fix(server): use weak comparison for If-None-Match

packages/vinext/src/server/http-conditional.ts

@@ -0,0 +1,72 @@
+/**
+ * Test an If-None-Match field value against a current entity tag.
+ *
+ * RFC 9110 requires weak comparison for If-None-Match: a weak and strong
+ * validator with the same opaque tag compare equal.
+ */
+export function matchesIfNoneMatch(ifNoneMatch: string | undefined, etag: string): boolean {
+  if (!ifNoneMatch) return false;
+
+  const current = parseEntityTag(etag, 0);
+  if (!current || current.end !== etag.length) return false;
+  const currentOpaqueTag = etag.slice(current.opaqueStart, current.opaqueEnd);
+
+  let index = skipOptionalWhitespace(ifNoneMatch, 0);
+  if (ifNoneMatch[index] === "*") {
+    return skipOptionalWhitespace(ifNoneMatch, index + 1) === ifNoneMatch.length;
+  }
+
+  let matched = false;
+  let sawTag = false;
+  while (index < ifNoneMatch.length) {
+    // RFC 9110's list extension allows recipients to ignore empty members.
+    if (ifNoneMatch[index] === ",") {
+      index = skipOptionalWhitespace(ifNoneMatch, index + 1);
+      continue;
+    }
+
+    const candidate = parseEntityTag(ifNoneMatch, index);
+    if (!candidate) return false;
+    sawTag = true;
+    matched ||= ifNoneMatch.slice(candidate.opaqueStart, candidate.opaqueEnd) === currentOpaqueTag;
+
+    index = skipOptionalWhitespace(ifNoneMatch, candidate.end);
+    if (index === ifNoneMatch.length) break;
+    if (ifNoneMatch[index] !== ",") return false;
+    index = skipOptionalWhitespace(ifNoneMatch, index + 1);
+  }
+
+  return sawTag && matched;
+}
+
+type ParsedEntityTag = {
+  opaqueStart: number;
+  opaqueEnd: number;
+  end: number;
+};
+
+function parseEntityTag(value: string, start: number): ParsedEntityTag | null {
+  let index = start;
+  if (value.startsWith("W/", index)) index += 2;
+  if (value[index] !== '"') return null;
+
+  const opaqueStart = ++index;
+  while (index < value.length && value[index] !== '"') {
+    const code = value.charCodeAt(index);
+    // etagc = %x21 / %x23-7E / obs-text. A backslash is an ordinary
+    // character here; entity tags do not use quoted-string escaping.
+    const isEtagCharacter =
+      code === 0x21 || (code >= 0x23 && code <= 0x7e) || (code >= 0x80 && code <= 0xff);
+    if (!isEtagCharacter) return null;
+    index++;
+  }
+  if (value[index] !== '"') return null;
+
+  return { opaqueStart, opaqueEnd: index, end: index + 1 };
+}
+
+function skipOptionalWhitespace(value: string, start: number): number {
+  let index = start;
+  while (value[index] === " " || value[index] === "\t") index++;
+  return index;
+}

packages/vinext/src/server/pages-page-data.ts

@@ -16,14 +16,14 @@ import { buildPagesCacheValue, type ISRCacheEntry } from "./isr-cache.js";
 import type { PagesPreviewData } from "./pages-preview.js";
 import {
   buildPagesNextDataScript,
-  etagMatches,
   generatePagesETag,
   isPagesStreamingBot,
   requestsNoCache,
   type PagesGsspResponse,
   type PagesI18nRenderContext,
   type PagesNextDataExtras,
 } from "./pages-page-response.js";
+import { matchesIfNoneMatch } from "./http-conditional.js";
 import {
   createPagesGetInitialPropsRouter,
   hasPagesGetInitialProps,
@@ -973,7 +973,7 @@ function applyBotETagAndCheck(
   const etag = generatePagesETag(html);
   cachedResponse.headers.set("ETag", etag);
   const noCacheRequested = requestsNoCache(options.requestCacheControl);
-  if (!noCacheRequested && options.ifNoneMatch && etagMatches(etag, options.ifNoneMatch)) {
+  if (!noCacheRequested && options.ifNoneMatch && matchesIfNoneMatch(options.ifNoneMatch, etag)) {
     return {
       kind: "response",
       response: new Response(null, {

