Log Tailer

This is a simple Sinatra app that emulates the Unix tail -f command.

It takes a given logfile and transmits the last ten lines of the file over a websocket connection to any clients connected.

On any update to the logfile, all connected clients will see the updates in their session, without having to reload the page.

If a new client connects after a change has been made, they will see the last ten lines including any new changes that have been made.

Uses a (relatively old, but stable) gem called Sinatra-Websocket, which gives websocket functionality out of the box on top of Sinatra applications, making use of EventMachine.

Application layout

The majority of the heavy lifting takes place in the /io directory. There are two classes that make up this module, and combined they emulate the full tail-f command.

• TailF
  • This class reads the file and seeks the last 10 lines of the file.
  • It makes some decisions whether to use IO's native seek function or File's readlines method, depending on the size of the file.
• ChangesPoller
  • This class monitors the given file for any changes using a simple one second poller.
  • Every second, it reads the last modified time of the given file and compares it to the last one it's seen.
  • If there has been a change, calculate the difference in bytes and then read those into the websocket connection
  • To maintain the information about the file, a simple model, LogFileDetails has been implemented.
    • This class simply stores the data about the last read position of the file, and the last time it was modified.
    • It also has a method to abstract away the calculation of determining the last time the file was modified.

Running the file

This is a Ruby application, to run it simply install the dependencies and execute the main file:

~/D/p/log-tailer ❯❯❯ bundle install
~/D/p/log-tailer ❯❯❯ ruby app.rb

You can access the client at http://localhost:4567/

I've included some sample log files that you can edit and play around with, if you do run this application.

Running tests

Tests using RSpec

~/D/p/log-tailer ❯❯❯ bundle exec rspec spec/
..........

Finished in 0.03997 seconds (files took 0.39372 seconds to load)
10 examples, 0 failures