Image attachment display broken

[pharkas@…]

Running Trac 0.8.1 on Apache 1.3.33 (Darwin) on an Apple xserve, I get intermittent image display. Attached images show up exactly every other time- the first time I load the image, it display properly, but the second time I load the image it shows up as a broken image (IE), or gives a "The image cannot be displayed, because it contains errors." error (Firefox).

I ran ethereal on the connection to grab the transferred data:

Success

GET /cgi-bin/mstl.cgi/attachment/wiki/JacobFarkas/thumbsup.jpg?format=raw HTTP/1.1
Host: aeroxserv.aero.calpoly.edu
User-Agent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X Mach-O; en-US; rv:1.7.5) Gecko/20041107 Firefox/1.0
Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
Cookie: trac_session=ae55ae88dea5e6e546e10bff; trac_auth=64a37dfce1bd402648a12f761732292f
Authorization: Basic amZhcmthczozYTVhZmp2MjM=
Cache-Control: max-age=0

HTTP/1.1 200
Date: Tue, 05 Apr 2005 00:23:17 GMT
Server: Apache/1.3.33 (Darwin) DAV/1.0.3 mod_ssl/2.8.22 OpenSSL/0.9.7b PHP/4.3.10
Expires: Mon, 26 Jul 1997 05:00:00 GMT
Pragma: no-cache
Cache-Control: max-age=60
Expires: Tue, 05 Apr 2005 00:24:17 GMT
Content-Length: 80897
Last-Modified: Sun, 27 Mar 2005 08:17:01 GMT
Connection: close
Content-Type: image/jpeg

[Image data cut]

Failure

GET /cgi-bin/mstl.cgi/attachment/wiki/JacobFarkas/thumbsup.jpg?format=raw HTTP/1.1
Host: aeroxserv.aero.calpoly.edu
User-Agent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X Mach-O; en-US; rv:1.7.5) Gecko/20041107 Firefox/1.0
Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
Cookie: trac_session=ae55ae88dea5e6e546e10bff; trac_auth=64a37dfce1bd402648a12f761732292f
If-Modified-Since: Sun, 27 Mar 2005 08:17:01 GMT
Authorization: Basic amZhcmthczozYTVhZmp2MjM=
Cache-Control: max-age=0


HTTP/1.1 200
Date: Tue, 05 Apr 2005 00:26:34 GMT
Server: Apache/1.3.33 (Darwin) DAV/1.0.3 mod_ssl/2.8.22 OpenSSL/0.9.7b PHP/4.3.10
Connection: close
Expires: Mon, 26 Jul 1997 05:00:00 GMT
Expires: Tue, 05 Apr 2005 00:27:34 GMT
Cache-Control: max-age=60

[Matthew Good]

Thanks for the headers, though I find it easier to use the Firefox plugin "Live HTTP Headers" instead of Ethereal.

So, it appears that there's a problem with the expiration headers that are being returned. There are two contradictory "Expires" headers and the "Pragma: no-cache" that don't seem to belong there. Then in the second request, the response code should be a 304 (Not Modified) instead of 200 (OK).

I'm not entirely sure why these headers are being added, but the "Mon, 26 Jul 1997 05:00:00 GMT" date in the expires header seems to be a convention in PHP for forcing immediate expiration. There may be something in your webserver and/or PHP configuration that is generating these expiration headers to prevent caching of PHP-related pages, but it is interfering with the operation of Trac as well.

[pharkas@…]

Thanks for the tip about Live HTTP Headers- that saved me some headaches!

I ran into this problem migrating from a Linux server to an OS X xserve, so I had a known working copy of the site to work against. Between migrating I also changed versions from Trac 0.8.0 to Trac 0.8.1. That appears to be what caused the problem.

In File.py the Cache-Control line was removed from version version 0.8.0 to version 0.8.1. This caused the images to load incorrectly every other time. I tested this by removing the line in my Trac 0.8.0 install and encountered the same problem.

Here are the lines that were removed:

File.py:80-82

        self.req.send_header('Cache-Control',
                             'no-store, no-cache, must-revalidate, max-age=0')
        self.req.send_header('Cache-Control', 'post-check=0, pre-check=0')

I noticed that more specifically, it seems that not having the 'no-store' property is causing the problem.

Since this happens on both the xserve 0.8.1 install and the Linux 0.8.0 install, I don't think it's related to any specific server, although I'm surprised no one else has run into this problem. Can anyone else confirm this problem?

I created a patch that adds the 'Cache-Control: no-store' header back in to File.py and have attached it to this ticket.

I looked at the code in Trunk and it looks like File.py has been refactored out, but the necessary Cache-Control line is still missing from attachment.py. I'll download and install the latest code on a test box and see if I can recreate the problem.

[pharkas@…]

Fixes broken loading of attached images

[pharkas@…]

I just confirmed this same problem on revision 1504. I've attached a patch to fix the problem.

[pharkas@…]

It looks like this may be related to Ticket #1020. Does adding no-store back in break Explorer?

[Emmanuel Blot]

Same patch for [1756]

[Matthew Good]

cmlenz: is this the same issue you fixed for #1680?

[Christopher Lenz]

#1680 applied only to trunk, while this one is about a similar but still different issue with 0.8.x. So no, I don't think this is fixed, but OTOH, the target milestone would be 0.8.5, which isn't planned yet.

[Matthew Good]

There aren't going to be anymore 0.8.x releases, so I'm going to close this ticket. However, there is a related ticket #2006 which applies to the trunk/0.9.