support `multiValueHeaders`

[rsteube]

Expected Behavior

Execute DataDog Synthetic Test and see trace linked to the executed request.

Actual Behavior

Traces are not linked.

Steps to Reproduce the Problem

In our case the headers are not passed via headers, but multiValueHeaders:

"multiValueHeaders": {
  "x-datadog-origin": [
    "synthetics"
  ],
  "x-datadog-parent-id": [
    "0"
  ],
  "x-datadog-sampling-priority": [
    "1"
  ],
  "x-datadog-trace-id": [
    "1775877486757059156"
  ],
}

datadog-lambda-go/internal/trace/context.go

Line 173 in 82f6bee

func getHeadersFromEventHeaders(ctx context.Context, ev json.RawMessage) map[string]string {

It is possible to set a custom TraceContextExtractor in the config, but would be nice to have this supported out of the box.

//	lambda.Start(ddlambda.WrapFunction(proxiedHandler, &ddlambda.Config{
//		DDTraceEnabled:        true,
//		DebugLogging:          false,
//		TraceContextExtractor: getHeadersFromEventHeaders,
//	}))


type eventWithHeaders struct {
	MultiValueHeaders map[string][]string `json:"multiValueHeaders"`
}

func getHeadersFromEventHeaders(ctx context.Context, ev json.RawMessage) map[string]string {
	eh := eventWithHeaders{}

	headers := map[string]string{}

	err := json.Unmarshal(ev, &eh)
	if err != nil {
		return headers
	}

	lowercaseHeaders := map[string]string{}
	for k, v := range eh.MultiValueHeaders {
		if len(v) > 0 {
			lowercaseHeaders[strings.ToLower(k)] = v[0]
		}
	}

	return lowercaseHeaders
}

Additionally we had to patch getTraceContext to include x-datadog-origin:

datadog-lambda-go/internal/trace/context.go

Line 130 in 82f6bee

func getTraceContext(ctx context.Context, headers map[string]string) (TraceContext, bool) {

	tc[samplingPriorityHeader] = samplingPriority
	tc[traceIDHeader] = traceID
	tc[parentIDHeader] = parentID
	if origin, ok := headers["x-datadog-origin"]; ok {
		tc["x-datadog-origin"] = origin
	}

	return tc, true

Otherwise it is missing for the check in extractTextMap (no origin, thus ErrSpanContextNotFound):

https://github.com/DataDog/dd-trace-go/blob/fb51babc4beed2e0037c41df97848313e7e43af3/ddtrace/tracer/textmap.go#L557

Specifications

• Datadog Go Lambda package version: 1.20.0
• Go version: 1.24.0