Implement the eth_getBalance JSON-RPC endpoint

api/api.go

@@ -33,10 +33,13 @@ var (
 )
 
 //go:embed cadence/scripts/bridged_account_call.cdc
-var bridgedAccountCall []byte
+var BridgedAccountCall []byte
 
 //go:embed cadence/transactions/evm_run.cdc
-var evmRunTx []byte
+var EVMRunTx []byte
+
+//go:embed cadence/scripts/evm_address_balance.cdc
+var EVMAddressBalance []byte
 
 func SupportedAPIs(blockChainAPI *BlockChainAPI) []rpc.API {
 	return []rpc.API{
@@ -141,7 +144,7 @@ func (api *BlockChainAPI) SendRawTransaction(
 	}
 
 	tx := flow.NewTransaction().
-		SetScript(evmRunTx).
+		SetScript(EVMRunTx).
 		SetProposalKey(account.Address, accountKey.Index, accountKey.SequenceNumber).
 		SetReferenceBlockID(block.ID).
 		SetPayer(account.Address).
@@ -228,7 +231,29 @@ func (s *BlockChainAPI) GetBalance(
 	address common.Address,
 	blockNumberOrHash *rpc.BlockNumberOrHash,
 ) (*hexutil.Big, error) {
-	return (*hexutil.Big)(big.NewInt(101)), nil
+	addressBytes := make([]cadence.Value, 0)
+	for _, bt := range address.Bytes() {
+		addressBytes = append(addressBytes, cadence.UInt8(bt))
+	}
+	evmAddress := cadence.NewArray(
+		addressBytes,
+	).WithType(cadence.NewConstantSizedArrayType(20, cadence.TheUInt8Type))
+
+	value, err := s.FlowClient.ExecuteScriptAtLatestBlock(
+		ctx,
+		EVMAddressBalance,
+		[]cadence.Value{evmAddress},
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	balance, ok := value.(cadence.UFix64)
+	if !ok {
+		return nil, fmt.Errorf("script doesn't return UFix64 as it should")
+	}
+
+	return (*hexutil.Big)(big.NewInt(int64(balance))), nil
 }
 
 // eth_getCode (returns the code for the given address)
@@ -795,7 +820,7 @@ func (s *BlockChainAPI) Call(
 
 	value, err := s.FlowClient.ExecuteScriptAtLatestBlock(
 		ctx,
-		bridgedAccountCall,
+		BridgedAccountCall,
 		[]cadence.Value{encodedTx, encodedTo},
 	)
 	if err != nil {

api/api_test.go

@@ -198,6 +198,13 @@ func TestBlockChainAPI(t *testing.T) {
 	})
 
 	t.Run("GetBalance", func(t *testing.T) {
+		mockFlowClient := new(mocks.MockAccessClient)
+		blockchainAPI = api.NewBlockChainAPI(config, store, mockFlowClient)
+
+		result, err := cadence.NewUFix64("1500.0")
+		require.NoError(t, err)
+		mockFlowClient.On("ExecuteScriptAtLatestBlock", mock.Anything, mock.Anything, mock.Anything).Return(result, nil)
+
 		key, _ := crypto.GenerateKey()
 		addr := crypto.PubkeyToAddress(key.PublicKey)
 		balance, err := blockchainAPI.GetBalance(
@@ -207,7 +214,7 @@ func TestBlockChainAPI(t *testing.T) {
 		)
 		require.NoError(t, err)
 
-		assert.Equal(t, balance, (*hexutil.Big)(big.NewInt(101)))
+		assert.Equal(t, balance, (*hexutil.Big)(big.NewInt(150000000000)))
 	})
 
 	t.Run("GetProof", func(t *testing.T) {

api/cadence/scripts/evm_address_balance.cdc

@@ -0,0 +1,8 @@
+import EVM from 0xf8d6e0586b0a20c7
+
+access(all)
+fun main(addressBytes: [UInt8; 20]): UFix64 {
+    let address = EVM.EVMAddress(bytes: addressBytes)
+
+    return address.balance().flow
+}

