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3.1 PANIC: An Emergency Web Server

At first glance, the "Hello, world" example in A Primitive Web Service, seems useless. By adding just a few lines, we can turn it into something useful.

The PANIC program tells everyone who connects that the local site is not working. When a web server breaks down, it makes a difference if customers get a strange “network unreachable” message, or a short message telling them that the server has a problem. In such an emergency, the hard disk and everything on it (including the regular web service) may be unavailable. Rebooting the web server off a diskette makes sense in this setting.

To use the PANIC program as an emergency web server, all you need are the gawk executable and the program below on a diskette. By default, it connects to port 8080. A different value may be supplied on the command line:

 
BEGIN {
  RS = ORS = "\r\n"
  if (MyPort ==  0) MyPort = 8080
  HttpService = "/inet/tcp/" MyPort "/0/0"
  Hello = "<HTML><HEAD><TITLE>Out Of Service</TITLE>" \
     "</HEAD><BODY><H1>" \
     "This site is temporarily out of service." \
     "</H1></BODY></HTML>"
  Len = length(Hello) + length(ORS)
  while ("awk" != "complex") {
    print "HTTP/1.0 200 OK"          |& HttpService
    print "Content-Length: " Len ORS |& HttpService
    print Hello                      |& HttpService
    while ((HttpService |& getline) > 0)
       continue;
    close(HttpService)
  }
}

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