Getting the source address of an incoming socket connection

Question

I have a server with a incoming socket from a client. I need the get the IP address of the remote client. Tried searching google for in_addr but it's a bit troublesome. Any suggestions?

Solution 1

You need the getpeername function:

// assume s is a connected socket

socklen_t len;
struct sockaddr_storage addr;
char ipstr[INET6_ADDRSTRLEN];
int port;

len = sizeof addr;
getpeername(s, (struct sockaddr*)&addr, &len);

// deal with both IPv4 and IPv6:
if (addr.ss_family == AF_INET) {
    struct sockaddr_in *s = (struct sockaddr_in *)&addr;
    port = ntohs(s->sin_port);
    inet_ntop(AF_INET, &s->sin_addr, ipstr, sizeof ipstr);
} else { // AF_INET6
    struct sockaddr_in6 *s = (struct sockaddr_in6 *)&addr;
    port = ntohs(s->sin6_port);
    inet_ntop(AF_INET6, &s->sin6_addr, ipstr, sizeof ipstr);
}

printf("Peer IP address: %s\n", ipstr);

Solution 2

Assuming you're using accept() to accept incoming socket connections, getpeername() isn't needed. The address information is available via the 2nd and 3rd parameters of the accept() call.

Here is Eli's answer modified to do it without getpeername():

int client_socket_fd;
socklen_t len;
struct sockaddr_storage addr;
char ipstr[INET6_ADDRSTRLEN];
int port;

len = sizeof addr;
client_socket_fd = accept(server_socket_fd, (struct sockaddr*)&addr, &len);

// deal with both IPv4 and IPv6:
if (addr.ss_family == AF_INET) {
    struct sockaddr_in *s = (struct sockaddr_in *)&addr;
    port = ntohs(s->sin_port);
    inet_ntop(AF_INET, &s->sin_addr, ipstr, sizeof ipstr);
} else { // AF_INET6
    struct sockaddr_in6 *s = (struct sockaddr_in6 *)&addr;
    port = ntohs(s->sin6_port);
    inet_ntop(AF_INET6, &s->sin6_addr, ipstr, sizeof ipstr);
}

printf("Peer IP address: %s\n", ipstr);

Solution 3

Since you say it is an incoming connection from a client, as an alternative to getpeername you can just save the address that was returned by the accept() call, in the second and third parameters.

Comments

[iammilind]

+1 for directly using accept(). However don't we have to free any memory for this?

[iammilind]

+1. However don't we have to free any memory for this?

[Exectron]

@iammilind: I don't think any memory needs to be freed—I can't see any dynamic allocations being done. It's all done with statically allocated variables.

[Exectron]

I notice the struct sockaddr_in *s shadows the socket s in the outer scope. Having a shadowed variable isn't ideal.

[Bionix1441]

is there a way to get the socketDescriptor from the address

[kbridge4096]

@RecolicKeghart try wayback machine :)

[recolic]

@brk It works! Please use this link if you're suffering from 404 too.