I am using boost::asio, TCP communication and C++ to create a client and a server that talk over a TCP socket. I need both the client and the server to be able send and receive data to each other. I am able to make them communicate over a socket where the server is continuously sending some data and the client is continuously reading on the socket. It works.
Now for the other way communication : For client to send some data and the server to be able to read it, can I use the same socket for this? Or Do I need to use a separate socket? Is it possible to read and write on the same socket for two applications communicating over TCP?
A boost::asio based example to illustrate this will be great if available. But I am able to find examples which are about only one-way communications.
For client to send some data & server to be able to read it, can I use the same socket for this? Or Do I need to use a separate socket ? Is it possible to read and write on the same socket for two applications communicating over TCP ?
Yes. TCP is full duplex. Applications define the protocol of what/how messages are exchanged between client and server. Weather they do asynchronously or synchronously, TCP doesn't care.
The client server paradigm in tcp is one where the client initiates the connection and the server listens for incoming connections. Once tge connection is established, it is up to higher layer protocol like http to establish how data is exchanged. As far as tcp is concerned both client and server may send or receive data any way they choose. Tcp is full duplex.
Related
so I want to send an int32 (or any 4 bytes data) from one pc to another, the size of the data will always be the same, I don't need any checking to see if both pcs are online or any disconnect function, if pc2 didn't receive the data or he went offline, I just want pc1 to send the data, if pc2 is offline nothing happens and if it's online it store it somewhere.
Most tutorials I've found uses a server way of connecting, so there are 3 pcs, 2 clients and 1 server, client1 sends data to the server and the server sends it to client2, but is there a way to send it directly to client2, as if client2 is the server?
There are two common protocols used to send raw data over an ip based network. They are called TCP and UDP and serve slightly different approaches.
TCP is connection oriented and relies heavily on the server client model. On host acts as a server and accepts incoming requests on a predefined socekt. After the TCP connection is setup, you have a duplex (two-way) stream that you can use to exchange data.
UDP is a packet oriented protocol. One host (usually called the server) listens to imcoming packets and can answer them. No real "connection" is established tough.
You probably want to use UDP. Note that altough this protocol does not establish a connecion, there still needs to be at least one host, that is waiting for incoming data on a predefined port. This one is usually called the "server". However also the client can bind its UDP socket to a specific port and thus can act as a "client" and a "server" during the same time.
You can setup both hosts to listen and send on/to the same preefined port number and achieve a connectionless packetoriented way to exchange data. That way both hosts act as server and client simultaneously.
How you actually implement this, depends on your operating system. On Linux (and other POSIX compatible OSes) you can use standard UDP sockets, on Windows there is some equivalent API. Either way I suggest you to first follow a tutorial on how to program a standard TCP server and client, as most of the operations on the sockets are similar (create the socket, bind it to an address:port, and read/write data from it).
I have a UDP server, but I have no UDP capability on client side. Is there a way to send packet via TCP so that UDP server can receive it normally? UDP server cannot be transformed into TCP server.
Reason for wanting to do this is that I'm using a SOCKS5 proxy that does not support UDP associate capability, but I have to use that proxy.
No. The UDP server cannot complete the 3-way handshake required for TCP. If you have IP-raw sockets, it is actually easier to implement UDP on top. However it seems extremely unlikely that you don't have a UDP-stack.
When you talk about "no UDP capability" do you mean the client has no UDP-stack, or is he just behind some firewall that blocks UDP? In the latter case use a proxy.
No, UDP server will not going to accept TCP packets at all (it's a different protocol, so network stack will never propagate those to the application).
If you have to use SOCKS5 proxy, the only way to connect to the said server is by using another proxy-like application, which will stand beyond SOCKS5, accept TCP connections (initiated by app behind SOCKS5 proxy) and retransmit data as UDP.
I have been looking at a lot of Boost.Asio tutorials, especially this one:
TCP daytime server
After a server creates a tcp_connection with a client, it seems like the communication is only one-way between the server and that specific client. How can I make it so a server has the ability to relay client messages to all of the clients connected? Or even choose which clients to send messages to.
TCP create only connexion between the server and a specific client. You can use UDP connexion to broadcast message to several clients.
Like JTejedor says in comments, you can also create a TCP socket for each client.
Dear Stackoverflowers,
I am researching networking a bit and I decided I'd like to create a small and simple networking library with Winsock. (I am using Completion Ports and Overlapped IO though)
As I researched a bit I came to the following steps for a TCP Listener(Correct me if I am wrong):
Create a Listening Socket
Bind it to a port/IP
Listen on it
When a new connection is created, give a seperate Socket for that connection.
Listener continue's to listen, the specific connection is handled as needed.
EDIT: With a 'connection' from here I mean communication between the server and distinct clients.
Though for an UDP Listener we need to make use of WSARecvFrom which returns the IP address at the lpFrom parameter. Now I was wondering the following:
Is it better to make one UDP Socket listen to incoming connections on a specific port with WSARecvFrom and create new sockets for every specific connection? Or could I just use the UDP Socket itself with WSASendTo. Would that cause any performance penalties if one UDP Socket is used for for example 1000 connections? Or would it be the same or even better then creating/duplicating seperate Sockets for each different incoming connection?
Note: If multiple sockets are needed how would you handle sockets listening on the same port or could a client accept UDP from different ports?
Hope you guys can help!
Ps. Extra tips are always welcome!
Unlike TCP, UDP is connection-less, and as such you don't need to create separate sockets for each party. One UDP socket can handle everything. Bind it to a local IP/Port and call WSARecvFrom() once, and when it reports data to your IOCP you can process the data as needed (if another thread if needed) and then call WSARecvFrom() again. Each time new data arrives, you have to look at the reported lpFrom address to know the IP/Port of the sender. And yes, you can use the same UDP socket for sending data to each sender when needed.
I saw the official async udp server example from boost doc.
There you create a single udp socket, bind it to a local port and do something like this:
socket(ioService, boost::asio::ip::udp::endpoint(boost::asio::ip::udp::v4(), port))
socket.async_receive_from(buffer(data, max_length), senderEndpoint, boost::bind(&Request::HandleReceiveFrom, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
How can I handle multiple concurrent udp connections from clients, because if I try to create another socket using
socket(ioService, boost::asio::ip::udp::endpoint(boost::asio::ip::udp::v4(), port))
i get bind errors because I already have a socket bound to the same port.
EDIT
I can send clients back responses using a different server source port but they will not recognize the response even though I sent the response back to the same client ip/client destination port.
UDP is a connectionless transport so the concept of connections is meaningless as far as UDP is concerned.
If you want to send data back to the originator of the message you'll need to keep a copy of the sender_endpoint returned in the async_receive_from callback and pass it back in the async_send_to.
This also assumes that the client is also polling/reading and expecting a reply. It need not listen on the same bound port as the server (you don't need to bind with UDP on the client side).
I recommend you have a read of Beej's guide to network programming to help you understand what's going on under the hood of boost ASIO. Boost ASIO complicates things a lot IMHO.
http://beej.us/guide/bgnet/output/html/singlepage/bgnet.html#sendtorecv
If your clients send their messages to the same port on your server then the only way to distinguish them is by the remote port or a combination of remote port and remote ip.
You create some sort of mapping from client-id (e.g. pair<remote_ip, remote_port>) to a dispatcher type (e.g map< pair<remote_ip, remote_port>, dispatcher>). This then it's up to you to make it threaded in order to support concurrent requests.
As it seems the solution can be to use the same socket for sending back responses to clients. Have a look at this question response: Use same udp socket for async receive/send