packages/vinext/src/server/pages-page-response.ts

@@ -33,6 +33,7 @@ import {
 } from "./pages-document-asset-props.js";
 import { isBotUserAgent } from "../utils/html-limited-bots.js";
 import { NEXTJS_CACHE_HEADER } from "./headers.js";
+import { matchesIfNoneMatch } from "./http-conditional.js";
 
 // ---------------------------------------------------------------------------
 // Bot / crawler detection for Pages Router edge-runtime SSR
@@ -60,28 +61,6 @@ export function generatePagesETag(payload: string): string {
   return '"' + fnv1a52(payload).toString(36) + payload.length.toString(36) + '"';
 }
 
-/**
- * Mirrors Next.js `sendEtagResponse` semantics (weak/strong comparison).
- *
- * A weak ETag `W/"..."` matches both `W/"..."` and `"..."` in `If-None-Match`.
- * A strong ETag `"..."` only matches the same strong token.
- * `*` always matches.
- */
-export function etagMatches(etag: string, ifNoneMatch: string): boolean {
-  if (ifNoneMatch === "*") return true;
-  // Normalise: strip the W/ prefix for comparison. Next.js's
-  // `sendEtagResponse` (packages/next/src/server/send-payload.ts) uses the
-  // `fresh` package, which treats a weak token in `If-None-Match` as matching
-  // the corresponding strong ETag and vice versa (RFC 7232 §2.3.2 weak
-  // comparison). We replicate that behaviour here.
-  const normalize = (t: string) => t.replace(/^W\//, "");
-  const etagNorm = normalize(etag.trim());
-  for (const token of ifNoneMatch.split(",")) {
-    if (normalize(token.trim()) === etagNorm) return true;
-  }
-  return false;
-}
-
 /**
  * Returns true when a request `Cache-Control` header asks to bypass the 304
  * short-circuit. Mirrors the `fresh` package's check used by Next.js's
@@ -768,7 +747,7 @@ export async function renderPagesPageResponse(
     const etag = generatePagesETag(fullHtml);
     responseHeaders.set("ETag", etag);
     const noCacheRequested = requestsNoCache(options.requestCacheControl);
-    if (!noCacheRequested && options.ifNoneMatch && etagMatches(etag, options.ifNoneMatch)) {
+    if (!noCacheRequested && options.ifNoneMatch && matchesIfNoneMatch(options.ifNoneMatch, etag)) {
       return new Response(null, {
         status: 304,
         headers: responseHeaders,

packages/vinext/src/server/prod-server.ts

@@ -92,6 +92,7 @@ import {
   parseAcceptedEncodings,
   selectContentEncoding,
 } from "./accept-encoding.js";
+import { matchesIfNoneMatch } from "./http-conditional.js";
 import type { NextI18nConfig } from "../config/next-config.js";
 import { readTrustedRevalidationHostname } from "./revalidation-host.js";
 
