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