How to add a custom SpanProcessor?

[juicemia]

We are trying to implement a custom SpanProcessor to filter out some spans with certain attributes.

This is what we have so far:

  const sdk = new NodeSDK({
    serviceName,
    spanProcessors: [new CustomSpanProcessor(getExporter())],
    instrumentations: [
        // stuff
    ],
  })

function getExporter():
  | GrpcTraceExporter
  | JsonTraceExporter
  | ProtoTraceExporter {
  switch (process.env.OTEL_EXPORTER_OTLP_PROTOCOL) {
    case 'grpc':
      return new GrpcTraceExporter()
    case 'http/json':
      return new JsonTraceExporter()
    case 'http/proto':
      return new ProtoTraceExporter()
    case '':
      return new ProtoTraceExporter()
    case undefined:
      return new ProtoTraceExporter()
    case null:
      return new ProtoTraceExporter()
  }

  throw new Error(
    `Cannot get OTLP exporter for protocol ${process.env.OTEL_EXPORTER_OTLP_PROTOCOL}`,
  )
}

import { BatchSpanProcessor, ReadableSpan } from '@opentelemetry/sdk-trace-base'

export class CustomSpanProcessor extends BatchSpanProcessor {
  onEnd(span: ReadableSpan): void {
    if (
      // If this attribute is there it's always a string.
      (span.attributes['some.attribute'] as string)?.startsWith(
        'remove_me',
      )
    ) {
      return
    }

    super.onEnd(span)
  }
}

So far this seems to work, but the issue is that in order to instantiate CustomSpanProcessor which inherits from BatchSpanProcessor, we have to pass it an exporter. To do that, we basically have to reimplement how the SDK sets up its exporter(s).

Is there a way of adding a custom SpanProcessor without losing the default that's created in BasicTracerProvider?