Generate an image an show it in a html page without write it on the disk

Question

In a my project in Ruby On Rails (but this is not important), when I load a html page, I need to decrypt an image (jpg) and show it in the web page: after the page request, the image is decrypted an the file is write on the server disk, so the browser can show the image.

I don't want to write the image on the server, but I want to encrypt the image on the fly !

I think that ajax (jquery) could be helpfull, but I don't know how use it to the image on the fly (without write the image on the disk).

Do you have any Idea ?

thank you, Alessandro

Answer 1

The only way to do this is the data URI scheme.

It allows you to embed the image data directly as the src property of the <img> element .

However, it has its limitations: It doesn't work at all in IE < 8, and has a 32k size limit in IE 8.

• MDC on data URIs for Mozilla

• MSDN Article on Data URIs for IE

• Here is an article that claims to provide a workaround for IE < 8 (haven't tested)

Answer 2

You can use send_data instead of rendering a page. Take a look here. With this you can generate your file and send it without saveing to disk. However normal page won't be rendered. But you can use it like this:

1.Create normal html view, on example for index action:

# controller
def index
  @some_resources = SomeResources.all # just whatever you need
end

# somewhere in index.html.erb view
<img src="rendered_images/my_rendered_image.jpg" />

2.Add route for rendered_images

# routes
match "rendered_images/:filename" => "application#render_image"

3.Add render image action in application controller

# application controller
def render_image
  send_data my_function_to_generate_file, :filename => params[:filename], :type => 'image/jpeg', :disposition => :inline
end

I haven't tested it. I hope it will give you something to start with!