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A reference client implementation for the playback of MPEG DASH via Javascript and compliant browsers.
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<h1 class="page-title">Source: streaming/net/FetchLoader.js</h1>
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<pre
class="sunlight-highlight-javascript linenums">/**
* The copyright in this software is being made available under the BSD License,
* included below. This software may be subject to other third party and contributor
* rights, including patent rights, and no such rights are granted under this license.
*
* Copyright (c) 2013, Dash Industry Forum.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modification,
* are permitted provided that the following conditions are met:
* * Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation and/or
* other materials provided with the distribution.
* * Neither the name of Dash Industry Forum nor the names of its
* contributors may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS AS IS AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
import FactoryMaker from '../../core/FactoryMaker.js';
import Settings from '../../core/Settings.js';
import Constants from '../constants/Constants.js';
import AastLowLatencyThroughputModel from '../models/AastLowLatencyThroughputModel.js';
/**
* @module FetchLoader
* @ignore
* @description Manages download of resources via HTTP using fetch.
*/
function FetchLoader() {
const context = this.context;
const aastLowLatencyThroughputModel = AastLowLatencyThroughputModel(context).getInstance();
const settings = Settings(context).getInstance();
let instance, dashMetrics, boxParser;
function setConfig(cfg) {
dashMetrics = cfg.dashMetrics;
boxParser = cfg.boxParser
}
/**
* Load request
* @param {CommonMediaLibrary.request.CommonMediaRequest} httpRequest
* @param {CommonMediaLibrary.request.CommonMediaResponse} httpResponse
*/
function load(httpRequest, httpResponse) {
// Variables will be used in the callback functions
const fragmentRequest = httpRequest.customData.request;
const headers = new Headers();
if (httpRequest.headers) {
for (let header in httpRequest.headers) {
let value = httpRequest.headers[header];
if (value) {
headers.append(header, value);
}
}
}
let abortController;
if (typeof window.AbortController === 'function') {
abortController = new AbortController(); /*jshint ignore:line*/
httpRequest.customData.abortController = abortController;
abortController.signal.onabort = httpRequest.customData.onabort;
}
httpRequest.customData.abort = abort.bind(httpRequest);
const reqOptions = {
method: httpRequest.method,
headers: headers,
credentials: httpRequest.credentials,
signal: abortController ? abortController.signal : undefined
};
const calculationMode = settings.get().streaming.abr.throughput.lowLatencyDownloadTimeCalculationMode;
const requestTime = performance.now();
let throughputCapacityDelayMS = 0;
new Promise((resolve) => {
if (calculationMode === Constants.LOW_LATENCY_DOWNLOAD_TIME_CALCULATION_MODE.AAST && aastLowLatencyThroughputModel) {
throughputCapacityDelayMS = aastLowLatencyThroughputModel.getThroughputCapacityDelayMS(fragmentRequest, dashMetrics.getCurrentBufferLevel(fragmentRequest.mediaType) * 1000);
if (throughputCapacityDelayMS) {
// safely delay the "fetch" call a bit to be able to measure the throughput capacity of the line.
// this will lead to first few chunks downloaded at max network speed
return setTimeout(resolve, throughputCapacityDelayMS);
}
}
resolve();
})
.then(() => {
let markBeforeFetch = performance.now();
fetch(httpRequest.url, reqOptions)
.then((response) => {
httpResponse.status = response.status;
httpResponse.statusText = response.statusText;
httpResponse.url = response.url;
if (!response.ok) {
httpRequest.customData.onerror();
}
const responseHeaders = {};
for (const key of response.headers.keys()) {
responseHeaders[key] = response.headers.get(key);
}
httpResponse.headers = responseHeaders;
const totalBytes = parseInt(response.headers.get('Content-Length'), 10);
let bytesReceived = 0;
let signaledFirstByte = false;
let receivedData = new Uint8Array();
let offset = 0;
if (calculationMode === Constants.LOW_LATENCY_DOWNLOAD_TIME_CALCULATION_MODE.AAST && aastLowLatencyThroughputModel) {
_aastProcessResponse(markBeforeFetch, httpRequest, requestTime, throughputCapacityDelayMS, responseHeaders, response);
} else {
httpRequest.customData.reader = response.body.getReader();
}
let downloadedData = [];
let moofStartTimeData = [];
let mdatEndTimeData = [];
let lastChunkWasFinished = true;
/**
* Callback function for the reader.
* @param value - some data. Always undefined when done is true.
* @param done - true if the stream has already given you all its data.
