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/**
* The `node:diagnostics_channel` module provides an API to create named channels
* to report arbitrary message data for diagnostics purposes.
*
* It can be accessed using:
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
* ```
*
* It is intended that a module writer wanting to report diagnostics messages
* will create one or many top-level channels to report messages through.
* Channels may also be acquired at runtime but it is not encouraged
* due to the additional overhead of doing so. Channels may be exported for
* convenience, but as long as the name is known it can be acquired anywhere.
*
* If you intend for your module to produce diagnostics data for others to
* consume it is recommended that you include documentation of what named
* channels are used along with the shape of the message data. Channel names
* should generally include the module name to avoid collisions with data from
* other modules.
* @since v15.1.0, v14.17.0
* @see [source](https://github.com/nodejs/node/blob/v20.2.0/lib/diagnostics_channel.js)
*/
declare module "diagnostics_channel" {
import { AsyncLocalStorage } from "node:async_hooks";
/**
* Check if there are active subscribers to the named channel. This is helpful if
* the message you want to send might be expensive to prepare.
*
* This API is optional but helpful when trying to publish messages from very
* performance-sensitive code.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
*
* if (diagnostics_channel.hasSubscribers('my-channel')) {
* // There are subscribers, prepare and publish message
* }
* ```
* @since v15.1.0, v14.17.0
* @param name The channel name
* @return If there are active subscribers
*/
function hasSubscribers(name: string | symbol): boolean;
/**
* This is the primary entry-point for anyone wanting to publish to a named
* channel. It produces a channel object which is optimized to reduce overhead at
* publish time as much as possible.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
*
* const channel = diagnostics_channel.channel('my-channel');
* ```
* @since v15.1.0, v14.17.0
* @param name The channel name
* @return The named channel object
*/
function channel(name: string | symbol): Channel;
type ChannelListener = (message: unknown, name: string | symbol) => void;
/**
* Register a message handler to subscribe to this channel. This message handler
* will be run synchronously whenever a message is published to the channel. Any
* errors thrown in the message handler will trigger an `'uncaughtException'`.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
*
* diagnostics_channel.subscribe('my-channel', (message, name) => {
* // Received data
* });
* ```
* @since v18.7.0, v16.17.0
* @param name The channel name
* @param onMessage The handler to receive channel messages
*/
function subscribe(name: string | symbol, onMessage: ChannelListener): void;
/**
* Remove a message handler previously registered to this channel with {@link subscribe}.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
*
* function onMessage(message, name) {
* // Received data
* }
*
* diagnostics_channel.subscribe('my-channel', onMessage);
*
* diagnostics_channel.unsubscribe('my-channel', onMessage);
* ```
* @since v18.7.0, v16.17.0
* @param name The channel name
* @param onMessage The previous subscribed handler to remove
* @return `true` if the handler was found, `false` otherwise.
*/
function unsubscribe(name: string | symbol, onMessage: ChannelListener): boolean;
/**
* Creates a `TracingChannel` wrapper for the given `TracingChannel Channels`. If a name is given, the corresponding tracing
* channels will be created in the form of `tracing:${name}:${eventType}` where`eventType` corresponds to the types of `TracingChannel Channels`.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
*
* const channelsByName = diagnostics_channel.tracingChannel('my-channel');
*
* // or...
*
* const channelsByCollection = diagnostics_channel.tracingChannel({
* start: diagnostics_channel.channel('tracing:my-channel:start'),
* end: diagnostics_channel.channel('tracing:my-channel:end'),
* asyncStart: diagnostics_channel.channel('tracing:my-channel:asyncStart'),
* asyncEnd: diagnostics_channel.channel('tracing:my-channel:asyncEnd'),
* error: diagnostics_channel.channel('tracing:my-channel:error'),
* });
* ```
* @since v19.9.0
* @experimental
* @param nameOrChannels Channel name or object containing all the `TracingChannel Channels`
* @return Collection of channels to trace with
*/
function tracingChannel<
StoreType = unknown,
ContextType extends object = StoreType extends object ? StoreType : object,
>(
nameOrChannels: string | TracingChannelCollection<StoreType, ContextType>,
): TracingChannel<StoreType, ContextType>;
/**
* The class `Channel` represents an individual named channel within the data
* pipeline. It is used to track subscribers and to publish messages when there
* are subscribers present. It exists as a separate object to avoid channel
* lookups at publish time, enabling very fast publish speeds and allowing
* for heavy use while incurring very minimal cost. Channels are created with {@link channel}, constructing a channel directly
* with `new Channel(name)` is not supported.
