Why won't my server implementation run concurrently properly? - c

Question

I am attempting to create a client/server system that can handle multiple concurrent connections using the unix system call fork.
The client enters a movie title, and the server will check if the movie was there or not. If it was there, it would tell the client the ranking, the name, and the box records.
looking at my forking implementation, the client asks for user input, however the program just simply goes pass it.
OUTPUT EXAMPLE:
connection made with client 127.0.0.1
PID IS 27270
--> all messages read - connection being closed
CLIENT: Please input an string: PID IS 0
At this line, CLIENT: Please input an string: PID IS 0, the user was suppose to input a string, however the program glances over it. How do I make the program take in the string from the client?
SERVER CODE:
int main()
{
int sock, clientsock, mlen, addrsize, msgct, chc, chct, pid;
struct sockaddr_in addr; //ipv4 address
char ch, buf[80];
/*
* Create a socket.
*/
sock = socket(AF_INET, SOCK_STREAM,0); //create socket (AF_NET shows its ipv4 internet connection, SOCK_STREAM shows its a tcp)
if (sock == -1)
{
perror("opening socket");
exit(-1);
}
//Bind socket to local address
/*
* Bind a name to the socket. Since the server will bind with
* any client, the machine address is zero or INADDR_ANY. The port
* has to be the same as the client uses.
*/
addr.sin_family = AF_INET;
addr.sin_port = htons (32351); //port number for local address
addr.sin_addr.s_addr = htonl (INADDR_ANY); //ip address (you can also hard code it)
if (bind(sock, (struct sockaddr *) &addr, //binding, first parameter : is the socket you created, &addr is the
sizeof (struct sockaddr_in)) == -1) //error checking
{
perror ("on bind");
exit (-1);
} //(at this moment we have binded socket)
/*
* Make the socket available for potential clients.
*/
//if there is connection or not?
if (listen(sock,1) == -1)
{
perror("on listen");
exit(-1);
}
//-------Text File Implementation-----------
FILE *fp;
char data[5][200];
char rank[5][2];
char name[5][255];
char value[5][100];
/* opening file for reading */
fp = fopen("movie.txt", "r");
if(fp == NULL) {
perror("Error opening file");
return(-1);
}
fgets (data[0], 200, fp);
int i = 1;
while(fgets (data[i], 200, fp)!=NULL)
{
/* writing content to stdout */
sscanf(data[i],"%s %[^$] %s",rank[i],name[i],value[i]);
puts(data[i]);
i+=1;
}
//CODE DOES NOT IMPLEMENT AFTER THIS WHILE LOOP
//close the file
fclose(fp);
addrsize = sizeof(struct sockaddr_in);
//THIS WHILE LOOP IS NOT BEING IMPLEMENTED...
while(1)
{
clientsock = accept(sock, (struct sockaddr *) &addr, &addrsize);
if (clientsock == -1)//error checking
{
perror("on accept");
exit(-1);
}
printf("connection made with client ");
printf ("%s\n", inet_ntoa (addr.sin_addr)); //also print client address
/* Create child process */
pid = fork();
if (pid < 0)
{
perror("ERROR on fork");
exit(1);
}
if (pid == 0)
{
/* This is the client process */
close(sock);
bool exist = false;
mlen = recv (clientsock, buf, 80, 0);
if (mlen < 0)
{
perror("ERROR reading from socket");
exit(1);
}
int lenS;
int which;
for(int i = 1; i<5; i++)
{
printf("%s\n\n", name[i]);
char *pch = strstr(name[i],buf);
if(pch != NULL)
{
which = i;
exist = true;
puts("GOOD");
}
else
{
puts("bad");
}
}
if(exist)
{
//SEND TO CLIENT FROM HERE!
printf("%s\n", rank[which]);
printf("%s\n", name[which]);
printf("%s\n", value[which]);
lenS = strlen(name[which]);
send (clientsock, name[which], lenS+1, 0);
}
else
{
//SEND TO CLIENT FROM HERE!!!!
printf("NOT HERE ");
send (clientsock, "NOT HERE", 9, 0);
}
printf("Here is the message: %s\n",buf);
exit(0);
}
else
{
close(clientsock);
printf(" --> all messages read - connection being closed\n");
}
}
}
CLIENT CODE:
int main()
{
int sock, addrsize;
struct sockaddr_in addr;
unsigned int in_address;
char buf[80];
int mlen;
/*
* Open a socket for Internet stream services.
*/
sock = socket(AF_INET, SOCK_STREAM,0); //creating a socket to connect to server, AF_INET : ipv4 internet connection, SOCK_STREAM tcp
if (sock == -1)
{ perror("opening socket");
exit(-1);
}
addr.sin_family = AF_INET;
addr.sin_port = htons (32351); //port number has to be the same as the one from server
in_address = 127 << 24 | 0 << 16 | 0 << 8 | 1; //ip address, local host, since we are running client and server on the same computer, it needs to have the same ip address
addr.sin_addr.s_addr = htonl (in_address);
if (connect (sock, (struct sockaddr *) &addr, //binding
sizeof (struct sockaddr_in)) == -1)
{
perror("on connect");
exit(-1);
}
char word[100];
int len;
printf("CLIENT: Please input an string: ");
scanf("%s", word);
//printf("You entered: %s\n", word);
len = strlen(word);
send (sock, word, len+1, 0);
mlen = recv (sock, buf, 80, 0);
printf ("%s\n\n\n\n\n\n\n", buf);
/*
* Do a shutdown to gracefully terminate by saying - "no more data"
* and then close the socket -- the shutdown is optional in a one way
* communication that is going to terminate, but a good habit to get
* into.
*/
if (shutdown(sock, 1) == -1)
{
perror("on shutdown");
exit(-1);
}
printf ("Client is done\n");
close(sock);
}

Answer 1

You are running the client and server programs on the same machine, with the same controlling terminal. The server master process, its client-service subprocess(es), and the independent client process therefore may all write to that terminal. They run independently and concurrently, so their outputs can be mashed up.
The fact that the PID IS 0 message is emitted after the prompt does not indicate that the client program has skipped accepting input, which indeed, I don't see how it could do. The prompt and the PID message come from different processes.
It would make things clearer to launch the server process and the client process from separate (virtual) terminals, so that their output is not mixed.