Hi Mark & all,
After using the Jpcap (java sniffer tool) to watch the http packets, We
Finally
found out the root cause of this problem is indeed the keep-live BUG of
Internet
Explorer, below is our finding for your reference :
Finding 1 : When using AJAX to make http requests, Internet Explorer always
sends
http header and body separately in 2 (or more) IP packets. and
in our
case the header is always sent in the first packet since the
header
length is never greater than 1460 bytes(Maximum packet data
size).
Finding 2 :
1) When apache httpd server detects the keep-live timeout, it will
send
a Fin (finish) Packet to Client (IE) telling it to close the
connection,
but at meanwhile Client is preparing to send another POST
request to Apache,
for unknown reasons (IE BUG!) IE still keeps sending the POST
head & body instead
of closing connection immediately.
2) Apache server will ignore the POST request. and send the ACK
Packet back
to Client.
3) and next, the Client sends a Fin(Finished) Packet to apache
server to confirm
closing connection.
4) Apache server sends an ACK packet to confirm ending this
connection.
5) Next, Client resend the POST header again to Apache server.
6) Apache Server confirm receiving the header.
7) after about 1.5 minutes, Client send a RST (Reset) packet to
Apache
Server asking reset the connection. In this case the POST body
is
never sent to Apache server that causes the request parameters
is
missing.
Following is the Packet flow for your reference : (Time format hhms.S)
Time From to SEQ ACK
Flag remark
======== ====== ====== ======= ========= ====
====================================
071249.751 Client Apache 1088748537 1807070026 previous
conversion sent from Client
071304.243 Apache Client 1807070026 1088748537
FIN time-out(idle 15 seconds)
071304.467 Client Apache 1088748537 1807070026 PSH Client still
sends POST header
1807070027 Apache Client 1807070027 1088749235
1088749235 Client Apache 1088749235 1807070026 PSH Client still
sends POST body
071304.479 Apache Client 1807070027 1088749316
071304.720 Client Apache 1088749316 1807070027
071304.721 Client Apache 1088749316 1807070027 Fin Finish the
connection
071304.722 Apache Client 1807070027 1088749317 Server
confirm ending the connection
071304.737 Client Apache 1959299521 1807484246 PSH Client resend
the Post header in another connection
071304.737 Apache Client 1807484246 1959300219 Apache
confirm receiving this header
071425.235 Client Apache 1959300219 1807484246 RST after about
1.5 minutes, Client request to reset the connection
In conclusion, the problem only happens when Keep-Alive is timeout, that's
why it's related to the apache keep-alive
setting, smaller keep-alive timeout will raise the timeout frequency and
cause more missing body part errors as well.
Unfortunately, so far there is no solution yet unless Microsoft fix the BUG.
Thanks
James.
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