An Ajax-Enhanced Web-Based Ethernet Analyzer
One final wrinkle is that the dns-watcher.rb program needs to be executed with root privilege, in order to switch the Web server's NIC into promiscuous mode. As would be expected, Apache2 does not, by default, execute CGI scripts as a root privilege, and for good reason. To get my Web-based analyzer to work, I added the following line to my /etc/sudoers file:
%www-data ALL=(root) NOPASSWD: /usr/bin/ruby
This allows the www-data user, which executes Apache2, to execute Ruby with root privilege, as it is the Ruby interpreter that executes the dns-watcher.rb code on behalf of Apache2. Such a situation may not be acceptable to you—due to the security concerns raised—and I'd be interested to know if any reader has a solution that allows me to execute the analyzer with root privilege more safely.
Figure 2 shows the results of a Web-based network analysis. The long-running, server-bound process is started by the Web server, runs in the background and—as results are generated—any and all output appears within the Web-based front end. Thanks to Ajax, the user's experience closely matches that of the command-line execution of the same program—as soon as data is ready, it's displayed. Adapting my solution to other uses is not difficult; all that's required is a mechanism to redirect some long-running, server-bound process' output to a file, and then access the file's contents via a CGI script that executes as a result of a single Ajax call. As I hope I've demonstrated, Ruby and Ajax make for a clean solution to this particular Web development pattern.
Paul's Ruby Tutorial: glasnost.itcarlow.ie/~barryp/ruby-tut.html
Ruby's libpcap Library: raa.ruby-lang.org/project/pcap
Ruby Net::DNS Page on RubyForge: rubyforge.org/projects/net-dns
The “who is doing what?” Perl Script: www.theperlreview.com/Issues/v0i6.shtml
Source Code for This Article: ftp.linuxjournal.com/pub/lj/issue157/9614.tgz
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