📦 socketio / engine.io-parser

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73import {
  ERROR_PACKET,
  PACKET_TYPES_REVERSE,
  Packet,
  BinaryType,
  RawData,
} from "./commons.js";
import { decode } from "./contrib/base64-arraybuffer.js";

const withNativeArrayBuffer = typeof ArrayBuffer === "function";

export const decodePacket = (
  encodedPacket: RawData,
  binaryType?: BinaryType,
): Packet => {
  if (typeof encodedPacket !== "string") {
    return {
      type: "message",
      data: mapBinary(encodedPacket, binaryType),
    };
  }
  const type = encodedPacket.charAt(0);
  if (type === "b") {
    return {
      type: "message",
      data: decodeBase64Packet(encodedPacket.substring(1), binaryType),
    };
  }
  const packetType = PACKET_TYPES_REVERSE[type];
  if (!packetType) {
    return ERROR_PACKET;
  }
  return encodedPacket.length > 1
    ? {
        type: PACKET_TYPES_REVERSE[type],
        data: encodedPacket.substring(1),
      }
    : {
        type: PACKET_TYPES_REVERSE[type],
      };
};

const decodeBase64Packet = (data, binaryType) => {
  if (withNativeArrayBuffer) {
    const decoded = decode(data);
    return mapBinary(decoded, binaryType);
  } else {
    return { base64: true, data }; // fallback for old browsers
  }
};

const mapBinary = (data, binaryType) => {
  switch (binaryType) {
    case "blob":
      if (data instanceof Blob) {
        // from WebSocket + binaryType "blob"
        return data;
      } else {
        // from HTTP long-polling or WebTransport
        return new Blob([data]);
      }
    case "arraybuffer":
    default:
      if (data instanceof ArrayBuffer) {
        // from HTTP long-polling (base64) or WebSocket + binaryType "arraybuffer"
        return data;
      } else {
        // from WebTransport (Uint8Array)
        return data.buffer;
      }
  }
};