instr-http SHOULD provide `http.request.header.<key>` at server span creation time

[trentm]

The spec (https://opentelemetry.io/docs/specs/semconv/http/http-spans/#http-server-span) says:

The following attributes can be important for making sampling decisions and SHOULD be provided at span creation time (if provided at all):

• ...
• http.request.header.<key>
• ...

currently instrumentation-http@0.211.0 does not:

opentelemetry-js/experimental/packages/opentelemetry-instrumentation-http/src/http.ts

Lines 648 to 670 in fcafab5

	const span = instrumentation._startHttpSpan(method, spanOptions, ctx);
	const rpcMetadata: RPCMetadata = {
	type: RPCType.HTTP,
	span,
	};
	return context.with(
	setRPCMetadata(trace.setSpan(ctx, span), rpcMetadata),
	() => {
	context.bind(context.active(), request);
	context.bind(context.active(), response);
	if (instrumentation.getConfig().requestHook) {
	instrumentation._callRequestHook(span, request);
	}
	if (instrumentation.getConfig().responseHook) {
	instrumentation._callResponseHook(span, response);
	}
	instrumentation._headerCapture.server.captureRequestHeaders(
	span,
	header => request.headers[header]
	);

The header capture should move above the _startHttpSpan call.
This is only a SHOULD requirement, so this isn't a bug.
Moving this above will mean a slight refactor to this._headerCapture, so that it modifies an Attributes object in-place (or returns attributes to apply), rather than calling span.setAttribute(...) itself. See export function headerCapture in src/utils.ts.

[vitorvasc]

Hi @trentm! I've just opened #6396 to address this one.

The approach taken was to have headerCapture return an Attributes object rather than modifying a span directly. I don't have a strong preference between returning attributes vs modifying an object in-place - happy to adjust if the other one is preferred.

Thanks :)