Bad file descriptor with BSD socket - sockets

Question

I keep getting a "Bad file descriptor" error when I try to send data from my tcp server to my tcp client. What does this mean in terms of sockets? I have been at this for awhile now and I don't see what could be wrong with my code. Its basically the same code I was using two days ago and that code worked fine. I was hoping someone could tell me what are common causes of bad file descriptors when trying to send over a socket and how I can go about checking/fixing them. Any help is appreciated. I will post some code below in case it helps.
/*Waits to connect a client. Returns true if successful*/
bool TcpServer::launchServer() {
int status;
struct addrinfo hints;
struct addrinfo *servinfo; //will point to the results
//store the connecting address and size
struct sockaddr_storage their_addr;
socklen_t their_addr_size;
memset(&hints, 0, sizeof hints); //make sure the struct is empty
hints.ai_family = AF_INET; //ipv4
hints.ai_socktype = SOCK_STREAM; //tcp
//get server info, put into servinfo
if ((status = getaddrinfo("192.168.2.3", port, &hints, &servinfo)) != 0) {
printf("\ngetaddrinfo error: %m", errno);
return false;
}
//make socket
fd = socket(servinfo->ai_family, servinfo->ai_socktype, servinfo->ai_protocol);
if (fd < 0) {
printf("\nserver socket failure %m", errno);
return false;
}
//allow reuse of port
int yes=1;
if (setsockopt(fd,SOL_SOCKET,SO_REUSEADDR,(char*) &yes,sizeof(int)) == -1) {
perror("setsockopt");
return false;
}
//bind
if(bind (fd, servinfo->ai_addr, servinfo->ai_addrlen) < 0) {
printf("\nBind error %m", errno);
return false;
}
//free up space
freeaddrinfo(servinfo);
//listen
if(listen(fd, 5) < 0) {
printf("\nListen error %m", errno);
return false;
}
their_addr_size = sizeof(their_addr);
//accept
comm_fd = accept(fd, (struct sockaddr*)&their_addr, &their_addr_size);
if( comm_fd < 0) {
printf("\nAccept error %m", errno);
return false;
}
return true;
} //END LAUNCHSERVER
void TcpServer::communicate() {
fd_set read_flags,write_flags; // the flag sets to be used
struct timeval waitd = {10, 0}; // the max wait time for an event
int sel; // holds return value for select();
int numRead; //holds return value for read()
int numSent; //holds return value for send()
char in[255]; //in buffer
char out[255]; //out buffer
//clear buffersz
memset(&in, 0, 255);
memset(&out, 0, 255);
while(!done) {
FD_ZERO(&read_flags);
FD_ZERO(&write_flags);
FD_SET(comm_fd, &read_flags);
FD_SET(comm_fd, &write_flags);
FD_SET(STDIN_FILENO, &read_flags);
FD_SET(STDIN_FILENO, &write_flags);
//call select
sel = select(comm_fd+1, &read_flags, &write_flags, (fd_set*)0, &waitd);
//if an error with select
if(sel < 0)
continue;
//if socket ready for reading
if(FD_ISSET(comm_fd, &read_flags)) {
//clear set
FD_CLR(comm_fd, &read_flags);
memset(&in, 0, 255);
numRead = recv(comm_fd, in, 255, 0);
//if an error, exit
if(numRead < 0) {
printf("\nError reading %m", errno);
myAgent->getRobot()->pauseSensorStream();
done = true;
} //end if error
//if connection closed, exit
else if(numRead == 0) {
printf("\nClosing socket");
close(comm_fd);
done = true;
} //end if connection closed
//if message, call getsendback
else if(in[0] != '\0') {
//std::cout<<"\nClient: "<<in;
getSendBack(in);
} //end if message
} //end if ready for read
//if stdin is ready for reading
if(FD_ISSET(STDIN_FILENO, &read_flags))
fgets(out, 255, stdin);
//if socket ready for writing
if(FD_ISSET(comm_fd, &write_flags)) {
//printf("\nSocket ready for write");
FD_CLR(comm_fd, &write_flags);
//check validity by checking for a digit
if(isdigit(out[0])) {
//create message to send
std::stringstream tosend;
tosend<<"# "<<out;
//std::cout<<"\ntosend: "<<tosend.str();
//send
//********ERROR HAPPENS HERE PRINTS OUT MESSAGE BELOW******
numSent = send(comm_fd, tosend.str().c_str(), tosend.str().length(), 0);
} //end if valid message
//if error, exit
if(numSent < 0) {
printf("\nError sending %m", errno);
done = true;
} //end if error
//wait for message to get there, then clear
usleep(5000);
memset(&out, 0, 255);
} //end if
} //end while
} //END COMMUNICATE
Client code is basically the same.

Answer 1

Your program prints "Bad file descriptor" when errno is EBADF.
From man page of send:
EBADF = An invalid descriptor was specified.
I'm quite sure that the socket is closed before the send() call.
That can happen, because program can go to "ready for writing" branch after "connection closed," branch.
Try the following:
else if(numRead == 0) {
printf("\nClosing socket");
close(comm_fd);
break;
}
Instead of:
else if(numRead == 0) {
printf("\nClosing socket");
close(comm_fd);
done = true;
}

Answer 2

You answered your own question. Without explicitly initializing numSent and numRead, you get garbage, which may happen to be a negative number for numSent, which would cause it to error if there was no digit in the out[] array.