#19 Add gas usage estimation on ERC20 transfer.

iguana/exchanges/etomicswap/etomiccurl.c

@@ -186,7 +186,7 @@ char* getEthBalanceRequest(char* address)
     return balance;
 }
 
-char* ethCall(char* to, const char* data)
+char *ethCall(char *to, const char *data)
 {
     cJSON *params = cJSON_CreateArray();
     cJSON *txObject = cJSON_CreateObject();
@@ -205,6 +205,26 @@ char* ethCall(char* to, const char* data)
     return result;
 }
 
+uint64_t estimateGas(char *from, char *to, const char *data)
+{
+    cJSON *params = cJSON_CreateArray();
+    cJSON *txObject = cJSON_CreateObject();
+    cJSON_AddStringToObject(txObject, "from", from);
+    cJSON_AddStringToObject(txObject, "to", to);
+    cJSON_AddStringToObject(txObject, "data", data);
+    cJSON_AddItemToArray(params, txObject);
+    cJSON_AddItemToArray(params, cJSON_CreateString("latest"));
+    cJSON *resultJson = sendRpcRequest("eth_estimateGas", params);
+    cJSON_Delete(params);
+    uint64_t result = 0;
+    if (resultJson != NULL && is_cJSON_String(resultJson) && resultJson->valuestring != NULL) {
+        result = (uint64_t)strtoul(resultJson->valuestring, NULL, 0);
+        result = (result / 100) * 120; // add 20% because real gas usage might differ from estimate
+    }
+    cJSON_Delete(resultJson);
+    return result;
+}
+
 EthTxReceipt getEthTxReceipt(char *txId)
 {
     EthTxReceipt result;

iguana/exchanges/etomicswap/etomiccurl.h

@@ -39,6 +39,7 @@ typedef struct
 char* sendRawTx(char* rawTx);
 char* sendRawTxWaitConfirm(char* rawTx);
 char* ethCall(char* to, const char* data);
+uint64_t estimateGas(char *from, char *to, const char *data);
 int64_t getNonce(char* address);
 char* getEthBalanceRequest(char* address);
 EthTxReceipt getEthTxReceipt(char *txId);

iguana/exchanges/etomicswap/etomiclib.cpp

@@ -624,15 +624,21 @@ char *sendErc20(char *tokenAddress, char *to, char *amount, char *privKey, uint8
 {
     TransactionSkeleton tx;
     char *from = privKey2Addr(privKey), *result;
+    std::stringstream ss = getErc20TransferData(tokenAddress, to, amount);
+
     tx.from = jsToAddress(from);
     tx.to = jsToAddress(tokenAddress);
     tx.value = 0;
-    tx.gas = 60000;
+    uint64_t gas = estimateGas(from, tokenAddress, ss.str().c_str());
+    if (gas > 0) {
+        tx.gas = gas;
+    } else {
+        tx.gas = 150000;
+    }
     tx.gasPrice = getGasPriceFromStation() * boost::multiprecision::pow(u256(10), 9);
     tx.nonce = getNonce(from);
     free(from);
 
-    std::stringstream ss = getErc20TransferData(tokenAddress, to, amount);
     tx.data = jsToBytes(ss.str());
 
     char *rawTx = signTx(tx, privKey);