react-native/packager/react-packager/src/Server/MultipartResponse.js

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 */
'use strict';

const CRLF = '\r\n';
const BOUNDARY = '3beqjf3apnqeu3h5jqorms4i';

class MultipartResponse {
  static wrap(req, res) {
    if (acceptsMultipartResponse(req)) {
      return new MultipartResponse(res);
    }
    // Ugly hack, ideally wrap function should always return a proxy
    // object with the same interface
    res.writeChunk = () => {}; // noop
    return res;
  }

  constructor(res) {
    this.res = res;
    this.headers = {};

    res.writeHead(200, {
      'Content-Type': `multipart/mixed; boundary="${BOUNDARY}"`,
    });
    res.write('If you are seeing this, your client does not support multipart response');
  }

  writeChunk(headers, data, isLast = false) {
    let chunk = `${CRLF}--${BOUNDARY}${CRLF}`;
    if (headers) {
      chunk += MultipartResponse.serializeHeaders(headers) + CRLF + CRLF;
    }

    if (data) {
      chunk += data;
    }

    if (isLast) {
      chunk += `${CRLF}--${BOUNDARY}--${CRLF}`;
    }

    this.res.write(chunk);
  }

  writeHead(status, headers) {
    // We can't actually change the response HTTP status code
    // because the headers have already been sent
    this.setHeader('X-Http-Status', status);
    if (!headers) {
      return;
    }
    for (const key in headers) {
      this.setHeader(key, headers[key]);
    }
  }

  setHeader(name, value) {
    this.headers[name] = value;
  }

  end(data) {
    this.writeChunk(this.headers, data, true);
    this.res.end();
  }

  static serializeHeaders(headers) {
    return Object.keys(headers)
      .map((key) => `${key}: ${headers[key]}`)
      .join(CRLF);
  }
}

function acceptsMultipartResponse(req) {
  return req.headers && req.headers.accept === 'multipart/mixed';
}

module.exports = MultipartResponse;