eliasen - Weird API for MessageContext

Monday, 06 July 2009

Hi all

So, yesterday I had to loop through all properties on a message inside a pipeline component.

When you program a general pipeline component, you get an Execute method that looks like this:

public IBaseMessage Execute(IPipelineContext pContext, IBaseMessage pInMsg)

Now, in order to loop through the properties, the common solution is like this (and you can find this in many many blog posts around the great internet):

for (int i = 0; i <= pInMsg.CountProperties; i++)
{
string name;
string ns;
object value = pInMsg.Context.ReadAt(i, out name, out ns);
// Do something with the vale, name and namespace
}

Now, this is quite all right as it is, but there is one small pitfall that I don’t think most people realize; The CountProperties property is a uint, meaning that it can contain values up to 2^32 = 4294967296. Unfortunately, the first parameter to the ReadAt method is an int, which only holds values up to (2^31) – 1 = 2147483647. So, if there are, say 3000000000 properties, then the CountProperties property will return the correct number of properties, but there is no way of calling the ReadAt method to get the property.

This is kind of silly.

Now, to be fair, I think that the most properties I have seen on a message ever may have been around 40-50 properties. So there is a looooong way to 2 billion properties :-) So in real life, I don’t expect anyone to run into this limitation – if you do, I’ll buy you a beer! :-)

BUT, just to be sure, what you should do to be absolutely correct in your code is this:

uint counter = pInMsg.CountProperties;
string name;
string ns;
if (counter > int.MaxValue)
{
counter = int.MaxValue;
}
for (int i = 0; i < counter; i++)
{
object value = pInMsg.Context.ReadAt(i, out name, out ns);
// Do something with the vale, name and namespace
}

And then, off course, you should somehow notify someone that there were more properties than you could handle – like a Debug statement, an error in the eventlog or the such… perhaps even throw an exception BEFORE trying to enumerate the properties, sine it would be useless, the result you get.