nim-eth/eth/p2p/blockchain_sync.nim

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import
sets, options, random, hashes,
chronos, chronicles, eth/common/eth_types,
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private/p2p_types, rlpx, peer_pool, rlpx_protocols/eth_protocol,
../p2p
const
minPeersToStartSync* = 2 # Wait for consensus of at least this
# number of peers before syncing
type
SyncStatus* = enum
syncSuccess
syncNotEnoughPeers
syncTimeOut
WantedBlocksState = enum
Initial,
Requested,
Received,
Persisted
WantedBlocks = object
startIndex: BlockNumber
numBlocks: uint
state: WantedBlocksState
headers: seq[BlockHeader]
bodies: seq[BlockBody]
SyncContext = ref object
workQueue: seq[WantedBlocks]
endBlockNumber: BlockNumber
finalizedBlock: BlockNumber # Block which was downloaded and verified
chain: AbstractChainDB
peerPool: PeerPool
trustedPeers: HashSet[Peer]
hasOutOfOrderBlocks: bool
proc hash*(p: Peer): Hash {.inline.} = hash(cast[pointer](p))
proc endIndex(b: WantedBlocks): BlockNumber =
result = b.startIndex
result += (b.numBlocks - 1).toBlockNumber
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proc availableWorkItem(ctx: SyncContext): int =
var maxPendingBlock = ctx.finalizedBlock
trace "queue len", length = ctx.workQueue.len
result = -1
for i in 0 .. ctx.workQueue.high:
case ctx.workQueue[i].state
of Initial:
return i
of Persisted:
result = i
else:
discard
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let endBlock = ctx.workQueue[i].endIndex
if endBlock > maxPendingBlock:
maxPendingBlock = endBlock
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let nextRequestedBlock = maxPendingBlock + 1
if nextRequestedBlock >= ctx.endBlockNumber:
return -1
if result == -1:
result = ctx.workQueue.len
ctx.workQueue.setLen(result + 1)
var numBlocks = (ctx.endBlockNumber - nextRequestedBlock).toInt
if numBlocks > maxHeadersFetch:
numBlocks = maxHeadersFetch
ctx.workQueue[result] = WantedBlocks(startIndex: nextRequestedBlock, numBlocks: numBlocks.uint, state: Initial)
proc persistWorkItem(ctx: SyncContext, wi: var WantedBlocks) =
case ctx.chain.persistBlocks(wi.headers, wi.bodies)
of ValidationResult.OK:
ctx.finalizedBlock = wi.endIndex
wi.state = Persisted
of ValidationResult.Error:
wi.state = Initial
# successful or not, we're done with these blocks
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wi.headers = @[]
wi.bodies = @[]
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proc persistPendingWorkItems(ctx: SyncContext) =
var nextStartIndex = ctx.finalizedBlock + 1
var keepRunning = true
var hasOutOfOrderBlocks = false
trace "Looking for out of order blocks"
while keepRunning:
keepRunning = false
hasOutOfOrderBlocks = false
for i in 0 ..< ctx.workQueue.len:
let start = ctx.workQueue[i].startIndex
if ctx.workQueue[i].state == Received:
if start == nextStartIndex:
trace "Persisting pending work item", start
ctx.persistWorkItem(ctx.workQueue[i])
nextStartIndex = ctx.finalizedBlock + 1
keepRunning = true
break
else:
hasOutOfOrderBlocks = true
ctx.hasOutOfOrderBlocks = hasOutOfOrderBlocks
proc returnWorkItem(ctx: SyncContext, workItem: int): ValidationResult =
let wi = addr ctx.workQueue[workItem]
let askedBlocks = wi.numBlocks.int
let receivedBlocks = wi.headers.len
let start = wi.startIndex
if askedBlocks == receivedBlocks:
trace "Work item complete",
start,
askedBlocks,
receivedBlocks
if wi.startIndex != ctx.finalizedBlock + 1:
trace "Blocks out of order", start, final = ctx.finalizedBlock
ctx.hasOutOfOrderBlocks = true
if ctx.hasOutOfOrderBlocks:
ctx.persistPendingWorkItems()
else:
ctx.persistWorkItem(wi[])
else:
trace "Work item complete but we got fewer blocks than requested, so we're ditching the whole thing.",
start,
askedBlocks,
receivedBlocks
return ValidationResult.Error
proc newSyncContext(chain: AbstractChainDB, peerPool: PeerPool): SyncContext =
new result
result.chain = chain
result.peerPool = peerPool
result.trustedPeers = initSet[Peer]()
