C socket get IP address from filedescriptor returned from accept

user_743194 0
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I know this question seems typical and multiple times answered but I think if you read the details it is not so common (I did not find it).

The point is that I am developing a unix service in c that opens a socket and waits for connections, when I have a connection I create a new process to treat it, so there can be multiple connections opened at the same time.

int newfd = accept(sockfd, (struct sockaddr *)&clientaddr, (socklen_t*)&clientaddr_size);

Later on (after and inside some other methods and code) the child process save the connection information to the BBDD and I need also, in that precise moment, to get the IP address that opened that connection being treated.

As there can be multiple connections at the same time and the variable struct sockaddr_in clientaddr that I pass to the accept method is shared for all the process I am not sure that later on is a good idea to get the IP address information from that way because then I could get the IP address from another connection opened.

I would like to be able to access the IP address from the file descriptor int newfd that I get from the accept method (the returned integer). Is it possible? Or I misunderstood the file descriptor function?

file-descriptor sockets unix fork c
4 Answers

Statefull connection is uniquely identified by two end points Peer(address:port)<=>My(address:port). Both getpeername() and getsockname() are needed to get this information.

user_22904130

Found this helpful example

This is how I did it

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <time.h> 

int main(int argc, char *argv[])
{
    int listenfd = 0, connfd = 0;
    struct sockaddr_in serv_addr; 
    socklen_t len; 


    char sendBuff[1025];

    time_t ticks; 

    listenfd = socket(AF_INET, SOCK_STREAM, 0);
    memset(&serv_addr, '0', sizeof(serv_addr));
    memset(sendBuff, '0', sizeof(sendBuff)); 

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port = htons(5000); 

    bind(listenfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr)); 

    listen(listenfd, 10); 

    while(1)
    {
        connfd = accept(listenfd, (struct sockaddr*)NULL, NULL); 

        ticks = time(NULL);
        snprintf(sendBuff, sizeof(sendBuff), "%.24s\r\n", ctime(&ticks));
        printf("%d \n",connfd);
        
        getpeername(connfd, (struct sockaddr*)&serv_addr, &len );
        printf("Peer connected %s:%d\n", inet_ntoa(serv_addr.sin_addr),ntohs(serv_addr.sin_port));

        write(connfd, sendBuff, strlen(sendBuff)); 

        close(connfd);
        sleep(1);
     }
}
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