*/
const _processResult = ({ value, done }) => { // Bug fix Parse whenever data is coming [value] better than 1ms looking that increase CPU
if (done) {
_handleRequestComplete()
return;
}
if (value && value.length > 0) {
_handleDataReceived(value)
}
_read(httpRequest, httpResponse, _processResult);
};
/**
* Once a request is completed throw final progress event with the calculated bytes and download time
* @private
*/
function _handleRequestComplete() {
if (receivedData) {
if (calculationMode !== Constants.LOW_LATENCY_DOWNLOAD_TIME_CALCULATION_MODE.AAST) {
// If there is pending data, call progress so network metrics
// are correctly generated
// Same structure as https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequestEventTarget/
let calculatedThroughput = null;
let calculatedTime = null;
if (calculationMode === Constants.LOW_LATENCY_DOWNLOAD_TIME_CALCULATION_MODE.MOOF_PARSING) {
calculatedThroughput = _calculateThroughputByChunkData(moofStartTimeData, mdatEndTimeData);
if (calculatedThroughput) {
calculatedTime = bytesReceived * 8 / calculatedThroughput;
}
} else if (calculationMode === Constants.LOW_LATENCY_DOWNLOAD_TIME_CALCULATION_MODE.DOWNLOADED_DATA) {
calculatedTime = calculateDownloadedTime(downloadedData, bytesReceived);
}
httpRequest.customData.onprogress({
loaded: bytesReceived,
total: isNaN(totalBytes) ? bytesReceived : totalBytes,
lengthComputable: true,
time: calculatedTime
});
}
httpResponse.data = receivedData.buffer;
}
httpRequest.customData.onload();
httpRequest.customData.onloadend();
}
/**
* Called every time we received data
* @param value
* @private
*/
function _handleDataReceived(value) {
receivedData = _concatTypedArray(receivedData, value);
bytesReceived += value.length;
downloadedData.push({
ts: performance.now(),
bytes: value.length
});
if (calculationMode === Constants.LOW_LATENCY_DOWNLOAD_TIME_CALCULATION_MODE.MOOF_PARSING && lastChunkWasFinished) {
// Parse the payload and capture the 'moof' box
const boxesInfo = boxParser.findLastTopIsoBoxCompleted(['moof'], receivedData, offset);
if (boxesInfo.found) {
// Store the beginning time of each chunk download in array StartTimeData
lastChunkWasFinished = false;
moofStartTimeData.push({
ts: performance.now(),
bytes: value.length
});
}
}
const boxesInfo = boxParser.findLastTopIsoBoxCompleted(['moov', 'mdat'], receivedData, offset);
if (boxesInfo.found) {
const endOfLastBox = boxesInfo.lastCompletedOffset + boxesInfo.size;
// Store the end time of each chunk download with its size in array EndTimeData
if (calculationMode === Constants.LOW_LATENCY_DOWNLOAD_TIME_CALCULATION_MODE.MOOF_PARSING && !lastChunkWasFinished) {
lastChunkWasFinished = true;
mdatEndTimeData.push({
ts: performance.now(),
bytes: receivedData.length
});
}
// Make the data that we received available for playback
// If we are going to pass full buffer, avoid copying it and pass
// complete buffer. Otherwise, clone the part of the buffer that is completed
// and adjust remaining buffer. A clone is needed because ArrayBuffer of a typed-array
// keeps a reference to the original data
let data;
if (endOfLastBox === receivedData.length) {
data = receivedData;
receivedData = new Uint8Array();
} else {
data = new Uint8Array(receivedData.subarray(0, endOfLastBox));
receivedData = receivedData.subarray(endOfLastBox);
}
// Announce progress but don't track traces. Throughput measures are quite unstable
// when they are based in small amount of data
httpRequest.customData.onprogress({
data: data.buffer,
lengthComputable: false,
noTrace: true
});
offset = 0;
} else {
offset = boxesInfo.lastCompletedOffset;
// Call progress, so it generates traces that will be later used to know when the first byte
// were received
if (!signaledFirstByte) {
httpRequest.customData.onprogress({
lengthComputable: false,
noTrace: true
});
signaledFirstByte = true;
}
}
}
_read(httpRequest, httpResponse, _processResult);
})
.catch(function (e) {
if (httpRequest.customData.onerror) {
httpRequest.customData.onerror(e);
}
});
});
}
function _aastProcessResponse(markBeforeFetch, httpRequest, requestTime, throughputCapacityDelayMS, responseHeaders, response) {
let markA = markBeforeFetch;
let markB = 0;
function fetchMeassurement(stream) {
const reader = stream.getReader();
const measurement = [];
const fragmentRequest = httpRequest.customData.request;
reader.read()
.then(function processFetch(args) {
const value = args.value;
const done = args.done;
markB = performance.now();
if (value && value.length) {
const chunkDownloadDurationMS = markB - markA;
const chunkBytes = value.length;
measurement.push({
chunkDownloadTimeRelativeMS: markB - markBeforeFetch,
chunkDownloadDurationMS,
chunkBytes,
kbps: Math.round(8 * chunkBytes / (chunkDownloadDurationMS / 1000)),
bufferLevel: dashMetrics.getCurrentBufferLevel(fragmentRequest.mediaType)
});
}
if (done) {
