add hardhat_getForkedChainId JSON-RPC method

docs/guides/mainnet-forking.md

@@ -114,6 +114,19 @@ await network.provider.request({
 
 This will reset Hardhat Network, starting a new instance in the state described [here](../hardhat-network/README.md#hardhat-network-initial-state).
 
+## Getting the chainId of the original chain
+
+You can query the original chainId of the network that this fork was forked from:
+
+```ts
+await network.provider.request({
+  method: "hardhat_getForkedChainId",
+  params: [],
+)};
+```
+
+Returns the chanId of the forked network, or null if this chain is not a fork.
+
 ## Troubleshooting
 
 ### "Project ID does not have access to archive state"

docs/hardhat-network/README.md

@@ -381,6 +381,7 @@ To customise it, take a look at [the configuration section](/config/README.md#ha
 - `hardhat_dropTransaction` – Remove a transaction from the mempool
 - `hardhat_impersonateAccount` – see the [Mainnet Forking guide](../guides/mainnet-forking.md)
 - `hardhat_reset` – see the [Mainnet Forking guide](../guides/mainnet-forking.md)
+- `hardhat_getForkedChainId` - see the [Mainnet Forking guide](../guides/mainnet-forking.md)
 - `hardhat_setBalance` – Modifies the balance of an account.
 - `hardhat_setCode` – Modifies the code of an account.
 - `hardhat_setLoggingEnabled` – Enable or disable logging in Hardhat Network

packages/hardhat-core/src/internal/hardhat-network/jsonrpc/client.ts

@@ -28,6 +28,7 @@ export class JsonRpcClient {
   constructor(
     private _httpProvider: HttpProvider,
     private _networkId: number,
+    private _chainId: number | undefined,
     private _latestBlockNumberOnCreation: number,
     private _maxReorg: number,
     private _forkCachePath?: string
@@ -37,6 +38,10 @@ export class JsonRpcClient {
     return this._networkId;
   }
 
+  public getChainId(): number | undefined {
+    return this._chainId;
+  }
+
   public async getDebugTraceTransaction(transactionHash: Buffer): Promise<any> {
     return this._perform(
       "debug_traceTransaction",

packages/hardhat-core/src/internal/hardhat-network/provider/modules/hardhat.ts

@@ -74,6 +74,11 @@ export class HardhatModule {
       case "hardhat_reset":
         return this._resetAction(...this._resetParams(params));
 
+      case "hardhat_getForkedChainId":
+        return this._getForkedChainIdAction(
+          ...this._getForkedChainIdParams(params)
+        );
+
       case "hardhat_setLoggingEnabled":
         return this._setLoggingEnabledAction(
           ...this._setLoggingEnabledParams(params)
@@ -198,6 +203,16 @@ export class HardhatModule {
     return true;
   }
 
+  // hardhat_getForkedChainId
+
+  private _getForkedChainIdParams(params: any[]): [] {
+    return validateParams(params);
+  }
+
+  private async _getForkedChainIdAction(): Promise<number | null> {
+    return (await this._node.getForkedChainId()) ?? null;
+  }
+
   // hardhat_setLoggingEnabled
 
   private _setLoggingEnabledParams(params: any[]): [boolean] {

packages/hardhat-core/src/internal/hardhat-network/provider/node.ts

@@ -131,6 +131,7 @@ export class HardhatNode extends EventEmitter {
     let initialBlockTimeOffset: BN | undefined;
 
     let forkNetworkId: number | undefined;
+    let forkChainId: number | undefined;
 
     if ("forkConfig" in config) {
       const {
@@ -141,6 +142,7 @@ export class HardhatNode extends EventEmitter {
       common = await makeForkCommon(config);
 
       forkNetworkId = forkClient.getNetworkId();
+      forkChainId = forkClient.getChainId();
 
       this._validateHardforks(
         config.forkConfig.blockNumber,
@@ -200,7 +202,8 @@ export class HardhatNode extends EventEmitter {
       initialBlockTimeOffset,
       genesisAccounts,
       tracingConfig,
-      forkNetworkId
+      forkNetworkId,
+      forkChainId
     );
 
     return [common, node];
@@ -271,7 +274,8 @@ Hardhat Network's forking functionality only works with blocks from at least spu
     private _blockTimeOffsetSeconds: BN = new BN(0),
     genesisAccounts: GenesisAccount[],
     tracingConfig?: TracingConfig,
-    private _forkNetworkId?: number
+    private _forkNetworkId?: number,
+    private _forkChainId?: number
   ) {
     super();
 
@@ -1099,6 +1103,10 @@ Hardhat Network's forking functionality only works with blocks from at least spu
     );
   }
 
