RPC: Gather EVM-calling functions to one place; rpcSetupComputation

Start gathering the functions that call the EVM into one place,
`transaction/call_evm.nim`.

This is first of a series of changes to gather all ways the EVM is called to
one place.  Duplicate, slightly different setup functions have accumulated over
time, each with some knowledge of EVM internals.  When they are brought
together, these methods will be changed to use a single entry point to the EVM,
allowing the entry point to be refactored, EVMC to be completed, and async
concurrency to be implemented on top.  This also simplifies the callers.

First, a helper function used by RPC and GraphQL to make EVM calls without
permanently modifying the account state.  `setupComputation` ->
`rpcSetupComputation`.

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

nimbus/graphql/ethapi.nim

@@ -15,7 +15,8 @@ import
   graphql/common/types, graphql/httpserver,
   ../db/[db_chain, state_db], ../errors, ../utils,
   ../transaction, ../rpc/rpc_utils, ../vm_state, ../config,
-  ../vm_computation, ../vm_state_transactions
+  ../vm_computation, ../vm_state_transactions,
+  ../transaction/call_evm
 
 from eth/p2p import EthereumNode
 export httpserver
@@ -716,9 +717,9 @@ proc blockAccount(ud: RootRef, params: Args, parent: Node): RespResult {.apiPrag
   let address = hexToByteArray[20](params[0].val.stringVal)
   ctx.accountNode(h.header, address)
 
-proc toCallData(n: Node): (CallData, bool) =
+proc toCallData(n: Node): (RpcCallData, bool) =
   # phew, probably need to use macro here :)
-  var cd: CallData
+  var cd: RpcCallData
   var gasLimit = false
   if n[0][1].kind != nkEmpty:
     cd.source = hextoByteArray[20](n[0][1].stringVal)
@@ -744,14 +745,14 @@ proc toCallData(n: Node): (CallData, bool) =
 
   (cd, gasLimit)
 
-proc makeCall(ctx: GraphqlContextRef, callData: CallData, header: BlockHeader, chainDB: BaseChainDB): RespResult =
+proc makeCall(ctx: GraphqlContextRef, callData: RpcCallData, header: BlockHeader, chainDB: BaseChainDB): RespResult =
   # TODO: handle revert
   var
     # we use current header stateRoot, unlike block validation
     # which use previous block stateRoot
     vmState = newBaseVMState(header.stateRoot, header, chainDB)
     fork    = toFork(chainDB.config, header.blockNumber)
-    comp    = setupComputation(vmState, callData, fork)
+    comp    = rpcSetupComputation(vmState, callData, fork)
 
   let gas = comp.gasMeter.gasRemaining
   comp.execComputation()

nimbus/rpc/rpc_utils.nim

@@ -11,7 +11,8 @@ import hexstrings, eth/[common, rlp, keys, trie/db], stew/byteutils, nimcrypto,
   ../db/[db_chain, accounts_cache], strutils, algorithm, options, times, json,
   ../constants, stint, hexstrings, rpc_types, ../config,
   ../vm_state_transactions, ../vm_state, ../vm_types, ../vm_types2,
-  ../vm_computation, ../p2p/executor, ../utils, ../transaction
+  ../vm_computation, ../p2p/executor, ../utils, ../transaction,
+  ../transaction/call_evm
 
 type
   UnsignedTx* = object
@@ -23,15 +24,6 @@ type
     payload* : Blob
     contractCreation* {.rlpIgnore.}: bool
 
-  CallData* = object
-    source*: EthAddress
-    to*: EthAddress
-    gas*: GasInt
-    gasPrice*: GasInt
-    value*: UInt256
-    data*: seq[byte]
-    contractCreation*: bool
-
 proc read(rlp: var Rlp, t: var UnsignedTx, _: type EthAddress): EthAddress {.inline.} =
   if rlp.blobLen != 0:
     result = rlp.read(EthAddress)
@@ -161,7 +153,7 @@ proc signTransaction*(tx: UnsignedTx, chain: BaseChainDB, privateKey: PrivateKey
     S: Uint256.fromBytesBE(sig[32..63])
     )
 
-proc callData*(call: EthCall, callMode: bool = true, chain: BaseChainDB): CallData =
+proc callData*(call: EthCall, callMode: bool = true, chain: BaseChainDB): RpcCallData =
   if call.source.isSome:
     result.source = toAddress(call.source.get)
 
@@ -188,40 +180,20 @@ proc callData*(call: EthCall, callMode: bool = true, chain: BaseChainDB): CallDa
   if call.data.isSome:
     result.data = hexToSeqByte(call.data.get.string)
 
-proc setupComputation*(vmState: BaseVMState, call: CallData, fork: Fork) : Computation =
-  vmState.setupTxContext(
-    origin = call.source,
-    gasPrice = call.gasPrice,
-    forkOverride = some(fork)
-  )
-
-  let msg = Message(
-    kind: evmcCall,
-    depth: 0,
-    gas: call.gas,
-    sender: call.source,
-    contractAddress: call.to,
-    codeAddress: call.to,
-    value: call.value,
-    data: call.data
-    )
-
-  result = newComputation(vmState, msg)
-
-proc doCall*(call: CallData, header: BlockHeader, chain: BaseChainDB): HexDataStr =
+proc doCall*(call: RpcCallData, header: BlockHeader, chain: BaseChainDB): HexDataStr =
   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)
-    comp    = setupComputation(vmState, call, fork)
+    comp    = rpcSetupComputation(vmState, call, fork)
 
   comp.execComputation()
   result = hexDataStr(comp.output)
   # TODO: handle revert and error
   # TODO: handle contract ABI
 
-proc estimateGas*(call: CallData, header: BlockHeader, chain: BaseChainDB, haveGasLimit: bool): GasInt =
+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

nimbus/transaction/call_evm.nim

@@ -0,0 +1,41 @@
+# Nimbus - Various ways of calling the EVM
+#
+# Copyright (c) 2018-2021 Status Research & Development GmbH
+# Licensed under either of
+#  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
+#  * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
+# at your option. This file may not be copied, modified, or distributed except according to those terms.
+
+import
+  eth/common/eth_types, stint, options,
+  ".."/[vm_types, vm_types2, vm_state, vm_computation]
+
+type
+  RpcCallData* = object
+    source*: EthAddress
+    to*: EthAddress
+    gas*: GasInt
+    gasPrice*: GasInt
+    value*: UInt256
+    data*: seq[byte]
+    contractCreation*: bool
+
+proc rpcSetupComputation*(vmState: BaseVMState, call: RpcCallData, fork: Fork): Computation =
+  vmState.setupTxContext(
+    origin = call.source,
+    gasPrice = call.gasPrice,
+    forkOverride = some(fork)
+  )
+
+  let msg = Message(
+    kind: evmcCall,
+    depth: 0,
+    gas: call.gas,
+    sender: call.source,
+    contractAddress: call.to,
+    codeAddress: call.to,
+    value: call.value,
+    data: call.data
+    )
+
+  return newComputation(vmState, msg)