recv() socket loop never end C - c++

Question

A am writing a client-server program in C. It sends a directory name and receives a list of files as answer. The problem I have is that it gets stuck in an infinite loop.
If I send only one directory name it works, but if I send a list of directories it never ends and outputs nothing.
Server
while(recv(sock, name, BUFSIZE, 0) > 0){
if ((fddir=opendir(name)) == NULL){
send(sock, strerror(errno), strlen(strerror(errno)), 0);
close(sock);
return 1;
}
send(sock, name, strlen(name), 0);
send(sock, ":", strlen(":"), 0);
send(sock, "\n", strlen("\n"), 0);
while ((dirbuf = readdir(fddir)) != NULL){
buf[0] = '\0';
strcat(buf, dirbuf->d_name);
strcat(buf, "\t");
send(sock, buf, BUFSIZE, 0);
}
}
Client
for (int i=1;i<3;i++){
send(sock, argv[i], strlen(path), 0);
while(recv(sock, buf, BUFSIZE, 0) > 0)
printf("%s", buf);
}
The server waits until all directory names are received, and then the client wait until server send all files in it. How do I trace where the program gets stuck?

Answer 1

TCP is not message based, so you have no way of knowing where the boundaries between two client send() calls is when you call recv() on the server. Thus when you send multiple names back-to-back it is possible for the server to receive them all in a single recv() (or however many bytes you allocated for BUFSIZE). This is probably mangling your directory names, causing opendir to fail. This would be more obvious to you if you were checking for errors from send and recv and Captain Obvlious describes in another answer.

Answer 2

You need to check the calls to recv for errors. It returns 0 if the connection was disconnected and -1 on an error. You are only checking for values > 0 which will not work. The example below shows how to approach checking the errors.
while(true)
{
const int result = recv(sock, buf, BUFSIZE, 0);l
if(result == -1)
{
std::cout << "Error: " << errno << std::endl;
break;
}
else if(result == 0)
{
std::cout << "Disconnected" << std::endl;
break;
}
// process the data here. No errors
}
You should also be checking the value returned by send as it works in the same way.