Copying, modifying and sending request POST Fiddler - fiddler

Question

sorry for my English)))
I have been trying to solve my problem for a long time, but unfortunately so far without success ((((
I have a POST request of a certain type, I need to change it and send it to another address, and the original request should go further to its address. I'm trying to work with the exchange. More to the point, I have a request like this :
https://api.binance.com/api/v3/order?symbol=CELRBTC&orderId=73902412&recvWindow=55000&timestamp=1635266807744&signature=556b9c4121eb819d96a440b54661181e75ab2324a9d3b5fe0a73dd793626cb96
I need to send this request after the original one
https://fapi/binance.com/fapi/v1/order?symbol=KEEPUSDT&side=BUY&type=MARKET&quantity=100&timeInForce=GTC&recvWindow=5000&timestamp=1591702613943&signature= 3c661234138461fcc7a7d8746c6558c9842d4e10870d2ecbedf7777cad694af
In addition, the public API is passed in the header
Connection: Keep-Alive
Content-Type: application/x-www-form-urlencoded
Accept: application/json, text/plain; q=0.9, text/html;q=0.8,
Accept-Charset: UTF-8, *;q=0.8
Accept-Encoding: gzip, deflate
X-MBX-APIKEY: YIGXAtXbQg0790CnIvKzo3oIQPmEPwiySjdQj28h0H3g87D2rwcun0kRWvh4m9J6
Host: api.binance.com
I tried to do all this work in the onBeforeRequest method
static function OnBeforeRequest(oSession: Session) {
if (oSession.RequestMethod == "POST" && oSession.uriContains("order") ) {
oSession.utilDecodeResponse()
var strBody=oSession.GetRequestBodyAsString();
// timestamp, time ms
var timestampSTART= oSession.url.IndexOf("timestamp=") + 10;
var timestampEND= oSession.url.IndexOf("&", timestampSTART);
var timestamp = oSession.url.Substring(timestampSTART, 13);
// SYMBOL
var symbolStart = oSession.url.IndexOf("symbol=")+7;
var symbolend = oSession.url.IndexOf("BTC", symbolStart)+3;
var symbol = oSession.url.Substring(symbolStart, symbolend-symbolStart);
// Signature (timestamp+SecretAPIKey=Hmac Sha256) theoretically, it can be taken from the original request, but it is more reliable to make your own
var signStart = oSession.url.IndexOf("signature=")+10;
var sign = oSession.url.Substring(signStart);
//PRICE
var PriceStart = oSession.url.IndexOf("price=")+6;
var PriceEND = oSession.url.IndexOf("&", PriceStart);
var priceStr = oSession.url.Substring(PriceStart, PriceEND-PriceStart);
var price = parseFloat(priceStr);
// Quantity
var quantity = 50/ price*63000;
var apiBIN = "https://fapi.binance.com/fapi/v1/order?" ;
// var result = apiBIN+"symbol="+symbol+"&side=BUY&type=MARKET&quantity="+ quantity+"&timeInForce=GTC&recvWindow=5000&timestamp="+timestamp+"&signature="+sign;
// oSession.utilSetRequestBody(result)
// FiddlerApplication.oProxy.SendRequest(oSession.RequestHeaders, oSession.requestBodyBytes, null);
have selected the necessary parameters from the request, but I do not understand how to send it in any way, and I also lose the header with the API key.
Separately, I want to note the "Signature" parameter, which is created using the Hmac Sha256 algorithm from the secret API key and time, which I also can't figure out how to describe it in the code.
I would be very grateful for any help, with the possibility of some payment for substantial help.

Answer 1

I used C# to solve the problem. I didn't know Fiddler could choose the language. Technically, I have achieved my goal, but currently finance is writing an incorrect request. I will deal with this separately. Special thanks to Robert for his help.
public static void OnBeforeResponse(Session oSession)
{
if (oSession.HTTPMethodIs("POST") && oSession.uriContains("order"))
{
String strBody = oSession.GetRequestBodyAsString();
//Price
int PriceStart = strBody.IndexOf("price=")+6;
int PriceEND = strBody.IndexOf("&", PriceStart);
string priceStr = strBody.Substring(PriceStart, PriceEND-PriceStart);
float priceF = float.Parse(priceStr, System.Globalization.CultureInfo.InvariantCulture);
// SYMBOL
int symbolStart = strBody.IndexOf("symbol=")+7;
int symbolend = strBody.IndexOf("BTC", symbolStart);
string symbol = strBody.Substring(symbolStart, symbolend-symbolStart);
// Quantity
int quantStart = strBody.IndexOf("quantity=")+9;
int quantend = strBody.IndexOf("&price", quantStart);
string quant = strBody.Substring(quantStart, quantend-quantStart);
float quantity = float.Parse(quant, System.Globalization.CultureInfo.InvariantCulture)*2;
// timestamp
decimal timestamp = Math.Round(Convert.ToDecimal(DateTime.UtcNow.Subtract(new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)).TotalMilliseconds), 0);
//Sign
Encoding ascii = Encoding.ASCII;
string secretKey = "lfaeGkjitNwvyG2lqDueMhSAOzRFlzL73w5pKRCAvSy7YrxyTkvwKCcHBHj...";
HMACSHA256 hmac = new HMACSHA256(ascii.GetBytes(secretKey));
// string query_string_LIMIT = "symbol="+symbol+"USDT&side=BUY&type=LIMIT&timeInForce=GTC&quantity="+quantity+"&price="+priceF+"&recvWindow=5000&timestamp="+timestamp+"&signature=";
string result = "symbol="+symbol+"USDT&side=BUY&type=MARKET&quantity="+ quantity+"&recvWindow=5000&timestamp="+timestamp+"&signature=";
String signature = BitConverter.ToString(hmac.ComputeHash(ascii.GetBytes(result))).Replace("-","");
oSession.host="fapi.binance.com";
string resultRequest = "symbol="+symbol+"USDT&side=BUY&type=MARKET&quantity="+ quantity+"&recvWindow=5000&timestamp="+timestamp+"&signature="+signature;
byte[] resulByte = System.Text.Encoding.ASCII.GetBytes(resultRequest);
//oSession.utilReplaceInRequest("api/v3/order","fapi/v1/order?"+resultFin);
oSession.url = oSession.url.Replace("api/v3/order", "fapi/v1/order?"+resultRequest);
FiddlerApplication.oProxy.SendRequest (oSession.RequestHeaders, resulByte, null);
}