TCP Echo Server: str_echo Function

The function str_echo performs the server processing for each client: It reads data from the client and echoes it back to the client.

1 #include    "unp.h"

2 void
3 str_echo(int sockfd)
4 {
5     ssize_t n;
6     char    buf[MAXLINE];

7   again:
8     while ( (n = read(sockfd, buf, MAXLINE)) > 0)
9         Writen(sockfd, buf, n);

10     if (n < 0 && errno == EINTR)
11         goto again;
12     else if (n < 0)
13         err_sys("str_echo: read error");
14 }

Read a buffer and echo the buffer

8–9 read reads data from the socket and the line is echoed back to the client by Writen. If the client closes the connection (the normal scenario), the receipt of the client's FIN causes the child's read to return 0. This causes the str_echo function to return, which terminates the child.