TCP server accept call does not return - tcp

Question

We need some help with a TCP client server code. The client timesout from its connect call and the server does not return from accept. Here's the strace.
strace -p 7167 -p 7168 -p 7297
Process 7167 attached - interrupt to quit
Process 7168 attached - interrupt to quit
Process 7297 attached - interrupt to quit
[pid 7167] accept(4, <unfinished ...>
[pid 7168] accept(4, <unfinished ...>
[pid 7297] connect(3, {sa_family=AF_INET, sin_port=htons(24465), sin_addr=inet_addr("215.47.142.168")}, 16
We rebooted the system but the problem persists even immediately after reboot.
Could it be a SYN Flood problem. How do we deal with such connections? Also, do the half made connections queue up in the listen queue(argument 2 of listen call) and stop any further accepts from any client OR does the TCP some how blocks that particular client only.
Here's the code...
client.all this is inside a function that returns socket
int sock = socket(nmspace,style,protocol);
int ret;
struct hostent *hinfo;
if(sock<0){
printf("Error occurred while creating socket:%d\n",sock);
printf("%s\n",strerror(errno));
return -1;
}
memset(&dest, 0, sizeof(struct sockaddr_in));
hinfo = gethostbyname(rmserver);
if(hinfo == NULL)
printf("getbyname failed!\n");
dest.sin_family = AF_INET;
dest.sin_addr = *(struct in_addr *)(hinfo->h_addr);
dest.sin_port = htons(port);
ret = connect(sock, (struct sockaddr *)&dest, sizeof(struct sockaddr));
if(ret<0){
printf("Error occurred while connecting on the socket:%d\n",sock);
printf("%s\n",strerror(errno));
close(sock);
return -1;
}
server
making the server socket...all this is inside a function that returns the socket>>>>>>
struct sockaddr_in serv;
int mysocket,r;
mysocket = socket(AF_INET, SOCK_STREAM, 0);
memset(&serv, 0, sizeof(struct sockaddr_in));
serv.sin_family = AF_INET;
serv.sin_addr.s_addr = INADDR_ANY;
serv.sin_port = htons(port);
r = bind(mysocket, (struct sockaddr *)&serv, sizeof(struct sockaddr));
if(r<0) {
printf("Error occurred binding the socket:%d to the server port:%d\n",mysocket,port);
printf("%s",strerror(errno));
close(mysocket);
return -1;
}
r = listen(mysocket, 5);
if(r<0) {
printf("Error occurred while enabling listen on the socket:%d\n",mysocket);
printf("%s",strerror(errno));
close(mysocket);
return -1;
}
server accept call>>>>>>
struct sockaddr_in dest;
int socksize=sizeof(struct sockaddr_in);
int consocket;
consocket = accept(sock, (struct sockaddr *)&dest, (socklen_t *)&socksize);
if(consocket<0) {
printf("Error occurred while accepting on the socket:%d\n",sock);
printf("%s\n",strerror(errno));
}
Not using select. I hope we don't need that as the sockets are by default blocking.
cheers...raman

Answer 1

Your client should be using connect (man page) rather than accept. Servers use accept to accept incoming connections and to get a new socket unique to that connection, leaving the original file descriptor free for listening and accepting new connections. Clients just use the same socket after the connection is made.
Also, I recommend taking a look at how to use select (man page).