Chore: add external download stat report

Build/index.ts

@@ -27,6 +27,7 @@ import { buildDeprecateFiles } from './build-deprecate-files';
 import path from 'node:path';
 import { ROOT_DIR } from './constants/dir';
 import { isCI } from 'ci-info';
+import { printExternalDownloadStats } from './lib/download-stats';
 
 process.on('uncaughtException', (error) => {
   console.error('Uncaught exception:', error);
@@ -123,6 +124,7 @@ const buildFinishedLock = path.join(ROOT_DIR, '.BUILD_FINISHED');
       printTraceResult(t);
     });
     printStats(traces);
+    printExternalDownloadStats();
 
     await Promise.all([
       microsoftCdnWorker.end(),

Build/lib/create-file.ts

@@ -10,6 +10,11 @@ import { promisify } from 'node:util';
 
 const fileEqual = createCompareSource(fileEqualWithCommentComparator);
 
+/**
+ * To keep metadata comment `last updated` not change if real content is the same,
+ * we compare real content lines and only write if actual content is different,
+ * and the new `last updated` will be written along with new content.
+ */
 export async function compareAndWriteFile(span: Span, linesA: string[], filePath: string) {
   // readFileByLine will not include last empty line. So we always pop the linesA for comparison purpose
   if (linesA.length > 0 && linesA[linesA.length - 1] === '') {

Build/lib/download-stats.ts

@@ -0,0 +1,143 @@
+import picocolors from 'picocolors';
+import { createPrettyBits, prettyBandwidth, prettyTraffic } from 'xbits';
+
+export type ExternalDownloadOutcome = 'winner' | 'aborted' | 'failed';
+
+export interface ExternalDownloadAttempt {
+  url: string,
+  kind: 'primary' | 'fallback',
+  outcome: ExternalDownloadOutcome,
+  startedAt: number,
+  headersAt: number | null,
+  bodyStartedAt: number | null,
+  endedAt: number,
+  bytes: number
+}
+
+export interface ExternalDownloadStatsSnapshot {
+  startedAt: number | null,
+  endedAt: number | null,
+  totalBytes: number,
+  usefulBytes: number,
+  wastedBytes: number,
+  winners: number,
+  aborted: number,
+  failed: number
+}
+
+function createEmptySnapshot(): ExternalDownloadStatsSnapshot {
+  return {
+    startedAt: null,
+    endedAt: null,
+    totalBytes: 0,
+    usefulBytes: 0,
+    wastedBytes: 0,
+    winners: 0,
+    aborted: 0,
+    failed: 0
+  };
+}
+
+let stats = createEmptySnapshot();
+const prettyBinaryByteSpeed = createPrettyBits({
+  bits: false,
+  binary: true,
+  speed: true,
+  largeK: true
+});
+
+export function downloadTimestamp() {
+  return performance.timeOrigin + performance.now();
+}
+
+export function formatDownloadSpeed(bytes: number, duration: number) {
+  if (duration <= 0) {
+    return 'n/a';
+  }
+  const bytesPerSecond = bytes / duration * 1000;
+  return `${prettyBinaryByteSpeed(bytesPerSecond)} (${prettyBandwidth(bytesPerSecond * 8)})`;
+}
+
