Enable request completion time in Rails3 Metal

Make sure you include the following modules in ApplicationController

include ActionController::RackDelegation
include ActionController::Instrumentation

Completed in 5ms (View: 2, DB: 0) | 200 OK [http://0.0.0.0/items]

IE throws “File Download Security Warning” on form submit

I came across with this weird IE bug(occurs in IE-6 and IE-7 not in IE-8) that throws a File Download Security Warning on form post.

File download security warning

This is the code for the corresponding action inside controller

def update
 respond_to do |format|
  format.js   {....}
  format.html {....}
 end
end

* I guess this bug will only propagate if respond_to is used

I put a debugger after the respond_to line and made a http post request through IE6 and IE7 browsers and hooked into the request parameters.

request.format => #<Mime::Type:0x7b567a4 @string="image/jpeg", @synonyms=[], @symbol=nil >
request.format.html? => nil

Making the same the request through Firefox returned this

request.format => #<Mime::Type:0x55da8b8 @string="text/html", @synonyms=["application/xhtml+xml"], @symbol=:html >
request.format.html? => true
request.format.js? => false

So one thing came into light that there is no Mime::Type registered for “images/jpeg” i.e format sent by IE

Looking at Rails 2.1.0 code actionpack/lib/action_controller/request.rb line no: 92

# Returns the Mime type for the format used in the request. If there is no format available, the first of the 
# accept types will be used. 
def format
  @format ||= parameters[:format] ? Mime::Type.lookup_by_extension(parameters[:format]) : accepts.first
end

And that brought me to the solution.If no request format is available, which is the case with IE, then the first format will be picked up.So moving format.html above the format.js will solve the problem(or i should say format.html should be the first format defined)

def update
 respond_to do |format|
  format.html {....}
  format.js   {....}
 end
end

Or we can also use format.any to our rescue(instead of moving format.html)

def update
 respond_to do |format|
  format.js   {....}
  format.any  {....}
 end
end

date_select, time_select doesn’t work with auto_prefix (object[])

I ran into the following issue while i was dealing with a multi-model form where a Sport is being saved with associated Events


<%= render(:partial => "event", :collection => @sport.events) %>

This partial is being rendered for collection of events for new/edit Sport

<% new_or_existing = event.new_record? ? 'new' : 'existing' %>
<% prefix = "sport[#{new_or_existing}_event_attributes][]" %>

<% fields_for prefix, event do |e| -%>
 <%= e.time_select("best_time") %>
<% end -%>


Here is the problem:

For new Event, time_select name attribute should be:	sport[new][][best_time(5i)]
but this was being assigned:	sport[new][best_time(5i)]

Following error is thrown when this form is submitted

Status: 500 Internal Server Error
Conflicting types for parameter containers. Expected an instance of Hash but found an instance of Array


For more information regarding this issue you can go through this ticket

After digging into rails code this came into light

# rails/actionpack/lib/action_view/helpers/form_helper.rb:508

if @object_name.sub!(/\[\]$/,"")
  if object ||= @template_object.instance_variable_get("@#{Regexp.last_match.pre_match}") and object.respond_to?(:to_param)
   @auto_index = object.to_param
  else
   raise ArgumentError, "object[] naming but object param and @object var don't exist or don't respond to to_param: #{object.inspect}"
  end
end


So here @object_name would be “sport[new_event_attributes][]“
and @object_name.sub!(/\[\]$/,”") will return “sport[new_event_attributes]“
and @auto_index will set to nil

select_time internally calls option_with_prefix to assign name attribute for select element

#rails/actionpack/lib/action_view/helpers/date_helper.rb:664

def options_with_prefix(position, options)
 prefix = "#{@object_name}"
 if options[:index]
  prefix << "[#{options[:index]}]"
 elsif @auto_index
  prefix < "#{prefix}[#{@method_name}(#{position}i)]")
 end
end


Work around: pass a non nil index value along with date_select or time_select

<% new_or_existing = event.new_record? ? 'new' : 'existing' %>
<% prefix = "sport[#{new_or_existing}_event_attributes][]" %>

<% fields_for prefix, event do |e| -%>
 <%= e.time_select("best_time", :index => event.id || "") %>
<% end -%>


time_zone_select showing only US time zones

time_zone_select produces option tags for almost any time zones in the world but if you want the list of US time zones only, without using the TZInfo library then you should add a file under the lib directory say us.rb and add the following code

class US
 def self.all
  TimeZone.us_zones
 end
end

and in you views use

<%= time_zone_select object, method, nil, :model=>US %>


Etag in Rails

What is an ETag and How does it work??

When a request is made for the first time then during page render, etag header is automatically inserted on 200 OK responses. The etag is calculated using MD5 of the response body.
On subsequent requests the etag is send along as request.headers['HTTP_IF_NONE_MATCH'] and compared with response.headers['ETAG'] . If they are equal then the response is changed to a 304 Not Modified and the response body is set to an empty string.

So how does that help??

• ETag is used to expire the browser caching and for saving transfer of course!!
• aggregators can tell which version of feed they have and thus server sends data only if some newer version is there.
• no more cache based on page expiration.

A ruby snippet for showing ETags


require 'net/http'
# my rails app running on edge rails
http = Net::HTTP.new("localhost", 3000)

# /controller/action
data = http.get2("/say")
p data.body
p data.header.each{|k,v| p "#{k} = #{v}"}

data2 = http.request_get("/say", {'If-None-Match' => data.header['etag']})
p data2.body
p data2.header.each{|k,v| p "#{k} = #{v}"}
# 304 not modified n body empty coz of no change in content