C#•9mo ago

❔ Constructing big endian byte message from multiple integers

Hey all, I'm following the torrent protocol trying to create messages for the protocol to give trackers; I'm not getting a response back and I'm not 100% sure what I got wrong, here is some sample code and the protocol itself:

4 Replies

Asher•9mo ago

example for this particular request:

Offset  Size            Name            Value
0       64-bit integer  protocol_id     0x41727101980 // magic constant
8       32-bit integer  action          0 // connect
12      32-bit integer  transaction_id  // this is a random number
16

Offset  Size            Name            Value
0       64-bit integer  protocol_id     0x41727101980 // magic constant
8       32-bit integer  action          0 // connect
12      32-bit integer  transaction_id  // this is a random number
16

in total byte[16] my struct for this:

public struct ConnectRequest
    {
        public Int64 protocol_id = 0x41727101980;

        // 0 = connect
        public Int32 action = 0;

        public Int32 transaction_id;

        public const int BYTE_COUNT = 16;

        public ConnectRequest()
        {
            // random 32-bit integer
            Random r = new Random();
            transaction_id = r.Next(Int32.MinValue, Int32.MaxValue);
        }

        public byte[] Serialize()
        {
            byte[] bytes = new byte[BYTE_COUNT];
            byte[] protocolId, action, transactionId;

            protocolId = BitConverter.GetBytes(protocol_id);

            // 4 bytes = 32 bits
            action = new byte[] { 0, 0, 0, 0 };
            transactionId = BitConverter.GetBytes(transaction_id);

            bytes = protocolId.Concat(action.Concat(transactionId)).ToArray();
            if (bytes.Length > 16) throw new Exception("Wrong length");

            return bytes;
        }

        /// <summary>
        /// checks if the transaction ids match
        /// </summary>
        /// <param name="cr"></param>
        /// <returns></returns>
        public bool CheckResponse(ConnectResponse cr) => cr.transaction_id == transaction_id;
    }

public struct ConnectRequest
    {
        public Int64 protocol_id = 0x41727101980;

        // 0 = connect
        public Int32 action = 0;

        public Int32 transaction_id;

        public const int BYTE_COUNT = 16;

        public ConnectRequest()
        {
            // random 32-bit integer
            Random r = new Random();
            transaction_id = r.Next(Int32.MinValue, Int32.MaxValue);
        }

        public byte[] Serialize()
        {
            byte[] bytes = new byte[BYTE_COUNT];
            byte[] protocolId, action, transactionId;

            protocolId = BitConverter.GetBytes(protocol_id);

            // 4 bytes = 32 bits
            action = new byte[] { 0, 0, 0, 0 };
            transactionId = BitConverter.GetBytes(transaction_id);

            bytes = protocolId.Concat(action.Concat(transactionId)).ToArray();
            if (bytes.Length > 16) throw new Exception("Wrong length");

            return bytes;
        }

        /// <summary>
        /// checks if the transaction ids match
        /// </summary>
        /// <param name="cr"></param>
        /// <returns></returns>
        public bool CheckResponse(ConnectResponse cr) => cr.transaction_id == transaction_id;
    }

Asher•9mo ago

this is the big endian part, which I assume I haven't done yet

Asher•9mo ago

I checked my hardware and its little endian, does that mean I need to reverse each number's bytes? or just reverse the entire array? for example: for array : { 0x36, 0xf9, 0x1b, 0x8d } (together: 36F91B8D) first option: 639FB1D8 or the entire array: D8B119F36

Accord•9mo ago

Looks like nothing has happened here. I will mark this as stale and this post will be archived until there is new activity.

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❔ Constructing big endian byte message from multiple integers