Cgi script send a bad image to the browser

Ruby
1

Hi everyone,
I’d like to use a ruby script to generate an image (directed graph) and
sand it to an ajax-like javascript script that display the image in the
browser.
I tryed to do it but what the browser display only a lot of strange
characters. I think it’s a headers problem but I really don’t know how
to solve it.
When I run the script in a shell and redirect the input to a file, the
generated image is good
What is the best way to send the image to the browser?
Any idea is welcome,
thanks in advance.

Alex

#this is the ruby script#

require “graphviz”
g = GraphViz::new( “G” )
main = g.add_node( “main” )
parse = g.add_node( “parse” )
g.add_edge( main, parse )
puts “Content-Type: image/png”
puts
g.output( “output” => “png” )

############## This is the client-side javascript to display the
gener0ated image ##############

################################################

2

On Mar 11, 2006, at 3:43 PM, Alex wrote:

generated image is good
main = g.add_node( “main” )
var request = false;
}
if (request.readyState == 4) {
var url =“nph-script.rb”;
request.open(“GET”, url, true);
request.onreadystatechange = updatePage;
request.send(null);
}

################################################

Maybe you want to use the CGI class.
require ‘cgi’
cgi = CGI.new
cgi.header[‘Content-Type’] = ‘image/png’
cgi.print cgi.header

3

On Mar 11, 2006, at 3:43 PM, Alex wrote:

generated image is good
main = g.add_node( “main” )
var request = false;
}
if (request.readyState == 4) {
var url =“nph-script.rb”;
request.open(“GET”, url, true);
request.onreadystatechange = updatePage;
request.send(null);
}

################################################

Actually forgot what i just said, you’re doing this all wrong. src
points to a url, not the actual image data. Ajax is also probably
pretty silly for this. Do this in your html:

no javascript, no ajax, just good old fashioned cgi. If you do want
this graph to be more dynamic than that, you’re going to have to
learn how the img tag works (like I said src is not image data its a
url).

4

Logan C. wrote:
…

Actually forgot what i just said, you’re doing this all wrong. src
points to a url, not the actual image data. Ajax is also probably
pretty silly for this. Do this in your html:

no javascript, no ajax, just good old fashioned cgi. If you do want
this graph to be more dynamic than that, you’re going to have to learn
how the img tag works (like I said src is not image data its a url).

You might be able to us JavaScript to get a reference to the desired
Image object (in document.images )and update the src property.

–
James B.

http://www.ruby-doc.org - Ruby Help & Documentation
Ruby Code & Style - The Journal By & For Rubyists
http://www.rubystuff.com - The Ruby Store for Ruby Stuff
http://refreshingcities.org - Design, technology, usability

5

Thanks a lot!

Yes, you are right when you said i’m using the img tag in a wrong
way…
Now I’ll start working in a different way.
Thanks again

Ale

6

I’d like do do something like this:

1)The user insert some data in a field, than press a button
2)A script receive the data and return some textual info and an image

With ajax I can make an interface with an instant textual answer from
the system (without page refresh), but I’d like to do the same thing
with the image.
If I use this technique:

The image is updated only when I refresh the page.
Ummm… maybe I simply cannot do it.

Any hints?

Thanks a lot!

Alex

7

I understand, thank you for your help.

Alex

8

Alex wrote:

The image is updated only when I refresh the page.
Ummm… maybe I simply cannot do it.

See my previous response to your initial message

“You might be able to us JavaScript to get a reference to the desired
Image object (in document.images )and update the src property.”

Google around for DHTML, JavaScript, and image replacement/preloading.

–
James B.

“You harmonize; then you customize.”

  • Wilson Pickett