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// Run the SHIPPED player functions against a fake SourceBuffer.
//
// The point is that nothing here is a paraphrase of app.js: `bufferedAhead`,
// `evictBehind`, `flushQueue` and `pump` are lifted out of the file as text and
// executed. A model of a fix, written by whoever wrote the fix, agrees with it
// by construction — which is how a passing test sat next to a player that still
// hung. What is modelled here is the *browser*: a SourceBuffer with a ceiling,
// and `updateend` firing for removals as well as appends.
//
// Usage: node mse_harness.mjs <path to app.js> <json config>
import { readFileSync } from 'fs';
const app = readFileSync(process.argv[2], 'utf8');
const cfg = JSON.parse(process.argv[3] || '{}');
const {
playing = false, // does the viewer actually press play
capMB = 100, // where the browser refuses the append
fileMB = 493.5, // the film, from a real upload
durationS = 3936,
netMBs = 35, // measured node throughput
wallS = 600,
} = cfg;
const grab = (name) => {
const start = app.indexOf(`const ${name} = useCallback(`);
if (start < 0) throw new Error(`${name} not found in app.js`);
const deps = app.indexOf('\n }, [', start);
const end = app.indexOf(');', deps) + 2;
return app.slice(start, end);
};
const useCallback = (fn) => fn;
const src = ['bufferedAhead', 'evictBehind', 'flushQueue', 'pump']
.map(grab).join('\n');
const SEG = 256 * 1024;
const CAP = capMB * 1048576;
const BITRATE = fileMB * 1048576 / durationS;
// Read from app.js too, so a change to the constants is a change to the test.
const constOf = (name) => {
const m = app.match(new RegExp(`const ${name} = (\\d+)`));
if (!m) throw new Error(`${name} not found`);
return Number(m[1]);
};
const BUFFER_BEHIND_S = constOf('BUFFER_BEHIND_S');
const STREAM_WINDOW = constOf('STREAM_WINDOW');
const BUFFER_AHEAD_S = constOf('BUFFER_AHEAD_S');
const QUEUE_HIGH_WATER = constOf('QUEUE_HIGH_WATER');
const CREDIT_KEEPALIVE_MS = constOf('CREDIT_KEEPALIVE_MS');
let bytes = 0, ranges = [], appended = 0, removes = 0;
let granted = 0, keepalives = 0, sent = 0, credit = 0, quotaRefusals = 0;
const sb = {
updating: false,
get buffered() {
return {
get length() { return ranges.length; },
start: (i) => ranges[i][0],
end: (i) => ranges[i][1],
};
},
appendBuffer(chunk) {
if (bytes + chunk.byteLength > CAP) {
quotaRefusals++;
const e = new Error('quota'); e.name = 'QuotaExceededError'; throw e;
}
const at = ranges.length ? ranges[ranges.length - 1][1] : 0;
ranges.push([at, at + chunk.byteLength / BITRATE]);
bytes += chunk.byteLength;
appended++;
},
remove(a, b) {
removes++;
let dropped = 0;
ranges = ranges.filter(([s, e]) => {
if (e <= b && s >= a) { dropped += (e - s) * BITRATE; return false; }
return true;
});
bytes -= dropped;
// A real remove() is asynchronous and fires updateend when it lands. That
// event is indistinguishable from an append's unless the player kept track.
pendingRemoveEvents++;
},
};
let pendingRemoveEvents = 0;
const video = { currentTime: 0 };
const sbRef = { current: sb }, videoRef = { current: video };
const msRef = { current: { readyState: 'open', endOfStream() {} } };
const queueRef = { current: [] };
const appendingRef = { current: false }, endedRef = { current: false };
const outstandingRef = { current: 0 }, lastPokeRef = { current: 0 };
const quotaRef = { current: 0 }, stalledRef = { current: false };
const transportRef = {
current: {
connected: true,
grantStreamCredit(n) {
if (n === 0) { keepalives++; return; }
granted += n; credit += n;
},
},
};
const fns = new Function(
'sbRef,videoRef,msRef,queueRef,appendingRef,endedRef,outstandingRef,' +
'lastPokeRef,transportRef,BUFFER_BEHIND_S,BUFFER_AHEAD_S,QUEUE_HIGH_WATER,' +
'CREDIT_KEEPALIVE_MS,STREAM_WINDOW,quotaRef,stalledRef,console,useCallback',
src + '\n return {bufferedAhead, evictBehind, flushQueue, pump};'
)(sbRef, videoRef, msRef, queueRef, appendingRef, endedRef, outstandingRef,
lastPokeRef, transportRef, BUFFER_BEHIND_S, BUFFER_AHEAD_S, QUEUE_HIGH_WATER,
CREDIT_KEEPALIVE_MS, STREAM_WINDOW, quotaRef, stalledRef, console, useCallback);
// The player's own `updateend` listener, transcribed — the one part of the
// component that is a listener rather than a callback, and the place the
// remove/append distinction lives.
const updateend = () => {
appendingRef.current = false;
fns.pump();
};
credit = STREAM_WINDOW;
outstandingRef.current = STREAM_WINDOW;
let wall = 0;
const TICK = 0.05;
while (wall < wallS) {
wall += TICK;
if (playing) {
const end = ranges.length ? ranges[ranges.length - 1][1] : 0;
video.currentTime = Math.min(video.currentTime + TICK, end);
}
fns.pump(); // the 1 s timer and timeupdate
while (pendingRemoveEvents > 0) { pendingRemoveEvents--; updateend(); }
let budget = netMBs * 1048576 * TICK;
while (credit > 0 && budget >= SEG) {
credit--; budget -= SEG; sent++;
outstandingRef.current = Math.max(0, outstandingRef.current - 1);
queueRef.current.push({ byteLength: SEG });
fns.flushQueue();
if (appendingRef.current) updateend();
while (pendingRemoveEvents > 0) { pendingRemoveEvents--; updateend(); }
}
}
console.log(JSON.stringify({
sentMB: +(sent * SEG / 1048576).toFixed(1),
heldInBufferMB: +(bytes / 1048576).toFixed(1),
queueDepth: queueRef.current.length,
bufferedAheadS: +fns.bufferedAhead().toFixed(1),
watchedS: +video.currentTime.toFixed(1),
grants: granted,
keepalives,
removes,
quotaRefusals: quotaRef.current,
hitCeiling: bytes >= CAP * 0.99,
}));
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