fetch: resolve empty compressed responses as empty bodies

src/http/InternalState.rs

@@ -243,6 +243,15 @@ impl<'a> InternalState<'a> {
         body_out_str: &mut MutableString,
         is_final_chunk: bool,
     ) -> Result<(), Error> {
+        // A response that declared a Content-Encoding but sent zero body bytes
+        // (e.g. an empty chunked gzip response) has nothing to decompress.
+        // Running the decompressor anyway makes it report a truncated stream
+        // (ZlibError); Node treats this as an empty body.
+        if buffer.is_empty() && self.total_body_received == 0 {
+            self.compressed_body.reset();
+            return Ok(());
+        }
+
         // PORT NOTE: Zig `defer this.compressed_body.reset()` runs on every exit. scopeguard would
         // hold &mut self.compressed_body across the body and conflict with &mut self.decompressor,
         // so each early-return below calls `self.compressed_body.reset()` explicitly.

test/js/web/fetch/fetch-gzip.test.ts

@@ -3,6 +3,7 @@ import { beforeAll, describe, expect, it } from "bun:test";
 import { gcTick } from "harness";
 import { once } from "node:events";
 import { createServer } from "node:http";
+import { createServer as createNetServer } from "node:net";
 import { brotliCompressSync, deflateSync, gzipSync, zstdCompressSync } from "node:zlib";
 import path from "path";
 
@@ -197,7 +198,9 @@ it("fetch() with a gzip response works (multiple chunks, TCP server)", async don
   let pending,
     pendingChunks = [];
   const server = Bun.listen({
-    hostname: "localhost",
+    // Explicit IPv4 loopback: "localhost" may bind only ::1 while fetch()
+    // resolves it to 127.0.0.1, giving ConnectionRefused on some hosts.
+    hostname: "127.0.0.1",
     port: 0,
     socket: {
       drain(socket) {
@@ -293,3 +296,27 @@ it("fetch() with a gzip response works (multiple chunks, TCP server)", async don
   server.stop();
   done();
 });
+
+describe("empty compressed responses", () => {
+  // A response that declares Content-Encoding but sends zero body bytes must
+  // resolve as an empty body, like Node — not fail with ZlibError.
+  // https://github.com/oven-sh/bun/issues/23149
+  for (const [name, write] of Object.entries({
+    "chunked": `HTTP/1.1 200 OK\r\nContent-Encoding: gzip\r\nTransfer-Encoding: chunked\r\n\r\n0\r\n\r\n`,
+    "content-length-0": `HTTP/1.1 200 OK\r\nContent-Encoding: gzip\r\nContent-Length: 0\r\n\r\n`,
+  })) {
+    it(`empty gzip body via ${name} resolves as empty`, async () => {
+      // end() rather than write(): FIN the connection after the response so
+      // nothing is left parked in the keep-alive pool when the server closes.
+      const raw = createNetServer(socket => void socket.end(write));
+      await new Promise<void>(resolve => raw.listen(0, () => resolve()));
+      const port = (raw.address() as { port: number }).port;
+      try {
+        const res = await fetch(`http://127.0.0.1:${port}/`);
+        expect(await res.text()).toBe("");
+      } finally {
+        raw.close();
+      }
+    });
+  }
+});