How can I create an OpenTelemetry Span from a string TraceID in Go?

Creating an OpenTelemetry Span from a String TraceID

To create a new span on the subscriber side using the traceID, one cannot directly create a span using the received traceID string. Instead, you must construct a [trace.SpanContext](https://pkg.go.dev/go.opentelemetry.io/otel/trace#SpanContext) using the provided traceID.

Construct the SpanContext

To generate the SpanContext, it is recommended to wrap the code in a separate function, such as this:

<code class="go">func constructNewSpanContext(request NewRequest) (spanContext trace.SpanContext, err error) {
    // Assuming the trace and span IDs are provided as strings in request struct.

    var traceID trace.TraceID
    traceID, err = trace.TraceIDFromHex(request.TraceID)
    if err != nil {
        fmt.Println("error:", err)
        return
    }

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

    spanContextConfig := trace.SpanContextConfig{
        TraceID: traceID,
        SpanID:  spanID,
        // Other TraceFlag bits if desired
    }

    spanContext = trace.NewSpanContext(spanContextConfig)
    return spanContext, nil
}</code>

Enrich a Context with the SpanContext

Once the SpanContext is created, enrich a new context with it:

<code class="go">spanContext, err := constructNewSpanContext(request)
if err != nil {
    fmt.Println("ERROR:", err)
}

fmt.Println("IS VALID?", spanContext.IsValid()) // Check if the `spanContext` is valid

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

// Start a new span within the enriched context
var requestInLoopSpan trace.Span
childContext, requestInLoopSpan := otel.Tracer("inboundmessage").Start(requestContext, "requestInLoopSpan")

requestInLoopSpan.AddEvent("processing....") // Should now work</code>

By performing these steps, you can successfully create a new Span on the subscriber side using the traceID received from the request headers.

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