74 lines
1.7 KiB
JavaScript
74 lines
1.7 KiB
JavaScript
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'use strict'
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const { maxUnsigned16Bit } = require('./constants')
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/** @type {import('crypto')} */
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let crypto
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try {
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crypto = require('crypto')
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} catch {
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}
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class WebsocketFrameSend {
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/**
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* @param {Buffer|undefined} data
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*/
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constructor (data) {
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this.frameData = data
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this.maskKey = crypto.randomBytes(4)
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}
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createFrame (opcode) {
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const bodyLength = this.frameData?.byteLength ?? 0
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/** @type {number} */
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let payloadLength = bodyLength // 0-125
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let offset = 6
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if (bodyLength > maxUnsigned16Bit) {
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offset += 8 // payload length is next 8 bytes
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payloadLength = 127
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} else if (bodyLength > 125) {
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offset += 2 // payload length is next 2 bytes
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payloadLength = 126
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}
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const buffer = Buffer.allocUnsafe(bodyLength + offset)
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// Clear first 2 bytes, everything else is overwritten
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buffer[0] = buffer[1] = 0
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buffer[0] |= 0x80 // FIN
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buffer[0] = (buffer[0] & 0xF0) + opcode // opcode
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/*! ws. MIT License. Einar Otto Stangvik <einaros@gmail.com> */
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buffer[offset - 4] = this.maskKey[0]
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buffer[offset - 3] = this.maskKey[1]
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buffer[offset - 2] = this.maskKey[2]
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buffer[offset - 1] = this.maskKey[3]
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buffer[1] = payloadLength
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if (payloadLength === 126) {
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buffer.writeUInt16BE(bodyLength, 2)
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} else if (payloadLength === 127) {
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// Clear extended payload length
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buffer[2] = buffer[3] = 0
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buffer.writeUIntBE(bodyLength, 4, 6)
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}
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buffer[1] |= 0x80 // MASK
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// mask body
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for (let i = 0; i < bodyLength; i++) {
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buffer[offset + i] = this.frameData[i] ^ this.maskKey[i % 4]
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}
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return buffer
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}
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}
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module.exports = {
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WebsocketFrameSend
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}
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