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Subject: [Bug 57589] New: "If-Modified-Since" header detected in HTTP
 unconditional GET request
Date: Wed, 18 Feb 2015 07:24:56 +0000
Message-ID: <bug-57589-43213@https.bz.apache.org/bugzilla/>
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https://bz.apache.org/bugzilla/show_bug.cgi?id=3D57589

            Bug ID: 57589
           Summary: "If-Modified-Since" header detected in HTTP
                    unconditional GET request
           Product: APR
           Version: HEAD
          Hardware: PC
            Status: NEW
          Severity: normal
          Priority: P5
         Component: APR
          Assignee: bugs@apr.apache.org
          Reporter: bala@adobe.com

Our product is Adobe Media Server (AMS). It uses the Apache web server for
streaming multimedia over HTTP. There are 4 Apache httpd modules developed =
by
us that are included in our Apache build. One of these modules =E2=80=93 mo=
d_f4fhttp.so
is concerned with live streaming of multimedia using the HDS standard.

Issue: For some unconditional GET requests, querying the Apache APR API
apr_table_get for =E2=80=9CIf-Modified-Since=E2=80=9D header field returns =
a valid value.

This issue is observed only in the release build of Apache web server. The
setup consists of Flash Media Live Encoder (FMLE) as the live video publish=
er
and 3 video subscribers (OSMF Player 2.0 instances embedded in web browsers=
).
With Apache httpd release build, the issue crops up within 10 minutes of li=
ve
streaming. When the debug build is used, the issue does not appear even aft=
er 2
hours of streaming.

The mod_f4fhttp.so module uses the Apache API function apr_table_get to que=
ry
the request object for the presence of =E2=80=9CIf-Modified-Since=E2=80=9D =
header field. The
problem arises when this API returns a valid non-null value for the
=E2=80=9CIf-Modified-Since=E2=80=9D header field even when it is not presen=
t (i.e. it=E2=80=99s an
unconditional GET) in the HTTP request.  This can be confirmed by the logs
(attached) of packet capture tools.

This behavior causes the mod_f4fhttp.so module to think that the HTTP reque=
st
is a conditional one and so it returns a 304 response code. This is a probl=
em
for the client since it had generated an unconditional GET request.

This (querying the =E2=80=9CIf-Modified-Since=E2=80=9D header) was done at =
the entry point of
the module mod_f4fhttp.so, so this eliminates the possibility of the module
itself inserting this field in the request.

It does not matter whether the debug or release version of mod_f4fhttp.so
module is used =E2=80=93 regardless of that, the issue can be seen in the A=
pache httpd
release build only. The issue cannot be reproduced in the debug build of Ap=
ache
httpd.

Three different network packet capture tools were used =E2=80=93 Wireshark,=
 Windump and
HTTPDebugger.  There are no differences between their capture logs i.e. 304
responses for unconditional GET requests can be seen in all of them. The lo=
gs
are attached here.

Steps to reproduce the issue:
1. Install Adobe Media Player (AMS) 5.0.7. During installation, when it asks
for a serial number, leave it blank =E2=80=93 this will install the =E2=80=
=9CStarter Edition=E2=80=9D.
Leave all other options unchanged during installation. The limitation of
=E2=80=9CStarter Edition=E2=80=9D is that it allows 10 minutes of streaming=
, which is enough to
reproduce this issue.=20
2. Copy crossdomain.xml to =E2=80=9Cwebroot=E2=80=9D folder in the AMS inst=
allation.
3. Install Flash Media Live Encoder (FMLE) 3.2.
4. Launch FMLE.=20
    o Ensure the following settings in the presets
    Video:
    Format: H.264
    Profile: Main
    Level: 3.1
    Keyframe Frequency: 4 seconds
    Frame Rate: 30.00 fps
    Input Size: 320x240
    Bit Rate: 200 Kbps
    Output Size: 320x240

    Audio:
    Format: Mp3
    Channels: Stereo
    Sample Rate: 44100 Hz
    Bit Rate: 96 Kbps

    o Set the following fields in the Output box
        =EF=82=A7 Check =E2=80=9CStream to Flash Media Player=E2=80=9D
        =EF=82=A7 FMS URL: rtmp://localhost/livepkgr
        =EF=82=A7 Stream: livestream?adbe-live-event=3Dliveevent

    o Click on Connect. [The button=E2=80=99s caption should now change to
=E2=80=9CDisconnect=E2=80=9D].
    o Click on Start (the green button at the bottom of the window). This w=
ill
start the publishing stream from FMLE to AMS.
5. Launch OSMF Player instances. The player has to be hosted on an http ser=
ver.
A second machine can be used for this. In a web browser, open the OSMF Play=
er
web page. E.g. http://localhost/OSMFP/OSMFPlayer.html. The attached OSMFPla=
yer
build can be used. Two more instances of the player can launched =E2=80=93 =
either in
the same browser or different ones. If the player launches successfully, a
control console will be visible in a smaller window on the web page. Click =
on
the =E2=80=9CEject=E2=80=9D button to open the =E2=80=9CMedia URL=E2=80=9D =
textbox. Enter the URL of the live
stream manifest in this box =E2=80=93 http://<hostname or IP address where =
AMS is
installed>/hds-live/livepkgr/_definst_/liveevent/livestream.f4m - and press
Enter. The live stream should now start playing in the window.


Notes
=E2=80=A2 When caching is disabled (by commenting out "CacheEnable disk /hd=
s-live" in
httpd.conf), this issue does not arise.=20
=E2=80=A2 The same issue is also confirmed to be present in Apache httpd v2=
.2.21

Download links:
Adobe Media Server (AMS) -
http://www.adobe.com/in/products/adobe-media-server-standard.html
Flash Media Live Encode (FMLE) -
http://www.adobe.com/in/products/flash-media-encoder.html
OSMF Player 2.0 source -
http://sourceforge.net/projects/osmf.adobe/files/OSMF%202.0%20Release%20%28=
final%20source%2C%20ASDocs%2C%20pdf%20guides%20and%20release%20notes%29/


Attachments
=E2=80=A2 Packet capture logs
    o Wireshark =E2=80=93 =E2=80=9Cwireshark-s.pcapng=E2=80=9D. Frame 297 i=
s the HTTP request for a
video fragment. Its response is in Frame 298.
    o Windump =E2=80=93 =E2=80=9Cwindump.log=E2=80=9D. Check the end of the=
 log for the 304 response.
    o HTTPDebugger =E2=80=93 =E2=80=9Chttp debugger - headers.txt=E2=80=9D
=E2=80=A2 crossdomain.xml
=E2=80=A2 OSMF Player

--=20
You are receiving this mail because:
You are the assignee for the bug.=

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