Unix™ Systems Programming [Electronic resources] : Communication, Concurrency, and Threads نسخه متنی

19.6 Tunnel Server Implementation

A tunnel is a blind relay that ceases to exist when both ends of a connection are closed. The passmonitor program of Section 19.5 is technically not a tunnel because it resumes listening for another connection request after closing its connections to the client and the destination server. It acts as a server for the tunnel function. One limitation of passmonitor is that it handles only one communication at a time.

Modify the passmonitor program of Section 19.5 to fork a child to handle the communication. The child should call the tunnel function and print to standard output a message containing the total number of bytes written. Call the new program tunnelserver.

The parent, which you can base on Program 18.2 on page 623, should clean up zombies by calling waitpid with the WNOHANG option and resume listening for additional requests.

Exercise 19.19

How would you start tunnelserver on port 15002 to service the web server www.usp.cs.utsa.edu running on port 8080 instead of port 80?

Answer:

tunnelserver 15002 www.usp.cs.utsa.edu 8080

Exercise 19.20

Why can't the child process of tunnelserver return the total number of bytes processed to the parent process in its return value?

Answer:

Only 8 bits of the process return value can be stored in the status value from wait.