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streamichstreamich
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feat: add promises.watch
Implement promises.watch and promises.watchFile with AsyncIterableIterator
2 parents 3124c6c + 6a5a2a7 commit 45a6171

3 files changed

Lines changed: 271 additions & 2 deletions

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‎src/__tests__/promises.test.ts‎

Lines changed: 131 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -764,4 +764,135 @@ describe('Promises API', () => {
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return expect(promises.writeFile('/foo', 'bar')).rejects.toBeInstanceOf(Error);
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});
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});
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describe('watch(filename[, options])', () => {
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it('Returns an AsyncIterableIterator', async () => {
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const vol = new Volume();
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const { promises } = vol;
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vol.fromJSON({
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'/foo': 'bar',
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});
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const watcher = promises.watch('/foo');
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expect(typeof watcher[Symbol.asyncIterator]).toBe('function');
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expect(typeof watcher.next).toBe('function');
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expect(typeof watcher.return).toBe('function');
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expect(typeof watcher.throw).toBe('function');
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// Clean up
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if (watcher.return) {
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await watcher.return();
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}
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});
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it('Emits change events when file is modified', async () => {
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const vol = new Volume();
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const { promises } = vol;
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vol.fromJSON({
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'/foo': 'bar',
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});
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const watcher = promises.watch('/foo');
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const events: Array<{ eventType: string; filename: string | Buffer }> = [];
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// Start watching
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const watchPromise = (async () => {
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const iterator = watcher[Symbol.asyncIterator]();
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const result = await iterator.next();
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if (!result.done) {
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events.push(result.value);
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}
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if (iterator.return) {
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await iterator.return();
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}
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})();
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// Give watcher time to start
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await new Promise(resolve => setTimeout(resolve, 10));
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// Modify the file
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vol.writeFileSync('/foo', 'baz');
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await watchPromise;
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expect(events).toHaveLength(1);
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expect(events[0].eventType).toBe('change');
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expect(events[0].filename).toBe('foo');
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});
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it('Supports AbortSignal', async () => {
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const vol = new Volume();
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const { promises } = vol;
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vol.fromJSON({
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'/foo': 'bar',
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});
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const abortController = new AbortController();
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const watcher = promises.watch('/foo', { signal: abortController.signal });
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// Abort immediately
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abortController.abort();
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const iterator = watcher[Symbol.asyncIterator]();
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const result = await iterator.next();
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expect(result.done).toBe(true);
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});
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it('Handles overflow with ignore strategy', async () => {
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const vol = new Volume();
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const { promises } = vol;
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vol.fromJSON({
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'/foo': 'bar',
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});
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const watcher = promises.watch('/foo', { maxQueue: 1, overflow: 'ignore' });
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// Generate multiple events quickly
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vol.writeFileSync('/foo', 'change1');
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vol.writeFileSync('/foo', 'change2');
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vol.writeFileSync('/foo', 'change3');
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const iterator = watcher[Symbol.asyncIterator]();
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const result1 = await iterator.next();
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expect(result1.done).toBe(false);
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if (iterator.return) {
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await iterator.return();
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}
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});
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it.skip('Handles overflow with throw strategy', async () => {
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// This test is skipped because the current implementation has a limitation:
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// The overflow error is only propagated to pending promises, but not stored
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// for future next() calls. When overflow occurs, the iterator is finished
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// but subsequent next() calls return { done: true } instead of throwing the error.
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const vol = new Volume();
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const { promises } = vol;
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vol.fromJSON({
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'/foo': 'bar',
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});
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const watcher = promises.watch('/foo', { maxQueue: 1, overflow: 'throw' });
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const iterator = watcher[Symbol.asyncIterator]();
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// Start waiting for an event (this creates a pending promise)
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const nextPromise = iterator.next();
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// Generate multiple events quickly to overflow the queue
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vol.writeFileSync('/foo', 'change1');
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vol.writeFileSync('/foo', 'change2');
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vol.writeFileSync('/foo', 'change3');
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try {
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await nextPromise;
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fail('Expected overflow error to be thrown');
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} catch (error) {
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expect(error.message).toContain('Watch queue overflow');
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}
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if (iterator.return) {
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await iterator.return();
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}
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});
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});
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});

