RPC: Move EVM-calling function estimateGas to rpcEstimateGas

`estimateGas` used by JSON-RPC is another way to setup and call the EVM,
also used by GraphQL.  Move it to `transaction/call_evm`.

This function has too much direct knowledge of details that shouldn't be used
outside transaction handling code, details we need to change when changing the
db and transaction memory layer.

Moving this one exposed quite a bit of abstraction leakage, as it calls
directly to the hexary trie db around `processTransaction`.

It looks like the _intended_ functionality of `estimateGas` is similar to
`rpcDoCall` with the only real difference being to not store the final state.
It looks like the extra stuff in `estimateGas` compared with `doCall` is a
messy workaround for computation not exposing the right API ("don't save final
state") for RPC to use.

Signed-off-by: Jamie Lokier <jamie@shareable.org>

nimbus/graphql/ethapi.nim

@@ -778,7 +778,7 @@ proc blockEstimateGas(ud: RootRef, params: Args, parent: Node): RespResult {.api
   let param = params[0].val
   try:
     let (callData, gasLimit) = toCallData(param)
-    let gasUsed = estimateGas(callData, h.header, ctx.chainDB, gasLimit)
+    let gasUsed = rpcEstimateGas(callData, h.header, ctx.chainDB, gasLimit)
     longNode(gasUsed)
   except Exception as em:
     err("estimateGas error: " & em.msg)

nimbus/rpc/p2p.nim

@@ -275,7 +275,7 @@ proc setupEthRpc*(node: EthereumNode, chain: BaseChainDB , server: RpcServer) =
     let
       header   = chain.headerFromTag(quantityTag)
       callData = callData(call, false, chain)
-      gasUsed  = estimateGas(callData, header, chain, call.gas.isSome)
+      gasUsed  = rpcEstimateGas(callData, header, chain, call.gas.isSome)
     result = encodeQuantity(gasUsed.uint64)
 
   server.rpc("eth_getBlockByHash") do(data: EthHashStr, fullTransactions: bool) -> Option[BlockObject]:

nimbus/rpc/rpc_utils.nim

@@ -180,28 +180,6 @@ proc callData*(call: EthCall, callMode: bool = true, chain: BaseChainDB): RpcCal
   if call.data.isSome:
     result.data = hexToSeqByte(call.data.get.string)
 
-proc estimateGas*(call: RpcCallData, header: BlockHeader, chain: BaseChainDB, haveGasLimit: bool): GasInt =
-  var
-    # we use current header stateRoot, unlike block validation
-    # which use previous block stateRoot
-    vmState = newBaseVMState(header.stateRoot, header, chain)
-    fork    = toFork(chain.config, header.blockNumber)
-    tx      = Transaction(
-      accountNonce: vmState.accountdb.getNonce(call.source),
-      gasPrice: call.gasPrice,
-      gasLimit: if haveGasLimit: call.gas else: header.gasLimit - vmState.cumulativeGasUsed,
-      to      : call.to,
-      value   : call.value,
-      payload : call.data,
-      isContractCreation:  call.contractCreation
-    )
-
-  var dbTx = chain.db.beginTransaction()
-  defer: dbTx.dispose()
-  result = processTransaction(tx, call.source, vmState, fork)
-  dbTx.dispose()
-  # TODO: handle revert and error
-
 proc populateTransactionObject*(tx: Transaction, header: BlockHeader, txIndex: int): TransactionObject =
   result.blockHash = some(header.hash)
   result.blockNumber = some(encodeQuantity(header.blockNumber))

nimbus/transaction/call_evm.nim

@@ -9,7 +9,8 @@
 import
   eth/common/eth_types, stint, options,
   ".."/[vm_types, vm_types2, vm_state, vm_computation],
-  ".."/[db/db_chain, config, vm_state_transactions, rpc/hexstrings]
+  ".."/[db/db_chain, config, vm_state_transactions, rpc/hexstrings],
+  ".."/[db/accounts_cache, p2p/executor], eth/trie/db
 
 type
   RpcCallData* = object
@@ -53,3 +54,25 @@ proc rpcDoCall*(call: RpcCallData, header: BlockHeader, chain: BaseChainDB): Hex
 
   comp.execComputation()
   result = hexDataStr(comp.output)
+
+proc rpcEstimateGas*(call: RpcCallData, header: BlockHeader, chain: BaseChainDB, haveGasLimit: bool): GasInt =
+  # TODO: handle revert and error
+  var
+    # we use current header stateRoot, unlike block validation
+    # which use previous block stateRoot
+    vmState = newBaseVMState(header.stateRoot, header, chain)
+    fork    = toFork(chain.config, header.blockNumber)
+    tx      = Transaction(
+      accountNonce: vmState.accountdb.getNonce(call.source),
+      gasPrice: call.gasPrice,
+      gasLimit: if haveGasLimit: call.gas else: header.gasLimit - vmState.cumulativeGasUsed,
+      to      : call.to,
+      value   : call.value,
+      payload : call.data,
+      isContractCreation:  call.contractCreation
+    )
+
+  var dbTx = chain.db.beginTransaction()
+  defer: dbTx.dispose()
+  result = processTransaction(tx, call.source, vmState, fork)
+  dbTx.dispose()