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WIP: Implement class Frame #477

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WIP: Implement class Frame #477

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1f26327
Implement class Frame
MarhiievHE Nov 6, 2023
ede8de9
fix decode
MarhiievHE Nov 7, 2023
7df26af
Rewrite class Frame
MarhiievHE Nov 8, 2023
509564f
Removed commented line
MarhiievHE Nov 8, 2023
302bd63
Fix flag masked
MarhiievHE Nov 9, 2023
e67f5bd
Reduced max payload size to the max safe integer in JS
MarhiievHE Nov 10, 2023
c474f02
Fix unmask logic
MarhiievHE Nov 10, 2023
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146 changes: 105 additions & 41 deletions lib/websocket.js
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Original file line number Diff line number Diff line change
Expand Up @@ -17,29 +17,109 @@ const OPCODE_SHORT = 0x81;
const LEN_16_BIT = 126;
const MAX_16_BIT = 65536;
const LEN_64_BIT = 127;
const MAX_64_BIT_PAYLOAD = Number.MAX_SAFE_INTEGER;
const HEAD_LENGTH = 2;
const EXTENDED_PAYLOAD_16_LENGTH = 2;
const EXTENDED_PAYLOAD_64_LENGTH = 8;

const calcOffset = (frame, length) => {
if (length < LEN_16_BIT) return [2, 6];
if (length === LEN_16_BIT) return [4, 8];
return [10, 14];
};
class Frame {
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Typically in a constructor you just assign some props for instance. Make some configuration. But you don't do some complex logic of how inputs should be mapped correctly to Frame class props. This is not the responsibility of the constructor. So we can create from method that will take this responsibility. See in the example below. Also we should not handle encode or decode logic in constructor. Because when you create frame with string or buffer there is no difference. new Frame('1234') and new Frame(buffer). Code becomes implicit and less readable. Instead you can do Frame.from(data).decode() and Frame.from(data).decode(). This makes clear what happens in this code. See in the example below. So, please use interface described in example below.

class Frame {
  #buffer = null

  constructor(buffer) {
    this.#buffer = buffer
  }


  encode() {
    ...
  }

  decode() {
    ...
  }


  static from(data) {
    if (Buffer.isBuffer(data)) {
      return new Frame(data)
    } 

    if (typeof data === 'string') {
      return new Frame(Buffer.from(data))
    }

    throw new Error('Unsupported')
  }
}

// USAGE

send(text) {
  const frame = Frame.from(text).encode()
  this.socket.write(frame.data);
}

receive(data) {
  console.log('data: ', data[0], data.length);
  if (data[0] !== OPCODE_SHORT) return;
  const frame = Frame.from(data).decode()
  const text = frame.toString();
  this.send(`Echo "${text}"`);
  console.log('Message:', text);
}

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Okay, with the factory, yeah, that's probably better. But creating a text frame of a protocol from a string and just saving the finished frame in a class field is not the same action. Then it is probably better to just accept a ready frame by constructor and create a protocol frame from input data by static method. Thanks.

#frame = null;
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Suggested change
#frame = null;
#data = null;

#masked = null;
#dataOffset = null;
#mask = null;
#length = null;

const parseFrame = (frame) => {
const length = frame[1] ^ 0x80;
const [maskOffset, dataOffset] = calcOffset(frame, length);
const mask = frame.subarray(maskOffset, maskOffset + MASK_LENGTH);
const data = frame.subarray(dataOffset);
return { mask, data };
};
constructor(frame) {
this.#frame = frame;
const length = this.#frame[1] & 0x7f;
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Looks like new Frame() will return error.
Uncaught TypeError: Cannot read properties of undefined (reading '1')
Is it ok here?

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Because it doesn't have to work that way, pass a reference to the buffer with WebSocket frame to the constructor.