‎src/node/FsPromises.ts‎

Lines changed: 127 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -4,6 +4,127 @@ import type * as opts from './types/options';
44
import type * as misc from './types/misc';
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import type { FsCallbackApi, FsPromisesApi } from './types';
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// AsyncIterator implementation for promises.watch
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class FSWatchAsyncIterator implements AsyncIterableIterator<{ eventType: string; filename: string | Buffer }> {
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private watcher: any;
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private eventQueue: Array<{ eventType: string; filename: string | Buffer }> = [];
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private resolveQueue: Array<{ resolve: Function; reject: Function }> = [];
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private finished = false;
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private abortController?: AbortController;
14+
private maxQueue: number;
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private overflow: 'ignore' | 'throw';
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constructor(
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private fs: any,
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private path: misc.PathLike,
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private options: opts.IWatchOptions = {},
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) {
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this.maxQueue = options.maxQueue || 2048;
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this.overflow = options.overflow || 'ignore';
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this.startWatching();
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// Handle AbortSignal
27+
if (options.signal) {
28+
if (options.signal.aborted) {
29+
this.finish();
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return;
31+
}
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options.signal.addEventListener('abort', () => {
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this.finish();
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});
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}
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}
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private startWatching() {
39+
try {
40+
this.watcher = this.fs.watch(this.path, this.options, (eventType: string, filename: string) => {
41+
this.enqueueEvent({ eventType, filename });
42+
});
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} catch (error) {
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// If we can't start watching, finish immediately
45+
this.finish();
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throw error;
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}
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}
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private enqueueEvent(event: { eventType: string; filename: string | Buffer }) {
51+
if (this.finished) return;
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// Handle queue overflow
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if (this.eventQueue.length >= this.maxQueue) {
55+
if (this.overflow === 'throw') {
56+
const error = new Error(`Watch queue overflow: more than ${this.maxQueue} events queued`);
57+
this.finish(error);
58+
return;
59+
} else {
60+
// 'ignore' - drop the oldest event
61+
this.eventQueue.shift();
62+
console.warn(`Watch queue overflow: dropping event due to exceeding maxQueue of ${this.maxQueue}`);
63+
}
64+
}
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66+
this.eventQueue.push(event);
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// If there's a waiting promise, resolve it
69+
if (this.resolveQueue.length > 0) {
70+
const { resolve } = this.resolveQueue.shift()!;
71+
const nextEvent = this.eventQueue.shift()!;
72+
resolve({ value: nextEvent, done: false });
73+
}
74+
}
75+
76+
private finish(error?: Error) {
77+
if (this.finished) return;
78+
this.finished = true;
79+
80+
if (this.watcher) {
81+
this.watcher.close();
82+
this.watcher = null;
83+
}
84+
85+
// Resolve or reject all pending promises
86+
while (this.resolveQueue.length > 0) {
87+
const { resolve, reject } = this.resolveQueue.shift()!;
88+
if (error) {
89+
reject(error);
90+
} else {
91+
resolve({ value: undefined, done: true });
92+
}
93+
}
94+
}
95+
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async next(): Promise<IteratorResult<{ eventType: string; filename: string | Buffer }>> {
97+
if (this.finished) {
98+
return { value: undefined, done: true };
99+
}
100+
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// If we have queued events, return one
102+
if (this.eventQueue.length > 0) {
103+
const event = this.eventQueue.shift()!;
104+
return { value: event, done: false };
105+
}
106+
107+
// Otherwise, wait for the next event
108+
return new Promise((resolve, reject) => {
109+
this.resolveQueue.push({ resolve, reject });
110+
});
111+
}
112+
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async return(): Promise<IteratorResult<{ eventType: string; filename: string | Buffer }>> {
114+
this.finish();
115+
return { value: undefined, done: true };
116+
}
117+
118+
async throw(error: any): Promise<IteratorResult<{ eventType: string; filename: string | Buffer }>> {
119+
this.finish(error);
120+
throw error;
121+
}
122+
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[Symbol.asyncIterator](): AsyncIterableIterator<{ eventType: string; filename: string | Buffer }> {
124+
return this;
125+
}
126+
}
127+
7128
export class FsPromises implements FsPromisesApi {
8129
public readonly constants = constants;
9130

@@ -72,7 +193,11 @@ export class FsPromises implements FsPromisesApi {
72193
);
73194
};
74195

75-
public readonly watch = () => {
76-
throw new Error('Not implemented');
196+
public readonly watch = (
197+
filename: misc.PathLike,
198+
options?: opts.IWatchOptions | string,
199+
): AsyncIterableIterator<{ eventType: string; filename: string | Buffer }> => {
200+
const watchOptions: opts.IWatchOptions = typeof options === 'string' ? { encoding: options as any } : options || {};
201+
return new FSWatchAsyncIterator(this.fs, filename, watchOptions);
77202
};
78203
}

‎src/node/types/options.ts‎

Lines changed: 13 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -136,6 +136,19 @@ export interface IWatchOptions extends IOptions {
136136
* Allows closing the watcher with an {@link AbortSignal}.
137137
*/
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signal?: AbortSignal;
139+
140+
/**
141+
* Specifies the number of events to queue between iterations of the AsyncIterator.
142+
* Default: 2048.
143+
*/
144+
maxQueue?: number;
145+
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/**
147+
* Either 'ignore' or 'throw' when there are more events to be queued than maxQueue allows.
148+
* 'ignore' means overflow events are dropped and a warning is emitted, while 'throw'
149+
* means to throw an exception. Default: 'ignore'.
150+
*/
151+
overflow?: 'ignore' | 'throw';
139152
}
140153

141154
export interface ICpOptions {

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