Capturing SOAP message on localhost using Fiddler

fiddlerhttpsoap

I am unable to capture local HTTP traffic when my Java client makes a SOAP request to my local Tomcat instance.

My current configuration is

Tomcat instance – run on localhost:8080
Local Java client – run from Windows cmd line
Fiddler – run on localhost:8888

I used Axis2 wsdl2java to create my client SOAP stub, and used my machines IP address when specifying the WSDL (hosted on Tomcat)

wsdl2java -uri http://192.168.0.5:8080/axis2/services/Version?wsdl -p sample.axisversion -d adb -s

So, the generated code has lines like this throughout:

  public VersionStub(org.apache.axis2.context.ConfigurationContext configurationContext) throws org.apache.axis2.AxisFault {
    this(configurationContext,"http://192.168.0.5:8080/axis2/services/Version.VersionHttpSoap12Endpoint/" );
}

My client app uses the generated stub and I set the Java proxy to Fiddler using the following code (which gets called before the SOAP stub is actually used):

System.getProperties().put("proxySet", "true");
System.getProperties().put("proxyHost", "localhost");
System.getProperties().put("proxyPort", "8888");

…but still I don't see any request or response traffic in Fiddler. What's missing?

Best Answer

Instead of localhost, try to use ipv4.fiddler, which makes sure your localhost traffic goes through fiddler. See also: http://www.fiddler2.com/Fiddler/Help/hookup.asp#Q-LocalTraffic

Simple explanation about SOAP and REST

SOAP - "Simple Object Access Protocol"

SOAP is a method of transferring messages, or small amounts of information, over the Internet. SOAP messages are formatted in XML and are typically sent using HTTP (hypertext transfer protocol).

Rest - Representational state transfer

Rest is a simple way of sending and receiving data between client and server and it doesn't have very many standards defined. You can send and receive data as JSON, XML or even plain text. It's light weighted compared to SOAP.

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

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.

Best Answer

Related Solutions

Rest – Representational state transfer (REST) and Simple Object Access Protocol (SOAP)

Simple explanation about SOAP and REST

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

Tracking it down

Cause

Solution

Related Topic