export const handler: StreamifyHandler = awslambda.streamifyResponse(
    async (event: unknown, responseStream: awslambda.HttpResponseStream, context: Context) =>
        const requestStream = Readable.from(Buffer.from(JSON.stringify(event)));
        await pipeline(requestStream, responseStream);
);

declare global {
    namespace awslambda {
        class HttpResponseStream extends Writable {
            static from(
                writable: Writable,
                metadata: Record<string, unknown>,
            ): HttpResponseStream;
            setContentType: (contentType: string) => void;
        }

// ...

class HttpResponseStream {
  static from(underlyingStream, prelude) {
    underlyingStream.setContentType(METADATA_PRELUDE_CONTENT_TYPE);
    
    // JSON.stringify is required. NULL byte is not allowed in metadataPrelude.
    const metadataPrelude = JSON.stringify(prelude);

    underlyingStream._onBeforeFirstWrite = (write) => {
      write(metadataPrelude);

      // Write 8 null bytes after the JSON prelude.
      write(new Uint8Array(DELIMITER_LEN));
    };

    return underlyingStream;
  }
}

module.exports.HttpResponseStream = HttpResponseStream;

declare global {
    namespace awslambda {
        // Extending Writable is still not strictly correct because the lambda version 
        // does not implement several `Writable` methods such as `fromWeb` but it's
        // probably the most pragmatic way to deal with this Stream-like object
        class ResponseStream extends Writable {
          setContentType: (contentType: string) => void;
          _onBeforeFirstWrite: (write: (data: any) => void) => void;
        }

        class HttpResponseStream {
            static from(
                writable: ResponseStream,
                metadata: Record<string, unknown>,
            ): ResponseStream;
        }

// ...