C, TCP, recvAll block is not receing anything - c

Question

I am new to both C and socket programming, so please bear with me. The following code is mostly from Beej networking guide, with some changes. I have the receiver code attached (which is TCP server in this case), that listens to multiple TCP connections. I have a transmitter (client) who is constantly sending fixed chunks of data to this receiver. This code (which I cleaned and removed some function definitions unrelated to my issue) works if instead of calling recv_all function, I only call recv(). But the problem with that I need to do processing on each chunk of received data, so I need the whole chunk. So I thought I should use the recv_all().
Now the problem is it gets stuck in an infinite loop in the while in recv_all(), because n is always 0. I truly appreciate your help.
#define PORT "3490" // the port users will be connecting to
#define BACKLOG 20 // how many pending connections queue will hold
#define MAXDATASIZE 801 // max number of bytes we can get at once
int recv_all(int socket, char *buffer, int *length)
{
int total = 0; // how many bytes we've sent
int bytesleft = *length; // how many we have left to send
int n;
while(total < *length) {
n = recv(socket, buffer+total, bytesleft, 0);
if (n == -1) { break; }
total += n;
bytesleft -= n;
}
*length = total; // return number actually received here
return n==-1?-1:0; // return -1 on failure, 0 on success
}
int main(void)
{
int sockfd, new_fd; // listen on sock_fd, new connection on new_fd
struct addrinfo hints, *servinfo, *p;
struct sockaddr_storage their_addr; // connector's address information
socklen_t sin_size;
struct sigaction sa;
int yes=1;
char s[INET6_ADDRSTRLEN];
int rv;
double buf[MAXDATASIZE];
int lenRecv;
struct sockaddr_in local_addr; // For the new addition to bind it to an interface
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE; // use my IP
if ((rv = getaddrinfo(NULL, PORT, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
return 1;
}
// loop through all the results and bind to the first we can
for(p = servinfo; p != NULL; p = p->ai_next) {
if ((sockfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol)) == -1) {
perror("server: socket");
continue;
}
if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) {
perror("setsockopt");
exit(1);
}
if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
close(sockfd);
perror("server: bind");
continue;
}
break;
}
freeaddrinfo(servinfo); // all done with this structure
if (listen(sockfd, BACKLOG) == -1) {
perror("listen");
exit(1);
}
sa.sa_handler = sigchld_handler; // reap all dead processes
sigemptyset(&sa.sa_mask);
sa.sa_flags = SA_RESTART;
if (sigaction(SIGCHLD, &sa, NULL) == -1) {
perror("sigaction");
exit(1);
}
printf("server: waiting for connections...\n");
while(1) { // main accept() loop
sin_size = sizeof their_addr;
new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);
if (new_fd == -1) {
perror("accept");
continue;
}
inet_ntop(their_addr.ss_family, get_in_addr((struct sockaddr *)&their_addr), s, sizeof s);
printf("server: got connection from %s\n", s);
if (!fork()) { // this is the child process
close(sockfd); // child doesn't need the listener
for (int i=0; i<1000000; i++) {
int rowInfoSize;
//if ((numbytes = recv(sockfd, buf, sizeof (buf), 0)) == -1) {
//if ((numbytes = recv(new_fd, buf, sizeof (buf), MSG_WAITALL)) == -1) { // I THINK THE BETTER WAY IS to CHECK THE OUTPUT AND LOOP UNTIL COMPLETE.
lenRecv = sizeof (buf);
//if (recv_all(new_fd, (char *)buf, &lenRecv) == -1) {
if (recv_all(new_fd, buf, &lenRecv) == -1) {
perror("sendall");
printf("We only sent %d bytes because of the error!\n", lenRecv);
}
}
close(new_fd);
exit(0);
}
close(new_fd); // parent doesn't need this
}
return 0;
}

Answer 1

You are ignoring end of stream. If n == 0 the peer has disconnected. Your code will loop forever.
Throw it all away and use recv() with the MSG_WAITALL option.

Answer 2

give recv_all a timeout value
int recv_all(int socket, char *buffer, int *length, int timeout)
and use select before recv()
int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
looks like this
int recv_all(int socket, char *buffer, int *length)
{
int total = 0; // how many bytes we've sent
int bytesleft = *length; // how many we have left to send
int n = -1;
struct timeval timeout;
fd_set rset;
int rc;
timeout.tv_sec = 1;
timeout.tv_usec = 0;
while(total < *length) {
FD_ZERO(&rset);
FD_SET(socket, &rset);
rc = select(socket + 1, &rset, NULL, NULL, &timeout);
if(rc < 0)
{
// errno
n = -1;
break;
}
if(0 == rc)
{
// timeout
n = -1;
break;
}
if(FD_ISSET(socket, &rset))
{
n = recv(socket, buffer+total, bytesleft, 0);
if (n == -1) { break; }
total += n;
bytesleft -= n;
timeout.tv_sec = 1;
timeout.tv_usec = 0;
}
}
*length = total; // return number actually received here
return n==-1?-1:0; // return -1 on failure, 0 on success
}