server can't send message to Client over Socket in C - c

Question

Hi I'm writing 2 Programs (Server, Client) which should communicate with each other over sockets. The Client is able to send its first message to the server with no problem, but when the server tries to answer, the client receives just an empty msg: recv(...) is 0.
The server suddenly stops after the send(...) function is called.
Here is my Code:
Server:
/* Create a new TCP/IP socket `sockfd`, and set the SO_REUSEADDR
option for this socket. Then bind the socket to localhost:portno,
listen, and wait for new connections, which should be assigned to
`connfd`. Terminate the program in case of an error.
*/
struct sockaddr_in sin,
peer_addr;
//-----gen socket-----//
if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
bail_out(EXIT_PARITY_ERROR, "could not create Socket");
//-----bind-----//
memset(&sin, 0, sizeof (sin));
sin.sin_family = AF_INET;
sin.sin_port = htons(options.portno);
sin.sin_addr.s_addr = INADDR_ANY;
if (bind(sockfd, (struct sockaddr *)&sin, sizeof sin) < 0)
bail_out(EXIT_PARITY_ERROR, "Failed to bind to Port");
//-----listen-----//
if (listen(sockfd, 5) < 0)
bail_out(EXIT_PARITY_ERROR, "Server can't accepted connection");
//-----accept-----//
int sock_len = sizeof peer_addr;
if ((connfd = accept(sockfd, (struct sockaddr*)&peer_addr, (socklen_t *)&sock_len)) < 0) //fragen
bail_out(EXIT_PARITY_ERROR, "Can't accept connection to Client");
/* accepted the connection */
//Some other Code which has nothing to do with my Error!
/* read from client (WORKS FINE!!)*/
if (read_from_client(connfd, &buffer[0], READ_BYTES) == NULL) {
if (quit) break; /* caught signal */
bail_out(EXIT_FAILURE, "read_from_client");
}
request = (buffer[1] << 8) | buffer[0];
DEBUG("Round %d: Received 0x%x\n", round, request);
/* compute answer */
correct_guesses = compute_answer(request, buffer, options.secret);
if (round == MAX_TRIES && correct_guesses != SLOTS) {
buffer[0] |= 1 << GAME_LOST_ERR_BIT;
}
DEBUG("Sending byte 0x%x\n", buffer[0]);
/* send message to client */
if (send_to_client(sockfd, &buffer[0], WRITE_BYTES) == NULL) { //Error in this Method!
if (quit) break; /* caught signal */
bail_out(EXIT_FAILURE, "can't send message!");
}
Methods:
static uint8_t *send_to_client(int fd, uint8_t *buffer, size_t n)
{
/* loop, as packet can arrive in several partial reads */
size_t bytes_send = 0;
do {
ssize_t r = send(fd, buffer + bytes_send, n - bytes_send, 0); //Program stops HERE!
printf("%d\n", (int)r); //This and the following lines will not be executed!
if (r <= 0) {
return NULL;
}
bytes_send += r;
} while (bytes_send < n);
if (bytes_send < n) {
return NULL;
}
return buffer;
}
Client: (Might be usefull)
sockfd = cnt_to_server(argv[1], argv[2]);
uint8_t buffer;
uint16_t msg_buffer;
do
{
msg_buffer = generate_msg(&msg);
printf("Sending byte 0x%x\n", msg_buffer);
if (send_to_server(sockfd, &msg_buffer, WRITE_BYTES) == NULL) //works
error_exit(EXIT_FAILURE, "can't send message!");
if (read_from_server(sockfd, &buffer, READ_BYTES) == NULL) //NULL
error_exit(EXIT_FAILURE, "can't read message!");
printf("received byte 0x%x\n", buffer);
} while (game_continue(buffer, &msg));
(void)close(sockfd);
Methods:
uint8_t* read_from_server(int fd, uint8_t *buffer, int n)
{
/* loop, as packet can arrive in several partial reads */
size_t bytes_recv = 0;
do {
ssize_t r;
r = recv(fd, buffer + bytes_recv, n - bytes_recv, 0); //0
printf("%d\n", (int)r);
if (r <= 0) {
return NULL;
}
bytes_recv += r;
} while (bytes_recv < n);
if (bytes_recv < n) {
return NULL;
}
return buffer;
}
int cnt_to_server(const char *par_server, const char *par_port)
{
struct sockaddr_in server;
struct hostent *hp;
int sockfd;
if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
error_exit(EXIT_FAILURE, "could not create Socket");
server.sin_family = AF_INET;
if ((hp = gethostbyname(par_server)) == 0)
error_exit(EXIT_FAILURE, "host error!");
memcpy(&server.sin_addr, hp->h_addr, hp->h_length);
server.sin_port = htons(parse_port(par_port));
if (connect(sockfd, (struct sockaddr*) &server, sizeof server) < 0)
error_exit(EXIT_FAILURE, "could not connect!");
return sockfd;
}
Thx for helping me out with this!

Answer 1

Change
if (send_to_client(sockfd, &buffer[0], WRITE_BYTES) == NULL)
to
if (send_to_client(connfd, &buffer[0], WRITE_BYTES) == NULL)

Answer 2

The solution is to use connfd (File descriptor for connection socket) instead of sockfd:
/* read from client */
if (read_from_client(connfd, &buffer[0], READ_BYTES) == NULL) {
if (quit) break; /* caught signal */
bail_out(EXIT_FAILURE, "read_from_client");
}