Resolving NullReferenceException in .NET SOAP Extensions

Are you facing a `NullReferenceException` in your .NET SOAP Extension? This blog provides a clear solution by examining the proper initialization order of SOAP message properties.
---

Visit these links for original content and any more details, such as alternate solutions, comments, revision history etc. For example, the original title of the Question was: .NET SOAP Extension is throwing NullReferenceException inside MethodInfo?

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding the Issue with .NET SOAP Extensions

When working with .NET web services, utilizing SOAP extensions can greatly improve your logging and monitoring capabilities. However, developers often encounter frustrating issues during implementation, one of the most common being the dreaded NullReferenceException. This blog aims to clarify this problem and guide you through the steps to effectively resolve it.

The Scenario

You are configuring a SOAP extension to log web service calls to your database. After setting up the extension as per the configuration file, you run your web service only to be met with an unexpected exception:

[[See Video to Reveal this Text or Code Snippet]]

This error occurs when your logging method attempts to access the MethodInfo property during the BeforeDeserialize stage of the ProcessMessage method. So, how can you solve this issue?

The Solution

After troubleshooting and experimenting with different approaches, it has been concluded that the error arises because the SoapMessage object is not fully initialized at the BeforeDeserialize stage. Let's break down the solution clearly.

Key Observations

Initialization Timing: Properties like Action and MethodInfo are not available during the BeforeDeserialize phase, which leads to exceptions when accessed. However, these properties are correctly initialized by the AfterSerialize stage.

Log Entry Structure: You need the MethodInfo to log the method name properly, but it must be accessed after the message is fully set up.

Recommended Steps to Implement the Fix

To avoid running into the NullReferenceException, adjust the execution order of your logging routine as follows:

1. BeforeDeserialize Stage

a. Read the Server URL directly from the message.

b. Collect any necessary request information such as certificates and user host address.

c. Proceed to read the request contents from the stream.

Example Code:

[[See Video to Reveal this Text or Code Snippet]]

2. AfterSerialize Stage

a. Here is where to read exceptions if any are thrown.

b. Now, it's safe to access the MethodInfo and Action properties.

c. Finally, proceed with reading the response contents from the stream.

Example Code:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By understanding the lifecycle of the SoapMessage object and its properties, you can prevent NullReferenceExceptions and enable your logging to work seamlessly. Always remember the correct order of access and adjust your logging logic accordingly to fit within the web service message processing lifecycle. Don't hesitate to revisit your implementation if you face similar issues in the future; sometimes, the solution lies in the timing of how and when you access properties of the objects involved.

Implement these changes, and your logging setup should function effortlessly, allowing you to monitor your web services without the headache of exceptions!