result.finalizedBlock = chain.getBestBlockHeader().blockNumber
proc handleLostPeer(ctx: SyncContext) =
# TODO: ask the PeerPool for new connections and then call
# `obtainBlocksFromPeer`
discard
proc getBestBlockNumber(p: Peer): Future[BlockNumber] {.async.} =
let request = BlocksRequest(
startBlock: HashOrNum(isHash: true,
hash: p.state(eth).bestBlockHash),
maxResults: 1,
skip: 0,
reverse: true)
let latestBlock = await p.getBlockHeaders(request)
if latestBlock.isSome and latestBlock.get.headers.len > 0:
result = latestBlock.get.headers[0].blockNumber
proc obtainBlocksFromPeer(syncCtx: SyncContext, peer: Peer) {.async.} =
# Update our best block number
try:
let bestBlockNumber = await peer.getBestBlockNumber()
if bestBlockNumber > syncCtx.endBlockNumber:
trace "New sync end block number", number = bestBlockNumber
syncCtx.endBlockNumber = bestBlockNumber
except TransportError:
debug "Transport got closed during obtainBlocksFromPeer"
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except CatchableError:
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debug "Exception in getBestBlockNumber()",
exc = getCurrentException().name,
err = getCurrentExceptionMsg()
# no need to exit here, because the context might still have blocks to fetch
# from this peer
while (let workItemIdx = syncCtx.availableWorkItem(); workItemIdx != -1 and
peer.connectionState notin {Disconnecting, Disconnected}):
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template workItem: auto = syncCtx.workQueue[workItemIdx]
workItem.state = Requested
trace "Requesting block headers", start = workItem.startIndex, count = workItem.numBlocks, peer
let request = BlocksRequest(
startBlock: HashOrNum(isHash: false, number: workItem.startIndex),
maxResults: workItem.numBlocks,
skip: 0,
reverse: false)
var dataReceived = false
try:
let results = await peer.getBlockHeaders(request)
if results.isSome:
shallowCopy(workItem.headers, results.get.headers)
var bodies = newSeq[BlockBody]()
var hashes = newSeq[KeccakHash]()
var nextIndex = workItem.startIndex
for i in workItem.headers:
if i.blockNumber != nextIndex:
raise newException(CatchableError, "The block numbers are not in sequence. Not processing this workItem.")
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else:
nextIndex = nextIndex + 1
hashes.add(blockHash(i))
if hashes.len == maxBodiesFetch:
let b = await peer.getBlockBodies(hashes)
if b.isNone:
raise newException(CatchableError, "Was not able to get the block bodies.")
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hashes.setLen(0)
bodies.add(b.get.blocks)
if hashes.len != 0:
let b = await peer.getBlockBodies(hashes)
if b.isNone:
raise newException(CatchableError, "Was not able to get the block bodies.")
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bodies.add(b.get.blocks)
if bodies.len == workItem.headers.len:
shallowCopy(workItem.bodies, bodies)
dataReceived = true
else:
warn "Bodies len != headers.len", bodies = bodies.len, headers = workItem.headers.len
except TransportError:
debug "Transport got closed during obtainBlocksFromPeer"
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except CatchableError:
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# the success case sets `dataReceived`, so we can just fall back to the
# failure path below. If we signal time-outs with exceptions such
# failures will be easier to handle.
debug "Exception in obtainBlocksFromPeer()",
exc = getCurrentException().name,
err = getCurrentExceptionMsg()
var giveUpOnPeer = false
if dataReceived:
workItem.state = Received
if syncCtx.returnWorkItem(workItemIdx) != ValidationResult.OK:
giveUpOnPeer = true
else:
giveUpOnPeer = true
if giveUpOnPeer:
workItem.state = Initial
try:
await peer.disconnect(SubprotocolReason)
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except CatchableError:
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discard
syncCtx.handleLostPeer()
