detect gas limit for a node (#545)

src/main/kotlin/io/emeraldpay/dshackle/upstream/ethereum/EthereumUpstreamSettingsDetector.kt

@@ -11,6 +11,7 @@ import io.emeraldpay.dshackle.upstream.Upstream
 import io.emeraldpay.dshackle.upstream.rpcclient.ListParams
 import reactor.core.publisher.Flux
 import reactor.core.publisher.Mono
+import kotlin.text.toBigInteger
 
 const val ZERO_ADDRESS = "0x0000000000000000000000000000000000000000"
 
@@ -24,6 +25,7 @@ class EthereumUpstreamSettingsDetector(
         return Flux.merge(
             detectNodeType(),
             detectArchiveNode(),
+            detectGasLabels(),
         )
     }
 
@@ -43,6 +45,50 @@ class EthereumUpstreamSettingsDetector(
         return version
     }
 
+    /**
+     * We use this smart contract to get gas limit
+     * pragma solidity ^0.8.0;
+     *
+     * contract GasChecker {
+     *
+     *     // Function to return the amount of gas left
+     *     function getGasLeft() external view returns (uint256) {
+     *         return gasleft();
+     *     }
+     * }
+     *
+     */
+    private fun detectGasLabels(): Flux<Pair<String, String>> {
+        return upstream.getIngressReader().read(
+            ChainRequest(
+                "eth_call",
+                ListParams(
+                    mapOf(
+                        "to" to "0x53Daa71B04d589429f6d3DF52db123913B818F22",
+                        "data" to "0x51be4eaa",
+                    ),
+                    "latest",
+                    mapOf(
+                        "0x53Daa71B04d589429f6d3DF52db123913B818F22" to mapOf(
+                            "code" to "0x6080604052348015600e575f80fd5b50600436106026575f3560e01c806351be4eaa14602a575b5f80fd5b60306044565b604051603b91906061565b60405180910390f35b5f5a905090565b5f819050919050565b605b81604b565b82525050565b5f60208201905060725f8301846054565b9291505056fea2646970667358221220a85b088da3911ea743505594ac7cfdd1a65865de64499ee1f3c6bd9cdad4552364736f6c634300081a0033",
+                        ),
+                    ),
+                ),
+            ),
+        ).flatMap {
+            it.requireResult()
+        }.flatMapMany {
+            val gaslimit = String(it).drop(3).dropLast(1).toBigInteger(16) + (21180).toBigInteger()
+            val labels = mutableListOf(Pair("gas-limit", gaslimit.toString(10)))
+            if (gaslimit >= (600_000_000).toBigInteger()) {
+                labels.add(Pair("extra_gas_limit", "600000000"))
+            }
+            Flux.fromIterable(labels)
+        }.onErrorResume {
+            Flux.empty()
+        }
+    }
+
     private fun detectArchiveNode(): Mono<Pair<String, String>> {
         if (upstream.getLabels().firstOrNull { it.getOrDefault("archive", "") == "false" } != null) {
             return Mono.empty()