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Or use static method 'from()' to create new instance

this.#masked = (frame[1] & 0x80) === 0x80;
if (length < 126) {
this.#dataOffset = HEAD_LENGTH + MASK_LENGTH;
this.#mask = frame.subarray(HEAD_LENGTH, HEAD_LENGTH + MASK_LENGTH);
this.#length = length;
} else if (length === 126) {
this.#dataOffset = HEAD_LENGTH + EXTENDED_PAYLOAD_16_LENGTH + MASK_LENGTH;
this.#mask = frame.subarray(
HEAD_LENGTH + EXTENDED_PAYLOAD_16_LENGTH,
HEAD_LENGTH + EXTENDED_PAYLOAD_16_LENGTH + MASK_LENGTH,
);
this.#length = this.#frame.readUInt16BE(2);
} else {
this.#dataOffset = HEAD_LENGTH + EXTENDED_PAYLOAD_64_LENGTH + MASK_LENGTH;
this.#mask = frame.subarray(
HEAD_LENGTH + EXTENDED_PAYLOAD_64_LENGTH,
HEAD_LENGTH + EXTENDED_PAYLOAD_64_LENGTH + MASK_LENGTH,
);
this.#length = (frame.readUInt32BE(2) << 32) + frame.readUInt32BE(4);
}
}

const unmask = (buffer, mask) => {
const data = Buffer.allocUnsafe(buffer.length);
buffer.copy(data);
for (let i = 0; i < data.length; i++) {
data[i] ^= mask[i & 3];
unmask() {
if (!this.#masked) return;
for (let i = 0; i < this.#length; ++i) {
this.#frame[this.#dataOffset + i] ^= this.#mask[i & 3];
}
this.#masked = false;
}

toString() {
return this.#frame.toString(
'utf8',
this.#dataOffset,
this.#dataOffset + this.#length,
);
}

get frame() {
return this.#frame;
}
return data;
};

static from(data) {
if (Buffer.isBuffer(data)) {
if (data.length === 0) throw new Error('Empty frame!');
if ((data[1] & 0x80) !== 0x80) throw new Error('1002: protocol error');
//
// The maximum safe integer in JavaScript is 2^53 - 1. An error is returned
// if payload length is greater than this number.
//
if ((data[2] & 0x7f) === 127) {
const upperInt = data.readUInt32BE(2);
if (upperInt > MAX_64_BIT_PAYLOAD >> 32)
throw new Error(
'1009: Unsupported WebSocket frame: payload length > 2^53 - 1',
);
}
return new Frame(data);
}

if (typeof data === 'string') {
if (data.length === 0) throw new Error('Empty string!');
const payload = Buffer.from(data);
const length = payload.length;
let meta = Buffer.alloc(2);
meta[0] = 0x81; // FIN = 1, RSV = 0b000, opcode = 0b0001 (text frame)
if (length < LEN_16_BIT) {
meta[1] = length;
} else if (length < MAX_16_BIT) {
const len = Buffer.alloc(2);
len.writeUint16BE(length, 0);
meta[1] = LEN_16_BIT;
meta = Buffer.concat([meta, len]);
} else if (length < MAX_64_BIT_PAYLOAD) {
const len = Buffer.alloc(8);
len.writeBigUInt64BE(BigInt(length), 0);
meta[1] = LEN_64_BIT;
this.meta = Buffer.concat([meta, len]);
} else {
throw new Error('string is too long to encode in one frame!');
}
const frame = Buffer.concat([meta, payload]);
return new Frame(Buffer.from(frame));
}

throw new Error('Unsupported');
}
}

class Connection {
constructor(socket) {
Expand All @@ -56,34 +136,18 @@ class Connection {
}

send(text) {
const data = Buffer.from(text);
let meta = Buffer.alloc(2);
const length = data.length;
meta[0] = OPCODE_SHORT;
if (length < LEN_16_BIT) {
meta[1] = length;
} else if (length < MAX_16_BIT) {
const len = Buffer.from([(length & 0xff00) >> 8, length & 0x00ff]);
meta = Buffer.concat([meta, len]);
meta[1] = LEN_16_BIT;
} else {
const len = Buffer.alloc(8);
len.writeBigInt64BE(BigInt(length), 0);
meta = Buffer.concat([meta, len]);
meta[1] = LEN_64_BIT;
}
const frame = Buffer.concat([meta, data]);
this.socket.write(frame);
const frame = Frame.from(text);
this.socket.write(frame.frame);
}

receive(data) {
console.log('data: ', data[0], data.length);
if (data[0] !== OPCODE_SHORT) return;
const frame = parseFrame(data);
const msg = unmask(frame.data, frame.mask);
const text = msg.toString();
this.send(`Echo "${text}"`);
const frame = Frame.from(data);
frame.unmask();
const text = frame.toString();
console.log('Message:', text);
this.send(`Echo "${text}"`);
}

accept(key) {
Expand Down