Develop Reference

Receive UDP packet to Class. Design/Implementation assistance appreciated

I receive UDP data from localhost. This data needs to be used and kept track of. There could be >250k packets sent over the course of about 5 minutes. Currently, I create the IPEndPoint, and Receive the data. I then get the byte[] data into a string. Then I split the string into an array because the data is comma separated. From this array, I instantiate an object with the correct values from the array.
The incoming data has 4 properties and looks like this: ProductId=1284,Quantity=48623,Time=08:45:12.034,Date=2019-09-09
Currently I am able to Console.WriteLine the incoming packets, and cast each packet to an object (Product). Currently I do not store the data anywhere.
I need to monitor Quantity levels, and send alerts if the Quantity goes above or below certain thresholds. Secondly, I need to send another alert if the change in Quantity exceeds thresholds. This I will implement with if statements later and do not require assistance with at the moment. This alerts do need to be sent as UDP packets are received.
My questions are:
1) Should I implement this Asynchronously, or on a different thread?
2) Should I be sending the UDP Data directly to a Queue of type byte[], and then Dequeue each byte[] into an object? or keep instantiating new objects (or updating the quantity for each product) on the fly as the UDP data is received? Does Queue reduce the risk of dropped packets?
3) What is the best way to store each packet? To a List (This would keep everything in memory), a database (A bit beyond my current needs), or append each object to a text file (easy to write to, and can eventually build a database from)?
4) Is 250k packets over 5 minutes, and creating objects for all those packets considered a lot for a computer to handle?
Please advise if I can clarify anything. I apologize if any of my terminology is incorrect, I will learn and fix it. The coding I should be able to figure out on my own, it is the design and proper implementation that I am asking for guidance on. Thank you.
Below is code for setting up the UDP connection, and the class. I will be able to figure out the monitoring/messaging Quantity information after the UDP has been setup properly. I do have a Product Class not shown, it has several properties including ProductId, Quantity, Initial Quantity, Change in Quantity, Time and Date.
class Program
{
static void Main(string[] args)
{
int port = 22486;
var client = new UdpClient();
IPEndPoint localEp = new IPEndPoint(IPAddress.Any, port);
client.Client.Bind(localEp);
while (true)
{
try
{
byte[] data = client.Receive(ref localEp);
string text = Encoding.UTF8.GetString(data);
string[] message = text.Split(',', '=');
Product product = new Product();
product.ProductId = message[1];
product.Quantity = message[3];
}
catch (Exception err)
{
Console.WriteLine(err.ToString());
}
}
}
}

If you need to do other things while listening on that port, make it a thread.
queue it up in a byte array... a buffer of sorts.
Are azure blobs an option for you? you can use the storage emulator and if you change your mind about storing a file in blob, you can switch to table storage (this is like a nosql approach where you provide a partition name.)
No

C# switch - infinite loops with winpcap

I'm making program that should receive packet and send it on the other port on PC (other port is doing the same, also send what he gets), based on MAC address. But when I open device like this:
device_port1.Open(DeviceMode.Promiscuous);
and then send some packet on one port, that same port get that same packet like it was received. And when both adapters are doing the same, they are sending each other one packet over and over.
How could I stopped this? I tried
device_port1.Open(OpenFlags.NoCaptureLocal, 1000);
but then it wasn't sending anything thru that program (and then it's useless).
This is the code:
device_port0 = devices[pole[0]];
device_port0.OnPacketArrival += new SharpPcap.PacketArrivalEventHandler(device_OnPacketArrival_port0);
//device_port0.Open(OpenFlags.NoCaptureLocal, 1000);
device_port0.Open(DeviceMode.Promiscuous);
device_port0.StartCapture();
And onPacketArrival
private void device_OnPacketArrival_port0(object sender, CaptureEventArgs packet)
{
device_port1 = devices[pole[1]];
device_port1.Open();
try
{
device_port1.SendPacket(packet.Packet.Data);
}
catch (Exception ee)
{
Console.Writeline("Exception: " + ee.Message);
}
}
And on the port1 is the same. It just send what he gets and that's the reason for the loop.

