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poller.ts
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poller.ts
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// Copyright (c) Microsoft Corporation.
// Licensed under the MIT license.
import { PollOperation, PollOperationState } from "./pollOperation";
import { AbortSignalLike } from "@azure/abort-controller";
/**
* CancelOnProgress is used as the return value of a Poller's onProgress method.
* When a user invokes onProgress, they're required to pass in a function that will be
* called as a callback with the new data received each time the poll operation is updated.
* onProgress returns a function that will prevent any further update to reach the original callback.
*/
export type CancelOnProgress = () => void;
/**
* PollProgressCallback<TState> is the type of the callback functions sent to onProgress.
* These functions will receive a TState that is defined by your implementation of
* the Poller class.
*/
export type PollProgressCallback<TState> = (state: TState) => void;
/**
* When a poller is manually stopped through the `stopPolling` method,
* the poller will be rejected with an instance of the PollerStoppedError.
*/
export class PollerStoppedError extends Error {
constructor(message: string) {
super(message);
this.name = "PollerStoppedError";
Object.setPrototypeOf(this, PollerStoppedError.prototype);
}
}
/**
* When a poller is cancelled through the `cancelOperation` method,
* the poller will be rejected with an instance of the PollerCancelledError.
*/
export class PollerCancelledError extends Error {
constructor(message: string) {
super(message);
this.name = "PollerCancelledError";
Object.setPrototypeOf(this, PollerCancelledError.prototype);
}
}
/**
* Abstract representation of a poller, intended to expose just the minimal API that the user needs to work with.
*/
// eslint-disable-next-line no-use-before-define
export interface PollerLike<TState extends PollOperationState<TResult>, TResult> {
/**
* Returns a promise that will resolve once a single polling request finishes.
* It does this by calling the update method of the Poller's operation.
*/
poll(options?: { abortSignal?: AbortSignalLike }): Promise<void>;
/**
* Returns a promise that will resolve once the underlying operation is completed.
*/
pollUntilDone(): Promise<TResult>;
/**
* Invokes the provided callback after each polling is completed,
* sending the current state of the poller's operation.
*
* It returns a method that can be used to stop receiving updates on the given callback function.
*/
onProgress(callback: (state: TState) => void): CancelOnProgress;
/**
* Returns true if the poller has finished polling.
*/
isDone(): boolean;
/**
* Stops the poller. After this, no manual or automated requests can be sent.
*/
stopPolling(): void;
/**
* Returns true if the poller is stopped.
*/
isStopped(): boolean;
/**
* Attempts to cancel the underlying operation.
*/
cancelOperation(options?: { abortSignal?: AbortSignalLike }): Promise<void>;
/**
* Returns the state of the operation.
* The TState defined in PollerLike can be a subset of the TState defined in
* the Poller implementation.
*/
getOperationState(): TState;
/**
* Returns the result value of the operation,
* regardless of the state of the poller.
* It can return undefined or an incomplete form of the final TResult value
* depending on the implementation.
*/
getResult(): TResult | undefined;
/**
* Returns a serialized version of the poller's operation
* by invoking the operation's toString method.
*/
toString(): string;
}
/**
* A class that represents the definition of a program that polls through consecutive requests
* until it reaches a state of completion.
*
* A poller can be executed manually, by polling request by request by calling to the `poll()` method repeatedly, until its operation is completed.
* It also provides a way to wait until the operation completes, by calling `pollUntilDone()` and waiting until the operation finishes.
* Pollers can also request the cancellation of the ongoing process to whom is providing the underlying long running operation.
*
* ```ts
* const poller = new MyPoller();
*
* // Polling just once:
* await poller.poll();
*
* // We can try to cancel the request here, by calling:
* //
* // await poller.cancelOperation();
* //
*
* // Getting the final result:
* const result = await poller.pollUntilDone();
* ```
*
* The Poller is defined by two types, a type representing the state of the poller, which
* must include a basic set of properties from `PollOperationState<TResult>`,
* and a return type defined by `TResult`, which can be anything.
*
* The Poller class implements the `PollerLike` interface, which allows poller implementations to avoid having
* to export the Poller's class directly, and instead only export the already instantiated poller with the PollerLike type.
*
* ```ts
* class Client {
* public async makePoller: PollerLike<MyOperationState, MyResult> {
* const poller = new MyPoller({});
* // It might be preferred to return the poller after the first request is made,
* // so that some information can be obtained right away.
* await poller.poll();
* return poller;
* }
* }
*
* const poller: PollerLike<MyOperationState, MyResult> = myClient.makePoller();
* ```
*
* A poller can be created through its constructor, then it can be polled until it's completed.
* At any point in time, the state of the poller can be obtained without delay through the getOperationState method.
* At any point in time, the intermediate forms of the result type can be requested without delay.
* Once the underlying operation is marked as completed, the poller will stop and the final value will be returned.
*
* ```ts
* const poller = myClient.makePoller();
* const state: MyOperationState = poller.getOperationState();
*
* // The intermediate result can be obtained at any time.
