accept

for ( ; ; )
{
    connfd = Accept(listenfd, (SA *) NULL, NULL);

    ticks = time(NULL);
    snprintf(buff, sizeof(buff), "%.24s\r\n", ctime(&ticks));
    Write(connfd, buff, strlen(buff));

    Close(connfd);
}

Normally, the server process is put to sleep in the call to accept, waiting for a client connection to arrive and be accepted. A TCP connection uses what is called a three-way handshake to establish a connection. When this handshake completes, accept returns, and the return value from the function is a new descriptor (connfd) that is called the connected descriptor. This new descriptor is used for communication with the new client. A new descriptor is returned by accept for each client that connects to our server.

snprintf was a relatively late addition to the ANSI C standard, introduced in the version referred to as ISO C99. Virtually all vendors provide it as part of the standard C library, and many freely available versions are also available. We use snprintf throughout the text, and we recommend using it instead of sprintf in all your programs for reliability.

It is remarkable how many network break-ins have occurred by a hacker sending data to cause a server's call to sprintf to overflow its buffer. Other functions that we should be careful with are gets, strcat, and strcpy, normally calling fgets, strncat, and strncpy instead. Even better are the more recently available functions strlcat and strlcpy, which ensure the result is a properly terminated string.