Add eth_chainId endpoint to light client proxy (#1232)

* Add eth_chainId endpoint

lc_proxy/lc_proxy.nim

@@ -39,6 +39,20 @@ proc initRpcClient(config: LcProxyConf): Future[RpcClient] {.async.} =
     await httpClient.connect(config.web3ClientConfig.url)
     return httpClient
 
+func getConfiguredChainId(networkMetadata: Eth2NetworkMetadata): Quantity =
+  if networkMetadata.eth1Network.isSome():
+    let
+      net = networkMetadata.eth1Network.get()
+      chainId = case net
+        of mainnet: 1.Quantity
+        of ropsten: 3.Quantity
+        of rinkeby: 4.Quantity
+        of goerli:  5.Quantity
+        of sepolia: 11155111.Quantity
+    return chainId
+  else:
+    return networkMetadata.cfg.DEPOSIT_CHAIN_ID.Quantity
+
 # TODO Find what can throw exception
 proc run() {.raises: [Exception, Defect].} =
   {.pop.}
@@ -54,7 +68,9 @@ proc run() {.raises: [Exception, Defect].} =
   notice "Launching light client proxy",
     version = fullVersionStr, cmdParams = commandLineParams(), config
 
-  let metadata = loadEth2Network(config.eth2Network)
+  let
+    metadata = loadEth2Network(config.eth2Network)
+    chainId = getConfiguredChainId(metadata)
 
   for node in metadata.bootstrapNodes:
     lcConfig.bootstrapNodes.add node
@@ -95,7 +111,7 @@ proc run() {.raises: [Exception, Defect].} =
       [initTAddress(config.rpcAddress, config.rpcPort)]
     )
 
-    lcProxy = LightClientRpcProxy(server: rpcHttpServer, client: rpcClient)
+    lcProxy = LightClientRpcProxy.new(rpcHttpServer, rpcClient, chainId)
 
     optimisticHandler = proc(signedBlock: ForkedMsgTrustedSignedBeaconBlock):
         Future[void] {.async.} =
@@ -140,7 +156,8 @@ proc run() {.raises: [Exception, Defect].} =
 
   waitFor network.startListening()
   waitFor network.start()
-  lcProxy.server.start()
+  rpcHttpServer.start()
+  waitFor lcProxy.verifyChaindId()
 
   proc onFinalizedHeader(
       lightClient: LightClient, finalizedHeader: BeaconBlockHeader) =

lc_proxy/rpc/rpc_eth_lc_api.nim

@@ -13,8 +13,9 @@ import
   chronicles,
   json_rpc/[rpcserver, rpcclient],
   web3,
-  web3/ethhexstrings,
+  web3/[ethhexstrings, ethtypes],
   beacon_chain/eth1/eth1_monitor,
+  beacon_chain/networking/network_metadata,
   beacon_chain/spec/forks,
   ../validate_proof
 
@@ -23,10 +24,11 @@ export forks
 logScope:
   topics = "light_proxy"
 
+proc `==`(x, y: Quantity): bool {.borrow, noSideEffect.}
+
 template encodeQuantity(value: UInt256): HexQuantityStr =
   hexQuantityStr("0x" & value.toHex())
 
-
 template encodeHexData(value: UInt256): HexDataStr =
   hexDataStr("0x" & toBytesBE(value).toHex)
 
@@ -35,9 +37,9 @@ template encodeQuantity(value: Quantity): HexQuantityStr =
 
 type LightClientRpcProxy* = ref object
   client*: RpcClient
-  server*: RpcHttpServer
+  server*: RpcServer
   executionPayload*: Opt[ExecutionPayloadV1]
-
+  chainId: Quantity
 
 template checkPreconditions(payload: Opt[ExecutionPayloadV1], quantityTag: string) =
   if payload.isNone():
@@ -55,6 +57,9 @@ template checkPreconditions(payload: Opt[ExecutionPayloadV1], quantityTag: strin
 proc installEthApiHandlers*(lcProxy: LightClientRpcProxy) =
   template payload(): Opt[ExecutionPayloadV1] = lcProxy.executionPayload
 
+  lcProxy.server.rpc("eth_chainId") do() -> HexQuantityStr:
+    return encodeQuantity(lcProxy.chainId)
+
   lcProxy.server.rpc("eth_blockNumber") do() -> HexQuantityStr:
     ## Returns the number of most recent block.
     if payload.isNone:
@@ -112,3 +117,37 @@ proc installEthApiHandlers*(lcProxy: LightClientRpcProxy) =
       return encodeHexData(slotValue)
     else:
       raise newException(ValueError, dataResult.error)
+
+proc new*(
+    T: type LightClientRpcProxy,
+    server: RpcServer,
+    client: RpcClient,
+    chainId: Quantity): T =
+
+  return LightClientRpcProxy(
+    client: client,
+    server: server,
+    chainId: chainId
+  )
+
+proc verifyChaindId*(p: LightClientRpcProxy): Future[void] {.async.} =
+  let localId = p.chainId
+
+  # retry 2 times, if the data provider will fail despite re-tries, propagate
+  # exception to the caller.
+  let providerId = awaitWithRetries(
+    p.client.eth_chainId(),
+    retries = 2,
+    timeout = seconds(30)
+  )
+
+  # this configuration error, in theory we could allow proxy to chung on, but
+  # it would only mislead the user. It is better to fail fast here.
+  if localId != providerId:
+    fatal "The specified data provider serves data for a different chain",
+      expectedChain = distinctBase(localId),
+      providerChain = distinctBase(providerId)
+    quit 1
+
+  return
+