* const result: MyResult | undefined = poller.getResult();
*
* // The final result can only be obtained after the poller finishes.
* const result: MyResult = await poller.pollUntilDone();
* ```
*
*/
// eslint-disable-next-line no-use-before-define
export abstract class Poller<TState extends PollOperationState<TResult>, TResult>
implements PollerLike<TState, TResult> {
private stopped: boolean = true;
private resolve?: (value: TResult) => void;
private reject?: (error: PollerStoppedError | PollerCancelledError | Error) => void;
private pollOncePromise?: Promise<void>;
private cancelPromise?: Promise<void>;
private promise: Promise<TResult>;
private pollProgressCallbacks: PollProgressCallback<TState>[] = [];
/**
* The poller's operation is available in full to any of the methods of the Poller class
* and any class extending the Poller class.
*/
protected operation: PollOperation<TState, TResult>;
/**
* A poller needs to be initialized by passing in at least the basic properties of the `PollOperation<TState, TResult>`.
*
* When writing an implementation of a Poller, this implementation needs to deal with the initialization
* of any custom state beyond the basic definition of the poller. The basic poller assumes that the poller's
* operation has already been defined, at least its basic properties. The code below shows how to approach
* the definition of the constructor of a new custom poller.
*
* ```ts
* export class MyPoller extends Poller<MyOperationState, string> {
* constructor({
* // Anything you might need outside of the basics
* }) {
* let state: MyOperationState = {
* privateProperty: private,
* publicProperty: public,
* };
*
* const operation = {
* state,
* update,
* cancel,
* toString
* }
*
* // Sending the operation to the parent's constructor.
* super(operation);
*
* // You can assign more local properties here.
* }
* }
* ```
*
* Inside of this constructor, a new promise is created. This will be used to
* tell the user when the poller finishes (see `pollUntilDone()`). The promise's
* resolve and reject methods are also used internally to control when to resolve
* or reject anyone waiting for the poller to finish.
*
* The constructor of a custom implementation of a poller is where any serialized version of
* a previous poller's operation should be deserialized into the operation sent to the
* base constructor. For example:
*
* ```ts
* export class MyPoller extends Poller<MyOperationState, string> {
* constructor(
* baseOperation: string | undefined
* ) {
* let state: MyOperationState = {};
* if (baseOperation) {
* state = {
* ...JSON.parse(baseOperation).state,
* ...state
* };
* }
* const operation = {
* state,
* // ...
* }
* super(operation);
* }
* }
* ```
*
* @param operation - Must contain the basic properties of `PollOperation<State, TResult>`.
*/
constructor(operation: PollOperation<TState, TResult>) {
this.operation = operation;
this.promise = new Promise<TResult>(
(
resolve: (result: TResult) => void,
reject: (error: PollerStoppedError | PollerCancelledError | Error) => void
) => {
this.resolve = resolve;
this.reject = reject;
}
);
// This prevents the UnhandledPromiseRejectionWarning in node.js from being thrown.
// The above warning would get thrown if `poller.poll` is called, it returns an error,
// and pullUntilDone did not have a .catch or await try/catch on it's return value.
this.promise.catch(() => {
/* intentionally blank */
});
}
/**
* Defines how much to wait between each poll request.
* This has to be implemented by your custom poller.
*
* \@azure/core-http has a simple implementation of a delay function that waits as many milliseconds as specified.
* This can be used as follows:
*
* ```ts
* import { delay } from "@azure/core-http";
*
* export class MyPoller extends Poller<MyOperationState, string> {
* // The other necessary definitions.
*
* async delay(): Promise<void> {
* const milliseconds = 1000;
* return delay(milliseconds);
* }
* }
* ```
*
*/
protected abstract delay(): Promise<void>;
/**
* @internal
* Starts a loop that will break only if the poller is done
* or if the poller is stopped.
*/
private async startPolling(): Promise<void> {
if (this.stopped) {
this.stopped = false;
}
while (!this.isStopped() && !this.isDone()) {
await this.poll();
await this.delay();
}
}
/**
* @internal
* pollOnce does one polling, by calling to the update method of the underlying
* poll operation to make any relevant change effective.
*
* It only optionally receives an object with an abortSignal property, from \@azure/abort-controller's AbortSignalLike.
*
* @param options - Optional properties passed to the operation's update method.
*/
private async pollOnce(options: { abortSignal?: AbortSignalLike } = {}): Promise<void> {
try {
if (!this.isDone()) {
this.operation = await this.operation.update({
abortSignal: options.abortSignal,
fireProgress: this.fireProgress.bind(this)
});
if (this.isDone() && this.resolve) {
// If the poller has finished polling, this means we now have a result.
// However, it can be the case that TResult is instantiated to void, so
// we are not expecting a result anyway. To assert that we might not
// have a result eventually after finishing polling, we cast the result
// to TResult.
this.resolve(this.operation.state.result as TResult);
}
}
} catch (e) {
this.operation.state.error = e;
if (this.reject) {
this.reject(e);
}
throw e;
}
}
/**
* @internal
* fireProgress calls the functions passed in via onProgress the method of the poller.
