When I'm trying to bind a UDP socket on a specific ip (other than 127.0.0.1/INADDR_LOOPBACK or 0.0.0.0/INADDR_ANY) it fails.
I need to have a dedicated UDP socket for each client (point to point connection).
If I don't bind the socket and use sendto and recvfrom function, the data never arrives.
Any obvious solution ?
You can't bind UDP sockets to nonlocal addresses -- binding a UDP socket to an address means that you want packets that are directed to that address, not ones that are being sent from that address. You'll need to figure out some way to share a single socket across all clients.
Related
Is it possible to set the default destination of a UDP socket just like connect does, but without loosing the ability to receive datagrams from other sources?
I'm talking about the native OS socket API (BSD-socket / winsock2) and I'm interested in answers for both linux and windows platforms.
[EDIT:]
In case this is unclear, here is the problematic part from the connect docs:
If the socket sockfd is of type SOCK_DGRAM then addr is the address to which datagrams are sent by default, and the only address from which datagrams are received.
Is it possible to set the default destination of a UDP socket just
like connect does, but without loosing the ability to receive packages from other sources?
As far as I can tell, it is not -- connect() on a UDP socket both sets a default-send-destination and installs a filter so that incoming UDP packets from all other destinations than the specified address/port are dropped.
My solution to the problem was to just call sendto() and recvfrom() instead (if you have a UDPSocket class or similar in your codebase, you can cache the default-send address as a private member variable in that class, so that the rest of your codebase can just call a Send() method, and leave it to that method to handle the sendto() arguments)
I found this defeinitons of funcion listen and recv in winsock library (TCP/IP stream communication).
The listen function places a socket in a state in which it is listening for an incoming connection.
The recv function receives data from a connected socket or a bound connectionless socket.
Does it mean that if I want to receive data from particular socket I should firstly use listen and then recv? I'm not sure if I understand this correctly.
The functions listen and recv have quite different functionalities and uses.
The listen function is designed to allow a server awaiting the connection of one or more clients to listen on a port for if anyone connects.
The recv function is used on an already established socket to receive data which has been sent from the machine at the other end of that socket.
As it has been mentioned in comments, I shall also mention connect. Connect is the counterpart of listen. It talks to the port which a listening machine is listening on and establishes a socket with that machine.
what the BSD socket and winsock libraries don't really make clear is that from a programmers perspective there are two quite different kinds of socket, a listening socket and an established one.
A server will first need to create a listen socket with which it waits for clients, this socket is not used for actually sending any data, it only exists in order to aid the creation of an established socket. However the listening socket does not become the established socket, when a client connects, the listen socket actually creates a second socket for the data transfer.
The established socket is the kind we recognise and use for most things. It is a socket with machines at both ends, listening and sending to perform data transfer.
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 have problems understanding the concept behind Boost.Asio's (using v1.49.0) boost::asio::ip::udp::socket sockets.
First I am gonna to to explain what I want to achieve:
I hide the Boost.Asio sockets behind a very simple interface (Pure Abstract Base Class), so I have two wrapper classes that allow to access either a stream socket or a datagram socket.
I want to configure both the local endpoint and the remote endpoint before passing the Boost.Asio socket to the constructor of my wrapper class.
I want to use the socket.receive (alternatively boost::asio::read) and socket.send (alternatively boost::asio::write) member functions instead of the socket.receive_from and socket.send_to member functions.
The only way to use socket.send and socket.receive with a boost::asio::ip::udp::socket seems to connect the socket.
A UDP socket can both be bound and connected:
Binding is achieved via the socket.bind member function.
Connecting is achieved via the socket.connect member function.
The problem is, that even though I am able to
Open the socket,
Set socket options,
Bind the socket,
Connect the socket,
and to be able to send data via the socket, I can not receive data from the socket. If I don't connect the socket, I can receive data via the bound local endpoint, but I am unable to send data with the approached described.
So my central question is: Am I trying something that is impossible to achieve?
Can I only use bind or connect with one socket instance?
If the answer to the two previous questions is no: What do I have to do, to be able to receive and send data via a bound and connected Boost.Asio UDP socket.
I know that UDP is in fact connectionless, therefore the text uses Boost.Asio terminology. I have also read connect on "connection less" boost::asio::ip::udp::socket which seems to indicate that it is impossible what I am trying.
You are missing one point from man page ofconnect:
If the socket sockfd is of type SOCK_DGRAM, then addr is the address to which datagrams are sent by default, and the only address from which datagrams are received.
This means, that if you want to connect the socket, then it will be able to receive datagrams only from remote endpoint (the connected one), i.e. peer will have to bind own socket before sending datagram to your socket waiting for data.
If you need to received data from more than one peer, you can connect udp socket to "any" address (i.e. 0.0.0.0 - udp::v4()) and some port.
I'm writting an UDP server for a game.
Do you know if is possible to have multisocket in UDP on one port ? or I must use dynamic port (one socket = one port) ?
thanks
It make no large sense to create multiple socket on one UDP port. UDP is not point 2 point protocol like TCP so using one "server" socket bind to specific port you can handle hundreds of clients.
See Using SO_REUSEADDR...:
Using SO_REUSEADDR
The SO_REUSEADDR socket option allows a socket to forcibly bind to a
port in use by another socket. The second socket calls setsockopt with
the optname parameter set to SO_REUSEADDR and the optval parameter set
to a boolean value of TRUE before calling bind on the same port as the
original socket. Once the second socket has successfully bound, the
behavior for all sockets bound to that port is indeterminate. For
example, if all of the sockets on the same port provide TCP service,
any incoming TCP connection requests over the port cannot be
guaranteed to be handled by the correct socket — the behavior is
non-deterministic. A malicious program can use SO_REUSEADDR to
forcibly bind sockets already in use for standard network protocol
services in order to deny access to those service. No special
privileges are required to use this option.
Bonus reading: What exactly does SO_REUSEADDR do? .
Sure you can have multiple UDP sockets on one port if SO_REUSEADDR is specified via setsockopt.
However, I doubt that what you really need is using one UDP socket to communicate with multiple clients, which is also feasible. UDP is not connection-oriented, UDP APIs like sendto and recvfrom could distinguish different peers on one socket.