socket.io/lib/encodePacket.browser.ts

import { PACKET_TYPES, Packet, RawData } from "./commons.js";

const withNativeBlob =
  typeof Blob === "function" ||
  (typeof Blob !== "undefined" &&
    Object.prototype.toString.call(Blob) === "[object BlobConstructor]");
const withNativeArrayBuffer = typeof ArrayBuffer === "function";

// ArrayBuffer.isView method is not defined in IE10
const isView = obj => {
  return typeof ArrayBuffer.isView === "function"
    ? ArrayBuffer.isView(obj)
    : obj && obj.buffer instanceof ArrayBuffer;
};

const encodePacket = (
  { type, data }: Packet,
  supportsBinary: boolean,
  callback: (encodedPacket: RawData) => void
) => {
  if (withNativeBlob && data instanceof Blob) {
    if (supportsBinary) {
      return callback(data);
    } else {
      return encodeBlobAsBase64(data, callback);
    }
  } else if (
    withNativeArrayBuffer &&
    (data instanceof ArrayBuffer || isView(data))
  ) {
    if (supportsBinary) {
      return callback(data);
    } else {
      return encodeBlobAsBase64(new Blob([data]), callback);
    }
  }
  // plain string
  return callback(PACKET_TYPES[type] + (data || ""));
};

const encodeBlobAsBase64 = (
  data: Blob,
  callback: (encodedPacket: RawData) => void
) => {
  const fileReader = new FileReader();
  fileReader.onload = function() {
    const content = (fileReader.result as string).split(",")[1];
    callback("b" + (content || ""));
  };
  return fileReader.readAsDataURL(data);
};

export default encodePacket;