fix: omit content headers from cached 304 responses (#7637)

test/backend-test/test-apicache.js

@@ -0,0 +1,57 @@
+const { after, before, describe, test } = require("node:test");
+const assert = require("node:assert");
+const http = require("node:http");
+const apicache = require("../../server/modules/apicache/apicache").newInstance();
+
+/**
+ * Request the test server.
+ * @param {number} port Server port
+ * @param {object} headers Request headers
+ * @returns {Promise<import("node:http").IncomingMessage>} Server response
+ */
+function request(port, headers = {}) {
+    return new Promise((resolve, reject) => {
+        const req = http.request({ port, path: "/cached", headers }, resolve);
+        req.on("error", reject);
+        req.end();
+    });
+}
+
+describe("API cache", () => {
+    let server;
+    let port;
+
+    before(async () => {
+        const cache = apicache.middleware("1 minute");
+        server = http.createServer((req, res) => {
+            cache(req, res, () => {
+                const body = "cached body";
+                res.setHeader("Content-Type", "text/plain");
+                res.setHeader("Content-Length", Buffer.byteLength(body));
+                res.setHeader("ETag", '"cached"');
+                res.end(body);
+            });
+        });
+        await new Promise((resolve) => server.listen(0, resolve));
+        port = server.address().port;
+    });
+
+    after(async () => {
+        apicache.clear("/cached");
+        await new Promise((resolve) => server.close(resolve));
+    });
+
+    test("cached response omits representation headers for a matching ETag", async () => {
+        const warmResponse = await request(port);
+        warmResponse.resume();
+        await new Promise((resolve) => warmResponse.on("end", resolve));
+
+        const response = await request(port, { "If-None-Match": '"cached"' });
+        response.resume();
+
+        assert.strictEqual(response.statusCode, 304);
+        assert.strictEqual(response.headers.etag, '"cached"');
+        assert.strictEqual(response.headers["content-length"], undefined);
+        assert.strictEqual(response.headers["content-type"], undefined);
+    });
+});