* @since v15.1.0, v14.17.0
*/
class Channel<StoreType = unknown, ContextType = StoreType> {
readonly name: string | symbol;
/**
* Check if there are active subscribers to this channel. This is helpful if
* the message you want to send might be expensive to prepare.
*
* This API is optional but helpful when trying to publish messages from very
* performance-sensitive code.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
*
* const channel = diagnostics_channel.channel('my-channel');
*
* if (channel.hasSubscribers) {
* // There are subscribers, prepare and publish message
* }
* ```
* @since v15.1.0, v14.17.0
*/
readonly hasSubscribers: boolean;
private constructor(name: string | symbol);
/**
* Publish a message to any subscribers to the channel. This will trigger
* message handlers synchronously so they will execute within the same context.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
*
* const channel = diagnostics_channel.channel('my-channel');
*
* channel.publish({
* some: 'message',
* });
* ```
* @since v15.1.0, v14.17.0
* @param message The message to send to the channel subscribers
*/
publish(message: unknown): void;
/**
* Register a message handler to subscribe to this channel. This message handler
* will be run synchronously whenever a message is published to the channel. Any
* errors thrown in the message handler will trigger an `'uncaughtException'`.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
*
* const channel = diagnostics_channel.channel('my-channel');
*
* channel.subscribe((message, name) => {
* // Received data
* });
* ```
* @since v15.1.0, v14.17.0
* @deprecated Since v18.7.0,v16.17.0 - Use {@link subscribe(name, onMessage)}
* @param onMessage The handler to receive channel messages
*/
subscribe(onMessage: ChannelListener): void;
/**
* Remove a message handler previously registered to this channel with `channel.subscribe(onMessage)`.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
*
* const channel = diagnostics_channel.channel('my-channel');
*
* function onMessage(message, name) {
* // Received data
* }
*
* channel.subscribe(onMessage);
*
* channel.unsubscribe(onMessage);
* ```
* @since v15.1.0, v14.17.0
* @deprecated Since v18.7.0,v16.17.0 - Use {@link unsubscribe(name, onMessage)}
* @param onMessage The previous subscribed handler to remove
* @return `true` if the handler was found, `false` otherwise.
*/
unsubscribe(onMessage: ChannelListener): void;
/**
* When `channel.runStores(context, ...)` is called, the given context data
* will be applied to any store bound to the channel. If the store has already been
* bound the previous `transform` function will be replaced with the new one.
* The `transform` function may be omitted to set the given context data as the
* context directly.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
* import { AsyncLocalStorage } from 'node:async_hooks';
*
* const store = new AsyncLocalStorage();
*
* const channel = diagnostics_channel.channel('my-channel');
*
* channel.bindStore(store, (data) => {
* return { data };
* });
* ```
* @since v19.9.0
* @experimental
* @param store The store to which to bind the context data
* @param transform Transform context data before setting the store context
*/
bindStore(store: AsyncLocalStorage<StoreType>, transform?: (context: ContextType) => StoreType): void;
/**
* Remove a message handler previously registered to this channel with `channel.bindStore(store)`.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
* import { AsyncLocalStorage } from 'node:async_hooks';
*
* const store = new AsyncLocalStorage();
*
* const channel = diagnostics_channel.channel('my-channel');
*
* channel.bindStore(store);
* channel.unbindStore(store);
* ```
* @since v19.9.0
* @experimental
* @param store The store to unbind from the channel.
* @return `true` if the store was found, `false` otherwise.
*/
unbindStore(store: any): void;
/**
* Applies the given data to any AsyncLocalStorage instances bound to the channel
* for the duration of the given function, then publishes to the channel within
* the scope of that data is applied to the stores.