@@ -410,15 +411,6 @@ function mergeVaryHeader(
   return merged;
 }
 
-function matchesIfNoneMatchHeader(ifNoneMatch: string | undefined, etag: string): boolean {
-  if (!ifNoneMatch) return false;
-  if (ifNoneMatch === "*") return true;
-  return ifNoneMatch
-    .split(",")
-    .map((value) => value.trim())
-    .some((value) => value === etag);
-}
-
 function installClientBuildManifestGlobals(
   clientDir: string,
   assetBase: string,
@@ -633,7 +625,7 @@ async function tryServeStatic(
     if (
       responseStatus === 200 &&
       typeof ifNoneMatch === "string" &&
-      matchesIfNoneMatchHeader(ifNoneMatch, entry.etag)
+      matchesIfNoneMatch(ifNoneMatch, entry.etag)
     ) {
       const notModifiedHeaders = variesByEncoding
         ? mergeVaryHeader({ ...entry.notModifiedHeaders, ...extraHeaders }, "Accept-Encoding")
@@ -721,7 +713,7 @@ async function tryServeStatic(
     if (
       responseStatus === 200 &&
       typeof ifNoneMatch === "string" &&
-      matchesIfNoneMatchHeader(ifNoneMatch, etag)
+      matchesIfNoneMatch(ifNoneMatch, etag)
     ) {
       const notModifiedHeaders = mergeVaryHeader(baseHeaders, "Accept-Encoding");
       if (encoding !== "identity") notModifiedHeaders["Content-Encoding"] = encoding;
@@ -757,7 +749,7 @@ async function tryServeStatic(
   if (
     responseStatus === 200 &&
     typeof ifNoneMatch === "string" &&
-    matchesIfNoneMatchHeader(ifNoneMatch, etag)
+    matchesIfNoneMatch(ifNoneMatch, etag)
   ) {
     res.writeHead(
       304,

tests/http-conditional.test.ts

@@ -0,0 +1,69 @@
+import { describe, expect, it } from "vitest";
+import { matchesIfNoneMatch } from "../packages/vinext/src/server/http-conditional.js";
+
+describe("matchesIfNoneMatch", () => {
+  it("matches an identical entity tag", () => {
+    expect(matchesIfNoneMatch('"asset"', '"asset"')).toBe(true);
+  });
+
+  it("uses weak comparison in either direction", () => {
+    expect(matchesIfNoneMatch('"asset"', 'W/"asset"')).toBe(true);
+    expect(matchesIfNoneMatch('W/"asset"', '"asset"')).toBe(true);
+  });
+
+  it("matches a validator within a comma-separated field value", () => {
+    expect(matchesIfNoneMatch('"other", W/"asset", "last"', '"asset"')).toBe(true);
+  });
+
+  it("does not split commas inside an opaque tag", () => {
+    // RFC 9110 permits commas in opaque tags. This is intentionally stricter
+    // than Next.js 16.2.7's compiled `fresh` parser, which splits every comma.
+    expect(matchesIfNoneMatch('"other", W/"asset,part"', '"asset,part"')).toBe(true);
+    expect(matchesIfNoneMatch('"asset,part"', '"asset"')).toBe(false);
+  });
+
+  it("treats backslashes as opaque characters rather than escapes", () => {
+    expect(matchesIfNoneMatch('W/"asset\\part"', '"asset\\part"')).toBe(true);
+  });
+
+  it("matches a wildcard with optional whitespace", () => {
+    expect(matchesIfNoneMatch(" \t * \t ", 'W/"asset"')).toBe(true);
+  });
+
+  it("rejects a wildcard mixed into an entity-tag list", () => {
+    expect(matchesIfNoneMatch('*, "asset"', '"asset"')).toBe(false);
+    expect(matchesIfNoneMatch('"other", *', '"asset"')).toBe(false);
+  });
+
+  it("does not match different opaque tags or case", () => {
+    expect(matchesIfNoneMatch('"other"', '"asset"')).toBe(false);
+    expect(matchesIfNoneMatch('"ASSET"', '"asset"')).toBe(false);
+  });
+
+  it("does not treat a lowercase weak prefix as W/", () => {
+    expect(matchesIfNoneMatch('w/"asset"', '"asset"')).toBe(false);
+  });
+
+  it("rejects malformed entity tags", () => {
+    expect(matchesIfNoneMatch('asset, "match"', '"match"')).toBe(false);
+    expect(matchesIfNoneMatch('"match", garbage', '"match"')).toBe(false);
+    expect(matchesIfNoneMatch('"unterminated', '"unterminated"')).toBe(false);
+    expect(matchesIfNoneMatch('W/ "asset"', '"asset"')).toBe(false);
+    expect(matchesIfNoneMatch('"asset" suffix', '"asset"')).toBe(false);
+    expect(matchesIfNoneMatch('"asset\x7fpart"', '"asset\x7fpart"')).toBe(false);
+  });
+
+  it("ignores empty list members", () => {
+    expect(matchesIfNoneMatch(' , W/"asset", ', '"asset"')).toBe(true);
+  });
+
+  it("rejects an invalid current entity tag", () => {
+    expect(matchesIfNoneMatch('"asset"', "asset")).toBe(false);
+    expect(matchesIfNoneMatch('"asset"', 'W/ "asset"')).toBe(false);
+  });
+
+  it("rejects an absent or empty field value", () => {
+    expect(matchesIfNoneMatch(undefined, '"asset"')).toBe(false);
+    expect(matchesIfNoneMatch("", '"asset"')).toBe(false);
+  });
+});

