From f7b384f8545af0070f5b077653ca53092f3b46c4 Mon Sep 17 00:00:00 2001
From: Georgios Konstantopoulos <me@gakonst.com>
Date: Tue, 30 Mar 2021 20:20:52 +0300
Subject: [PATCH] Sequencer Fee Pricing Part 1, fix: revive the
 binary-search-enabled DoEstimateGas from geth (#276)

* fix: add nil check when estimating gas to avoid panic during contract creation

* fix: revert DoEstimateGas changes introduced as a temp fix in #22

* Tweak fudge factor for Geth gas estimation (#292)

* experimenting with gas fudge factor

* fix formatting

* try using 1m gas constant

* Add log statement for the gas estimate

* Add more detail to gas estimate log

* one more log edit

* Try new formula

* Bump base gas

* Even more base gas

* even more

* Just 1m?

* one more time

* Final cleanup

* Minor fix

* Update internal/ethapi/api.go

* don't use cap-1

* Make sure data is not nil

Co-authored-by: Karl Floersch <karl@karlfloersch.com>

Co-authored-by: Ben Jones <ben@pseudonym.party>
Co-authored-by: smartcontracts <kelvinfichter@gmail.com>
Co-authored-by: Karl Floersch <karl@karlfloersch.com>
---
 core/state_transition_ovm.go |  7 ++-
 internal/ethapi/api.go       | 84 +++++++++++++++++++++++++++++++++---
 2 files changed, 84 insertions(+), 7 deletions(-)

diff --git a/core/state_transition_ovm.go b/core/state_transition_ovm.go
index ee4882c8897e..7d21a2c8c457 100644
--- a/core/state_transition_ovm.go
+++ b/core/state_transition_ovm.go
@@ -96,12 +96,17 @@ func AsOvmMessage(tx *types.Transaction, signer types.Signer, decompressor commo
 }
 
 func EncodeSimulatedMessage(msg Message, timestamp, blockNumber *big.Int, executionManager, stateManager dump.OvmDumpAccount) (Message, error) {
+	to := msg.To()
+	if to == nil {
+		to = &common.Address{0}
+	}
+
 	tx := ovmTransaction{
 		timestamp,
 		blockNumber, // TODO (what's the correct block number?)
 		uint8(msg.QueueOrigin().Uint64()),
 		*msg.L1MessageSender(),
-		*msg.To(),
+		*to,
 		big.NewInt(int64(msg.Gas())),
 		msg.Data(),
 	}
diff --git a/internal/ethapi/api.go b/internal/ethapi/api.go
index c26cf52aa503..0e4f04b29e19 100644
--- a/internal/ethapi/api.go
+++ b/internal/ethapi/api.go
@@ -997,13 +997,85 @@ func (s *PublicBlockChainAPI) Call(ctx context.Context, args CallArgs, blockNrOr
 }
 
 func DoEstimateGas(ctx context.Context, b Backend, args CallArgs, blockNrOrHash rpc.BlockNumberOrHash, gasCap *big.Int) (hexutil.Uint64, error) {
-	// Retrieve the block to act as the gas ceiling
-	block, err := b.BlockByNumberOrHash(ctx, blockNrOrHash)
-	if err != nil {
-		return 0, err
+	// Binary search the gas requirement, as it may be higher than the amount used
+	var (
+		lo  uint64 = params.TxGas - 1
+		hi  uint64
+		cap uint64
+	)
+	if args.Gas != nil && uint64(*args.Gas) >= params.TxGas {
+		hi = uint64(*args.Gas)
+	} else {
+		// Retrieve the block to act as the gas ceiling
+		block, err := b.BlockByNumberOrHash(ctx, blockNrOrHash)
+		if err != nil {
+			return 0, err
+		}
+		hi = block.GasLimit()
+	}
+	if gasCap != nil && hi > gasCap.Uint64() {
+		log.Warn("Caller gas above allowance, capping", "requested", hi, "cap", gasCap)
+		hi = gasCap.Uint64()
+	}
+	cap = hi
+
+	// Set sender address or use a default if none specified
+	if args.From == nil {
+		if wallets := b.AccountManager().Wallets(); len(wallets) > 0 {
+			if accounts := wallets[0].Accounts(); len(accounts) > 0 {
+				args.From = &accounts[0].Address
+			}
+		}
+	}
+	// Use zero-address if none other is available
+	if args.From == nil {
+		args.From = &common.Address{}
+	}
+	// Create a helper to check if a gas allowance results in an executable transaction
+	executable := func(gas uint64) bool {
+		args.Gas = (*hexutil.Uint64)(&gas)
+
+		_, _, failed, err := DoCall(ctx, b, args, blockNrOrHash, nil, vm.Config{}, 0, gasCap)
+		if err != nil || failed {
+			return false
+		}
+		return true
+	}
+	// Execute the binary search and hone in on an executable gas limit
+	for lo+1 < hi {
+		mid := (hi + lo) / 2
+		if !executable(mid) {
+			lo = mid
+		} else {
+			hi = mid
+		}
+	}
+
+	// Fudging to account for gas required to verify signatures + pass around data.
+	// Specifically, this line accounts for the fact that there's a bit of computation performed in
+	// a "real" transaction that won't be covered by an eth_call:
+	//  1. Going into the OVM_SequencerEntrypoint.
+	//  2. Going into the OVM_ProxyEOA + OVM_ECDSAContractAccount.
+	//  3. Verify signatures in various places.
+	// eth_call skips all of this and therefore won't correctly estimate gas by default. We need to
+	// tweak the gas estimate to account for this discrepancy. Cost is quite high here because of
+	// the EVM limitation that CALL can only pass 63/64 of total gas available -- so most of this
+	// gas isn't actually spent during execution but needs to be provided to avoid a revert.
+	hi += 1000000
+	if args.Data != nil {
+		hi += uint64(len([]byte(*args.Data))) * 128
+	}
+	if hi > cap {
+		hi = cap
+	}
+
+	// Reject the transaction as invalid if it still fails at the highest allowance
+	if hi == cap {
+		if !executable(hi) {
+			return 0, fmt.Errorf("gas required exceeds allowance (%d) or always failing transaction", cap)
+		}
 	}
-	// For now always return the gas limit
-	return hexutil.Uint64(block.GasLimit() - 1), nil
+	return hexutil.Uint64(hi), nil
 }
 
 // EstimateGas returns an estimate of the amount of gas needed to execute the