101 lines
3.9 KiB
JavaScript
101 lines
3.9 KiB
JavaScript
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class WebsocketFrame {
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constructor() {
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// Just defining the structure of the WebsocketFrame,
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// I could actually just use a normal object but I
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// might need to add some methods to this in the future
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// so it's good enough
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// 1 byte - first byte
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this.FIN = undefined;
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this.RSVx = undefined;
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this.Opcode = undefined;
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// 1 byte - second byte
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this.MASK = undefined;
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this.PayloadLen = undefined;
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// 4 bytes - masking key
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this.MaskingKey = undefined;
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// (Extension Data + Application Data[PayloadLen]) (kind of) - payload data
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// TODO: Separate extension data from application data
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this.PayloadData = undefined;
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}
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}
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const parseWebsocketFrame = (data) => {
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const firstByte = data.getUint8(0);
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const secondByte = data.getUint8(1);
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const frame = new WebsocketFrame();
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// 1 byte - first byte
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frame.FIN = (firstByte & 0x01); // 0x01[0b10000000] - Get most significant bit (FIN)
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frame.RSVx = (firstByte & 0x70) // 0x70[0b01110000] - Get the 3 bits after the most significant bit (RSVx)
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frame.Opcode = (firstByte & 0x0F) // 0xF[0b00001111] - Get the last 4 bits (Opcode)
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// 1 byte - second byte
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frame.MASK = (secondByte & 0x01) // 0x01[0b10000000] - Get most significant bit (MASK)
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frame.PayloadLen = (secondByte & 0x7F) // 0x7F[0b01111111] - Get last 7 bits (Payload len)
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let maskingKeyOffset = 2; // By default, theres a 2 byte offset. We will modify this in the cases below.
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// Handle Payload len cases and set the masking key offset
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if (frame.PayloadLen === 126) {
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frame.PayloadLen = data.getUint16(2);
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maskingKeyOffset = 4; // 4 byte offset, because we also read 2 bytes with getUint16 above (2 bytes (normal size) + 2 bytes)
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} else if (frame.PayloadLen === 127) {
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frame.PayloadLen = data.getBigUint64(2);
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maskingKeyOffset = 10; // 10 byte offset, because we also read 8 bytes with getBigUint64 above (2 bytes (normal size) + 8 bytes)
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}
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const maskingKeyEnd = maskingKeyOffset + 4; // (4 bytes because it is a 32 bit value)
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if (frame.MASK) frame.MaskingKey = data.buffer.slice(maskingKeyOffset, maskingKeyEnd); // Create a new buffer starting at the masking key offset and ending at the masking key end (duh).
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// TODO: Separate extension data from application data
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frame.PayloadData = data.buffer.slice(maskingKeyEnd, maskingKeyEnd + frame.PayloadLen); // Create a new buffer that starts at the end of the masking key and ends at (the end of the masking key + payload length)
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// TODO: implement unmasked string decoding
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if (frame.MASK) {
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switch (frame.Opcode) {
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case 1: { // Denotes a text frame
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const payloadDataView = new DataView(frame.PayloadData);
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const maskingKeyView = new DataView(frame.MaskingKey);
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let decoded = '';
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for (let i = 0; i < frame.PayloadData.byteLength; i++) {
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decoded += (String.fromCharCode(payloadDataView.getUint8(i) ^ maskingKeyView.getUint8(i % 4)));
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}
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frame.DecodedPayloadData = decoded;
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break;
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}
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case 2: { // Denotes a binary frame
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// TODO: untested
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const payloadDataView = new DataView(frame.PayloadData);
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const maskingKeyView = new DataView(frame.MaskingKey);
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const decoded = [];
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for (let i = 0; i < frame.PayloadData.byteLength; i++) {
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decoded.push(payloadDataView.getUint8(i) ^ maskingKeyView.getUint8(i % 4));
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}
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frame.DecodedPayloadData = decoded;
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break;
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}
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}
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}
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return frame;
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}
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module.exports = {
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WebsocketFrame,
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parseWebsocketFrame
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};
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