HttpWebRequest in .NET CF 2.0 - Sent XML File over 34K Corrupted


G

Greg Hellem

I have a .NET CF 2.0 Mobile Application that sends "collected data" to a
HTTPS Server (running Apache under Windows 2000) and the XML file (SOAP)
containing the collected data "occasionally" appears corrupted on the server
side, but only when the XML file is greater than 34K in size, and cannot be
properly parsed as an XML Document due to missing / corrupt XML Tags. I say
"occasionally" because I cannot reproduce this error myself and only a few
of our customers (2-3 out of 70) using the mobile application have
experienced this situation. The XML file is never corrupt as long as it is
under 34K in size.

In an attempt to reproduce this error I have sent "collected data" files as
large as 125K without any XML errors and did so using various Internet
Connections, i.e. using our corporate intranet, the Internet via ADSL from
my home and using ActiveSync running on a Desktop Machine connected to our
intranet and the Internet. I have NEVER been able to reproduce this error
which led me to believe that the problem was due to hardware failures of the
mobile device itself or the customers network, but after extensive research
and testing this does not appear to be the problem either. Also, the
"collected data" itself does not contain any characters that would violate
the XML standard and I went so far as to add some code to the mobile
application that validates the XML Structure prior to sending the data to
the host server and the structure is always validated before sending but
arrives at the host server corrupted!! I am assuming that the HTTPS / TCP/IP
protocols will handle corrupt packets via the packet checksum and request
the packet again, so I don't think data is being corrupted during its trip
to the host server but instead is actually corrupt when being transmitted
from the mobile device itself, hence the packet checksums are always
correct. The mobile device is a Symbol MC3090 running WinCE 5.0 and Symbol
(now Motorola) has no mention of any "data corruption" within their
knowledgebase regarding these devices.

I have read the Microsoft Article (ID 831578) regarding "Memory Leak When
SSL and Client Certificates are Used With the HttpWebRequest Object" but am
unsure if this applies to the .NET CF 2.0. We are using HTTPS / SSL and I am
using the standard example given for the
LocalCertificatePolicy.CheckValidationResult to eliminate certificate
problems such as mismatched certificate and machine names but I do not
ignore an invalid certificate.

Originally I was using .NET CF 1.1 when I created this application and ran
into a .NET CF bug regarding the use the HttpWebRequest class over HTTPS
whereby the workaround was to set AllowWriteStreamBuffering = True and to
not specify the ContentLength property. Even though the project has been
upgraded to .NET CF 2.0 I am still abiding by the workaround for the .NET CF
1.1 bug. Is this still an issue in .NET CF 2.0?

An example of the corrupted xml data: (closing tag of </ItemEnterpriseName>
is corrupt and opening <ItemName> tag is missing along with the data itself)
<Name>DEFAULT</Name>
<ItemEnterpriseName>Comtech Data</ItemEnterpriseNa4A</ItemName>
<SiteEnterpriseName>Comtech Data</SiteEnterpriseName>
.... data continues ...

The data should have appeared as:
<Name>DEFAULT</Name>
<ItemEnterpriseName>Comtech Data</ItemEnterpriseName>
<ItemName>IC/SO-NC7SBU3157</ItemName>
<SiteEnterpriseName>Comtech Data</SiteEnterpriseName>
.... data continues ...

Any assistance in the matter would be tremendously appreciated!!!
Thank you,
Greg Hellem
 
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G

Guest

I'd be inclined to add a CRC to the packet and validate that what I received
is what the server sent. If the CRC fails, resend.
 
G

Greg Hellem

Not easily accomplished, since the same server-side code used to receive
mobile SOAP requests are also used for non-mobile SOAP requests and it would
be a major modification to differentiate between the two. I was hoping
someone would recognize a known bug in .NET CF...
But thanks for the idea!
- Greg
 
G

Greg Hellem

Questions unanswered so far:
1) Does anyone know if the bug in .NET CF 1.1 regarding the use
HttpWebRequest over HTTPS is still an issue in .NET CF 2.0 or can I
disregard the workaround for that bug?
2) Does anyone know if the Microsoft Article (ID 831578) regarding "Memory
Leak When SSL and Client Certificates are Used With the HttpWebRequest
Object" only pertains to the Desktop .NET 2.0 Framework or does it also
include .NET CF 2.0?
Thank you for your time,
Greg Hellem
 
G

Guest

That does look a bit dodgy. Over what network was this corrupted? If GPRS it
could be the carrier not handling the encryption/decryption correctly. If so
contact the carrier. I would be inclined to reduce those packet sizes if at
all possible. Do you have any sort of status tracking or checksum? so if the
message appears corrupt, you simply do a resend.
 
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G

Greg Hellem

Customers are using Broadband Ethernet Networks for access to the Internet.
No telephony is involved at all; GPRS, CDMA or otherwise.

Also, I am not controlling packet sizes, ack/naks or checksums. I am simply
using the HttpWebRequest/HttpWebResponse objects for communications with the
host server. I create a SOAP Request on the mobile device, package it into a
single String (that gets converted to a byte array using UTF8Encoding) then
I simply get the request stream of the HttpWebRequest object and call
RequestStream.Write(bytes, 0, bytes.length). Also, as previously noted, I
have sent these SOAP Requests with strings as large as 125K in size without
issue and I cannot reproduce the problem that the very limited number of
customers are seeing (2-3 out of 70+). The data is always valid before I
send it, because I perform an XmlDocument.LoadXml(SoapString) within a
Try...Catch and it would hit the Catch if the XML Tag Structure was invalid
but it never hits the Catch statement (I have tested this functionality by
purposely making the XML Structure invalid by placing missing tags and
invalid data within the SOAP Request and the Catch does get called!)
However, the overall SOAP Request can end up corrupted on the server side
and I do not have the ability to request that the mobile device resend the
SOAP Request at this time.
Thanks for the advice though Simon!!

Questions still unanswered so far (as of 11/15/2007):
1) Does anyone know if the bug in .NET CF 1.1 regarding the use
HttpWebRequest over HTTPS is still an issue in .NET CF 2.0 or can I
disregard the workaround for that bug?
2) Does anyone know if the Microsoft Article (ID 831578) regarding "Memory
Leak When SSL and Client Certificates are Used With the HttpWebRequest
Object" only pertains to the Desktop .NET 2.0 Framework or does it also
include .NET CF 2.0?
Again, thank you for your time,
Greg Hellem
 
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