*
* If a transform function was given to `channel.bindStore(store)` it will be
* applied to transform the message data before it becomes the context value for
* the store. The prior storage context is accessible from within the transform
* function in cases where context linking is required.
*
* The context applied to the store should be accessible in any async code which
* continues from execution which began during the given function, however
* there are some situations in which `context loss` may occur.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
* import { AsyncLocalStorage } from 'node:async_hooks';
*
* const store = new AsyncLocalStorage();
*
* const channel = diagnostics_channel.channel('my-channel');
*
* channel.bindStore(store, (message) => {
* const parent = store.getStore();
* return new Span(message, parent);
* });
* channel.runStores({ some: 'message' }, () => {
* store.getStore(); // Span({ some: 'message' })
* });
* ```
* @since v19.9.0
* @experimental
* @param context Message to send to subscribers and bind to stores
* @param fn Handler to run within the entered storage context
* @param thisArg The receiver to be used for the function call.
* @param args Optional arguments to pass to the function.
*/
runStores(): void;
}
interface TracingChannelSubscribers<ContextType extends object> {
start: (message: ContextType) => void;
end: (
message: ContextType & {
error?: unknown;
result?: unknown;
},
) => void;
asyncStart: (
message: ContextType & {
error?: unknown;
result?: unknown;
},
) => void;
asyncEnd: (
message: ContextType & {
error?: unknown;
result?: unknown;
},
) => void;
error: (
message: ContextType & {
error: unknown;
},
) => void;
}
interface TracingChannelCollection<StoreType = unknown, ContextType = StoreType> {
start: Channel<StoreType, ContextType>;
end: Channel<StoreType, ContextType>;
asyncStart: Channel<StoreType, ContextType>;
asyncEnd: Channel<StoreType, ContextType>;
error: Channel<StoreType, ContextType>;
}
/**
* The class `TracingChannel` is a collection of `TracingChannel Channels` which
* together express a single traceable action. It is used to formalize and
* simplify the process of producing events for tracing application flow.{@link tracingChannel} is used to construct a`TracingChannel`. As with `Channel` it is recommended to create and reuse a
* single `TracingChannel` at the top-level of the file rather than creating them
* dynamically.
* @since v19.9.0
* @experimental
*/
class TracingChannel<StoreType = unknown, ContextType extends object = {}> implements TracingChannelCollection {
start: Channel<StoreType, ContextType>;
end: Channel<StoreType, ContextType>;
asyncStart: Channel<StoreType, ContextType>;
asyncEnd: Channel<StoreType, ContextType>;
error: Channel<StoreType, ContextType>;
/**
* Helper to subscribe a collection of functions to the corresponding channels.
* This is the same as calling `channel.subscribe(onMessage)` on each channel
* individually.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
*
* const channels = diagnostics_channel.tracingChannel('my-channel');
*
* channels.subscribe({
* start(message) {
* // Handle start message
* },
* end(message) {
* // Handle end message
* },
* asyncStart(message) {
* // Handle asyncStart message
* },
* asyncEnd(message) {
* // Handle asyncEnd message
* },
* error(message) {
* // Handle error message
* },
* });
* ```
* @since v19.9.0
* @experimental
* @param subscribers Set of `TracingChannel Channels` subscribers
*/
subscribe(subscribers: TracingChannelSubscribers<ContextType>): void;
/**
* Helper to unsubscribe a collection of functions from the corresponding channels.
* This is the same as calling `channel.unsubscribe(onMessage)` on each channel
* individually.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
*
* const channels = diagnostics_channel.tracingChannel('my-channel');
*
* channels.unsubscribe({
* start(message) {
* // Handle start message
* },
* end(message) {
* // Handle end message
* },
* asyncStart(message) {
* // Handle asyncStart message
* },
* asyncEnd(message) {
* // Handle asyncEnd message
* },
* error(message) {
* // Handle error message
* },
* });
* ```
* @since v19.9.0
* @experimental
* @param subscribers Set of `TracingChannel Channels` subscribers
* @return `true` if all handlers were successfully unsubscribed, and `false` otherwise.
