Add simple block cache. Handle numeric params (#1241)

* Add simple block cache. Handle numeric params

lc_proxy/block_cache.nim

@@ -0,0 +1,62 @@
+# light client proxy
+# Copyright (c) 2022 Status Research & Development GmbH
+# Licensed and distributed under either of
+#   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
+#   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
+# at your option. This file may not be copied, modified, or distributed except according to those terms.
+
+{.push raises: [Defect].}
+
+import
+  std/tables,
+  web3/ethtypes,
+  stew/[results, keyed_queue]
+
+
+## payloads received through block gossip (and validated by light client).
+## Payloads are stored in order of arrival. When cache is full the oldest
+## payload is deleted first.
+type BlockCache* = ref object
+  max: int
+  blocks: KeyedQueue[BlockHash, ExecutionPayloadV1]
+
+proc `==`(x, y: Quantity): bool {.borrow, noSideEffect.}
+
+proc new*(T: type BlockCache, max: uint32): T =
+  let maxAsInt = int(max)
+  return BlockCache(
+    max: maxAsInt,
+    blocks: KeyedQueue[BlockHash, ExecutionPayloadV1].init(maxAsInt)
+  )
+
+func len*(self: BlockCache): int =
+  return len(self.blocks)
+
+func isEmpty*(self: BlockCache): bool =
+  return len(self.blocks) == 0
+
+proc add*(self: BlockCache, payload: ExecutionPayloadV1) =
+  if self.blocks.hasKey(payload.blockHash):
+    return
+
+  if len(self.blocks) >= self.max:
+   discard self.blocks.shift()
+
+  discard self.blocks.append(payload.blockHash, payload)
+
+proc latest*(self: BlockCache): results.Opt[ExecutionPayloadV1] =
+  let latestPair = ? self.blocks.last()
+  return Opt.some(latestPair.data)
+
+proc getByNumber*(
+    self: BlockCache,
+    number: Quantity): Opt[ExecutionPayloadV1] =
+
+  var payloadResult: Opt[ExecutionPayloadV1]
+
+  for payload in self.blocks.prevValues:
+    if payload.blockNumber == number:
+      payloadResult = Opt.some(payload)
+      break
+
+  return payloadResult

lc_proxy/lc_proxy.nim

@@ -23,7 +23,8 @@ import
   beacon_chain/[light_client, nimbus_binary_common, version],
   ../nimbus/rpc/cors,
   ./rpc/rpc_eth_lc_api,
-  ./lc_proxy_conf
+  ./lc_proxy_conf,
+  ./block_cache
 
 from beacon_chain/gossip_processing/block_processor import newExecutionPayload
 from beacon_chain/gossip_processing/eth2_processor import toValidationResult
@@ -94,6 +95,8 @@ proc run() {.raises: [Exception, Defect].} =
       forkDigests, getBeaconTime, genesis_validators_root
     )
 
+    blockCache = BlockCache.new(uint32(64))
+
     # TODO: for now we serve all cross origin requests
     authHooks = @[httpCors(@[])]
 
@@ -105,7 +108,7 @@ proc run() {.raises: [Exception, Defect].} =
       authHooks
     )
 
-    lcProxy = LightClientRpcProxy.new(rpcProxy, chainId)
+    lcProxy = LightClientRpcProxy.new(rpcProxy, blockCache, chainId)
 
     optimisticHandler = proc(signedBlock: ForkedMsgTrustedSignedBeaconBlock):
         Future[void] {.async.} =
@@ -116,7 +119,7 @@ proc run() {.raises: [Exception, Defect].} =
         when stateFork >= BeaconStateFork.Bellatrix:
           if blck.message.is_execution_block:
             template payload(): auto = blck.message.body.execution_payload
-            lcProxy.executionPayload.ok payload.asEngineExecutionPayload()
+            blockCache.add(payload.asEngineExecutionPayload())
         else: discard
       return
 

lc_proxy/rpc/rpc_eth_lc_api.nim

@@ -8,8 +8,9 @@
 {.push raises: [Defect].}
 
 import
+  std/strutils,
   stint,
-  stew/byteutils,
+  stew/[byteutils, results],
   chronicles,
   json_rpc/[rpcproxy, rpcserver, rpcclient],
   web3,
@@ -17,7 +18,8 @@ import
   beacon_chain/eth1/eth1_monitor,
   beacon_chain/networking/network_metadata,
   beacon_chain/spec/forks,
-  ../validate_proof
+  ../validate_proof,
+  ../block_cache
 
 export forks
 
@@ -35,26 +37,79 @@ template encodeHexData(value: UInt256): HexDataStr =
 template encodeQuantity(value: Quantity): HexQuantityStr =
   hexQuantityStr(encodeQuantity(value.uint64))
 
-type LightClientRpcProxy* = ref object
-  proxy: RpcProxy
-  executionPayload*: Opt[ExecutionPayloadV1]
-  chainId: Quantity
+type
+  LightClientRpcProxy* = ref object
+    proxy: RpcProxy
+    blockCache: BlockCache
+    chainId: Quantity
 
