Creating an InstrumentationModule that requires external library

[oxeye-mher]

Hello everyone,

I'm currently working on an InstrumentationModule that needs to be loaded as an Extension. One of my AdviceMethods is responsible for creating a JSON text, and I'd like to utilize the com.google.gson.Gson Java library (or any other suitable library) for this purpose.

The build.gradle file contains the following line: implementation("com.google.code.gson:gson:2.10.1"), ensuring that the com.google.gson library exists within the extension.jar.

However, I've encountered an issue. I'm struggling to make Opentelemetry inject the Gson library into the application code. After reading the documentation, I tried using the getAdditionalHelperClassNames function. Unfortunately, since com.google.gson comprises multiple classes, using getAdditionalHelperClassNames would require listing all Gson classes in the correct order, which I believe is not the optimal solution.

Is there a way to inject the entire com.google.gson library into the application code so that I can use it without explicit instrumentation?

I did manage to make it work by adding the com.google.com library to the opentelemetry-javaagent. However, this solution isn't ideal for me as I prefer to use the original opentelemetry-javaagent and add my code only as an extension.

Any help would be greatly appreciated. Thank you!

[laurit]

I think you should be using isHelperClass instead of getAdditionalHelperClassNames. With isHelperClass you don't need to list full class names and can just use startsWith and don't need to worry about the order.
Injecting large libraries has helper classes isn't usually a good idea. If the application also contains gson you'd have to shade your copy of gson to avoid clashing with it. For large libraries it is possible that the amount of muzzle (our safety checker that determines whether instrumentation can be safely applied) collects so much info that the method generated based on it exceeds max method size in class file. Instead of an extension you may need to package your code as a custom distro and instead of injecting gson as helper classes add it to agent class loader and have an api in boot loader that lets you use gson in agent from application code.

[oxeye-mher]

Edit - I notice now that when I use the demo extension, IsHelperClass does exactly what you mentioned, but when I override IsHelperClass in my instrumentation class - is never called, any ideas where to look for an issue?

Thanks for the answer!
I tried to use isHelperClass but it didn't work.
but I managed to make it work using creating own javaagent distro.
But what will happen in case there is already Gson library in the instrumented code and I inject my javaagent that contains my Gson ? Should I do something special or javaagent is dealing with making the injection be safe?

[mateuszrzeszutek]

I tried to use isHelperClass but it didn't work.

Are you using the muzzle gradle plugin? It does some magic during compile time and registers the isHelperClass classes as helpers.

But what will happen in case there is already Gson library in the instrumented code and I inject my javaagent that contains my Gson ? Should I do something special or javaagent is dealing with making the injection be safe?

As Lauri mentioned, you should probably shade your gson copy. If the app contains an incompatible gson version the instrumentation might just not work.

[oxeye-mher]

You're right, I missed that I need to use muzzle for that, thank you very much! I will add muzzle plugin

[Henrique-rr-Martins]

Hello guys. Right now I am trying to create an extension from Opentelemtry JavaAgente but I have external libraries and I am using Maven with a pom.xml. I don't have experience with gradle. How could I reach the same result using Maven? is it possible?