52 lines
2.4 KiB
JavaScript
52 lines
2.4 KiB
JavaScript
import {finished} from 'node:stream/promises';
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import mergeStreams from '@sindresorhus/merge-streams';
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import {incrementMaxListeners} from '../utils/max-listeners.js';
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import {pipeStreams} from '../io/pipeline.js';
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// The piping behavior is like Bash.
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// In particular, when one subprocess exits, the other is not terminated by a signal.
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// Instead, its stdout (for the source) or stdin (for the destination) closes.
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// If the subprocess uses it, it will make it error with SIGPIPE or EPIPE (for the source) or end (for the destination).
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// If it does not use it, it will continue running.
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// This allows for subprocesses to gracefully exit and lower the coupling between subprocesses.
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export const pipeSubprocessStream = (sourceStream, destinationStream, maxListenersController) => {
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const mergedStream = MERGED_STREAMS.has(destinationStream)
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? pipeMoreSubprocessStream(sourceStream, destinationStream)
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: pipeFirstSubprocessStream(sourceStream, destinationStream);
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incrementMaxListeners(sourceStream, SOURCE_LISTENERS_PER_PIPE, maxListenersController.signal);
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incrementMaxListeners(destinationStream, DESTINATION_LISTENERS_PER_PIPE, maxListenersController.signal);
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cleanupMergedStreamsMap(destinationStream);
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return mergedStream;
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};
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// We use `merge-streams` to allow for multiple sources to pipe to the same destination.
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const pipeFirstSubprocessStream = (sourceStream, destinationStream) => {
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const mergedStream = mergeStreams([sourceStream]);
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pipeStreams(mergedStream, destinationStream);
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MERGED_STREAMS.set(destinationStream, mergedStream);
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return mergedStream;
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};
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const pipeMoreSubprocessStream = (sourceStream, destinationStream) => {
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const mergedStream = MERGED_STREAMS.get(destinationStream);
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mergedStream.add(sourceStream);
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return mergedStream;
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};
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const cleanupMergedStreamsMap = async destinationStream => {
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try {
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await finished(destinationStream, {cleanup: true, readable: false, writable: true});
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} catch {}
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MERGED_STREAMS.delete(destinationStream);
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};
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const MERGED_STREAMS = new WeakMap();
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// Number of listeners set up on `sourceStream` by each `sourceStream.pipe(destinationStream)`
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// Those are added by `merge-streams`
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const SOURCE_LISTENERS_PER_PIPE = 2;
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// Number of listeners set up on `destinationStream` by each `sourceStream.pipe(destinationStream)`
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// Those are added by `finished()` in `cleanupMergedStreamsMap()`
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const DESTINATION_LISTENERS_PER_PIPE = 1;
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