From 66de3f0aa849849c5cf5ad84265f3f3ce8ca5282 Mon Sep 17 00:00:00 2001
From: obscuren <geffobscura@gmail.com>
Date: Tue, 12 May 2015 14:14:08 +0200
Subject: [PATCH] xeth, rpc: implement eth_estimateGas. Closes #930

---
 cmd/mist/ui_lib.go |  2 +-
 rpc/api.go         | 31 ++++++++++++++++++++++++-------
 xeth/xeth.go       |  6 ++++--
 3 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/cmd/mist/ui_lib.go b/cmd/mist/ui_lib.go
index 4653e09800..0958294c34 100644
--- a/cmd/mist/ui_lib.go
+++ b/cmd/mist/ui_lib.go
@@ -127,7 +127,7 @@ func (self *UiLib) Transact(params map[string]interface{}) (string, error) {
 	)
 }
 
-func (self *UiLib) Call(params map[string]interface{}) (string, error) {
+func (self *UiLib) Call(params map[string]interface{}) (string, string, error) {
 	object := mapToTxParams(params)
 
 	return self.XEth.Call(
diff --git a/rpc/api.go b/rpc/api.go
index d53a9917db..774d26ea28 100644
--- a/rpc/api.go
+++ b/rpc/api.go
@@ -186,16 +186,24 @@ func (api *EthereumApi) GetRequestReply(req *RpcRequest, reply *interface{}) err
 			return err
 		}
 		*reply = v
-	case "eth_call":
-		args := new(CallArgs)
-		if err := json.Unmarshal(req.Params, &args); err != nil {
-			return err
-		}
-
-		v, err := api.xethAtStateNum(args.BlockNumber).Call(args.From, args.To, args.Value.String(), args.Gas.String(), args.GasPrice.String(), args.Data)
+	case "eth_estimateGas":
+		_, gas, err := api.doCall(req.Params)
 		if err != nil {
 			return err
 		}
+
+		// TODO unwrap the parent method's ToHex call
+		if len(gas) == 0 {
+			*reply = newHexData([]byte{})
+		} else {
+			*reply = newHexData(gas)
+		}
+	case "eth_call":
+		v, _, err := api.doCall(req.Params)
+		if err != nil {
+			return err
+		}
+
 		// TODO unwrap the parent method's ToHex call
 		if v == "0x0" {
 			*reply = newHexData([]byte{})
@@ -571,3 +579,12 @@ func (api *EthereumApi) GetRequestReply(req *RpcRequest, reply *interface{}) err
 	glog.V(logger.Detail).Infof("Reply: %T %s\n", reply, reply)
 	return nil
 }
+
+func (api *EthereumApi) doCall(params json.RawMessage) (string, string, error) {
+	args := new(CallArgs)
+	if err := json.Unmarshal(params, &args); err != nil {
+		return "", "", err
+	}
+
+	return api.xethAtStateNum(args.BlockNumber).Call(args.From, args.To, args.Value.String(), args.Gas.String(), args.GasPrice.String(), args.Data)
+}
diff --git a/xeth/xeth.go b/xeth/xeth.go
index bf5844770a..1ddd4c6e40 100644
--- a/xeth/xeth.go
+++ b/xeth/xeth.go
@@ -773,7 +773,7 @@ func (self *XEth) PushTx(encodedTx string) (string, error) {
 	return tx.Hash().Hex(), nil
 }
 
-func (self *XEth) Call(fromStr, toStr, valueStr, gasStr, gasPriceStr, dataStr string) (string, error) {
+func (self *XEth) Call(fromStr, toStr, valueStr, gasStr, gasPriceStr, dataStr string) (string, string, error) {
 	statedb := self.State().State() //self.eth.ChainManager().TransState()
 	var from *state.StateObject
 	if len(fromStr) == 0 {
@@ -807,8 +807,10 @@ func (self *XEth) Call(fromStr, toStr, valueStr, gasStr, gasPriceStr, dataStr st
 	block := self.CurrentBlock()
 	vmenv := core.NewEnv(statedb, self.backend.ChainManager(), msg, block)
 
+	initialGas := new(big.Int).Set(msg.gas)
 	res, err := vmenv.Call(msg.from, msg.to, msg.data, msg.gas, msg.gasPrice, msg.value)
-	return common.ToHex(res), err
+
+	return common.ToHex(res), initialGas.Sub(initialGas, msg.gas).String(), err
 }
 
 func (self *XEth) ConfirmTransaction(tx string) bool {