How to pass “Null” (a real surname!) to a SOAP web service in ActionScript 3

Question

We have an employee whose surname is Null. Our employee lookup application is killed when that last name is used as the search term (which happens to be quite often now). Th

Answer 1

Tracking it down

At first I thought this was a coercion bug where null was getting coerced to "null" and a test of "null" == null was passing. It's not. I was close, but so very, very wrong. Sorry about that!

I've since done lots of fiddling on wonderfl.net and tracing through the code in mx.rpc.xml.*. At line 1795 of XMLEncoder (in the 3.5 source), in setValue, all of the XMLEncoding boils down to

currentChild.appendChild(xmlSpecialCharsFilter(Object(value)));

which is essentially the same as:

currentChild.appendChild("null");

This code, according to my original fiddle, returns an empty XML element. But why?

Cause

According to commenter Justin Mclean on bug report FLEX-33664, the following is the culprit (see last two tests in my fiddle which verify this):

var thisIsNotNull:XML = <root>null</root>;
if(thisIsNotNull == null){
    // always branches here, as (thisIsNotNull == null) strangely returns true
    // despite the fact that thisIsNotNull is a valid instance of type XML
}

When currentChild.appendChild is passed the string "null", it first converts it to a root XML element with text null, and then tests that element against the null literal. This is a weak equality test, so either the XML containing null is coerced to the null type, or the null type is coerced to a root xml element containing the string "null", and the test passes where it arguably should fail. One fix might be to always use strict equality tests when checking XML (or anything, really) for "nullness."

Solution

The only reasonable workaround I can think of, short of fixing this bug in every damn version of ActionScript, is to test fields for "null" and escape them as CDATA values.

CDATA values are the most appropriate way to mutate an entire text value that would otherwise cause encoding/decoding problems. Hex encoding, for instance, is meant for individual characters. CDATA values are preferred when you're escaping the entire text of an element. The biggest reason for this is that it maintains human readability.

Answer 2

The problem could be in Flex's SOAP encoder. Try extending the SOAP encoder in your Flex application and debug the program to see how the null value is handled.

My guess is, it's passed as NaN (Not a Number). This will mess up the SOAP message unmarshalling process sometime (most notably in the JBoss 5 server...). I remember extending the SOAP encoder and performing an explicit check on how NaN is handled.

Answer 3

As a hack, you could consider having a special handling on the client side, converting 'Null' string to something that will never occur, for example, XXNULLXX and converting back on the server.

It is not pretty, but it may solve the issue for such a boundary case.