TCP-Socket Programming in C - c

Question

I have two files: tcp-demo-client.c and tcp-demo-server.c
Functionality: If the connection succeeds, the client receives a simple timestamp from the server. I like to modify the code that the server only sends the timestamp if the client hits the space key. How can I do that?
(It's my first socket project)
tcp-demo-client.c:
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <time.h>
int main(int argc, char **argv)
{
int ret; // return value from functions
// Check command line arguments
if (argc != 3) {
fprintf(stderr,
"Missing parameters. Usage: %s <server-name-or-ip> <server-port>\n",
argv[0]);
return 1;
}
// Address information structure
struct addrinfo aii;
// Set whole structure to 0s
memset(&aii, 0, sizeof(aii));
// A stream (TCP) connection
aii.ai_socktype = SOCK_STREAM;
// We do not care whether it is IPv4 or IPv6
aii.ai_family = PF_UNSPEC;
struct addrinfo *aio;
// Get address information.
// First parameter is host string, either hostname or numerical IPv4/IPv6 address
// Second parameter is port/service string, either as port number
// or well-known identifier, e.g. http
// So, e.g. getaddrinfo( "www.compeng.uni-frankfurt.de", "http", ... getaddrinfo( "141.2.248.1", "80", ...
// Third parameter is input address info structure (cf. above)
// Fourth parameter is output address info structure, a linked list of potential addresses
ret = getaddrinfo(argv[1], argv[2], &aii, &aio);
if (ret) {
fprintf(stderr, "Error getting address for %s:%s: %s\n",
argv[1], argv[2], gai_strerror(ret));
return 1;
}
// File descriptor for the socket
int sock = -1;
struct addrinfo *iter;
// Iterate over linked list of specified output addresses,
// use first address to which a connection can be established
for (iter = aio; iter != NULL && sock == -1; iter = iter->ai_next) {
// Create socket given the parameters from the found address info.
sock =
socket(iter->ai_family, iter->ai_socktype,
iter->ai_protocol);
if (sock < 0)
continue; // Appropriate socket could not be created, try next address
// Socket created successfully, now try to connect to remote target address
// taken from address info
ret = connect(sock, iter->ai_addr, iter->ai_addrlen);
if (ret) {
// Socket could not be connected to remote target
close(sock); // Close socket
sock = -1;
continue; // try next address
}
}
freeaddrinfo(aio); // Release address information allocated in getaddrinfo
if (sock == -1) {
// No connection at all could be established to remote target
fprintf(stderr, "Unable to establish any connection to %s:%s\n",
argv[1], argv[2]);
return 1;
}
// Maximum size of incoming message
int msglen = 100;
// Buffer for message
char buf[msglen + 1]; // One more to ensure that there is a trailing NULL char.
memset(buf, 0, msglen + 1);
ret = read(sock, buf, msglen); // Return value is amount of bytes read, -1 in case of error
printf("Data read: '%s'\n", buf);
// Clean up after us and close the socket.
close(sock);
return 0;
}
tcp-demo-server.c:
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <time.h>
#define MAXPENDING 5
int main(int argc, char **argv)
{
unsigned short listen_port; // Server port */
int listen_sock; // Socket descriptor for server
int client_sock; // Socket descriptor for client
struct sockaddr_in listen_addr; // Local address */
struct sockaddr_in client_addr; // Client address */
// Check command line arguments
if (argc != 2) {
fprintf(stderr, "Missing parameters. Usage: %s <server-port>\n",
argv[0]);
return 1;
}
// Create socket for incoming connections
if ((listen_sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0) {
perror("socket() failed");
return 1;
}
// Construct local address structure
listen_port = atoi(argv[1]); // First arg: listening port number
memset(&listen_addr, 0, sizeof(listen_addr)); // Zero out structure
listen_addr.sin_family = AF_INET; // Internet address family
listen_addr.sin_addr.s_addr = htonl(INADDR_ANY); // Any incoming interface
listen_addr.sin_port = htons(listen_port); // Local port
// Bind to the local address
if (bind
(listen_sock, (struct sockaddr *)&listen_addr,
sizeof(listen_addr)) < 0) {
perror("bind() failed");
return 1;
}
// Mark the socket so it will listen for incoming connections
if (listen(listen_sock, MAXPENDING) < 0) {
perror("listen() failed");
return 1;
}
for (;;) { /* Run forever */
socklen_t addr_len = sizeof(client_addr);
// Wait for a client to connect */
if ((client_sock =
accept(listen_sock, (struct sockaddr *)&client_addr,
&addr_len)) < 0) {
perror("accept() failed");
return 1;
}
// client_sock is connected to a client
printf("New connection from %s\n",
inet_ntoa(client_addr.sin_addr));
// Create message to send
time_t t = time(NULL);
char *msg = ctime(&t);
int msglen = strlen(msg) + 1;
int ret;
// Write the whole message in one go, fail if this does not work
ret = write(client_sock, msg, msglen);
// Return value is amount of bytes written, -1 in case of error
if (ret != msglen) {
perror("Error during write");
return 1;
}
close(client_sock);
}
/* NOT REACHED */
return 1;
}

Answer 1

I presume you mean you want the space char as unbuffered input. For POSIX, you could use something along the lines of this to capture the keypress:
#include <termios.h>
[...]
struct termios t;
int c, r;
[...]
tcgetattr(0, &t);
t.c_lflag &= ~(ICANON | ECHO);
t.c_cc[VMIN] = 1;
tcsetattr(0, TCSANOW, &t);
c = getchar();
r = send(sock, c, 1, 0);
Have a look at this for additional information:
setvbuf not able to make stdin unbuffered
http://c-faq.com/osdep/cbreak.html