const fetchDuration = markB - markBeforeFetch;
const bytesAllChunks = measurement.reduce((prev, curr) => prev + curr.chunkBytes, 0);
aastLowLatencyThroughputModel.addMeasurement(fragmentRequest, fetchDuration, measurement, requestTime, throughputCapacityDelayMS, responseHeaders);
httpRequest.progress({
loaded: bytesAllChunks,
total: bytesAllChunks,
lengthComputable: true,
time: aastLowLatencyThroughputModel.getEstimatedDownloadDurationMS(fragmentRequest)
});
return;
}
markA = performance.now();
return reader.read().then(processFetch);
});
}
// tee'ing streams is supported by all current major browsers
// https://developer.mozilla.org/en-US/docs/Web/API/ReadableStream/tee
const [forMeasure, forConsumer] = response.body.tee();
fetchMeassurement(forMeasure);
httpRequest.customData.reader = forConsumer.getReader();
}
/**
* Reads the response of the request. For details refer to https://developer.mozilla.org/en-US/docs/Web/API/ReadableStreamDefaultReader/read
* @param httpRequest
* @param processResult
* @private
*/
function _read(httpRequest, httpResponse, processResult) {
httpRequest.customData.reader.read()
.then(processResult)
.catch(function (e) {
if (httpRequest.customData.onerror && httpResponse.status === 200) {
// Error, but response code is 200, trigger error
httpRequest.customData.onerror(e);
}
});
}
/**
* Creates a new Uint8 array and adds the existing data as well as new data
* @param receivedData
* @param data
* @returns {Uint8Array|*}
* @private
*/
function _concatTypedArray(receivedData, data) {
if (receivedData.length === 0) {
return data;
}
const result = new Uint8Array(receivedData.length + data.length);
result.set(receivedData);
// set(typedarray, targetOffset)
result.set(data, receivedData.length);
return result;
}
/**
* Use the AbortController to abort a request
* @param request
*/
function abort() {
// this = httpRequest (CommonMediaRequest)
if (this.customData.abortController) {
// For firefox and edge
this.customData.abortController.abort();
} else if (this.customData.reader) {
// For Chrome
try {
this.customData.reader.cancel();
this.onabort();
} catch (e) {
// throw exceptions (TypeError) when reader was previously closed,
// for example, because a network issue
}
}
}
/**
* Default throughput calculation
* @param downloadedData
* @param bytesReceived
* @returns {number|null}
* @private
*/
function calculateDownloadedTime(downloadedData, bytesReceived) {
try {
downloadedData = downloadedData.filter(data => data.bytes > ((bytesReceived / 4) / downloadedData.length));
if (downloadedData.length > 1) {
let time = 0;
const avgTimeDistance = (downloadedData[downloadedData.length - 1].ts - downloadedData[0].ts) / downloadedData.length;
downloadedData.forEach((data, index) => {
// To be counted the data has to be over a threshold
const next = downloadedData[index + 1];
if (next) {
const distance = next.ts - data.ts;
time += distance < avgTimeDistance ? distance : 0;
}
});
return time;
}
return null;
} catch (e) {
return null;
}
}
/**
* Moof based throughput calculation
* @param startTimeData
* @param endTimeData
* @returns {number|null}
* @private
*/
function _calculateThroughputByChunkData(startTimeData, endTimeData) {
try {
let datum, datumE;
// Filter the last chunks in a segment in both arrays [StartTimeData and EndTimeData]
datum = startTimeData.filter((data, i) => i < startTimeData.length - 1);
datumE = endTimeData.filter((dataE, i) => i < endTimeData.length - 1);
let chunkThroughputs = [];
// Compute the average throughput of the filtered chunk data
if (datum.length > 1) {
let shortDurationBytesReceived = 0;
let shortDurationStartTime = 0;
for (let i = 0; i < datum.length; i++) {
if (datum[i] && datumE[i]) {
let chunkDownloadTime = datumE[i].ts - datum[i].ts;
if (chunkDownloadTime > 1) {
chunkThroughputs.push((8 * datumE[i].bytes) / chunkDownloadTime);
shortDurationStartTime = 0;
} else {
if (shortDurationStartTime === 0) {
shortDurationStartTime = datum[i].ts;
shortDurationBytesReceived = 0;
}
let cumulatedChunkDownloadTime = datumE[i].ts - shortDurationStartTime;
if (cumulatedChunkDownloadTime > 1) {
shortDurationBytesReceived += datumE[i].bytes;
chunkThroughputs.push((8 * shortDurationBytesReceived) / cumulatedChunkDownloadTime);
shortDurationStartTime = 0;
} else {
// continue cumulating short duration data
shortDurationBytesReceived += datumE[i].bytes;
}
}
}
}
if (chunkThroughputs.length > 0) {
const sumOfChunkThroughputs = chunkThroughputs.reduce((a, b) => a + b, 0);
return sumOfChunkThroughputs / chunkThroughputs.length;
}
}
return null;
} catch (e) {
return null;
}
}
instance = {
load,
abort,
setConfig,
calculateDownloadedTime
};
return instance;
}
FetchLoader.__dashjs_factory_name = 'FetchLoader';
const factory = FactoryMaker.getClassFactory(FetchLoader);
export default factory;
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