*/
unsubscribe(subscribers: TracingChannelSubscribers<ContextType>): void;
/**
* Trace a synchronous function call. This will always produce a `start event` and `end event` around the execution and may produce an `error event` if the given function throws an error.
* This will run the given function using `channel.runStores(context, ...)` on the `start` channel which ensures all
* events should have any bound stores set to match this trace context.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
*
* const channels = diagnostics_channel.tracingChannel('my-channel');
*
* channels.traceSync(() => {
* // Do something
* }, {
* some: 'thing',
* });
* ```
* @since v19.9.0
* @experimental
* @param fn Function to wrap a trace around
* @param context Shared object to correlate events through
* @param thisArg The receiver to be used for the function call
* @param args Optional arguments to pass to the function
* @return The return value of the given function
*/
traceSync<ThisArg = any, Args extends any[] = any[]>(
fn: (this: ThisArg, ...args: Args) => any,
context?: ContextType,
thisArg?: ThisArg,
...args: Args
): void;
/**
* Trace a promise-returning function call. This will always produce a `start event` and `end event` around the synchronous portion of the
* function execution, and will produce an `asyncStart event` and `asyncEnd event` when a promise continuation is reached. It may also
* produce an `error event` if the given function throws an error or the
* returned promise rejects. This will run the given function using `channel.runStores(context, ...)` on the `start` channel which ensures all
* events should have any bound stores set to match this trace context.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
*
* const channels = diagnostics_channel.tracingChannel('my-channel');
*
* channels.tracePromise(async () => {
* // Do something
* }, {
* some: 'thing',
* });
* ```
* @since v19.9.0
* @experimental
* @param fn Promise-returning function to wrap a trace around
* @param context Shared object to correlate trace events through
* @param thisArg The receiver to be used for the function call
* @param args Optional arguments to pass to the function
* @return Chained from promise returned by the given function
*/
tracePromise<ThisArg = any, Args extends any[] = any[]>(
fn: (this: ThisArg, ...args: Args) => Promise<any>,
context?: ContextType,
thisArg?: ThisArg,
...args: Args
): void;
/**
* Trace a callback-receiving function call. This will always produce a `start event` and `end event` around the synchronous portion of the
* function execution, and will produce a `asyncStart event` and `asyncEnd event` around the callback execution. It may also produce an `error event` if the given function throws an error or
* the returned
* promise rejects. This will run the given function using `channel.runStores(context, ...)` on the `start` channel which ensures all
* events should have any bound stores set to match this trace context.
*
* The `position` will be -1 by default to indicate the final argument should
* be used as the callback.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
*
* const channels = diagnostics_channel.tracingChannel('my-channel');
*
* channels.traceCallback((arg1, callback) => {
* // Do something
* callback(null, 'result');
* }, 1, {
* some: 'thing',
* }, thisArg, arg1, callback);
* ```
*
* The callback will also be run with `channel.runStores(context, ...)` which
* enables context loss recovery in some cases.
*
* ```js
* import diagnostics_channel from 'node:diagnostics_channel';
* import { AsyncLocalStorage } from 'node:async_hooks';
*
* const channels = diagnostics_channel.tracingChannel('my-channel');
* const myStore = new AsyncLocalStorage();
*
* // The start channel sets the initial store data to something
* // and stores that store data value on the trace context object
* channels.start.bindStore(myStore, (data) => {
* const span = new Span(data);
* data.span = span;
* return span;
* });
*
* // Then asyncStart can restore from that data it stored previously
* channels.asyncStart.bindStore(myStore, (data) => {
* return data.span;
* });
* ```
* @since v19.9.0
* @experimental
* @param fn callback using function to wrap a trace around
* @param position Zero-indexed argument position of expected callback
* @param context Shared object to correlate trace events through
* @param thisArg The receiver to be used for the function call
* @param args Optional arguments to pass to the function
* @return The return value of the given function
*/
traceCallback<Fn extends (this: any, ...args: any) => any>(
fn: Fn,
position: number | undefined,
context: ContextType | undefined,
thisArg: any,
...args: Parameters<Fn>
): void;
}
}
declare module "node:diagnostics_channel" {
export * from "diagnostics_channel";
}