How to Construct Spans from Trace IDs in Non-HTTP Contexts?

Constructing Spans from Trace IDs in Non-HTTP Contexts

When propagating traces using headers in non-HTTP contexts, you need to manually construct spans using the provided trace and span IDs. Here's how to achieve this:

Subscriber Side:

Inside a function that handles incoming messages with trace and span headers:

1. Extract the trace and span IDs from the headers.
2. Use the trace.TraceIDFromHex() and trace.SpanIDFromHex() functions to convert the string IDs into appropriate types.
3. Construct a trace.SpanContext by providing the extracted trace ID, span ID, and trace flags.
4. Enrich the current context with the newly created span context using context.Background(), followed by trace.ContextWithSpanContext().
5. Start a new span using the enriched context with a appropriate name.

Example:

<code class="go">func handleIncomingMessage(request NewRequest) {
    traceID, err := trace.TraceIDFromHex(request.TraceID)
    if err != nil {
        fmt.Println("error: ", err)
        return
    }

    spanID, err := trace.SpanIDFromHex(request.SpanID)
    if err != nil {
        fmt.Println("error: ", err)
        return
    }

    spanContext := trace.NewSpanContext(trace.SpanContextConfig{
        TraceID: traceID,
        SpanID:  spanID,
        TraceFlags:   01,
        Remote:  false,
    })

    ctx := context.Background()
    ctx = trace.ContextWithSpanContext(ctx, spanContext)

    _, span := otel.Tracer("requestInLoop").Start(ctx, "requestInLoopSpan")
    span.AddEvent("processing....")
}</code>

In this example, NewRequest is a custom type that contains the trace and span IDs. The handleIncomingMessage function takes a NewRequest struct as input and creates a span with the provided trace and span IDs.

Note: Ensure that new spans are not created if the IsRemote field of the provided span context is set to true, as this indicates that the span was already exported remotely.

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