import type { SpanInfo } from "./types.mjs";
/**
* Called once per completed traced operation with the span info (derived from
* the completed payload, falling back to the start-time payload for `onStart`
* subscriptions), the operation start time (unix nanoseconds, as an OTLP
* `*UnixNano` string), the operation's error (`undefined` when it succeeded)
* and the state returned by `onStart` (`undefined` without one). A sink turns
* this into whatever its platform consumes — an OTLP export, a log line, a
* platform span, …
*/
export type SpanSink<S = unknown> = (info: SpanInfo, startTimeUnixNano: string, error: unknown, state: S | undefined) => void;
export interface SubscribeTracedChannelsOptions<S> {
	/**
	* Called synchronously when a traced operation starts, inside its execution
	* context — where platform span APIs like Cloudflare's `enterSpan` must be
	* called. Returned state is handed back to `onSpan` at completion.
	*/
	onStart?: (info: SpanInfo) => S | undefined;
}
/**
* Subscribes to the tracing channels declared in `TRACED_CHANNELS` (produced by
* h3, srvx, unstorage, …) and invokes `onSpan` once per traced operation:
* normally at `asyncEnd`, or at `end` when the traced function threw
* synchronously (`tracePromise` never publishes `asyncEnd` in that case).
*
* A `tracingChannel(<name>)` publishes to plain named channels
* (`tracing:<name>:start`, `tracing:<name>:asyncEnd`, …). Subscribing to those
* names directly — rather than wrapping `tracingChannel` — needs no global patch
* and works regardless of when the producer creates the channel: `subscribe`
* registers against the name whether the channel exists yet or not. Channels
* absent from `TRACED_CHANNELS` are never observed.
*
* A no-op when `node:diagnostics_channel` is unavailable (non-Node runtimes).
*/
export declare function subscribeTracedChannels<S = unknown>(onSpan: SpanSink<S>, options?: SubscribeTracedChannelsOptions<S>): void;