accounts/abi/bind, internal/ethapi: binary search gas estimation

accounts/abi/bind/backends/simulated.go

@@ -201,10 +201,32 @@ func (b *SimulatedBackend) SuggestGasPrice(ctx context.Context) (*big.Int, error
 func (b *SimulatedBackend) EstimateGas(ctx context.Context, call ethereum.CallMsg) (*big.Int, error) {
 	b.mu.Lock()
 	defer b.mu.Unlock()
-	defer b.pendingState.RevertToSnapshot(b.pendingState.Snapshot())
 
-	_, gas, err := b.callContract(ctx, call, b.pendingBlock, b.pendingState)
+	// Binary search the gas requirement, as it may be higher than the amount used
-	return gas, err
+	var lo, hi uint64
+	if call.Gas != nil {
+		hi = call.Gas.Uint64()
+	} else {
+		hi = b.pendingBlock.GasLimit().Uint64()
+	}
+	for lo+1 < hi {
+		// Take a guess at the gas, and check transaction validity
+		mid := (hi + lo) / 2
+		call.Gas = new(big.Int).SetUint64(mid)
+
+		snapshot := b.pendingState.Snapshot()
+		_, gas, err := b.callContract(ctx, call, b.pendingBlock, b.pendingState)
+		b.pendingState.RevertToSnapshot(snapshot)
+
+		// If the transaction became invalid or used all the gas (failed), raise the gas limit
+		if err != nil || gas.Cmp(call.Gas) == 0 {
+			lo = mid
+			continue
+		}
+		// Otherwise assume the transaction succeeded, lower the gas limit
+		hi = mid
+	}
+	return new(big.Int).SetUint64(hi), nil
 }
 
 // callContract implemens common code between normal and pending contract calls.

accounts/abi/bind/bind_test.go

@@ -341,11 +341,11 @@ var bindTests = []struct {
 	{
 		`NonExistent`,
 		`
-		contract NonExistent {
+			contract NonExistent {
-			function String() constant returns(string) {
+				function String() constant returns(string) {
-				return "I don't exist";
+					return "I don't exist";
+				}
 			}
-		}
 		`,
 		`6060604052609f8060106000396000f3606060405260e060020a6000350463f97a60058114601a575b005b600060605260c0604052600d60809081527f4920646f6e27742065786973740000000000000000000000000000000000000060a052602060c0908152600d60e081905281906101009060a09080838184600060046012f15050815172ffffffffffffffffffffffffffffffffffffff1916909152505060405161012081900392509050f3`,
 		`[{"constant":true,"inputs":[],"name":"String","outputs":[{"name":"","type":"string"}],"type":"function"}]`,
@@ -365,6 +365,49 @@ var bindTests = []struct {
 			}
 		`,
 	},
+	// Tests that gas estimation works for contracts with	weird gas mechanics too.
+	{
+		`FunkyGasPattern`,
+		`
+			contract FunkyGasPattern {
+				string public field;
+
+				function SetField(string value) {
+					// This check will screw gas estimation! Good, good!
+					if (msg.gas < 100000) {
+						throw;
+					}
+					field = value;
+				}
+			}
+		`,
+		`606060405261021c806100126000396000f3606060405260e060020a600035046323fcf32a81146100265780634f28bf0e1461007b575b005b6040805160206004803580820135601f8101849004840285018401909552848452610024949193602493909291840191908190840183828082843750949650505050505050620186a05a101561014e57610002565b6100db60008054604080516020601f600260001961010060018816150201909516949094049384018190048102820181019092528281529291908301828280156102145780601f106101e957610100808354040283529160200191610214565b60405180806020018281038252838181518152602001915080519060200190808383829060006004602084601f0104600302600f01f150905090810190601f16801561013b5780820380516001836020036101000a031916815260200191505b509250505060405180910390f35b505050565b8060006000509080519060200190828054600181600116156101000203166002900490600052602060002090601f016020900481019282601f106101b557805160ff19168380011785555b506101499291505b808211156101e557600081556001016101a1565b82800160010185558215610199579182015b828111156101995782518260005055916020019190600101906101c7565b5090565b820191906000526020600020905b8154815290600101906020018083116101f757829003601f168201915b50505050508156`,
+		`[{"constant":false,"inputs":[{"name":"value","type":"string"}],"name":"SetField","outputs":[],"type":"function"},{"constant":true,"inputs":[],"name":"field","outputs":[{"name":"","type":"string"}],"type":"function"}]`,
+		`
+			// Generate a new random account and a funded simulator
+			key, _ := crypto.GenerateKey()
+			auth := bind.NewKeyedTransactor(key)
+			sim := backends.NewSimulatedBackend(core.GenesisAccount{Address: auth.From, Balance: big.NewInt(10000000000)})
+
+			// Deploy a funky gas pattern contract
+			_, _, limiter, err := DeployFunkyGasPattern(auth, sim)
+			if err != nil {
+				t.Fatalf("Failed to deploy funky contract: %v", err)
+			}
+			sim.Commit()
+
+			// Set the field with automatic estimation and check that it succeeds
+			auth.GasLimit = nil
+			if _, err := limiter.SetField(auth, "automatic"); err != nil {
+				t.Fatalf("Failed to call automatically gased transaction: %v", err)
+			}
+			sim.Commit()
+
+			if field, _ := limiter.Field(nil); field != "automatic" {
+				t.Fatalf("Field mismatch: have %v, want %v", field, "automatic")
+			}
+		`,
+	},
 }
 
 // Tests that packages generated by the binder can be successfully compiled and

internal/ethapi/api.go

@@ -559,8 +559,34 @@ func (s *PublicBlockChainAPI) Call(ctx context.Context, args CallArgs, blockNr r
 
 // EstimateGas returns an estimate of the amount of gas needed to execute the given transaction.
 func (s *PublicBlockChainAPI) EstimateGas(ctx context.Context, args CallArgs) (*hexutil.Big, error) {
-	_, gas, err := s.doCall(ctx, args, rpc.PendingBlockNumber)
+	// Binary search the gas requirement, as it may be higher than the amount used
-	return (*hexutil.Big)(gas), err
+	var lo, hi uint64
+	if (*big.Int)(&args.Gas).BitLen() > 0 {
+		hi = (*big.Int)(&args.Gas).Uint64()
+	} else {
+		// Retrieve the current pending block to act as the gas ceiling
+		block, err := s.b.BlockByNumber(ctx, rpc.PendingBlockNumber)
+		if err != nil {
+			return nil, err
+		}
+		hi = block.GasLimit().Uint64()
+	}
+	for lo+1 < hi {
+		// Take a guess at the gas, and check transaction validity
+		mid := (hi + lo) / 2
+		(*big.Int)(&args.Gas).SetUint64(mid)
+
+		_, gas, err := s.doCall(ctx, args, rpc.PendingBlockNumber)
+
+		// If the transaction became invalid or used all the gas (failed), raise the gas limit
+		if err != nil || gas.Cmp((*big.Int)(&args.Gas)) == 0 {
+			lo = mid
+			continue
+		}
+		// Otherwise assume the transaction succeeded, lower the gas limit
+		hi = mid
+	}
+	return (*hexutil.Big)(new(big.Int).SetUint64(hi)), nil
 }
 
 // ExecutionResult groups all structured logs emitted by the EVM