Allow request body to be collected as a span attribute

[bhogayatakb]

Proposing a new feature, where user can get the request parameters, i.e. headers, body etc. in resource attributes.
This can be controlled via a feature toggle as @zeitlinger suggested to me on slack

I would like to give a PR for this myself.
Need inputs from the team on this.
Also, I would like to know if this can be done via any central class instead of implementing this in each instrumentation ?!

[laurit]

Instead of resource attribute you probably meant span attribute. Resource is immutable and can not be altered after sdk initialization. There already is an option to capture request & response headers, see https://opentelemetry.io/docs/instrumentation/java/automatic/agent-config/#capturing-http-request-and-response-headers also there is an experimental option to capture servlet request parameters https://opentelemetry.io/docs/instrumentation/java/automatic/agent-config/#capturing-servlet-request-parameters Check whether these would be sufficient for you, if not please do elaborate what exactly you need. Capturing request body is going to be tricky, you'd need to read the request and then somehow restore it so that the application can also read it. It would probably be easier to handle this inside the application and call setAttribute on the server span once you have access to the request body.

[bhogayatakb]

@laurit Yes, Span attribute makes more sense compared to resource attributes. Agreed !

Understood that using setAttribute from application side is a solution that can be performed without modifying anything in this project.

I need to capture request body in the span attributes for all the request handlers, in an application, irrespective of their framework,
I want user to just use otel JAR as -javaagent and provide a property i.e. -Dotel.traces.request.data-capture=true
So that user do not have to do setAttribute in all the request handlers.

3 Quick questions:

1. Is there a simpler way for user to perform setAttribute, instead of doing it in each and every request handler ?
2. Do you think this change might be helpful to this particular project ?
3. Is there a central class (framework-agnostic) that has access to incoming requests, where I can do the needful code ?

[zeitlinger]

I've heard this feature request before, so I think it might be useful to have.

As for getting started, you can look at the usages for

opentelemetry-java-instrumentation/javaagent-extension-api/src/main/java/io/opentelemetry/javaagent/bootstrap/internal/CommonConfig.java

Line 60 in 8d1ba17

public List<String> getServerRequestHeaders() {

.
You will probably create one along side it (boolean).
You will see that the usages branch out to different server technologies, such as tomcat - because each server framework has a different request object.

[laurit]

Understood that using setAttribute from application side is a solution that can be performed without modifying anything in this project.

I need to capture request body in the span attributes for all the request handlers, in an application, irrespective of their framework, I want user to just use otel JAR as -javaagent and provide a property i.e. -Dotel.traces.request.data-capture=true So that user do not have to do setAttribute in all the request handlers.

I don't think you realize how much work implementing this for all frameworks could be and what kind of problems you might run into. I'd still suggest you start with the framework you are using and attempt to prototype this inside the application to get a feel how this might work. Once you have it figured out inside your application you can try to build a generic instrumentation for the framework you use.

1. Is there a simpler way for user to perform setAttribute, instead of doing it in each and every request handler ?

Depends on the application and frameworks at hand. If the framework provides a way to intercept all the requests and has request body available at that point then it could be easy, if it does not you may need to instrument internals of the framework or resort to setting the attribute in multiple places. For example for java servlets you could use a servlet filter that wraps the http request. You could read the request input stream and in your request wrapper implement getInputStream/getReader to return what you already read.

2. Do you think this change might be helpful to this particular project ?

As this feature has been requested before we'd gladly accept it.

3. Is there a central class (framework-agnostic) that has access to incoming requests, where I can do the needful code ?

All http server instrumentations use https://github.com/open-telemetry/opentelemetry-java-instrumentation/blob/main/instrumentation-api-semconv/src/main/java/io/opentelemetry/instrumentation/api/instrumenter/http/HttpServerAttributesExtractor.java this extractor calls into various getter that extract information from the underlying request. The code that adds http headers to span attributes gets called in

opentelemetry-java-instrumentation/instrumentation-api-semconv/src/main/java/io/opentelemetry/instrumentation/api/instrumenter/http/HttpCommonAttributesExtractor.java

Lines 57 to 62 in cef9a5f

	for (String name : capturedRequestHeaders) {
	List<String> values = getter.getHttpRequestHeader(request, name);
	if (!values.isEmpty()) {
	internalSet(attributes, requestAttributeKey(name), values);
	}
	}

Though this is not where the complexity of adding request body as span attribute lies. The real problem is that the request body is often exposed as a stream that you can read only once. If you read it before the application does you need to somehow restore the stream to its original state or replace it with another stream. Additionally you generally won't know what character encoding the data will be in or whether you'll get a multipart request. The request you get might also be very large so can't just read it all and keep in the memory. For every framework and server you intend to support you'll probably have to come up with a separate instrumentation.

[bhogayatakb]

ohk, I see
Thanks @laurit , your inputs gave a lot more clarity on this.
At first, I'll be focused on implementing this in the Spring framework. Keeping in mind, the challenges you just mentioned above.

[trask]

linking related open-telemetry/oteps#234

[trask]

linking related open-telemetry/semantic-conventions#857

[Cirilla-zmh]

Thanks @trask , I am currently in the same boat with this requirement.

I concur with @laurit's point that capturing the HTTP request and response bodies for all HTTP Servers is a challenging task, requiring an in-depth exploration of each type of HTTP server framework. However, for applications integrated with specific web development frameworks (such as Spring MVC), we can leverage some provided hook methods or advice internal methods to capture the bodies. (For instance, ResponseBodyAdvice).

I have completed the preliminary validation and would be delighted to contribute the implementation of this feature. If feasible, please consider assigning this issue to me.

[steverao]

I have completed the preliminary validation and would be delighted to contribute the implementation of this feature. If feasible, please consider assigning this issue to me.

Feel free to create PR to solve it!