I take it both Network cards have the same address? If that is NOT the case then, before forwarding a packet you have to check if the packet's destination network is the network connected to the second network card.
If however both cards have the same address, then the only solution i can see (I'm no expert) is to have some sort of list where you store the packets for a short time after sending them. And every time you capture a packet you check if it already is in the list(to check if it's one you've already sent). This way of solving your problem is inefficient as every packet sent is resent back again But it beats infinity.

How can I read from a socket repeatedly?

To start I am coding in C#. I am writing data of varying sizes to a device through a socket. After writing the data I want to read from the socket because the device will write back an error code/completion message once it has finished processing all of the data. Currently I have something like this:
byte[] resultErrorCode = new byte[1];
resultErrorCode[0] = 255;
while (resultErrorCode[0] == 255)
{
try
{
ReadFromSocket(ref resultErrorCode);
}
catch (Exception)
{
}
}
Console.WriteLine(ErrorList[resultErrorCode[0] - 48]);
I use ReadFromSocket in other places, so I know that it is working correctly. What ends up happening is that the port I am connecting from (on my machine) changes to random ports. I think that this causes the firmware on the other side to have a bad connection. So when I write data on the other side, it tries to write data to the original port that I connected through, but after trying to read several times, the connection port changes on my side.
How can I read from the socket continuously until I receive a completion command? If I know that something is wrong with the loop because for my smallest test file it takes 1 min and 13 seconds pretty consistently. I have tested the code by removing the loop and putting the code to sleep for 1 min and 15 seconds. When it resumes, it successfully reads the completion command that I am expecting. Does anyone have any advice?

What you should have is a separate thread which will act like a driver of your external hardware. This thread will receive all data, parse it and transmit the appropriate messages to the rest of your application. This portion of code will give you an idea of how receive and parse data from your hardware.
public void ContinuousReceive(){
byte[] buffer = new byte[1024];
bool terminationCodeReceived = false;
while(!terminationCodeReceived){
try{
if(server.Receive(buffer)>0){
// We got something
// Parse the received data and check if the termination code
// is received or not
}
}catch (SocketException e){
Console.WriteLine("Oops! Something bad happened:" + e.Message);
}
}
}
Notes:
If you want to open a specific port on your machine (some external hardware are configured to talk to a predefined port) then you should specify that when you create your socket
Never close your socket until you want to stop your application or the external hardware API requires that. Keeping your socket open will resolve the random port change
using Thread.Sleep when dealing with external hardware is not a good idea. When possible, you should either use events (in case of RS232 connections) or blocking calls on separate threads as it is the case in the code above.

C# Sending Data over serial port between 2 PC using own Protocol

I have an assignment where I need to load some data like user (pouzivatel) and some int(stav odberu) through link modem with the serial port and store it in my local database. I know how to load data, send data over the serial port, but I need to make it happen in a structure on the image.
First I dial the telephone number of the device with AT command, btw this is working, but I do not know now how to stop and wait for SOH+adresa objektu (SOH+some string about address). Then send data about confirmation (ACK) and wait for new data to come.
The wait sequence is my biggest problem. How do I stop and wait for data being received.

Using the component and utilizing its DataReceived event as suggested in the comments would probably solve your problem easy and effectively. But you may have been looking for something more low-level to do it yourself.
If you want/need to do it in-line without any fancy event based system that would assume you are already in some message queue based environment like WinForms, you could do something like this.
while (true)
{
// check for new data
...
// if you got some, respond to it
...
if (someConditionThatTellsYouYouAreDoneOrSupposedToTerminate) break;
System.Threading.Thread.Sleep(50);
}

