C++ socket not sending data if sleep not added - c++

Question

I'm writing a client in C++ for my AI project that communicates with a server written in Java, to which I do not have access to the code. They use TCP sockets to communicate: the server sends me a message and the client performs an action accordingly, such as generating a move or updating the board or declaring victory, defeat and so on. Now I have noticed that sometimes the socket gets stuck and the server sends back a timeout message, even though the client has never generated a move and never entered in the "YOUR_MOVE" else if, which is weird, because it computes the move in no time (a handful of milliseconds) and if I add a 50 milliseconds sleep either before send or receive it works like a charm. I wonder what could possibly go wrong. That's the code:
#include <iostream>
#include <cstring> // Needed for memset
#include <sys/socket.h> // Needed for the socket functions
#include <netdb.h> // Needed for the socket functions
#include <unistd.h>
#include <string>
#include <boost/algorithm/string/predicate.hpp>
#include <boost/lexical_cast.hpp>
#include <chrono>
#include "AI.cpp"
#include <locale>
#include <thread>
using namespace::std;
void error(const char *msg)
{
perror(msg);
exit(0);
}
class Client{
private:
AI* ai;
public:
int socketfd;
Client(const char* serverAddress, const char* port){
int status;
struct sockaddr_in serv_addr;
struct hostent *server;
portno = 8901;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
error("ERROR opening socket");
server = gethostbyname("127.0.0.1");
if (server == NULL) {
fprintf(stderr,"ERROR, no such host\n");
exit(0);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
bcopy((char *)server->h_addr,
(char *)&serv_addr.sin_addr.s_addr,
server->h_length);
serv_addr.sin_port = htons(portno);
if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)
error("ERROR connecting");
ai = new AI();
(*ai).distance();
}
~Client(){
freeaddrinfo(host_info_list);
close(socketfd);
delete ai;
}
bool startsWith(char c1[], char c2[]){
int i=0;
while(c2[i] != 0){
if(c1[i]==0)
return false;
if(c1[i] != c2[i])
return false;
i++;
}
return true;
}
void substr(char c[], int pos, char* s){
int i;
for(i=pos; c[i]!=0; i++){
s[i-pos] = c[i];
}
s[i-pos] = 0;
}
void play(){
bzero(buffer,256);
n = read(sockfd,buffer,255);
if(startsWith(buffer, (char*)"WELCOME"))
printf(buffer);
string colour;
if(buffer[9]=='l')
colour="black";
else
colour="white";
char* msg = new char[256];
while(true){
bzero(buffer,256);
n = read(sockfd,buffer,255);
//printf(buffer);
if(startsWith(buffer, (char*)"VALID_MOVE"))
cout << "Valid move, please wait" << endl;
else if(startsWith(buffer, (char*)"OPPONENT_MOVE")){
substr(buffer, 14, msg);
ai->updateBoard(msg);
cout << "Opponent move: " << msg << endl;
}
else if(startsWith(buffer, (char*)"VICTORY")){
cout << "You win" << endl;
break;
}
else if(startsWith(buffer, (char*)"DEFEAT")){
cout << "You lose" <<endl;
break;
}
else if(startsWith(buffer, (char*)"TIE")){
cout << "You tied" << endl;
break;
}
else if(startsWith(buffer, (char*)"YOUR_TURN")){
cout << "YOUR_TURN branch" << endl;
string move = ai->generateNextMove(colour, 3);
cout << "Your move is: " << move << endl;
int i;
for(i=0;i<8; i++){
msg[i] = move.at(i);
}
msg[i] = 0;
sprintf(buffer, "MOVE %s\n", msg);
std::this_thread::sleep_for(std::chrono::milliseconds(40));
n = write(sockfd,buffer,strlen(buffer));
ai->updateBoard(move);
}
else if(startsWith(buffer, (char*)"TIMEOUT")){
cout << "Time out" << endl;
break;
}
else if(startsWith(buffer, (char*)"MESSAGE")){
substr(buffer, 8, msg);
cout << msg << endl;
}
}
close(sockfd);
}
};
int main()
{
const char serverAddr[]="127.0.0.1";
const char port[]="8901";
Client * client = new Client(serverAddr, port);
client->play();
delete client;
return 0;
}
P.S. This is my first post, please show forgiveness if I have involuntarily forgotten to provide some other information. Thank you.

Answer 1

For what I can see you are taking for granted that when you perform socket read with
n = read(sockfd,buffer,255);
You seem to be sure that you always receive an entire command, but think what happens if you receive only "YOUR TU" instead of "YOUR TURN"
You always clean the buffer and the next loop you receive just "RN" so you never process the command and the server remains waiting for your move.
What you should do is clean the buffer ONLY when you have received a full meaningful command.
If you uncomment the:
//printf(buffer);
You can check if my theory is correct.