allow streaming downloads to export channel feed data

app/controllers/stream_controller.rb

@@ -0,0 +1,83 @@
+class StreamController < ApplicationController
+  include ActionController::Live
+  require 'csv'
+
+  def channel_feed
+    channel = Channel.find(params[:id])
+    api_key = ApiKey.find_by_api_key(get_apikey)
+
+    # set timezone correctly
+    set_time_zone(params)
+
+    # output proper http response if error
+    render :text => '-1', :status => 400 and return if !channel_permission?(channel, api_key)
+
+    # set the attachment headers
+    response.headers['Content-Type'] = 'text/csv'
+    response.headers['Content-Disposition'] = 'attachment; filename=feeds.csv'
+
+    # get the feed headers
+    csv_headers = Feed.select_options(channel, params)
+
+    # set the total records and batch size
+    total_records = channel.feeds.count
+    batch = 1000
+
+    # write the headers row
+    response.stream.write "#{CSV.generate_line(csv_headers)}"
+
+    # for every 1000 records
+    (0..(total_records - batch).abs).step(batch) do |i|
+      # variable to hold the streaming output for this batch
+      batch_output = ""
+      # feeds query
+      feeds = Feed.where(:channel_id => channel.id).order('entry_id asc').offset(i).limit(batch)
+
+      # for each feed, add the data according to the csv_headers
+      feeds.each do |feed|
+        row = []
+        csv_headers.each { |attr| row.push(feed.send(attr)) }
+        batch_output += CSV.generate_line(row)
+      end
+
+      # write the output for this batch
+      response.stream.write batch_output
+      # add a slight delay between database queries
+      sleep 0.1
+    end
+  ensure
+    response.stream.close
+  end
+
+  def stream_example
+    # get the channel
+    channel = Channel.find(params[:channel_id])
+
+    # stream the response
+    response.headers['Content-Type'] = 'text/csv'
+    response.headers['Content-Disposition'] = 'attachment; filename=feeds.csv'
+    20.times {
+      response.stream.write "hello world\n"
+      sleep 1
+    }
+  ensure
+    response.stream.close
+  end
+
+  def stream_chunked_example
+    #response.headers['Content-Type'] = 'text/event-stream'
+    response.headers['Content-Type'] = 'text/csv'
+    response.headers['Content-Disposition'] = 'attachment; filename=feeds.csv'
+    response.headers['Transfer-Encoding'] = 'chunked'
+    10.times {
+      response.stream.write "4\n" # size must be in hex format?
+      response.stream.write "hel\n\n"
+      sleep 1
+    }
+    response.stream.write "0\n\n"
+  ensure
+    response.stream.close
+  end
+
+end
+