Handling dropped TCP packets in C#

I'm sending a large amount of data in one go between a client and server written C#. It works fine when I run the client and server on my local machine but when I put the server on a remote computer on the internet it seems to drop data.
I send 20000 strings using the socket.Send() method and receive them using a loop which does socket.Receive(). Each string is delimited by unique characters which I use to count the number received (this is the protocol if you like). The protocol is proven, in that even with fragmented messages each string is correctly counted. On my local machine I get all 20000, over the internet I get anything between 17000-20000. It seems to be worse the slower connection that the remote computer has. To add to the confusion, turning on Wireshark seems to reduce the number of dropped messages.
First of all, what is causing this? Is it a TCP/IP issue or something wrong with my code?
Secondly, how can I get round this? Receiving all of the 20000 strings is vital.
Socket receiving code:
private static readonly Encoding encoding = new ASCIIEncoding();
///...
while (socket.Connected)
{
byte[] recvBuffer = new byte[1024];
int bytesRead = 0;
try
{
bytesRead = socket.Receive(recvBuffer);
}
catch (SocketException e)
{
if (! socket.Connected)
{
return;
}
}
string input = encoding.GetString(recvBuffer, 0, bytesRead);
CountStringsIn(input);
}
Socket sending code:
private static readonly Encoding encoding = new ASCIIEncoding();
//...
socket.Send(encoding.GetBytes(string));

If you're dropping packets, you'll see a delay in transmission since it has to re-transmit the dropped packets. This could be very significant although there's a TCP option called selective acknowledgement which, if supported by both sides, it will trigger a resend of only those packets which were dropped and not every packet since the dropped one. There's no way to control that in your code. By default, you can always assume that every packet is delivered in order for TCP and if there's some reason that it can't deliver every packet in order, the connection will drop, either by a timeout or by one end of the connetion sending a RST packet.
What you're seeing is most likely the result of Nagle's algorithm. What it does is instead of sending each bit of data as you post it, it sends one byte and then waits for an ack from the other side. While it's waiting, it aggregates all the other data that you want to send and combines it into one big packet and then sends it. Since the max size for TCP is 65k, it can combine quite a bit of data into one packet, although it's extremely unlikely that this will occur, particularly since winsock's default buffer size is about 10k or so (I forget the exact amount). Additionally, if the max window size of the receiver is less than 65k, it will only send as much as the last advertised window size of the receiver. The window size also affects Nagle's algorithm as well in terms of how much data it can aggregate prior to sending because it can't send more than the window size.
The reason you see this is because on the internet, unlike your network, that first ack takes more time to return so Naggle's algorithm aggregates more of your data into a single packet. Locally, the return is effectively instantaneous so it's able to send your data as quickly as you can post it to the socket. You can disable Naggle's algorithm on the client side by using SetSockOpt (winsock) or Socket.SetSocketOption (.Net) but I highly recommend that you DO NOT disable Naggling on the socket unless you are 100% sure you know what you're doing. It's there for a very good reason.

Well there's one thing wrong with your code to start with, if you're counting the number of calls to Receive which complete: you appear to be assuming that you'll see as many Receive calls finish as you made Send calls.
TCP is a stream-based protocol - you shouldn't be worrying about individual packets or reads; you should be concerned with reading the data, expecting that sometimes you won't get a whole message in one packet and sometimes you may get more than one message in a single read. (One read may not correspond to one packet, too.)
You should either prefix each method with its length before sending, or have a delimited between messages.

It's definitely not TCP's fault. TCP guarantees in-order, exactly-once delivery.
Which strings are "missing"? I'd wager it's the last ones; try flushing from the sending end.
Moreover, your "protocol" here (I'm taking about the application-layer protocol you're inventing) is lacking: you should consider sending the # of objects and/or their length so the receiver knows when he's actually done receiving them.

How long are each of the strings? If they aren't exactly 1024 bytes, they'll be merged by the remote TCP/IP stack into one big stream, which you read big blocks of in your Receive call.
For example, using three Send calls to send "A", "B", and "C" will most likely come to your remote client as "ABC" (as either the remote stack or your own stack will buffer the bytes until they are read). If you need each string to come without it being merged with other strings, look into adding in a "protocol" with an identifier to show the start and end of each string, or alternatively configure the socket to avoid buffering and combining packets.