Rails - Aug 2007 - image caching from the browser.

Hello everyone,

    I am struck with the problem of retrieving an image from database. I
am using

<%= form_tag_with_upload_progress({:action =>
''update_plugin_content''},
            { :begin => "new
Effect.Appear(''loading'');",
              :finish => "do_finish(arguments[0]);new
Effect.Fade(''loading'');",
              :name => "message_form"}
     )%>

  (This form_tag_with_upload_progress is a method of uploading image
thru AJAX)

   for uploading the image into the database. Itz working properly.
After uploading I am doing an Ajax.Updater for getting the new image
from the database.
Here the problem is the image is getting fetched from the browser cache.

I have implemented the following to try to solve this problem.

1.  I had added a random number to the URL so that every request that
goes is a new URL and

var url
''/preference/get_user_logo?plugin_preferences_id=''+plugin_preferences_id+"&"+new
Date().getTime()+"="+new Date().getTime();

new Ajax.Updater(''uploaded_logo'',url, {asynchronous:true,
evalScripts:true,onLoading:function(){replace_logo_with_loading(''uploaded_logo'',''ipolipo_loading'');},onComplete:function(request){replace_logo_with_loading(''ipolipo_loading'',''uploaded_logo'');get_response();}});return
true;

This did not work.

2.  My friend who works in java had suggested to set the headers
cache-control to "no-cache"

so the full action became

def get_user_logo
  plugin_preference_id = params[:plugin_preferences_id]
  user_logo = PluginPreference.find(plugin_preference_id)

  image_of_user_logo = user_logo.image

  @response.headers["Expires"] = 0
  @response.headers["Pragma"] = "no-cache"
  @response.headers["Cache-Control"] = "no-cache"

  if user_logo.image == nil or image_of_user_logo.empty?
      #... code send a default image
  else
      send_data user_logo.image, :type => "image/png", :disposition
=>
"inline"
  end
end

But this also did not work.

3. just as suggested in the rails CookBook

<a href="http://manuals.rubyonrails.com/read/chapter/62"
target="blank">http://manuals.rubyonrails.com/read/chapter/62</a>

def image
    @photo = Photo.find(@params[''id''])
    minTime = Time.rfc2822(@request.env["HTTP_IF_MODIFIED_SINCE"])
rescue nil
    if minTime and @photo.updated_at <= minTime
      # use cached version
      render_text '''', ''304 Not Modified''
    else
      # send image
      @response.headers[''Content-Description''] =
@photo.description
      @response.headers[''Last-Modified''] =
@photo.updated_at.httpdate
      send_data @photo.data, :type => @photo.mimeType, :disposition =>
''inline''
    end
  end


I had modified my action like that suggested.

But the
"Time.rfc2822(@request.env["HTTP_IF_MODIFIED_SINCE"]" comes
as
nil and
"@photo.description" is not recognized i.e., not proceeding further
and
also not throwing exception.

Is the "@request.env["HTTP_IF_MODIFIED_SINCE"]" needs to be
set
anywhere. If so where it has to be set?

The problem is clearly with the browser cache. But I am unable to find
the solution. Please help me in this .
Thanks in advance...

Regards,
JazzyBuddy ...................
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