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concat_stream_providers.ts
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concat_stream_providers.ts
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/*
* Licensed to Elasticsearch B.V. under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch B.V. licenses this file to you under
* the Apache License, Version 2.0 (the "License"); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
import { PassThrough, TransformOptions } from 'stream';
/**
* Write the data and errors from a list of stream providers
* to a single stream in order. Stream providers are only
* called right before they will be consumed, and only one
* provider will be active at a time.
*/
export function concatStreamProviders(
sourceProviders: Array<() => NodeJS.ReadableStream>,
options: TransformOptions = {}
) {
const destination = new PassThrough(options);
const queue = sourceProviders.slice();
(function pipeNext() {
const provider = queue.shift();
if (!provider) {
return;
}
const source = provider();
const isLast = !queue.length;
// if there are more sources to pipe, hook
// into the source completion
if (!isLast) {
source.once('end', pipeNext);
}
source
// proxy errors from the source to the destination
.once('error', (error) => destination.destroy(error))
// pipe the source to the destination but only proxy the
// end event if this is the last source
.pipe(destination, { end: isLast });
})();
return destination;
}