CODEWITHSUNDEEP
socketsnetwork-programmingudp
54138qqqq
54138qqqq

Reputation: 127

Can 2 process receive UDP package from the same port?

I am writing a client program receiving data from a UDP server.

The client send a subscribe request to specified (ip, port) of server, and the server start sending UDP package to specified port of client. If some package is missing, the client send a request to another server requesting that package.

My questions, after I compile and run the client program, can I start another instance of the same client program?

Upvotes: 1

Views: 1794

Answers (1)

SKi
SKi

Reputation: 8466

You can run several instances of the same client program.

But, You can't bind the same UDP port number for 2 different UDP socket at the same time in a host (without SO_REUSEADDR).

So those client instances should use different client UDP port numbers. The best way to get different port numbers for clients: Let the OS allocate free port numbers for client sockets.

Usually that can be done by using port number zero, when binding the socket:

struct sockaddr_in addr;

memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = INADDR_ANY;
addr.sin_port = 0;

if (bind(sockfd, (const struct sockaddr *)&addr, sizeof(addr)) == -1)
{
    perror("bind failed");
    exit(EXIT_FAILURE);
}

edit:

For receiving UDP broadcast, you can use socket option SO_REUSEADDR between socket() and bind() calls:

int val = 1;
if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val)) == -1)
{
    perror("setsockopt failed");
    exit(EXIT_FAILURE);
}

struct sockaddr_in addr;

memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = INADDR_ANY;
addr.sin_port = htons(12345);

if (bind(sockfd, (const struct sockaddr *)&addr, sizeof(addr)) == -1)
{
    perror("bind failed");
    exit(EXIT_FAILURE);
}

That way several processes can bind the same port for receiving broadcast messages. --> A broadcast message will be delivered to all 'listeners'.

Upvotes: 2

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