-template checkPreconditions(payload: Opt[ExecutionPayloadV1], quantityTag: string) =
-  if payload.isNone():
+  QuantityTagKind = enum
+    LatestBlock, BlockNumber
+
+  QuantityTag = object
+    case kind: QuantityTagKind
+    of LatestBlock:
+      discard
+    of BlockNumber:
+      blockNumber: Quantity
+
+func parseHexIntResult(tag: string): Result[uint64, string] =
+  try:
+    ok(parseHexInt(tag).uint64)
+  except ValueError as e:
+    err(e.msg)
+
+func parseHexQuantity(tag: string): Result[Quantity, string] =
+  let hexQuantity = hexQuantityStr(tag)
+  if validate(hexQuantity):
+    let parsed = ? parseHexIntResult(tag)
+    return ok(Quantity(parsed))
+  else:
+    return err("Invalid Etheruem Hex quantity.")
+
+func parseQuantityTag(blockTag: string): Result[QuantityTag, string] =
+  let tag = blockTag.toLowerAscii
+  case tag
+  of "latest":
+    return ok(QuantityTag(kind: LatestBlock))
+  else:
+    let quantity = ? parseHexQuantity(tag)
+    return ok(QuantityTag(kind: BlockNumber, blockNumber: quantity))
+
+template checkPreconditions(proxy: LightClientRpcProxy) =
+  if proxy.blockCache.isEmpty():
     raise newException(ValueError, "Syncing")
 
-  if quantityTag != "latest":
-    # TODO: for now we support only latest block, as its semantically most straight
-    # forward, i.e it is last received and a valid ExecutionPayloadV1.
-    # Ultimately we could keep track of n last valid payloads and support number
-    # queries for this set of blocks.
-    # `Pending` could be mapped to some optimistic header with the block
-    # fetched on demand.
-    raise newException(ValueError, "Only latest block is supported")
-
 template rpcClient(lcProxy: LightClientRpcProxy): RpcClient = lcProxy.proxy.getClient()
 
+proc getPayloadByTag(
+    proxy: LightClientRpcProxy,
+    quantityTag: string): ExecutionPayloadV1 {.raises: [ValueError, Defect].} =
+  checkPreconditions(proxy)
+
+  let tagResult = parseQuantityTag(quantityTag)
+
+  if tagResult.isErr:
+    raise newException(ValueError, tagResult.error)
+
+  let tag = tagResult.get()
+
+  var payload: ExecutionPayloadV1
+
+  case tag.kind
+  of LatestBlock:
+    # this will always be ok as we always validate that cache is not empty
+    payload = proxy.blockCache.latest.get
+  of BlockNumber:
+    let payLoadResult = proxy.blockCache.getByNumber(tag.blockNumber)
+    if payLoadResult.isErr():
+      raise newException(
+        ValueError, "Block not stored in cache " & $tag.blockNumber
+      )
+    payload = payLoadResult.get
+
+  return payload
+
 proc installEthApiHandlers*(lcProxy: LightClientRpcProxy) =
   template payload(): Opt[ExecutionPayloadV1] = lcProxy.executionPayload
 
@@ -63,21 +118,17 @@ proc installEthApiHandlers*(lcProxy: LightClientRpcProxy) =
 
   lcProxy.proxy.rpc("eth_blockNumber") do() -> HexQuantityStr:
     ## Returns the number of most recent block.
-    if payload.isNone:
-      raise newException(ValueError, "Syncing")
+    checkPreconditions(lcProxy)
 
-    return encodeQuantity(payload.get.blockNumber)
+    return encodeQuantity(lcProxy.blockCache.latest.get.blockNumber)
 
-  # TODO quantity tag should be better typed
   lcProxy.proxy.rpc("eth_getBalance") do(address: Address, quantityTag: string) -> HexQuantityStr:
-    checkPreconditions(payload, quantityTag)
-
     # When requesting state for `latest` block number, we need to translate
     # `latest` to actual block number as `latest` on proxy and on data provider
     # can mean different blocks and ultimatly piece received piece of state
     # must by validated against correct state root
     let
-      executionPayload = payload.get
+      executionPayload = lcProxy.getPayloadByTag(quantityTag)
       blockNumber = executionPayload.blockNumber.uint64
 
     info "Forwarding get_Balance", executionBn = blockNumber
@@ -100,10 +151,8 @@ proc installEthApiHandlers*(lcProxy: LightClientRpcProxy) =
       raise newException(ValueError, accountResult.error)
 
   lcProxy.proxy.rpc("eth_getStorageAt") do(address: Address, slot: HexDataStr, quantityTag: string) -> HexDataStr:
-    checkPreconditions(payload, quantityTag)
-
     let
-      executionPayload = payload.get
+      executionPayload = lcProxy.getPayloadByTag(quantityTag)
       uslot = UInt256.fromHex(slot.string)
       blockNumber = executionPayload.blockNumber.uint64
 
@@ -132,10 +181,12 @@ proc installEthApiHandlers*(lcProxy: LightClientRpcProxy) =
 proc new*(
     T: type LightClientRpcProxy,
     proxy: RpcProxy,
+    blockCache: BlockCache,
     chainId: Quantity): T =
 
   return LightClientRpcProxy(
     proxy: proxy,
+    blockCache: blockCache,
     chainId: chainId
   )