From ac9fb3746517936ef8da809bd270425e7e84dda6 Mon Sep 17 00:00:00 2001
From: coffeepots <coffeepotsgh@gmail.com>
Date: Tue, 27 Nov 2018 18:21:28 +0000
Subject: [PATCH] Initial commit for eth_estimateGas

---
 nimbus/rpc/p2p.nim | 73 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 70 insertions(+), 3 deletions(-)

diff --git a/nimbus/rpc/p2p.nim b/nimbus/rpc/p2p.nim
index afe6500fa..e37524a49 100644
--- a/nimbus/rpc/p2p.nim
+++ b/nimbus/rpc/p2p.nim
@@ -13,7 +13,7 @@ import
   eth_common, eth_p2p, eth_keys, eth_trie/db, rlp,
   ../utils/header, ../transaction, ../config, ../vm_state, ../constants, ../vm_types,
   ../vm_state_transactions, ../utils/addresses,
-  ../db/[db_chain, state_db, storage_types],
+  ../vm/[interpreter_dispatch, computation],
   rpc_types, rpc_utils, ../vm/[message, computation]
 
 #[
@@ -33,6 +33,52 @@ template balance(addressDb: ReadOnlyStateDb, address: EthAddress): GasInt =
   # TODO: Account balance u256 but GasInt is int64?
   addressDb.getBalance(address).truncate(int64)
 
+proc binarySearchGas(vmState: var BaseVMState, transaction: Transaction, sender: EthAddress, gasPrice: GasInt, tolerance = 1): GasInt =
+  proc dummyComputation(vmState: var BaseVMState, transaction: Transaction, sender: EthAddress): BaseComputation =
+    # Note that vmState may be altered
+    setupComputation(
+        vmState.blockHeader,
+        vmState,
+        transaction,
+        sender)
+  
+  proc dummyTransaction(gasLimit, gasPrice: GasInt, destination: EthAddress, value: UInt256): Transaction =
+    Transaction(
+      accountNonce: 0.AccountNonce,
+      gasPrice: gasPrice,
+      gasLimit: gasLimit,
+      to: destination,
+      value: value
+    )
+  var
+    hiGas = vmState.gasLimit
+    loGas = transaction.intrinsicGas
+    gasPrice = transaction.gasPrice # TODO: Or zero?
+  
+  proc tryTransaction(vmState: var BaseVMState, gasLimit: GasInt): bool =
+    var
+      spoofTransaction = dummyTransaction(gasLimit, gasPrice, transaction.to, transaction.value)
+      computation = vmState.dummyComputation(spoofTransaction, sender)
+    computation.executeOpcodes
+    if not computation.isError:
+      return true
+
+  if vmState.tryTransaction(loGas):
+    return loGas
+  if not vmState.tryTransaction(hiGas):
+    return 0.GasInt # TODO: Reraise error from computation
+
+  var
+    minVal = vmState.gasLimit
+    maxVal = transaction.intrinsicGas
+  while loGas - hiGas > tolerance:
+    let midPoint = (loGas + hiGas) div 2
+    if vmState.tryTransaction(midPoint):
+      minVal = midPoint
+    else:
+      maxVal = midPoint
+  result = minVal
+
 proc setupEthRpc*(node: EthereumNode, chain: BaseChainDB, rpcsrv: RpcServer) =
 
   func getAccountDb(header: BlockHeader): ReadOnlyStateDB =
@@ -274,7 +320,7 @@ proc setupEthRpc*(node: EthereumNode, chain: BaseChainDB, rpcsrv: RpcServer) =
 
     discard comp.execComputation
     result = ("0x" & nimcrypto.toHex(comp.output)).HexDataStr
-
+  
   rpcsrv.rpc("eth_estimateGas") do(call: EthCall, quantityTag: string) -> GasInt:
     ## Generates and returns an estimate of how much gas is necessary to allow the transaction to complete.
     ## The transaction will not be added to the blockchain. Note that the estimate may be significantly more than
@@ -283,7 +329,28 @@ proc setupEthRpc*(node: EthereumNode, chain: BaseChainDB, rpcsrv: RpcServer) =
     ## call: the transaction call object.
     ## quantityTag:  integer block number, or the string "latest", "earliest" or "pending", see the default block parameter.
     ## Returns the amount of gas used.
-    discard
+    # TODO: Use optional fields with EthCall
+    var
+      header = chain.headerFromTag(quantityTag)
+      vmState = newBaseVMState(header, chain)
+    let
+      gasLimit = if call.gas > 0.GasInt: call.gas else: header.gasLimit
+      gasPrice = if call.gasPrice > 0: call.gasPrice else: 0.GasInt
+      curState = chain.getStateDb(header.stateRoot, true)
+      sender = call.source.string.strToAddress
+      destination = call.to.string.strToAddress
+      nonce = curState.getNonce(sender)
+      value = call.value
+      # TODO: Use initTransaction when merged
+      transaction = Transaction(
+        accountNonce: nonce,
+        gasPrice: gasPrice,
+        gasLimit: gasLimit,
+        to: destination,
+        value: value.u256,
+        payload: @[]
+      )
+    result = vmState.binarySearchGas(transaction, sender, gasPrice)
 
   func populateBlockObject(header: BlockHeader, blockBody: BlockBody): BlockObject =
     result.number = some(header.blockNumber)