tracing

type Span interface {
	// Sets the end timestamp and finalizes Span state.
	Finish()

	// Adds key/value pairs to the span.
	LogKV(alternatingKeyValues ...interface{})
}

type Tracer interface {
	// Returns a new child span and context from a given context.
	StartSpanFromContext(ctx context.Context, operationName string) (Span, context.Context)

	// Adds the required HTTP headers to pass context between nodes.
	InjectHTTPHeaders(r *http.Request)

	// Reads the HTTP headers to derive incoming context.
	ExtractHTTPHeaders(r *http.Request) (Span, context.Context)
}