Stream content of txt file in real time to rails view - ruby

Question

What would be the simplest approach to streaming the contents of a file to the web page, as it gets updated.
I currently have a .txt file that is constantly updated while a script is running, and I want to display that on the page for the users as it is updated.
Is there a simple gem or technology out there to accomplish this? Or is there an excellent pure Ruby approach?
My first thought was to use some kind of AJAX request to return diffs of the file, but I feel that would be a bad approach.

Answer 1

I used Celluloid's Reel by Tony Arcieri to accomplish this.
I run this in the background (received a lot of help from Adam Dalton on this part):
my_reel.rb
require 'reel'
CONNECTIONS = []
Reel::Server.supervise("0.0.0.0", 5000) do |connection|
while request = connection.request
case request
when Reel::Request
puts "Client requested: #{request.method} #{request.url} #{request.body}"
CONNECTIONS.each do |c|
c << request.body
end
request.respond :ok, 'YES! YOU GOT IT!'
when Reel::WebSocket
puts "Client made a WebSocket request to: #{request.url}"
CONNECTIONS << request
break
end
end
end
sleep
Then I wrote a command line script to send post requests to the Reel server. Had a lot of help from Writing Ruby Scripts That Respect Pipelines by Jesse Storimer.
~/bin/serve_it_up
#!/usr/bin/env ruby
require 'httparty'
ARGF.each_line do |line|
output_line = line.chop
HTTParty.post 'http://localhost:5000', body: output_line
end
Then to make it work, my Rails application uses Sidekiq (bundle exec sidekiq), and runs a script in the background when a button is clicked, which sends the output to a file, output.txt. So I run a forced tail and pipe it's output to my command line script.
tail -f output.txt | serve_it_up
In my web app, I have some JavaScript (CoffeeScript in this case) that hooks up to the web socket and puts the output on the page:
connection = new WebSocket('ws://localhost:5000')
connection.onmessage = (event) ->
$('#prompt').append(event.data + '<br/>')
prompt = document.getElementById('prompt')
prompt.scrollTop = prompt.scrollHeight
So anytime that output.txt changes, it'll take the output from tail -f and put it in the web browser. I also style the #prompt div to have a limited height, and I keep it always scrolled to the bottom.
Here is the style for it:
#prompt {
font-family: Consolas, Menlo, Monaco, Lucida Console, Liberation Mono, DejaVu Sans Mono, Bitstream Vera Sans Mono, Courier New, monospace, serif;
height: 200px;
overflow: auto;
}

Answer 2

You could look into using something like Faye or the gem private_pub (it makes Faye channels private) which allows you to make use of web sockets or long polling to push new data to the client. There is a lot of documentation on the Github page and also a RailsCast.
In your app or script you could then publish to the server which will push the new data to all subscribed channels.