HttpResponseStream.js

/**
 * Copyright 2022 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * HttpResponseStream is NOT used by the runtime.
 * It is only exposed in the `awslambda` variable for customers to use.
 */

'use strict';

const METADATA_PRELUDE_CONTENT_TYPE =
  'application/vnd.awslambda.http-integration-response';
const DELIMITER_LEN = 8;

// Implements the application/vnd.awslambda.http-integration-response content type.
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;