+function formatDuration(duration: number | null) {
+  return duration == null ? 'n/a' : `${duration.toFixed(1)}ms`;
+}
+
+export function recordExternalDownloadAttempt(attempt: ExternalDownloadAttempt) {
+  stats.startedAt = stats.startedAt == null ? attempt.startedAt : Math.min(stats.startedAt, attempt.startedAt);
+  stats.endedAt = stats.endedAt == null ? attempt.endedAt : Math.max(stats.endedAt, attempt.endedAt);
+  stats.totalBytes += attempt.bytes;
+
+  if (attempt.outcome === 'winner') {
+    stats.winners++;
+    stats.usefulBytes += attempt.bytes;
+  } else {
+    stats.wastedBytes += attempt.bytes;
+    if (attempt.outcome === 'aborted') {
+      stats.aborted++;
+    } else {
+      stats.failed++;
+    }
+  }
+
+  const ttfb = attempt.headersAt == null ? null : attempt.headersAt - attempt.startedAt;
+  const queueWait = attempt.headersAt == null || attempt.bodyStartedAt == null
+    ? null
+    : attempt.bodyStartedAt - attempt.headersAt;
+  const bodyDuration = attempt.bodyStartedAt == null ? null : attempt.endedAt - attempt.bodyStartedAt;
+  const speed = bodyDuration == null ? 'n/a' : formatDownloadSpeed(attempt.bytes, bodyDuration);
+
+  console.log(
+    picocolors.gray('[external download]'),
+    attempt.kind,
+    attempt.outcome,
+    prettyTraffic(attempt.bytes),
+    speed,
+    `ttfb=${formatDuration(ttfb)}`,
+    `queue=${formatDuration(queueWait)}`,
+    attempt.url
+  );
+}
+
+export function mergeExternalDownloadStats(snapshot: ExternalDownloadStatsSnapshot | undefined) {
+  if (!snapshot) {
+    return;
+  }
+
+  if (snapshot.startedAt != null) {
+    stats.startedAt = stats.startedAt == null ? snapshot.startedAt : Math.min(stats.startedAt, snapshot.startedAt);
+  }
+  if (snapshot.endedAt != null) {
+    stats.endedAt = stats.endedAt == null ? snapshot.endedAt : Math.max(stats.endedAt, snapshot.endedAt);
+  }
+  stats.totalBytes += snapshot.totalBytes;
+  stats.usefulBytes += snapshot.usefulBytes;
+  stats.wastedBytes += snapshot.wastedBytes;
+  stats.winners += snapshot.winners;
+  stats.aborted += snapshot.aborted;
+  stats.failed += snapshot.failed;
+}
+
+export function takeExternalDownloadStats() {
+  const snapshot = stats;
+  stats = createEmptySnapshot();
+  return snapshot;
+}
+
+export function printExternalDownloadStats() {
+  if (stats.startedAt == null || stats.endedAt == null) {
+    return;
+  }
+
+  const duration = stats.endedAt - stats.startedAt;
+  console.log(
+    picocolors.bold('[external downloads total]'),
+    `useful=${prettyTraffic(stats.usefulBytes)}`,
+    `transferred=${prettyTraffic(stats.totalBytes)}`,
+    `hedge-waste=${prettyTraffic(stats.wastedBytes)}`,
+    `avg=${formatDownloadSpeed(stats.totalBytes, duration)}`,
+    `wall=${formatDuration(duration)}`,
+    `winner=${stats.winners}`,
+    `aborted=${stats.aborted}`,
+    `failed=${stats.failed}`
+  );
+}

