EOleException on accessing message body

问题

A Windows service when trying to access the .Body property of a MSMQ message object throws an EOleException - but only when the Xml document contained in this message has an empty list node.

The EOleException message complains about insufficient memory (exception code -2147024882). Since the exception only occurs with the smallest possible Xml document, memory cannot be the real issue. The next thing that comes to mind is a problem with access rights but then again all "good" messages (as described below) are processed without problems.

The exception can be reproduced under any thinkable condition ("bad" message first, many "good" messages first - then "bad" message, run in debugger or just logging the exception); it doesn't matter if the code shown below is run as a service or as a simple excecutable.

Using the same COM object (MSMQ.MSMQQueueInfo) from within a VBScript on the same machine does not produce any errors.

Accessing any other properties apart from .Body doesn't throw an exception so the message object instance seems to be received sucessfully. Also the transaction receiving the message can be comitted sucessfully if the .Body property is not accessed.

Windows Service code

//...
qInfo    := CreateOleObject('MSMQ.MSMQQueueInfo');
qTxDisp  := CreateOleObject('MSMQ.MSMQTransactionDispenser');
//...
qTx := qTxDisp.BeginTransaction;
qMessage := qQueue.Receive(qTx, False, True, 0);
//...
sBody := qMessage.Body; //throws EOleException

The qMessage.BodyLength property returns the value 165 for "bad" messages as shown below.

"Bad" message

<?xml version="1.0" encoding="Windows-1252"?>
<response space="" Message="Entry_7">
    <query>
        <entrylist count="0">
        </entrylist>
    </query>
</response>

This message reliably makes the service code throw an EOleExecption.

"Good" message

<?xml version="1.0" encoding="Windows-1252"?>
<response space="" Message="Entry_7">
    <query>
        <entrylist count="2">
            <entry>
                <abc>123</abc>
                <def>456</def>
            </entry>
            <entry>
                <abc>789</abc>
                <def>000</def>
            </entry>
        </entrylist>
    </query>
</response>

This message is reliably processed without problems.

The problem first occured when moving the service from a Win2003 machine to a Win2008 (32-bit Standard).

回答1:

If the VBScript works fine, then I guess that it is something in the interaction between MSMQ and the Delphi service.

Have you tried to run the Delphi code in a standalone application?

I have not yet worked with MSMQ, but maybe you can also try to use a non transactional read from the message queue to see if it makes a difference (reduce the code to be as small/simple as possble).

A potential reason could be a different (newer) MSXML library on the Win2008 machine.

来源：https://stackoverflow.com/questions/4192217/eoleexception-on-accessing-message-body

标签

Delphi

exception

com

msmq

ole