[Varnish] #570: [2.0.4] Strange behaviour when using If-Modified-Since

[Varnish]

#570: [2.0.4] Strange behaviour when using If-Modified-Since
------------------------+---------------------------------------------------
 Reporter:  gdelacroix  |       Owner:  phk
     Type:  defect      |      Status:  new
 Priority:  normal      |   Milestone:     
Component:  varnishd    |     Version:  2.0
 Severity:  normal      |    Keywords:     
------------------------+---------------------------------------------------
 Hi !

 When sending a request with "If-Modified-Since" header in pass mode to a
 backend that does not correctly handle this header (never responds 304),
 it seems that Varnish (2.0.4) overrides this behaviour by replacing (when
 necessary) 200 with 304 and does not send any content => This is great !

 But it seems that, when doing this, Varnish follows a different path that
 forgets headers that are set in vcl_fetch...

 Here is my vcl_fetch sample :

 {{{
 vcl_fetch {
   if (req.http.Host == "www.site1.com") {
     set obj.http.MyTag = "Site1";
   } elseif (req.http.Host == "www.site2.com") {
     set obj.http.MyTag = "Site2";
   }
 }
 }}}


 In most cases (if backend sends 304 or no 304 is necessary), "MyTag"
 header will be sent.

 But only if the backend answers 200 but it should have answered 304 (Last-
 Modified <= If-Modified-Since), then Varnish will correct this and send
 304 without data, but "MyTag" header will not be sent...

 I have tried to add some kind of :

 {{{
 vcl_delivery {
   if (req.http.Host == "www.site1.com") {
     set resp.http.MyTag = "Site1";
   }
 ...
 }}}


 but vcl_delivery doesn't handle req.http...

 Here is some varnishlog to give you more details : (same requests, same
 VCL, only backend configuration changes)

 Normal behaviour (304 > 304) :

 {{{
    11 RxProtocol   b HTTP/1.1
 >  11 RxStatus     b 304
    11 RxResponse   b Not Modified
    11 RxHeader     b Connection: Keep-Alive
    11 RxHeader     b Date: Fri, 23 Oct 2009 17:20:13 GMT
    11 RxHeader     b ETag: "d022b2771de7c81:14ff"
    11 RxHeader     b Server: Microsoft-IIS/6.0
    11 RxHeader     b Last-Modified: Wed, 16 Jul 2008 08:25:12 GMT
    11 RxHeader     b Accept-Ranges: bytes
    11 RxHeader     b X-Powered-By: ASP.NET
     7 ObjProtocol  c HTTP/1.1
 >   7 ObjStatus    c 304
     7 ObjResponse  c Not Modified
     7 ObjHeader    c Date: Fri, 23 Oct 2009 17:20:13 GMT
     7 ObjHeader    c ETag: "d022b2771de7c81:14ff"
     7 ObjHeader    c Server: Microsoft-IIS/6.0
     7 ObjHeader    c Last-Modified: Wed, 16 Jul 2008 08:25:12 GMT
     7 ObjHeader    c X-Powered-By: ASP.NET
    11 BackendReuse b MyBackend
     7 TTL          c 110064484 RFC 3600 1256318401 0 0 0 0
     7 VCL_call     c fetch
     7 VCL_return   c pass
     7 Length       c 0
     7 VCL_call     c deliver
     7 VCL_return   c deliver
     7 TxProtocol   c HTTP/1.1
 >   7 TxStatus     c 304
     7 TxResponse   c Not Modified
     7 TxHeader     c ETag: "d022b2771de7c81:14ff"
     7 TxHeader     c Server: Microsoft-IIS/6.0
     7 TxHeader     c Last-Modified: Wed, 16 Jul 2008 08:25:12 GMT
     7 TxHeader     c X-Powered-By: ASP.NET
     7 TxHeader     c Content-Length: 0
 >   7 TxHeader     c MyTag: Site1
     7 TxHeader     c Date: Fri, 23 Oct 2009 17:20:01 GMT
     7 TxHeader     c X-Varnish: 110064484
     7 TxHeader     c Age: 0
     7 TxHeader     c Via: 1.1 varnish
     7 TxHeader     c Connection: keep-alive
     7 ReqEnd       c 110064484 1256318401.559283018 1256318401.564701557
 0.010328531 0.005382299 0.000036240
 }}}


 Strange behaviour (200 > 304) :

 {{{
    11 RxProtocol   b HTTP/1.1
 >  11 RxStatus     b 200
    11 RxResponse   b OK
    11 RxHeader     b Connection: Keep-Alive
    11 RxHeader     b Content-Length: 377
    11 RxHeader     b Date: Fri, 23 Oct 2009 17:27:19 GMT
    11 RxHeader     b Content-Type: image/gif
    11 RxHeader     b ETag: "d022b2771de7c81:1c82"
    11 RxHeader     b Last-Modified: Wed, 16 Jul 2008 08:25:12 GMT
    11 RxHeader     b Accept-Ranges: bytes
     7 ObjProtocol  c HTTP/1.1
 >   7 ObjStatus    c 200
     7 ObjResponse  c OK
     7 ObjHeader    c Date: Fri, 23 Oct 2009 17:27:19 GMT
     7 ObjHeader    c Content-Type: image/gif
     7 ObjHeader    c ETag: "d022b2771de7c81:1c82"
     7 ObjHeader    c Last-Modified: Wed, 16 Jul 2008 08:25:12 GMT
    11 BackendReuse b MyBackend
     7 TTL          c 110064485 RFC 3600 1256318831 0 0 0 0
     7 VCL_call     c fetch
     7 VCL_return   c pass
     7 Length       c 0
     7 VCL_call     c deliver
     7 VCL_return   c deliver
     7 TxProtocol   c HTTP/1.1
 >   7 TxStatus     c 304
     7 TxResponse   c Not Modified
     7 TxHeader     c Date: Fri, 23 Oct 2009 17:27:11 GMT
     7 TxHeader     c Via: 1.1 varnish
     7 TxHeader     c X-Varnish: 110064485
     7 TxHeader     c Last-Modified: Wed, 16 Jul 2008 08:25:12 GMT
     7 TxHeader     c Connection: keep-alive
     7 ReqEnd       c 110064485 1256318831.177328587 1256318831.183318853
 0.003719568 0.005955219 0.000035048

 Where is MyTag ??
 }}}

 It would be great if someone could explain me some fix or some
 workaround...cause I really miss MyTag ;o)

 Thanks !

-- 
Ticket URL: <http://varnish.projects.linpro.no/ticket/570>
Varnish <http://varnish.projects.linpro.no/>
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