Simple UDP example to send and receive data from same socket

Question

For some reason I am having a hard time sending and receiving data from the same socket  Anyways here is my client code   var client   new UdpClient    IPEndPoint ep   new IPEndPoint IPAddress Parse  127 0 0 1    11000      endpoint where server is listening  testing localy  client Connect ep        send data client Send new byte     1  2  3  4  5    5       then receive data var receivedData   client Receive ref ep       Exception  An existing connection was forcibly closed by the remote host   Basically I want to create a protocol where I send a udp packet and then I expect a response  Just like the HTTP protocol for every request there is a response  This code works if the server is on a different computer  There might be the case where the server and client are on the same computer though   Here is the server   UdpClient udpServer   new UdpClient UDP LISTEN PORT    while  true        var groupEP   new IPEndPoint IPAddress Any  11000      listen on any port     var data   udpServer Receive ref groupEP       udpServer Send new byte     1    1      if data is received reply letting the client know that we got his data                 Edit  the reason why I cannot use tcp is because sometimes the client is behind a NAT  router  and it is simpler to do UDP hole punching than TCP     Solution   thanks to markmnl answer here is my code   Server   UdpClient udpServer   new UdpClient 11000    while  true        var remoteEP   new IPEndPoint IPAddress Any  11000        var data   udpServer Receive ref remoteEP      listen on port 11000     Console Write  receive data from     remoteEP ToString         udpServer Send new byte     1    1  remoteEP      reply back     Client code   var client   new UdpClient    IPEndPoint ep   new IPEndPoint IPAddress Parse  127 0 0 1    11000      endpoint where server is listening client Connect ep       send data client Send new byte     1  2  3  4  5    5       then receive data var receivedData   client Receive ref ep    Console Write  receive data from     ep ToString      Console Read

User · Accepted Answer

I presume you are aware that using UDP User Datagram Protocol  does not guarantee delivery  checks for duplicates and congestion control and will just answer your question    In your server this line   var data   udpServer Receive ref groupEP     re-assigns groupEP from what you had to a the address you receive something on    This line   udpServer Send new byte     1    1      Will not work since you have not specified who to send the data to   It works on your client because you called connect which means send will always be sent to the end point you connected to  of course we don t want that on the server as we could have many clients   I would   UdpClient udpServer   new UdpClient UDP LISTEN PORT    while  true        var remoteEP   new IPEndPoint IPAddress Any  11000       var data   udpServer Receive ref remoteEP       udpServer Send new byte     1    1  remoteEP      if data is received reply letting the client know that we got his data               Also if you have server and client on the same machine you should have them on different ports

User · Answer

I ll try to keep this short  I ve done this a few months ago for a game I was trying to build  it does a UDP  Client-Server  connection that acts like TCP  you can send  message   message   object  using this  I ve done some testing with it and it works just fine  feel free to modify it if needed

User · Answer

here is my soln to define the remote and local port and then write out to a file the received data  put this all in a class of your choice with the correct imports     static UdpClient sendClient   new UdpClient        static int localPort   49999      static int remotePort   49000      static IPEndPoint localEP   new IPEndPoint IPAddress Any  localPort       static IPEndPoint remoteEP   new IPEndPoint IPAddress Parse  quot 127 0 0 1 quot    remotePort       static string logPath   System AppDomain CurrentDomain BaseDirectory    quot  recvd txt quot       static System IO StreamWriter fw   new System IO StreamWriter logPath  true         private static void initStuff                        fw AutoFlush   true          sendClient ExclusiveAddressUse   false          sendClient Client SetSocketOption SocketOptionLevel Socket  SocketOptionName ReuseAddress  true           sendClient Client Bind localEP           sendClient BeginReceive DataReceived  sendClient              private static void DataReceived IAsyncResult ar                UdpClient c    UdpClient ar AsyncState          IPEndPoint receivedIpEndPoint   new IPEndPoint IPAddress Any  0           Byte   receivedBytes   c EndReceive ar  ref receivedIpEndPoint           fw WriteLine DateTime Now ToString  quot HH mm ss ff tt quot       quot    quot    receivedBytes Length    quot  bytes  quot             c BeginReceive DataReceived  ar AsyncState               static void Main string   args                initStuff            byte   emptyByte               sendClient Send emptyByte  emptyByte Length  remoteEP

[c#] Simple UDP example to send and receive data from same socket

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