[Koa] Span never ends when a middleware layer throws an exception

[oguzbilgener]

What version of OpenTelemetry are you using?

Versions 0.12.0 and 0.13.0

What version of Node are you using?

Node 12.20.0

What did you do?

In Koa, a middleware can throw exceptions and this exception can be handled by another middleware to return an error message in the response. The @opentelemetry/koa-instrumentation plugin creates a new span for each Koa middleware, wraps the actual middleware call and once this async call is over, it calls span.end().

opentelemetry-js-contrib/plugins/node/opentelemetry-koa-instrumentation/src/koa.ts

Lines 133 to 136 in f039f1f

	return this._tracer.withSpan(span, async () => {
	const result = await middlewareLayer(context, next);
	span.end();
	return result;

What did you expect to see?

When an exception happens in the middlewareLayer, I expect the Koa plugin to account for it, mark the span for the middleware with an error by calling span.recordException(err), end the span, and then re-throw the exception.

This would be similar to what other plugins do. Below is an example from the graphql instrumentation plugin:

opentelemetry-js-contrib/plugins/node/opentelemetry-instrumentation-graphql/src/graphql.ts

Lines 213 to 223 in f039f1f

	return instrumentation.tracer.withSpan(span, () => {
	return safeExecuteInTheMiddle<
	PromiseOrValue<graphqlTypes.ExecutionResult>
	>(
	() => {
	return (original as executeFunctionWithObj).apply(this, [
	processedArgs,
	]);
	},
	err => {
	endSpan(span, err);

What did you see instead?

Because of the uncaught exception, a span.end() call is never made, so the span is completely missing.

---

I can gladly come up with a pull request using the safeExecuteInTheMiddle utility function, if you think the solution should be similar to what I expect to see.