break
trace "Finished obtaining blocks", peer
proc peersAgreeOnChain(a, b: Peer): Future[bool] {.async.} =
# Returns true if one of the peers acknowledges existence of the best block
# of another peer.
var
a = a
b = b
if a.state(eth).bestDifficulty < b.state(eth).bestDifficulty:
swap(a, b)
let request = BlocksRequest(
startBlock: HashOrNum(isHash: true,
hash: b.state(eth).bestBlockHash),
maxResults: 1,
skip: 0,
reverse: true)
let latestBlock = await a.getBlockHeaders(request)
result = latestBlock.isSome and latestBlock.get.headers.len > 0
proc randomTrustedPeer(ctx: SyncContext): Peer =
var k = rand(ctx.trustedPeers.len - 1)
var i = 0
for p in ctx.trustedPeers:
result = p
if i == k: return
inc i
proc startSyncWithPeer(ctx: SyncContext, peer: Peer) {.async.} =
trace "start sync", peer, trustedPeers = ctx.trustedPeers.len
if ctx.trustedPeers.len >= minPeersToStartSync:
# We have enough trusted peers. Validate new peer against trusted
if await peersAgreeOnChain(peer, ctx.randomTrustedPeer()):
ctx.trustedPeers.incl(peer)
asyncCheck ctx.obtainBlocksFromPeer(peer)
elif ctx.trustedPeers.len == 0:
# Assume the peer is trusted, but don't start sync until we reevaluate
# it with more peers
trace "Assume trusted peer", peer
ctx.trustedPeers.incl(peer)
else:
# At this point we have some "trusted" candidates, but they are not
# "trusted" enough. We evaluate `peer` against all other candidates.
# If one of the candidates disagrees, we swap it for `peer`. If all
# candidates agree, we add `peer` to trusted set. The peers in the set
# will become "fully trusted" (and sync will start) when the set is big
# enough
var
agreeScore = 0
disagreedPeer: Peer
for tp in ctx.trustedPeers:
if await peersAgreeOnChain(peer, tp):
inc agreeScore
else:
disagreedPeer = tp
let disagreeScore = ctx.trustedPeers.len - agreeScore
if agreeScore == ctx.trustedPeers.len:
ctx.trustedPeers.incl(peer) # The best possible outcome
elif disagreeScore == 1:
trace "Peer is no longer trusted for sync", peer
ctx.trustedPeers.excl(disagreedPeer)
ctx.trustedPeers.incl(peer)
else:
trace "Peer not trusted for sync", peer
if ctx.trustedPeers.len == minPeersToStartSync:
for p in ctx.trustedPeers:
asyncCheck ctx.obtainBlocksFromPeer(p)
proc onPeerConnected(ctx: SyncContext, peer: Peer) =
trace "New candidate for sync", peer
try:
let f = ctx.startSyncWithPeer(peer)
f.callback = proc(data: pointer) {.gcsafe.} =
if f.failed:
if f.error of TransportError:
debug "Transport got closed during startSyncWithPeer"
else:
error "startSyncWithPeer failed", msg = f.readError.msg, peer
except TransportError:
debug "Transport got closed during startSyncWithPeer"
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except CatchableError:
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debug "Exception in startSyncWithPeer()",
exc = getCurrentException().name,
err = getCurrentExceptionMsg()
proc onPeerDisconnected(ctx: SyncContext, p: Peer) =
trace "peer disconnected ", peer = p
ctx.trustedPeers.excl(p)
proc startSync(ctx: SyncContext) =
var po: PeerObserver
po.onPeerConnected = proc(p: Peer) {.gcsafe.} =
ctx.onPeerConnected(p)
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po.onPeerDisconnected = proc(p: Peer) {.gcsafe.} =
ctx.onPeerDisconnected(p)
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po.setProtocol eth
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ctx.peerPool.addObserver(ctx, po)
proc findBestPeer(node: EthereumNode): (Peer, DifficultyInt) =
var
bestBlockDifficulty: DifficultyInt = 0.stuint(256)
bestPeer: Peer = nil
for peer in node.peers(eth):
let peerEthState = peer.state(eth)
if peerEthState.initialized:
if peerEthState.bestDifficulty > bestBlockDifficulty:
bestBlockDifficulty = peerEthState.bestDifficulty
bestPeer = peer
result = (bestPeer, bestBlockDifficulty)
proc fastBlockchainSync*(node: EthereumNode): Future[SyncStatus] {.async.} =
## Code for the fast blockchain sync procedure:
## https://github.com/ethereum/wiki/wiki/Parallel-Block-Downloads
## https://github.com/ethereum/go-ethereum/pull/1889
# TODO: This needs a better interface. Consider removing this function and
# exposing SyncCtx
var syncCtx = newSyncContext(node.chain, node.peerPool)
syncCtx.startSync()