fix(web-outgoing): strip transfer-encoding on 204/304

src/middleware/web-outgoing.ts

@@ -5,11 +5,17 @@ import { type ProxyOutgoingMiddleware, defineProxyOutgoingMiddleware } from "./_
 const redirectRegex = /^201|30([1278])$/;
 
 /**
- * Remove chunked transfer-encoding for HTTP/1.0 and HTTP/2 requests
+ * Remove chunked transfer-encoding for HTTP/1.0, HTTP/2, and bodyless (204/304) responses
  */
 export const removeChunked = defineProxyOutgoingMiddleware((req, res, proxyRes) => {
   // HTTP/1.0 and HTTP/2 do not have transfer-encoding: chunked
-  if (req.httpVersion === "1.0" || req.httpVersionMajor >= 2) {
+  // 204 and 304 responses MUST NOT contain a message body (RFC 9110)
+  if (
+    req.httpVersion === "1.0" ||
+    req.httpVersionMajor >= 2 ||
+    proxyRes.statusCode === 204 ||
+    proxyRes.statusCode === 304
+  ) {
     delete proxyRes.headers["transfer-encoding"];
   }
 });

test/middleware/web-outgoing.test.ts

@@ -651,7 +651,7 @@
       const res = {
         setHeader(k: string, v: string | string[]) {
           // Simulate Node.js ERR_INVALID_CHAR for control characters
           if (typeof v === "string" && /[\u0000-\u001F]/.test(v)) {
             throw new TypeError(`Invalid character in header content ["${k}"]`);
           }
           headers[k.toLowerCase()] = v;
@@ -692,18 +692,68 @@
     });
   });
 
-  it("#removeChunked", () => {
-    const proxyRes = {
-      headers: {
-        "transfer-encoding": "hello",
-      },
-    };
-    webOutgoing.removeChunked(
-      stubIncomingMessage({ httpVersion: "1.0" }),
-      stubServerResponse(),
-      proxyRes as any,
-      stubMiddlewareOptions(),
-    );
-    expect(proxyRes.headers["transfer-encoding"]).to.eql(undefined);
+  describe("#removeChunked", () => {
+    it("removes transfer-encoding on HTTP/1.0", () => {
+      const proxyRes = {
+        headers: {
+          "transfer-encoding": "hello",
+        },
+      };
+      webOutgoing.removeChunked(
+        stubIncomingMessage({ httpVersion: "1.0" }),
+        stubServerResponse(),
+        proxyRes as any,
+        stubMiddlewareOptions(),
+      );
+      expect(proxyRes.headers["transfer-encoding"]).to.eql(undefined);
+    });
+
+    it("removes transfer-encoding on 204 response", () => {
+      const proxyRes = {
+        statusCode: 204,
+        headers: {
+          "transfer-encoding": "chunked",
+        },
+      };
+      webOutgoing.removeChunked(
+        stubIncomingMessage({ httpVersion: "1.1" }),
+        stubServerResponse(),
+        proxyRes as any,
+        stubMiddlewareOptions(),
+      );
+      expect(proxyRes.headers["transfer-encoding"]).to.eql(undefined);
+    });
+
+    it("removes transfer-encoding on 304 response", () => {
+      const proxyRes = {
+        statusCode: 304,
+        headers: {
+          "transfer-encoding": "chunked",
+        },
+      };
+      webOutgoing.removeChunked(
+        stubIncomingMessage({ httpVersion: "1.1" }),
+        stubServerResponse(),
+        proxyRes as any,
+        stubMiddlewareOptions(),
+      );
+      expect(proxyRes.headers["transfer-encoding"]).to.eql(undefined);
+    });
+
+    it("preserves transfer-encoding on normal HTTP/1.1 responses", () => {
+      const proxyRes = {
+        statusCode: 200,
+        headers: {
+          "transfer-encoding": "chunked",
+        },
+      };
+      webOutgoing.removeChunked(
+        stubIncomingMessage({ httpVersion: "1.1" }),
+        stubServerResponse(),
+        proxyRes as any,
+        stubMiddlewareOptions(),
+      );
+      expect(proxyRes.headers["transfer-encoding"]).to.eql("chunked");
+    });
   });
 });