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perf(observability): /api subset 响应头加 X-Timing-* 分阶段耗时

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38ms 请求定位用：X-Timing-Find/Read/Subset/Total 分别对应 findFontPath、
readFontBuffer、fontSubset、总计。本地实测 60ms 中 58ms 在读字体文件、
裁剪仅 1ms，证伪「裁剪慢」假设。缓存命中只返回 X-Timing-Total。

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
崮生（子虚） 2026-07-26 10:39:31 +08:00
parent 259cf7f2d8
commit 27c91bcdc2
1 changed files with 15 additions and 0 deletions
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15
backend/routes/subset.ts
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@ -25,6 +25,8 @@ const SUBSET_CACHE_KEY = `${PACKAGE_VERSION}:${PROCESS_START_TIME}`;
/** GET /api?font=...&text=... — 字体裁剪 */ /** GET /api?font=...&text=... — 字体裁剪 */
export async function handleFontSubset(req: Request, res: Response) { export async function handleFontSubset(req: Request, res: Response) {
/** 入口时间戳，用于响应头 X-Timing-* 分阶段耗时排查 */
const t0 = Date.now();
const url = parseUrl(req); const url = parseUrl(req);
const params = new URLSearchParams(url.search); const params = new URLSearchParams(url.search);
const font = params.get("font") || ""; const font = params.get("font") || "";
@ -34,6 +36,8 @@ export async function handleFontSubset(req: Request, res: Response) {
} }
const fontPath = await findFontPath(font); const fontPath = await findFontPath(font);
/** findFontPath 结束时间戳（含可能的 readdir 遍历字体目录） */
const t1 = Date.now();
if (!fontPath) { if (!fontPath) {
return { return {
req, req,
@ -67,6 +71,8 @@ export async function handleFontSubset(req: Request, res: Response) {
"Content-Type": contentTypes[outType] || "font/ttf", "Content-Type": contentTypes[outType] || "font/ttf",
"Cache-Control": "public, max-age=86400", "Cache-Control": "public, max-age=86400",
"X-Cache": "HIT", "X-Cache": "HIT",
/** 缓存命中时仅 findFontPath + cache.get 耗时（毫秒） */
"X-Timing-Total": `${t1 - t0}`,
}, },
}), }),
}; };
@ -85,11 +91,15 @@ export async function handleFontSubset(req: Request, res: Response) {
}), }),
}; };
} }
/** readFontBuffer 结束时间戳（磁盘 IO / buffer 缓存命中） */
const t2 = Date.now();
const newFont = await fontSubset(oldFontBuffer, text, { const newFont = await fontSubset(oldFontBuffer, text, {
outType: outType, outType: outType,
sourceType: fontType, sourceType: fontType,
}); });
/** fontSubset 结束时间戳（实际裁剪，亚毫秒级应在此体现） */
const t3 = Date.now();
/** 写入裁剪结果缓存 */ /** 写入裁剪结果缓存 */
subsetCache.set(cacheKey, newFont as ArrayBuffer); subsetCache.set(cacheKey, newFont as ArrayBuffer);
@ -104,6 +114,11 @@ export async function handleFontSubset(req: Request, res: Response) {
"Content-Type": contentTypes[outType] || "font/ttf", "Content-Type": contentTypes[outType] || "font/ttf",
"Cache-Control": "public, max-age=86400", "Cache-Control": "public, max-age=86400",
"X-Cache": "MISS", "X-Cache": "MISS",
/** 分阶段耗时（毫秒），供排查服务端处理时间分布 */
"X-Timing-Find": `${t1 - t0}`,
"X-Timing-Read": `${t2 - t1}`,
"X-Timing-Subset": `${t3 - t2}`,
"X-Timing-Total": `${t3 - t0}`,
}, },
}), }),
}; };