*
* It loops over all of the callbacks received from onProgress, and executes them, sending them
* the current operation state.
*
* @param state - The current operation state.
*/
private fireProgress(state: TState): void {
for (const callback of this.pollProgressCallbacks) {
callback(state);
}
}
/**
* @internal
* Invokes the underlying operation's cancel method, and rejects the
* pollUntilDone promise.
*/
private async cancelOnce(options: { abortSignal?: AbortSignalLike } = {}): Promise<void> {
this.operation = await this.operation.cancel(options);
if (this.reject) {
this.reject(new PollerCancelledError("Poller cancelled"));
}
}
/**
* Returns a promise that will resolve once a single polling request finishes.
* It does this by calling the update method of the Poller's operation.
*
* It only optionally receives an object with an abortSignal property, from \@azure/abort-controller's AbortSignalLike.
*
* @param options - Optional properties passed to the operation's update method.
*/
public poll(options: { abortSignal?: AbortSignalLike } = {}): Promise<void> {
if (!this.pollOncePromise) {
this.pollOncePromise = this.pollOnce(options);
const clearPollOncePromise = (): void => {
this.pollOncePromise = undefined;
};
this.pollOncePromise.then(clearPollOncePromise, clearPollOncePromise).catch(this.reject);
}
return this.pollOncePromise;
}
/**
* Returns a promise that will resolve once the underlying operation is completed.
*/
public async pollUntilDone(): Promise<TResult> {
if (this.stopped) {
this.startPolling().catch(this.reject);
}
return this.promise;
}
/**
* Invokes the provided callback after each polling is completed,
* sending the current state of the poller's operation.
*
* It returns a method that can be used to stop receiving updates on the given callback function.
*/
public onProgress(callback: (state: TState) => void): CancelOnProgress {
this.pollProgressCallbacks.push(callback);
return (): void => {
this.pollProgressCallbacks = this.pollProgressCallbacks.filter((c) => c !== callback);
};
}
/**
* Returns true if the poller has finished polling.
*/
public isDone(): boolean {
const state: PollOperationState<TResult> = this.operation.state;
return Boolean(state.isCompleted || state.isCancelled || state.error);
}
/**
* Stops the poller from continuing to poll.
*/
public stopPolling(): void {
if (!this.stopped) {
this.stopped = true;
if (this.reject) {
this.reject(new PollerStoppedError("This poller is already stopped"));
}
}
}
/**
* Returns true if the poller is stopped.
*/
public isStopped(): boolean {
return this.stopped;
}
/**
* Attempts to cancel the underlying operation.
*
* It only optionally receives an object with an abortSignal property, from \@azure/abort-controller's AbortSignalLike.
*
* If it's called again before it finishes, it will throw an error.
*
* @param options - Optional properties passed to the operation's update method.
*/
public cancelOperation(options: { abortSignal?: AbortSignalLike } = {}): Promise<void> {
if (!this.stopped) {
this.stopped = true;
}
if (!this.cancelPromise) {
this.cancelPromise = this.cancelOnce(options);
} else if (options.abortSignal) {
throw new Error("A cancel request is currently pending");
}
return this.cancelPromise;
}
/**
* Returns the state of the operation.
*
* Even though TState will be the same type inside any of the methods of any extension of the Poller class,
* implementations of the pollers can customize what's shared with the public by writing their own
* version of the `getOperationState` method, and by defining two types, one representing the internal state of the poller
* and a public type representing a safe to share subset of the properties of the internal state.
* Their definition of getOperationState can then return their public type.
*
* Example:
*
* ```ts
* // Let's say we have our poller's operation state defined as:
* interface MyOperationState extends PollOperationState<ResultType> {
* privateProperty?: string;
* publicProperty?: string;
* }
*
* // To allow us to have a true separation of public and private state, we have to define another interface:
* interface PublicState extends PollOperationState<ResultType> {
* publicProperty?: string;
* }
*
* // Then, we define our Poller as follows:
* export class MyPoller extends Poller<MyOperationState, ResultType> {
* // ... More content is needed here ...
*
* public getOperationState(): PublicState {
* const state: PublicState = this.operation.state;
* return {
* // Properties from PollOperationState<TResult>
* isStarted: state.isStarted,
* isCompleted: state.isCompleted,
* isCancelled: state.isCancelled,
* error: state.error,
* result: state.result,
*
* // The only other property needed by PublicState.
* publicProperty: state.publicProperty
* }
* }
* }
* ```
*
* You can see this in the tests of this repository, go to the file:
* `../test/utils/testPoller.ts`
* and look for the getOperationState implementation.
*/
public getOperationState(): TState {
return this.operation.state;
}
/**
* Returns the result value of the operation,
* regardless of the state of the poller.
* It can return undefined or an incomplete form of the final TResult value
* depending on the implementation.
*/
public getResult(): TResult | undefined {
const state: PollOperationState<TResult> = this.operation.state;
return state.result;
}
/**
* Returns a serialized version of the poller's operation
* by invoking the operation's toString method.
*/
public toString(): string {
return this.operation.toString();
}
}