Build/lib/fetch-assets.ts

@@ -8,23 +8,94 @@ import { AdGuardFilterIgnoreUnsupportedLinesStream } from './parse-filter/filter
 import { appendArrayInPlace } from 'foxts/append-array-in-place';
 
 import { newQueue } from '@henrygd/queue';
-import { AbortError } from 'foxts/abort-error';
+import { AbortError, isAbortErrorLike } from 'foxts/abort-error';
+import { downloadTimestamp, recordExternalDownloadAttempt } from './download-stats';
+import type { ExternalDownloadOutcome } from './download-stats';
 
 const reusedCustomAbortError = new AbortError();
 
 const queue = newQueue(18);
 
+const MIN_HEDGE_DELAY = 3000;
+const HEDGE_DELAY_STEP = 1200;
+const HEDGE_SPEED_SAMPLE_INTERVAL = 1000;
+const HEDGE_QUEUE_POLL_INTERVAL = 250;
+// 1 MiB/s is about 8.4 Mbps. A source throttled to 5 Mbps will be hedged,
+// while larger responses making healthy progress will not be raced merely
+// because their total download time exceeds three seconds.
+const MIN_ACCEPTABLE_DOWNLOAD_BYTES_PER_SECOND = 1024 * 1024;
+
+export function isDownloadThroughputSlow(bytesReceived: number, elapsed: number) {
+  return bytesReceived / elapsed * 1000 < MIN_ACCEPTABLE_DOWNLOAD_BYTES_PER_SECOND;
+}
+
+interface PrimaryDownloadProgress {
+  headersReceived: boolean,
+  bodyStartedAt: number | null,
+  bytesReceived: number,
+  failed: boolean
+}
+
 export async function fetchAssets(
   url: string, fallbackUrls: null | undefined | string[] | readonly string[],
   processLine = false, allowEmpty = false, filterAdGuardUnsupportedLines = false
 ) {
   const controller = new AbortController();
+  const primaryProgress: PrimaryDownloadProgress = {
+    headersReceived: false,
+    bodyStartedAt: null,
+    bytesReceived: 0,
+    failed: false
+  };
+
+  const waitForSlowPrimary = async (fallbackIndex: number) => {
+    await waitWithAbort(MIN_HEDGE_DELAY + fallbackIndex * HEDGE_DELAY_STEP, controller.signal);
+
+    let sampledAt: number | null = null;
+    let sampledBytes = 0;
+
+    while (!controller.signal.aborted) {
+      // No response headers after the initial delay, or an explicit primary
+      // failure, is sufficient reason to begin the fallback immediately.
+      if (!primaryProgress.headersReceived || primaryProgress.failed) {
+        return;
+      }
+
+      if (primaryProgress.bodyStartedAt == null) {
+        // The response is waiting for our local body-consumption queue. This is
+        // not an upstream slowdown and should not trigger a duplicate request.
+        // eslint-disable-next-line no-await-in-loop -- poll until local consumption starts
+        await waitWithAbort(HEDGE_QUEUE_POLL_INTERVAL, controller.signal);
+        continue;
+      }
+
+      sampledAt ??= primaryProgress.bodyStartedAt;
+      const now = performance.now();
+      const sampleDuration = now - sampledAt;
+
+      if (sampleDuration < HEDGE_SPEED_SAMPLE_INTERVAL) {
+        // eslint-disable-next-line no-await-in-loop -- collect a complete throughput sample
+        await waitWithAbort(HEDGE_SPEED_SAMPLE_INTERVAL - sampleDuration, controller.signal);
+        continue;
+      }
+
+      if (isDownloadThroughputSlow(primaryProgress.bytesReceived - sampledBytes, sampleDuration)) {
+        return;
+      }
+
+      sampledAt = now;
+      sampledBytes = primaryProgress.bytesReceived;
+      // eslint-disable-next-line no-await-in-loop -- periodically re-sample a healthy transfer
+      await waitWithAbort(HEDGE_SPEED_SAMPLE_INTERVAL, controller.signal);
+    }
+
+    throw reusedCustomAbortError;
+  };
 
   const createFetchFallbackPromise = async (url: string, index: number) => {
     if (index >= 0) {
-      // To avoid wasting bandwidth, we will wait for a few time before downloading from the fallback URL.
       try {
-        await waitWithAbort(1800 + (index + 1) * 1200, controller.signal);
+        await waitForSlowPrimary(index);
       } catch {
         throw reusedCustomAbortError;
       }
@@ -37,28 +108,82 @@ export async function fetchAssets(
       console.log(picocolors.yellowBright('[fetch fallback begin]'), picocolors.gray(url));
     }
 
-    // we don't queue add here
+    const isPrimary = index < 0;
-    const res = await $$fetch(url, { signal: controller.signal, ...defaultRequestInit });
+    const attemptStartedAt = downloadTimestamp();
+    let headersAt: number | null = null;
+    let bodyStartedAt: number | null = null;
+    let attemptBytes = 0;
+    let finalized = false;
 
