fix zlib deflate on fetch (#4483)

* fix zlib deflate on fetch

* mention issue on test

* more tests

* oops

3 files changed, 47 insertions, 8 deletions

diff --git a/src/http_client_async.zig b/src/http_client_async.zig
index 8a0e6548c..160a35716 100644
--- a/src/http_client_async.zig
+++ b/src/http_client_async.zig
@@ -1155,9 +1155,9 @@ pub const InternalState = struct {
                     // TODO: add br support today we support gzip and deflate only
                     // zlib.MAX_WBITS = 15
                     // to (de-)compress deflate format, use wbits = -zlib.MAX_WBITS
-                    // to (de-)compress zlib format, use wbits = zlib.MAX_WBITS
+                    // to (de-)compress deflate format with headers we use wbits = 0 (we can detect the first byte using 120)
                     // to (de-)compress gzip format, use wbits = zlib.MAX_WBITS | 16
-                    .windowBits = if (this.encoding == Encoding.gzip) Zlib.MAX_WBITS | 16 else -Zlib.MAX_WBITS,
+                    .windowBits = if (this.encoding == Encoding.gzip) Zlib.MAX_WBITS | 16 else (if (buffer.len > 1 and buffer[0] == 120) 0 else -Zlib.MAX_WBITS),
                 },
             );
             this.zlib_reader = reader;
diff --git a/src/zlib.zig b/src/zlib.zig
index 6b2e9dc48..090d0f3a0 100644
--- a/src/zlib.zig
+++ b/src/zlib.zig
@@ -439,7 +439,8 @@ pub const ZlibReaderArrayList = struct {
     }
 
     pub fn end(this: *ZlibReader) void {
-        if (this.state == State.Inflating) {
+        // always free with `inflateEnd`
+        if (this.state != State.End) {
             _ = inflateEnd(&this.zlib);
             this.state = State.End;
         }
@@ -846,7 +847,7 @@ pub const ZlibCompressorArrayList = struct {
     }
 
     pub fn end(this: *ZlibCompressor) void {
-        if (this.state == State.Inflating) {
+        if (this.state != State.End) {
             _ = deflateEnd(&this.zlib);
             this.state = State.End;
         }
@@ -981,13 +982,13 @@ pub const ZlibCompressorArrayList = struct {
 
             switch (rc) {
                 ReturnCode.StreamEnd => {
-                    this.state = State.End;
                     this.list.items.len = this.zlib.total_out;
-
                     this.end();
+
                     return;
                 },
                 ReturnCode.MemError => {
+                    this.end();
                     this.state = State.Error;
                     return error.OutOfMemory;
                 },
@@ -998,6 +999,7 @@ pub const ZlibCompressorArrayList = struct {
                 ReturnCode.VersionError,
                 ReturnCode.ErrNo,
                 => {
+                    this.end();
                     this.state = State.Error;
                     return error.ZlibError;
                 },
diff --git a/test/js/web/fetch/fetch.stream.test.ts b/test/js/web/fetch/fetch.stream.test.ts
index dc082fd2f..49cc0dd6a 100644
--- a/test/js/web/fetch/fetch.stream.test.ts
+++ b/test/js/web/fetch/fetch.stream.test.ts
@@ -3,7 +3,7 @@ import { readFileSync } from "fs";
 import { join } from "path";
 import { describe, expect, it } from "bun:test";
 import { gcTick } from "harness";
-
+import zlib from "zlib";
 const fixtures = {
   "fixture": readFileSync(join(import.meta.dir, "fixture.html")),
   "fixture.png": readFileSync(join(import.meta.dir, "fixture.png")),
@@ -17,6 +17,40 @@ const smallText = Buffer.from("Hello".repeat(16));
 const empty = Buffer.alloc(0);
 
 describe("fetch() with streaming", () => {
+  it("can deflate with and without headers #4478", async () => {
+    let server: Server | null = null;
+    try {
+      server = Bun.serve({
+        port: 0,
+        fetch(req) {
+          if (req.url.endsWith("/with_headers")) {
+            const content = zlib.deflateSync(Buffer.from("Hello, World"));
+            return new Response(content, {
+              headers: {
+                "Content-Type": "text/plain",
+                "Content-Encoding": "deflate",
+                "Access-Control-Allow-Origin": "*",
+              },
+            });
+          }
+          const content = zlib.deflateRawSync(Buffer.from("Hello, World"));
+          return new Response(content, {
+            headers: {
+              "Content-Type": "text/plain",
+              "Content-Encoding": "deflate",
+              "Access-Control-Allow-Origin": "*",
+            },
+          });
+        },
+      });
+      const url = `http://${server.hostname}:${server.port}/`;
+      expect(await fetch(`${url}with_headers`).then(res => res.text())).toBe("Hello, World");
+      expect(await fetch(url).then(res => res.text())).toBe("Hello, World");
+    } finally {
+      server?.stop();
+    }
+  });
+
   it("stream still works after response get out of scope", async () => {
     let server: Server | null = null;
     try {
@@ -467,12 +501,13 @@ describe("fetch() with streaming", () => {
     }
   }
 
-  type CompressionType = "no" | "gzip" | "deflate" | "br";
+  type CompressionType = "no" | "gzip" | "deflate" | "br" | "deflate_with_headers";
   type TestType = { headers: Record<string, string>; compression: CompressionType; skip?: boolean };
   const types: Array<TestType> = [
     { headers: {}, compression: "no" },
     { headers: { "Content-Encoding": "gzip" }, compression: "gzip" },
     { headers: { "Content-Encoding": "deflate" }, compression: "deflate" },
+    { headers: { "Content-Encoding": "deflate" }, compression: "deflate_with_headers" },
     // { headers: { "Content-Encoding": "br" }, compression: "br", skip: true }, // not implemented yet
   ];
 
@@ -482,6 +517,8 @@ describe("fetch() with streaming", () => {
         return Bun.gzipSync(data);
       case "deflate":
         return Bun.deflateSync(data);
+      case "deflate_with_headers":
+        return zlib.deflateSync(data);
       default:
         return data;
     }