mod_proxy_ajp error: renders html as text/plain, prompts user to "save as..." - apache

Question

We have an odd, intermittent error that occurs with mod_proxy_ajp, i.e. using apache as a front end to a tomcat server.
The error
User clicks on a link browser prompts
user to "save as...." (e.g. in
Firefox "You have chosen top open
thread.jsp which is a
application/octet-stream"...What
should firefox do with this file)
User says "Huh?" and presses "Cancel"
User clicks again on the same link
Browser displays the page correctly
This error occurs intermittently, but unfortunately rarely on our test server and frequently on production.
In firefox's LiveHttpHeaders I see the following in the above usecase:
first page download (i.e. click on link) is "text/plain"
second download is "text/html"
I thought the problem may stem from ProxyPassReverse (i.e. muddling up whether to use http or ajp), but all these proxypassreverse settings resulted in the same error:
ProxyPassReverse /ajp://localhost:8080/
ProxyPassReverse /pe http://localhost/pe
ProxyPassReverse /pe http://forumstest.company.com/pe
Additionally, I've checked the apache error logs (set to debug) and see no warnings or errors...
** But it works with mod_proxy_http ?? **
It appears that switching to mod_proxy_http 'solves' the problem. Limited testing, I have not been able to recreate the problem in the test environment.
Because the problem is intermittent, I'm not 100% sure that mod_proxy_http "solves" the problem
Environment
Apache 2.2 Windows
Jboss 4.2.2 back end (tomcat 6)
One other data point
For better or worse, a servlet filter in tomcat gzips the html before sending it to apache. (which means extra work as apache must unzip before it performs ProxyPassReverse's "find and replace"). I don't know if "gzip" messes up.
Questions
anyone seen this before?
what tools help analyze the cause?
thanks
Addendum 1: Here is the LiveHttpHeaders output
Browser Incorrectly sees html as "text/plain"
http://forums.customer.com/pe/action/forums/displaythread?rootPostID=10842016&channelID=1&portalPageId=1002
GET http://forums.customer.com/pe/action/forums/displaythread?rootPostID=10842016&channelID=1&portalPageId=1002 HTTP/1.1
Host: forums.customer.com
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.13) Gecko/20101203 Firefox/3.6.13 ( .NET CLR 3.5.30729)
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
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: 115
Proxy-Connection: keep-alive
Cookie: __utma=156962862.829309431.1260304144.1297956514.1297958674.234; __utmz=156962862.1296760237.232.50.utmcsr=forumstest.customer.com|utmccn=(referral)|utmcmd=referral|utmcct=/pe/action/forums/displaythread; s_vi=[CS]v1|258F5B88051D3FC3-40000105C056085F[CE]; inqVital=xd|0^sesMgr|{"sID":4,"lsts":1292598007}^incMgr|{"id":"755563420055418864","group":"CHAT","ltt":1292598006741,"sid":"755563549194447187","igds":"1290627502757","exempt":false}^inq|{"customerID":"755562378269271622"}^saleMgr|{"state":"UNSOLD","qDat":{},"sDat":{}}; inqState=sLnd|1^Lnd|{"c":4,"flt":1274728016,"lldt":17869990,"pgs":{"201198":{"c":1,"flt":1274728016,"lldt":0},"0":{"c":3,"flt":1274845009,"lldt":17752997}},"pq":["0","0","0","201198"],"fsld":1274728016697}; adv_search_results_page=10; ep_beta=1; visitorID=57307059; JSESSIONID=6jXLNdHRDjR9Th3B5gvTVkw1dZLn1zvhvKLR2r4GTLjylHJgjY3Q!683274050; __utmc=156962862; JSESSIONID=6jXLNdHRDjR9Th3B5gvTVkw1dZLn1zvhvKLR2r4GTLjylHJgjY3Q!683274050; TLTHID=5CCA50304DE99E28DB79A7B3267D4231; TLTSID=9DFCDE8045B374AAB752CC98A30E8311; AreCookiesEnabled=1; s_cc=true; SC_LINKS=%5B%5BB%5D%5D; s_sq=%5B%5BB%5D%5D; __utmb=156962862.64.10.1297958674; memberexists=T; ev1=greywolf%20hdtv%20whmx
Cache-Control: max-age=0
HTTP/1.0 200 OK
Date: Thu, 17 Feb 2011 17:38:42 GMT
Content-Type: text/plain
X-Cache: MISS from samus.company.com
X-Cache-Lookup: MISS from samus.company.com:3128
Via: 1.0 samus.company.com:3128 (squid/2.6.STABLE20)
Proxy-Connection: close
----------------------------------------------------------
Browser Correctly sees html as "text/html"
http://forums.customer.com/pe/action/forums/displaythread?rootPostID=10842016&channelID=1&portalPageId=1002
GET http://forums.customer.com/pe/action/forums/displaythread?rootPostID=10842016&channelID=1&portalPageId=1002 HTTP/1.1
Host: forums.customer.com
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.13) Gecko/20101203 Firefox/3.6.13 ( .NET CLR 3.5.30729)
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
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: 115
Proxy-Connection: keep-alive
Cookie: __utma=156962862.829309431.1260304144.1297956514.1297958674.234; __utmz=156962862.1296760237.232.50.utmcsr=forumstest.customer.com|utmccn=(referral)|utmcmd=referral|utmcct=/pe/action/forums/displaythread; s_vi=[CS]v1|258F5B88051D3FC3-40000105C056085F[CE]; inqVital=xd|0^sesMgr|{"sID":4,"lsts":1292598007}^incMgr|{"id":"755563420055418864","group":"CHAT","ltt":1292598006741,"sid":"755563549194447187","igds":"1290627502757","exempt":false}^inq|{"customerID":"755562378269271622"}^saleMgr|{"state":"UNSOLD","qDat":{},"sDat":{}}; inqState=sLnd|1^Lnd|{"c":4,"flt":1274728016,"lldt":17869990,"pgs":{"201198":{"c":1,"flt":1274728016,"lldt":0},"0":{"c":3,"flt":1274845009,"lldt":17752997}},"pq":["0","0","0","201198"],"fsld":1274728016697}; adv_search_results_page=10; ep_beta=1; visitorID=57307059; JSESSIONID=6jXLNdHRDjR9Th3B5gvTVkw1dZLn1zvhvKLR2r4GTLjylHJgjY3Q!683274050; __utmc=156962862; JSESSIONID=6jXLNdHRDjR9Th3B5gvTVkw1dZLn1zvhvKLR2r4GTLjylHJgjY3Q!683274050; TLTHID=5CCA50304DE99E28DB79A7B3267D4231; TLTSID=9DFCDE8045B374AAB752CC98A30E8311; AreCookiesEnabled=1; s_cc=true; SC_LINKS=%5B%5BB%5D%5D; s_sq=%5B%5BB%5D%5D; __utmb=156962862.64.10.1297958674; memberexists=T; ev1=greywolf%20hdtv%20whmx
Cache-Control: max-age=0
HTTP/1.0 200 OK
Date: Thu, 17 Feb 2011 17:38:44 GMT
X-Powered-By: Servlet 2.4; JBoss-4.2.1.GA (build: SVNTag=JBoss_4_2_1_GA date=200707131605)/Tomcat-5.5
Content-Encoding: gzip
Content-Type: text/html;charset=UTF-8
Content-Length: 24739
X-Cache: MISS from samus.company.com
X-Cache-Lookup: MISS from samus.company.com:3128
Via: 1.0 samus.company.com:3128 (squid/2.6.STABLE20)
Proxy-Connection: keep-alive
----------------------------------------------------------
Addendum 2: Additional Information
The browser did receive the "gzipped" file. I had earlier clicked "save as..." when a few of these errors occurred. Gunzip successfully processed the files and converted them to html.

