fix: allow adding custom Vary to static assets handler

src/runtime/internal/static.ts

@@ -6,6 +6,7 @@ import {
   getResponseHeader,
   removeResponseHeader,
   setResponseHeader,
+  appendResponseHeader,
   setResponseStatus,
 } from "h3";
 import type { PublicAsset } from "nitropack/types";
@@ -49,7 +50,7 @@ export default eventHandler((event) => {
     "",
   ];
   if (encodings.length > 1) {
-    setResponseHeader(event, "Vary", "Accept-Encoding");
+    appendResponseHeader(event, "Vary", "Accept-Encoding");
   }
 
   for (const encoding of encodings) {

test/fixture/plugins/vary.ts

@@ -0,0 +1,10 @@
+export default defineNitroPlugin((app) => {
+  app.hooks.hook("request", (event) => {
+    if (event.path.endsWith(".css")) {
+      setResponseHeader(event, "Vary", "Origin");
+    }
+    if (event.path.endsWith(".js")) {
+      setResponseHeader(event, "Vary", ["Origin"]);
+    }
+  });
+});

test/fixture/public/foo.js

@@ -0,0 +1 @@
+const hello = "world";

test/presets/cloudflare-pages.test.ts

@@ -48,6 +48,8 @@ describe.skipIf(isWindows)("nitro:preset:cloudflare-pages", async () => {
           "/_swagger",
           "/_unignored.txt",
           "/favicon.ico",
+          "/foo.css",
+          "/foo.js",
           "/json-string",
           "/prerender",
           "/prerender-custom",

test/tests.ts

@@ -311,6 +311,43 @@ export function testNitro(
     expect(data).toMatch("<h1 >Hello JSX!</h1>");
   });
 
+  it.runIf(ctx.nitro?.options.serveStatic)(
+    "handles custom Vary header",
+    async () => {
+      let headers = (
+        await callHandler({
+          url: "/foo.css",
+          headers: { "Accept-Encoding": "gzip" },
+        })
+      ).headers;
+      if (headers["vary"])
+        expect(
+          headers["vary"].includes("Origin") &&
+            headers["vary"].includes("Accept-Encoding")
+        ).toBeTruthy();
+
+      headers = (
+        await callHandler({
+          url: "/foo.css",
+          headers: { "Accept-Encoding": "" },
+        })
+      ).headers;
+      if (headers["vary"]) expect(headers["vary"]).toBe("Origin");
+
+      headers = (
+        await callHandler({
+          url: "/foo.js",
+          headers: { "Accept-Encoding": "gzip" },
+        })
+      ).headers;
+      if (headers["vary"])
+        expect(
+          headers["vary"].includes("Origin") &&
+            headers["vary"].includes("Accept-Encoding")
+        ).toBeTruthy();
+    }
+  );
+
   it("handles route rules - headers", async () => {
     const { headers } = await callHandler({ url: "/rules/headers" });
     expect(headers["cache-control"]).toBe("s-maxage=60");