aws / aws/aws-lambda-nodejs-runtime-interface-client

HttpResponseStream doesn't work when `end`ing the stream without a `write`

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Mô tả

When using `HttpResponseStream` to set the status code and headers on a streaming response, I noticed that if I never call `write` on the stream, the custom status code and headers don't work.

Example repro:

```js
export const handler = awslambda.streamifyResponse(
async (event, responseStream, context) => {
const metadata = {
statusCode: 404,
headers: { "Content-Type": "text/plain", "X-Foo": "Bar" }
};
responseStream = awslambda.HttpResponseStream.from(responseStream, metadata);
// This will cause a 502 with no custom response headers:
responseStream.end("Not Found");
// This will cause a 200 with no custom response headers:
responseStream.end();
}
);
```

I believe this is because `HttpResponseStream` relies on the `onBeforeFirstWrite` callback:

https://github.com/aws/aws-lambda-nodejs-runtime-interface-client/blob/7374a4e338fc3b070811d55ee337740f3f6cb382/src/HttpResponseStream.js#L22-L27

`onBeforeFirstWrite` is implemented by overriding http.ClientRequest stream's `write`:

```js
// https://github.com/aws/aws-lambda-base-images/tree/nodejs18.x -> /var/runtime/index.mjs
req.write = function(chunk, encoding, callback) {
vvverbose("ResponseStream::write", chunk.length, "callback:", typeof callback);
if (typeof chunk !== "string" && !Buffer.isBuffer(chunk) && chunk?.constructor !== Uint8Array) {
chunk = JSON.stringify(chunk);
}
if (status === STATUS_READY && typeof this._onBeforeFirstWrite === "function") {
this._onBeforeFirstWrite((ch) => origWrite(ch));
}
const ret = origWrite(chunk, encoding, callback);
// [snip]
```

But turns out Node's `ClientRequest` doesn't call `write` when `end`ing the stream with a final `chunk` of data, it calls an internal `write_` instead:

https://github.com/nodejs/node/blob/544cfc5ef151bca8d625fbccc581200a77b00bc0/lib/_http_outgoing.js#L1106

I guess this could also be considered a Node bug, because their documentation for [`ClientRequest.end`](https://nodejs.org/docs/latest/api/http.html#requestenddata-encoding-callback) says:

> If `data` is specified, it is equivalent to calling [`request.write(data, encoding)`](https://nodejs.org/docs/latest/api/http.html#requestwritechunk-encoding-callback) followed by `request.end(callback)`.

But even if it did implement that contract correctly, there's still the case of ending the stream with no data, i.e., `responseStream.end()`.

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