(state.root),
headBlockRoot = shortLog(state.blck.root),
stateSlot = humaneSlotNum(state.data.slot),
justifiedEpoch = humaneEpochNum(state.data.current_justified_epoch),
finalizedEpoch = humaneEpochNum(state.data.finalized_epoch)
let
# TODO there might not be a block at the epoch boundary - what then?
finalizedHead =
blck.findAncestorBySlot(state.data.finalized_epoch.get_epoch_start_slot())
doAssert (not finalizedHead.isNil),
"Block graph should always lead to a finalized block"
if finalizedHead != pool.finalizedHead:
info "Finalized block",
finalizedBlockRoot = shortLog(finalizedHead.root),
finalizedBlockSlot = humaneSlotNum(finalizedHead.slot),
headBlockRoot = shortLog(blck.root),
headBlockSlot = humaneSlotNum(blck.slot)
var cur = finalizedHead
while cur != pool.finalizedHead:
# Finalization means that we choose a single chain as the canonical one -
# it also means we're no longer interested in any branches from that chain
# up to the finalization point
# TODO technically, if we remove from children the gc should free the block
# because it should become orphaned, via mark&sweep if nothing else,
# though this needs verification
# TODO what about attestations? we need to drop those too, though they
# *should* be pretty harmless
# TODO remove from database as well.. here, or using some GC-like setup
# that periodically cleans it up?
for child in cur.parent.children:
if child != cur:
pool.blocks.del(child.root)
cur.parent.children = @[cur]
cur = cur.parent
pool.finalizedHead = finalizedHead
proc findLatestJustifiedBlock(
blck: BlockRef, depth: int, deepest: var tuple[depth: int, blck: BlockRef]) =
if blck.justified and depth > deepest.depth:
deepest = (depth, blck)
for child in blck.children:
findLatestJustifiedBlock(child, depth + 1, deepest)
proc latestJustifiedBlock*(pool: BlockPool): BlockRef =
## Return the most recent block that is justified and at least as recent
## as the latest finalized block
var deepest = (0, pool.finalizedHead)
findLatestJustifiedBlock(pool.finalizedHead, 0, deepest)
deepest[1]
proc latestState*(pool: BlockPool): BeaconState =
var b = pool.head
while true:
if b.isNil:
raise newException(Exception, "No state found")
if (let blk = pool.db.getBlock(b.root); blk.isSome()):
if (let state = pool.db.getState(blk.get().stateRoot); state.isSome()):
return state.get()
else:
error "Block from block pool not found in db", root = b.root
b = b.parent