api/fixtures/eth_json_rpc_requests.json

@@ -2,7 +2,6 @@
 {"jsonrpc":"2.0","id":1,"method":"eth_blockNumber","params": []}
 {"jsonrpc":"2.0","id":1,"method":"eth_syncing","params": []}
 {"jsonrpc":"2.0","id":1,"method":"eth_gasPrice","params":[]}
-{"jsonrpc":"2.0","id":1,"method":"eth_getBalance","params":["0x407d73d8a49eeb85d32cf465507dd71d507100c1","latest"]}
 {"jsonrpc":"2.0","id":1,"method":"eth_getCode","params":["0xa94f5374fce5edbc8e2a8697c15331677e6ebf0b","0x2"]}
 {"jsonrpc":"2.0","id":1,"method":"eth_getStorageAt","params":["0x295a70b2de5e3953354a6a8344e616ed314d7251","0x6661e9d6d8b923d5bbaab1b96e1dd51ff6ea2a93520fdc9eb75d059238b8c5e9","latest"]}
 {"jsonrpc":"2.0","id":1,"method":"eth_getTransactionCount","params":["0x407d73d8a49eeb85d32cf465507dd71d507100c1","latest"]}

api/fixtures/eth_json_rpc_responses.json

@@ -2,7 +2,6 @@
 {"jsonrpc":"2.0","id":1,"result":"0x0"}
 {"jsonrpc":"2.0","id":1,"result":false}
 {"jsonrpc":"2.0","id":1,"result":"0x1dfd14000"}
-{"jsonrpc":"2.0","id":1,"result":"0x65"}
 {"jsonrpc":"2.0","id":1,"result":"0x600160008035811a818181146012578301005b601b6001356025565b8060005260206000f25b600060078202905091905056"}
 {"jsonrpc":"2.0","id":1,"result":"0x600160008035811a818181146012578301005b601b6001356025565b8060005260206000f25b600060078202905091905056"}
 {"jsonrpc":"2.0","id":1,"result":"0x0"}

api/server_test.go

@@ -136,7 +136,12 @@ func TestServerJSONRPCOveHTTPHandler(t *testing.T) {
 		returnValue := cadence.NewArray(
 			toBytes,
 		).WithType(cadence.NewVariableSizedArrayType(cadence.TheUInt8Type))
-		mockFlowClient.On("ExecuteScriptAtLatestBlock", mock.Anything, mock.Anything, mock.Anything).Return(returnValue, nil)
+		mockFlowClient.On(
+			"ExecuteScriptAtLatestBlock",
+			mock.Anything,
+			api.BridgedAccountCall,
+			mock.Anything,
+		).Once().Return(returnValue, nil)
 
 		blockchainAPI = api.NewBlockChainAPI(config, store, mockFlowClient)
 
@@ -223,6 +228,30 @@ func TestServerJSONRPCOveHTTPHandler(t *testing.T) {
 
 		assert.Equal(t, expectedResponse, strings.TrimSuffix(string(content), "\n"))
 	})
+
+	t.Run("eth_getBalance", func(t *testing.T) {
+		request := `{"jsonrpc":"2.0","id":1,"method":"eth_getBalance","params":["0x407d73d8a49eeb85d32cf465507dd71d507100c1","latest"]}`
+		expectedResponse := `{"jsonrpc":"2.0","id":1,"result":"0x22ecb25c00"}`
+
+		result, err := cadence.NewUFix64("1500.0")
+		require.NoError(t, err)
+		mockFlowClient.On(
+			"ExecuteScriptAtLatestBlock",
+			mock.Anything,
+			api.EVMAddressBalance,
+			mock.Anything,
+		).Once().Return(result, nil)
+
+		resp := rpcRequest(url, request, "origin", "test.com")
+		defer resp.Body.Close()
+
+		content, err := io.ReadAll(resp.Body)
+		if err != nil {
+			panic(err)
+		}
+
+		assert.Equal(t, expectedResponse, strings.TrimSuffix(string(content), "\n"))
+	})
 }
 
 func TestServerJSONRPCOveWebSocketHandler(t *testing.T) {