+  public async getForkedChainId(): Promise<number | undefined> {
+    return this._forkChainId;
+  }
+
   private async _addPendingTransaction(tx: TypedTransaction): Promise<string> {
     await this._txPool.addTransaction(tx);
     await this._notifyPendingTransaction(tx);

packages/hardhat-core/src/internal/hardhat-network/provider/utils/makeForkClient.ts

@@ -39,6 +39,13 @@ export async function makeForkClient(
   );
 
   const networkId = await getNetworkId(provider);
+  let chainId;
+  try {
+    chainId = await _getChainIdFromEthChainId(provider);
+  } catch (error) {
+    chainId = await _getChainIdFromEthNetVersion(provider);
+  }
+
   const actualMaxReorg = getLargestPossibleReorg(networkId);
   const maxReorg = actualMaxReorg ?? FALLBACK_MAX_REORG;
 
@@ -86,6 +93,7 @@ Please use block number ${lastSafeBlock} or wait for the block to get ${
   const forkClient = new JsonRpcClient(
     provider,
     networkId,
+    chainId,
     latestBlock,
     maxReorg,
     cacheToDiskEnabled ? forkCachePath : undefined
@@ -110,9 +118,32 @@ async function getNetworkId(provider: HttpProvider) {
   const networkIdString = (await provider.request({
     method: "net_version",
   })) as string;
+
   return parseInt(networkIdString, 10);
 }
 
+async function _getChainIdFromEthChainId(
+  provider: HttpProvider
+): Promise<number> {
+  const id = (await provider.request({
+    method: "eth_chainId",
+  })) as string;
+
+  return rpcQuantityToNumber(id);
+}
+
+async function _getChainIdFromEthNetVersion(
+  provider: HttpProvider
+): Promise<number> {
+  const id = (await provider.request({
+    method: "net_version",
+  })) as string;
+
+  // There's a node returning this as decimal instead of QUANTITY.
+  // TODO: Document here which node does that
+  return id.startsWith("0x") ? rpcQuantityToNumber(id) : parseInt(id, 10);
+}
+
 async function getLatestBlockNumber(provider: HttpProvider) {
   const latestBlockString = (await provider.request({
     method: "eth_blockNumber",

packages/hardhat-core/test/internal/hardhat-network/jsonrpc/client.ts

@@ -74,6 +74,7 @@ describe("JsonRpcClient", () => {
           fakeProvider as any,
           1,
           123,
+          1,
           3
         );
 
@@ -88,6 +89,7 @@ describe("JsonRpcClient", () => {
           fakeProvider as any,
           1,
           123,
+          undefined,
           3
         );
 
@@ -102,6 +104,7 @@ describe("JsonRpcClient", () => {
           fakeProvider as any,
           1,
           123,
+          undefined,
           3
         );
 
@@ -122,6 +125,7 @@ describe("JsonRpcClient", () => {
             fakeProvider as any,
             1,
             123,
+            undefined,
             3,
             this.tmpDir
           );
@@ -149,6 +153,7 @@ describe("JsonRpcClient", () => {
             fakeProvider as any,
             1,
             123,
+            undefined,
             3,
             this.tmpDir
           );
@@ -183,6 +188,7 @@ describe("JsonRpcClient", () => {
           fakeProvider as any,
           1,
           123,
+          undefined,
           3
         );
 
@@ -213,6 +219,7 @@ describe("JsonRpcClient", () => {
           fakeProvider as any,
           1,
           123,
+          undefined,
           3
         );
 
@@ -242,6 +249,7 @@ describe("JsonRpcClient", () => {
           fakeProvider as any,
           1,
           123,
+          undefined,
           3
         );
         await assert.isRejected(
@@ -270,6 +278,7 @@ describe("JsonRpcClient", () => {
           fakeProvider as any,
           1,
           123,
+          undefined,
           3
         );
         await assert.isRejected(

packages/hardhat-core/test/internal/hardhat-network/provider/modules/hardhat.ts

@@ -376,6 +376,19 @@ describe("Hardhat module", function () {
         }
       });
 
+      describe("hardhat_getForkedChainId", function () {
+        it("gets correct chainId", async function () {
+          const hardhatChainId = await this.provider.send(
+            "hardhat_getForkedChainId"
+          );
+          if (isFork) {
+            assert.equal(hardhatChainId, 1);
+          } else {
+            assert.isNull(hardhatChainId);
+          }
+        });
+      });
+
       describe("hardhat_setBalance", function () {
         it("should reject an invalid address", async function () {
           await assertInvalidArgumentsError(