Answer 1

Answer is here: How to preserve the Content-Type header of a Tomcat HTTP response sent through an AJP connector to Apache using mod_proxy
set DefaultType to None in apache configuration.
# DefaultType: the default MIME type the server will use for a document
# if it cannot otherwise determine one, such as from filename extensions.
# If your server contains mostly text or HTML documents, "text/plain" is
# a good value. If most of your content is binary, such as applications
# or images, you may want to use "application/octet-stream" instead to
# keep browsers from trying to display binary files as though they are
# text.
#
DefaultType None

Answer 2

The first page download is of mime type "application/octet-stream". May be the zipped stream is being sent back to the browser? (You can confirm by saving the file and looking inside it.)
It would be really helpful to post the Live HTTP Header request / response traces for problematic and normal cases. If the content is same in both cases - the response HTML - may be forcing the mime type to be text/html (using ForceType directive) for that particular context can fix the issue.
If it turns out to be the case that gzipped content is being sent to the browser in the problematic case - then digging deeper would be necessary. Is this browser specific - only happens with Firefox or happens with all browsers?
Ok, based on the new information provided - looks like Squid is caching the problematic response and not sending the right headers back to the client. So the browsers are doing the right thing here - without the Content-Encoding and right Content-Type they cannot do much else.
Missing response headers for the problematic request :
X-Powered-By: Servlet 2.4; JBoss-4.2.1.GA (build: SVNTag=JBoss_4_2_1_GA date=200707131605)/Tomcat-5.5
Content-Encoding: gzip
Content-Type: text/html;charset=UTF-8
X-Powered-By : It sounds like the problematic requests don't actually hit your JBoss server. Can you verify this by checking access logs? Is Squid caching the response and then sending it back as text/plain?
Reconfiguring Squid to not cache that particular URL should help - see http://www.lirmm.fr/doc/Doc/FAQ/FAQ-7.html section 7.8 for example (which is specific to Squid 2 but later versions should have similar capabilities.)

Answer 3

Seems like a content-negotiation problem. Apache is guessing the content type using the "magic" byte and setting the content type incorrectly. That explains why it happens intermittently. Try disabling mod_negotiation and see what happens. See http://httpd.apache.org/docs/2.0/content-negotiation.html for more info.

Answer 4

I saw the following in your settings
ProxyPassReverse /ajp://localhost:8080/
But port 8080 is not ajp port. The default ajp port is 8009. Could this be your problem?

Answer 5

There is most likely something wrong with your web application, not Apache. If your web app sends back the correct Content-Type, Apache will gladly forward it to the client. No content negotiation will be done in that case. If you do not return any Content-Type, Apache will almost surely substitute text/plain, which is not what you want.
Test your web app without Apache in the middle, make sure that it sends back the correct Content-Type.

Answer 6

It uses to be when apache serves secure content in a non secure channel.