proxypin/lib/network/http/websocket.dart

/*
 * Copyright 2023 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import 'dart:convert';
import 'dart:io';
import 'dart:math';
import 'dart:typed_data';

class WebSocketFrame {
  final bool fin;

  /*
      0x00 denotes a continuation frame
      0x01 表示一个text frame
      0x02 表示一个binary frame
      0x03 ~~ 0x07 are reserved for further non-control frames,为将来的非控制消息片段保留测操作码
      0x08 表示连接关闭
      0x09 表示 ping (心跳检测相关)
      0x0a 表示 pong (心跳检测相关)
   */
  final int opcode; //4bit
  final bool mask; //1bit
  final int maskingKey;

  final int payloadLength;
  final Uint8List payloadData;

  bool isFromClient = false;
  final DateTime time = DateTime.now();

  WebSocketFrame({
    required this.fin,
    required this.opcode,
    required this.mask,
    required this.payloadLength,
    required this.maskingKey,
    required this.payloadData,
  });

  bool get isText => opcode == 0x01;

  String get payloadDataAsString {
    if (opcode == 0x08) {
      return '[连接关闭]';
    }
    if (opcode == 0x02) {
      return '[二进制数据]';
    }
    try {
      return utf8.decode(payloadData);
    } catch (e) {
      return String.fromCharCodes(payloadData);
    }
  }
}

///websocket 解码器
class WebSocketDecoder {
  WebSocketFrame? decode(Uint8List byteBuf) {
    var frame = _parseWebSocketFrame(byteBuf);
    return frame;
  }

  bool canParseWebSocketFrame(Uint8List data) {
    if (data.length < 2) {
      return false;
    }

    var reader = ByteData.sublistView(data);

    var opcode = reader.getUint8(0) & 0x0f;
    if (opcode > 0xA) {
      return false;
    }

    var mask = reader.getUint8(1) >> 7;
    int payloadStart = 2;
    if (mask == 1) {
      payloadStart += 4;
    }

    var payloadLength = reader.getUint8(1) & 0x7f;
    if (payloadLength == 126) {
      payloadStart += 2;
    } else if (payloadLength == 127) {
      payloadStart += 8;
    }

    if (data.length < payloadStart + payloadLength) {
      return false;
    }
    return true;
  }

  WebSocketFrame _parseWebSocketFrame(Uint8List data) {
    var reader = ByteData.sublistView(data);

    var fin = reader.getUint8(0) >> 7;
    //解析 rsv1
    var rsv1 = (reader.getUint8(0) >> 6) & 0x01;

    var opcode = reader.getUint8(0) & 0x0f;

    var mask = reader.getUint8(1) >> 7;

    var payloadLength = reader.getUint8(1) & 0x7f;

    int payloadStart = 2;

    if (payloadLength == 126) {
      payloadLength = reader.getUint16(2);
      payloadStart += 2;
    } else if (payloadLength == 127) {
      payloadLength = reader.getUint64(2);
      payloadStart += 8;
    }

    var maskingKey = 0;
    if (mask == 1) {
      maskingKey = reader.getUint32(payloadStart);
      payloadStart += 4;
    }

    var payloadData = data.sublist(payloadStart, min(payloadStart + payloadLength, data.length));

    //根据maskKey解密内容
    if (mask == 1) {
      payloadData = unmaskPayload(payloadData, maskingKey);
    }

    if (rsv1 == 1) {
      //inflate
      payloadData = decompress(payloadData);
    }
    return WebSocketFrame(
      fin: fin == 1,
      opcode: opcode,
      mask: mask == 1,
      maskingKey: maskingKey,
      payloadLength: payloadLength,
      payloadData: payloadData,
    );
  }

  ZLibDecoder? _decoder;

  ZLibDecoder _ensureDecoder() => _decoder ?? ZLibDecoder(raw: true);

  Uint8List decompress(Uint8List msg) {
    try {
      return Uint8List.fromList(_ensureDecoder().convert(msg));
    } catch (e) {
      return msg;
    }
  }

  Uint8List unmaskPayload(Uint8List payloadData, int maskingKey) {
    var unmaskedData = Uint8List(payloadData.length);
    for (var i = 0; i < payloadData.length; i++) {
      var keyByte = (maskingKey >> ((3 - (i % 4)) * 8)) & 0xff;
      unmaskedData[i] = payloadData[i] ^ keyByte;
    }
    return unmaskedData;
  }
}