Missing http.ServerResponse.flushHeaders function

[alexluke]

We have a nextjs 14.0.2 app that is built in standalone mode. We're using nginx unit for TLS termination.

When responding to a request, the following error is thrown.

2023/11/15 13:58:32 [info] 70#70 discovery started
2023/11/15 13:58:32 [notice] 70#70 no modules matching: "/usr/lib/unit/modules/*.unit.so" found
2023/11/15 13:58:32 [info] 1#1 controller started
2023/11/15 13:58:32 [notice] 1#1 process 70 exited with code 0
2023/11/15 13:58:32 [info] 72#72 router started
2023/11/15 13:58:32 [info] 72#72 OpenSSL 1.1.1w  11 Sep 2023, 1010117f
2023/11/15 13:58:32 [info] 73#73 "nextjs" prototype started
2023/11/15 13:58:32 [info] 74#74 "nextjs" application started
(node:74) ExperimentalWarning: `--experimental-loader` may be removed in the future; instead use `register()`:
--import 'data:text/javascript,import { register } from "node:module"; import { pathToFileURL } from "node:url"; register("unit-http/loader.mjs", pathToFileURL("./"));'
(Use `node --trace-warnings ...` to show where the warning was created)
   ▲ Next.js 14.0.2
   - Local:        http://95e6f3d5ed03:80
   - Network:      http://127.0.0.1:80

 ✓ Ready in 40ms
 ⨯ Error: failed to pipe response
    at ei (/app/node_modules/next/dist/compiled/next-server/app-page.runtime.prod.js:12:210527)
    at runNextTicks (node:internal/process/task_queues:60:5)
    at listOnTimeout (node:internal/timers:540:9)
    at process.processTimers (node:internal/timers:514:7)
    at async es.pipeToNodeResponse (/app/node_modules/next/dist/compiled/next-server/app-page.runtime.prod.js:12:212125)
    at async sendRenderResult (/app/node_modules/next/dist/server/send-payload.js:83:5)
    at async NextNodeServer.pipeImpl (/app/node_modules/next/dist/server/base-server.js:917:13)
    at async NextNodeServer.handleCatchallRenderRequest (/app/node_modules/next/dist/server/next-server.js:266:17)
    at async NextNodeServer.handleRequestImpl (/app/node_modules/next/dist/server/base-server.js:798:17) {
  [cause]: TypeError: e.flushHeaders is not a function
      at Object.write (/app/node_modules/next/dist/compiled/next-server/app-page.runtime.prod.js:12:210155)
      at ensureIsPromise (node:internal/webstreams/util:185:19)
      at writableStreamDefaultControllerProcessWrite (node:internal/webstreams/writablestream:1109:5)
      at writableStreamDefaultControllerAdvanceQueueIfNeeded (node:internal/webstreams/writablestream:1224:5)
      at writableStreamDefaultControllerWrite (node:internal/webstreams/writablestream:1098:3)
      at writableStreamDefaultWriterWrite (node:internal/webstreams/writablestream:988:3)
      at [kChunk] (node:internal/webstreams/readablestream:1545:31)
      at readableStreamFulfillReadRequest (node:internal/webstreams/readablestream:2087:24)
      at readableStreamDefaultControllerEnqueue (node:internal/webstreams/readablestream:2278:5)
      at transformStreamDefaultControllerEnqueue (node:internal/webstreams/transformstream:486:5)

This appears to be because the flushHeaders method doesn't exist on the ServerResponse under nginx unit. The app runs fine when using node's own http module.

https://github.com/vercel/next.js/blob/v14.0.2/packages/next/src/server/pipe-readable.ts#L48

https://nodejs.org/api/http.html#responseflushheaders

Please let me know what other detail would be helpful.

[andrey-zelenkov]

Hi @alexluke, thank you for your report.

Could you please try following patch if it works for you:

--- a/src/nodejs/unit-http/http_server.js
+++ b/src/nodejs/unit-http/http_server.js
@@ -160,6 +160,10 @@ ServerResponse.prototype._removeHeader =
     this.headers_len -= name_len + Buffer.byteLength(value + "", 'latin1');
 };

+ServerResponse.prototype.flushHeaders = function flushHeaders() {
+    this._sendHeaders();
+}
+
 ServerResponse.prototype.sendDate = function sendDate() {
     throw new Error("Not supported");
 };

[ac000]

--- a/src/nodejs/unit-http/http_server.js
+++ b/src/nodejs/unit-http/http_server.js
@@ -160,6 +160,10 @@ ServerResponse.prototype._removeHeader =
     this.headers_len -= name_len + Buffer.byteLength(value + "", 'latin1');
 };

+ServerResponse.prototype.flushHeaders = function flushHeaders() {
+    this._sendHeaders();
+}

Any reason there's no trailing ; here?

[andrey-zelenkov]

No, it was just my inattention. Thank you for noticing! Additionally, I've moved this code slightly higher to reduce the confusion between private and public methods ordering for headers:

diff --git a/src/nodejs/unit-http/http_server.js b/src/nodejs/unit-http/http_server.js
--- a/src/nodejs/unit-http/http_server.js
+++ b/src/nodejs/unit-http/http_server.js
@@ -138,6 +138,10 @@ ServerResponse.prototype.removeHeader = 
     }
 };

+ServerResponse.prototype.flushHeaders = function flushHeaders() {
+    this._sendHeaders();
+};
+
 ServerResponse.prototype._removeHeader = function _removeHeader(lc_name) {
     let entry = this.headers[lc_name];
     let name_len = Buffer.byteLength(entry[0] + "", 'latin1');

[ac000]

I can't honestly say whether this is correct or not, but it looks simple enough, so assuming it works... consider it...

Reviewed-by: Andrew Clayton <a.clayton@nginx.com>