tests/pages-page-response.test.ts

@@ -4,7 +4,6 @@ import {
   renderPagesPageResponse,
   isPagesStreamingBot,
   generatePagesETag,
-  etagMatches,
 } from "../packages/vinext/src/server/pages-page-response.js";
 import { resolvePagesPageData } from "../packages/vinext/src/server/pages-page-data.js";
 
@@ -1030,7 +1029,7 @@ describe("pages page response", () => {
   // If-None-Match / 304 handling and ISR cache-HIT ETag
   // ---------------------------------------------------------------------------
 
-  it("returns 304 when If-None-Match matches ETag on bot response (fresh-MISS path)", async () => {
+  it("returns 304 for a weak If-None-Match on a strong bot ETag", async () => {
     const common = createCommonOptions();
 
     // First request: compute the ETag from a full bot render.
@@ -1041,12 +1040,12 @@ describe("pages page response", () => {
     const etag = firstResponse.headers.get("etag");
     expect(etag).toBeTruthy();
 
-    // Second request: send If-None-Match matching the ETag.
+    // Second request: send the strong ETag as a weak validator.
     const common2 = createCommonOptions();
     const notModifiedResponse = await renderPagesPageResponse({
       ...common2.options,
       userAgent: "Googlebot",
-      ifNoneMatch: etag as string,
+      ifNoneMatch: `W/${etag}`,
     });
 
     expect(notModifiedResponse.status).toBe(304);
@@ -1095,14 +1094,6 @@ describe("pages page response", () => {
     expect(browserResponse.headers.get("etag")).toBeNull();
   });
 
-  it("ETag weak-comparison: W/ prefix is ignored when matching If-None-Match", async () => {
-    expect(etagMatches('"abc123"', 'W/"abc123"')).toBe(true);
-    expect(etagMatches('W/"abc123"', '"abc123"')).toBe(true);
-    expect(etagMatches('"abc123"', '"abc123"')).toBe(true);
-    expect(etagMatches('"abc123"', '"other"')).toBe(false);
-    expect(etagMatches('"abc123"', "*")).toBe(true);
-  });
-
   it("attaches ETag to ISR cache-HIT response for bot UAs", async () => {
     // Build a fake cached ISR entry and confirm that cache-HIT + bot UA yields ETag.
     const cachedHtml =

tests/serve-static.test.ts

@@ -338,14 +338,15 @@ describe("tryServeStatic (with StaticFileCache)", () => {
 
   // ── 304 Not Modified (conditional requests) ────────────────────
 
-  it("returns 304 when If-None-Match matches the ETag", async () => {
+  it("returns 304 when a strong If-None-Match matches a weak ETag", async () => {
     await writeFile(clientDir, "_next/static/cached-aaa111.js", "cached content");
 
     const cache = await StaticFileCache.create(clientDir);
     const entry = cache.lookup("/_next/static/cached-aaa111.js");
     const etag = entry!.etag;
+    expect(etag).toMatch(/^W\//);
 
-    const req = mockReq(undefined, { "if-none-match": etag });
+    const req = mockReq(undefined, { "if-none-match": etag.slice(2) });
     const { res, captured } = mockRes();
 
     const served = await tryServeStatic(