accounts/abi/bind, internal/ethapi: binary search gas estimation (#3587)

Gas estimation currently mostly works, but can underestimate for more funky
refunds. This is because various ops (e.g. CALL) need more gas to run than they
actually consume (e.g. 2300 stipend that is refunded if not used). With more
intricate contract interplays, it becomes almost impossible to return a proper
value to the user.

This commit swaps out the simplistic gas estimation to a binary search approach,
honing in on the correct gas use. This does mean that gas estimation needs to
rerun the transaction log(max-price) times to measure whether it fails or not,
but it's a price paid by the transaction issuer, and it should be worth it to
support proper estimates.

1 files changed, 47 insertions, 4 deletions

diff --git a/accounts/abi/bind/bind_test.go b/accounts/abi/bind/bind_test.go
index 6ebc8ea0a..eb46bc081 100644
--- a/accounts/abi/bind/bind_test.go
+++ b/accounts/abi/bind/bind_test.go
@@ -341,11 +341,11 @@ var bindTests = []struct {
 	{
 		`NonExistent`,
 		`
-		contract NonExistent {
-			function String() constant returns(string) {
-				return "I don't exist";
+			contract NonExistent {
+				function String() constant returns(string) {
+					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;
+				}
+			}
+		`,
+		`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`,
+		`[{"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