Extract context from AWS SQS message attribute

[dhenard]

I have a lambda that publishes a message to aws sqs queue using OpenTelemetry 0.18.0. I'm able to get {"traceId":"c878ad222c04776c3b3dbbbe9156170c","spanId":"0b0ed509527d73ab","traceFlags":1}
as one of the message attributes and now I need another lambda to process the message. I would like it to continue as part of the same trace, since it is the same request, but can't seem to figure out how to take the above and turn it back into a context. All the docs seem to point to automatic telemetry and I can't find an example of extracting the context from a string.

Is that the correct object to send for downstream processing?
How do you get the context back on the downstream processor?

Sending lambda - message attribute is created with the below snippet:

...
  function createAttributes(entity, ctxTrace) {
      return {
        traceHeaders: { DataType: "String", StringValue: JSON.stringify(ctxTrace)
      };
    }

const params = {
  MessageAttributes: createAttributes(entity, parentSpan.context());
};
... 

Receiving Lambda -

const { tracing } = require('./tracing');
const optl = require('@opentelemetry/api');
...
exports.handler = async(event, context) => {
  // manually trying to get it to work and then will pull from message header.  I've tried several different things but this seems to be the closest
  const traceHeader = JSON.parse("{\"traceId\":\"c878ad222c04776c3b3dbbbe9156170c\",\"spanId\":\"0b0ed509527d73ab\",\"traceFlags\":1}");
  const tracer = tracing;
  const parentSpan = tracer.startSpan('test_span', {}, optl.setSpan(optl.context.active(), traceHeader));
  // This gives an error message of TypeError: _a.context is not a function
}

tracing file

const opentelemetry = require('@opentelemetry/api');
const { LogLevel } = require("@opentelemetry/core");
const { NodeTracerProvider } = require("@opentelemetry/node");
const { BatchSpanProcessor } = require("@opentelemetry/tracing");
const { CollectorTraceExporter } = require("@opentelemetry/exporter-collector");
const { B3Propagator } = require("@opentelemetry/propagator-b3");

const exporter = new CollectorTraceExporter({
  serviceName: process.env.SERVICE_NAME,
  headers:{
    'Lightstep-Access-Token': process.env.LIGHTSTEP_TOKEN
  },
  url:'https://ingest.lightstep.com:443/api/v2/otel/trace',
});

const provider = new NodeTracerProvider();

provider.addSpanProcessor(new BatchSpanProcessor(exporter));

provider.register({
  propagator: new B3Propagator(),
});

const tracer = opentelemetry.trace.getTracer(process.env.SERVICE_NAME);
exports.tracing=tracer;

Any guidance would be appreciated.

UPDATE: With the help of Flarna's comment and the one below. I was able to put all the pieces together using the provided B3Propagator. The thing that was messing me up was I wasn't aware how much things changed from version 0.14.0 to 0.18.0 in relation to creating child spans of parents.

[Flarna]

What you create here is named propagator, see e.g. HttpTraceContext how to covert you strings into a context.

Maybe it is even possible to use the HttpTraceContext as is and just pass custom getter/setter to extract/inject. But I assume this would require to put each string into a separate attribute.

[gDaugirdas]

@dhenard can you share a code snipped that worked for you?

[dhenard]

Using version 0.18

To save the context into the message carrier which starts as an empty object.

const ctx = optl.setSpan(optl.context.active(), requestSpan);
optl.propagation.inject(ctx, messageCarrier);

Save messageCarrier value to the SQS message, either as an attribute or inside the body of the message.

To pull it back out:

// Set traceparentValue to the value from the SQS message from above.
tracer.startSpan('span_name', { kind: optl.SpanKind.INTERNAL }, optl.propagation.extract(optl.context.active(), traceparentValue));