-    let stream = nullthrow(res.body, url + ' has an empty body')
+    const finalizeAttempt = (outcome: ExternalDownloadOutcome) => {
-      .pipeThrough(new TextDecoderStream())
+      if (finalized) {
-      .pipeThrough(new TextLineStream({ skipEmptyLines: processLine }));
+        return;
-    if (processLine) {
+      }
-      stream = stream.pipeThrough(new ProcessLineStream());
+      finalized = true;
+      recordExternalDownloadAttempt({
+        url,
+        kind: isPrimary ? 'primary' : 'fallback',
+        outcome,
+        startedAt: attemptStartedAt,
+        headersAt,
+        bodyStartedAt,
+        endedAt: downloadTimestamp(),
+        bytes: attemptBytes
+      });
+    };
+
+    try {
+      // We intentionally acquire the body-consumption queue after receiving
+      // headers. Request scheduling will be handled separately.
+      const res = await $$fetch(url, { signal: controller.signal, ...defaultRequestInit });
+      headersAt = downloadTimestamp();
+
+      let body = nullthrow(res.body, url + ' has an empty body');
+      if (isPrimary) {
+        primaryProgress.headersReceived = true;
+      }
+      body = body.pipeThrough(new TransformStream<Uint8Array, Uint8Array>({
+        transform(chunk, streamController) {
+          attemptBytes += chunk.byteLength;
+          if (isPrimary) {
+            primaryProgress.bytesReceived += chunk.byteLength;
+          }
+          streamController.enqueue(chunk);
+        }
+      }));
+
+      let stream = body
+        .pipeThrough(new TextDecoderStream())
+        .pipeThrough(new TextLineStream({ skipEmptyLines: processLine }));
+      if (processLine) {
+        stream = stream.pipeThrough(new ProcessLineStream());
+      }
+      if (filterAdGuardUnsupportedLines) {
+        stream = stream.pipeThrough(new AdGuardFilterIgnoreUnsupportedLinesStream());
+      }
+
+      const arr = await queue.add(() => {
+        bodyStartedAt = downloadTimestamp();
+        if (isPrimary) {
+          primaryProgress.bodyStartedAt = performance.now();
+        }
+        return Array.fromAsync(stream);
+      });
+
+      if (arr.length < 1 && !allowEmpty) {
+        throw new ResponseError(res, url, 'empty response w/o 304');
+      }
+
+      finalizeAttempt('winner');
+      controller.abort();
+      return arr;
+    } catch (error) {
+      if (isPrimary) {
+        primaryProgress.failed = true;
+      }
+      finalizeAttempt(isAbortErrorLike(error) ? 'aborted' : 'failed');
+      throw error;
     }
-    if (filterAdGuardUnsupportedLines) {
-      stream = stream.pipeThrough(new AdGuardFilterIgnoreUnsupportedLinesStream());
-    }
-
-    // we does queue during downloading
-    const arr = await queue.add(() => Array.fromAsync(stream));
-
-    if (arr.length < 1 && !allowEmpty) {
-      throw new ResponseError(res, url, 'empty response w/o 304');
-    }
-
-    controller.abort();
-    return arr;
   };
 
   const primaryPromise = createFetchFallbackPromise(url, -1);

Build/trace/index.ts

@@ -3,6 +3,8 @@ import { noop } from 'foxts/noop';
 import { basename, extname } from 'node:path';
 import process from 'node:process';
 import picocolors from 'picocolors';
+import { mergeExternalDownloadStats, takeExternalDownloadStats } from '../lib/download-stats';
+import type { ExternalDownloadStatsSnapshot } from '../lib/download-stats';
 
 export const SPAN_STATUS_START = 0;
 export const SPAN_STATUS_END = 1;
@@ -82,8 +84,9 @@ export function makeSpan(rawSpan: RawSpan): Span {
 
     async traceWorkerChild<T>(name: string, factory: (rawSpan: RawSpan) => Promise<WorkerJobResult<T>>): Promise<T> {
       const childSpan = traceChild(name);
-      const { result, traceResult, workerTimeOrigin } = await factory(childSpan.rawSpan);
+      const { result, traceResult, workerTimeOrigin, externalDownloadStats } = await factory(childSpan.rawSpan);
       mergeWorkerTrace(childSpan, traceResult, workerTimeOrigin);
+      mergeExternalDownloadStats(externalDownloadStats);
       childSpan.stop();
       return result;
     }
@@ -207,7 +210,8 @@ function mergeWorkerTrace(
 export interface WorkerJobResult<T> {
   result: T,
   traceResult: TraceResult,
-  workerTimeOrigin: number
+  workerTimeOrigin: number,
+  externalDownloadStats: ExternalDownloadStatsSnapshot
 }
 
 /**
@@ -231,7 +235,8 @@ export async function workerJob<T>(
   return {
     result,
     traceResult: span.traceResult,
-    workerTimeOrigin: performance.timeOrigin
+    workerTimeOrigin: performance.timeOrigin,
+    externalDownloadStats: takeExternalDownloadStats()
   };
 }
 

package.json

@@ -13,6 +13,7 @@
     "dexnode": "SWC_NODE_IGNORE_DYNAMIC=true dexnode -r @swc-node/register",
     "build": "pnpm run node ./Build/index.ts",
     "build-profile": "pnpm run dexnode -r @swc-node/register ./Build/index.ts",
+    "bench-download": "pnpm run node ./Build/benchmark-download-client.ts",
     "lint": "eslint --format=sukka .",
     "test": "SWC_NODE_IGNORE_DYNAMIC=true SWC_NODE_PROJECT=tsconfig.test.json mocha --require @swc-node/register --watch-extensions ts,tsx"
   },