v4: the API's JSON and the page are sent compressed — a page of the feed went out as it was, twenty kilobytes where a fifth does: only the built frontend's files were compressed, at build time, and Deno's server leaves alone a response whose length Oak has set. compressMiddleware (api/middleware/compress.ts), installed after the error middleware and around everything that sets a body, sends an object or array, and a string whose type its route set, in brotli or gzip as the request's Accept-Encoding takes, a coding refused with q=0 not being taken, from a kilobyte up, the threshold the build compresses from. Brotli is at quality 5, the frontend's files, compressed once, staying at 11. Files, streams and bytes, a response already encoded, a HEAD and one marked no-transform go out as they are, and a compressible answer says Vary: Accept-Encoding whether compressed or not.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

api/test/middleware/compress.test.ts

@@ -0,0 +1,90 @@
+import { BASE_URL } from "../helpers.ts";
+import { assertEquals } from "@std/assert";
+import { Application } from "@oak/oak";
+import { brotliDecompressSync, gunzipSync } from "node:zlib";
+import { compressMiddleware } from "../../middleware/compress.ts";
+
+const BIG = { success: true, data: { items: Array(200).fill("dump title") } };
+
+function makeApp(): Application {
+  const app = new Application();
+  app.use(compressMiddleware);
+  app.use((ctx) => {
+    const path = ctx.request.url.pathname;
+    if (path === "/big") ctx.response.body = BIG;
+    if (path === "/small") ctx.response.body = { success: true };
+    if (path === "/html") {
+      ctx.response.type = "text/html";
+      ctx.response.body = `<!doctype html>${"<p>gerbeur</p>".repeat(200)}`;
+    }
+    if (path === "/bytes") ctx.response.body = new Uint8Array(4096);
+    if (path === "/encoded") {
+      ctx.response.headers.set("Content-Encoding", "br");
+      ctx.response.type = "text/css";
+      ctx.response.body = "x".repeat(4096);
+    }
+  });
+  return app;
+}
+
+async function get(path: string, acceptEncoding?: string) {
+  const res = await makeApp().handle(
+    new Request(`${BASE_URL}${path}`, {
+      headers: acceptEncoding ? { "Accept-Encoding": acceptEncoding } : {},
+    }),
+  );
+  if (!res) throw new Error("no response");
+  return { res, bytes: new Uint8Array(await res.arrayBuffer()) };
+}
+
+const text = (bytes: Uint8Array) => new TextDecoder().decode(bytes);
+
+Deno.test("compressMiddleware: JSON goes out in brotli, or gzip for a client without it", async () => {
+  const br = await get("/big", "gzip, deflate, br");
+  assertEquals(br.res.headers.get("Content-Encoding"), "br");
+  assertEquals(
+    br.res.headers.get("Content-Type"),
+    "application/json; charset=UTF-8",
+  );
+  assertEquals(br.res.headers.get("Vary"), "Accept-Encoding");
+  assertEquals(JSON.parse(text(brotliDecompressSync(br.bytes))), BIG);
+
+  const gzip = await get("/big", "gzip");
+  assertEquals(gzip.res.headers.get("Content-Encoding"), "gzip");
+  assertEquals(JSON.parse(text(gunzipSync(gzip.bytes))), BIG);
+
+  const refused = await get("/big", "br;q=0, gzip;q=0.5");
+  assertEquals(refused.res.headers.get("Content-Encoding"), "gzip");
+});
+
+Deno.test("compressMiddleware: a client that accepts no coding gets the JSON as it is", async () => {
+  for (const accept of [undefined, "identity", "br;q=0"]) {
+    const { res, bytes } = await get("/big", accept);
+    assertEquals(res.headers.get("Content-Encoding"), null);
+    // A cache still has to tell this answer from the compressed one.
+    assertEquals(res.headers.get("Vary"), "Accept-Encoding");
+    assertEquals(JSON.parse(text(bytes)), BIG);
+  }
+});
+
+Deno.test("compressMiddleware: the HTML page is compressed too", async () => {
+  const { res, bytes } = await get("/html", "br");
+  assertEquals(res.headers.get("Content-Encoding"), "br");
+  assertEquals(res.headers.get("Content-Type"), "text/html; charset=UTF-8");
+  assertEquals(text(brotliDecompressSync(bytes)).startsWith("<!doctype"), true);
+});
+
+Deno.test("compressMiddleware: short answers, bytes and encoded files are left alone", async () => {
+  const small = await get("/small", "br");
+  assertEquals(small.res.headers.get("Content-Encoding"), null);
+  assertEquals(small.res.headers.get("Vary"), null);
+  assertEquals(JSON.parse(text(small.bytes)), { success: true });
+
+  const bytes = await get("/bytes", "br");
+  assertEquals(bytes.res.headers.get("Content-Encoding"), null);
+  assertEquals(bytes.bytes.length, 4096);
+
+  const encoded = await get("/encoded", "br");
+  assertEquals(encoded.res.headers.get("Content-Encoding"), "br");
+  assertEquals(text(encoded.bytes), "x".repeat(4096));
+});