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'use strict'
const { createInflateRaw, Z_DEFAULT_WINDOWBITS } = require('node:zlib')
const { isValidClientWindowBits } = require('./util')
const { MessageSizeExceededError } = require('../../core/errors')
const tail = Buffer.from([0x00, 0x00, 0xff, 0xff])
const kBuffer = Symbol('kBuffer')
const kLength = Symbol('kLength')
class PerMessageDeflate {
/** @type {import('node:zlib').InflateRaw} */
#inflate
#options = {}
#maxPayloadSize = 0
/**
* @param {Map<string, string>} extensions
*/
constructor (extensions, options) {
this.#options.serverNoContextTakeover = extensions.has('server_no_context_takeover')
this.#options.serverMaxWindowBits = extensions.get('server_max_window_bits')
this.#maxPayloadSize = options.maxPayloadSize
}
/**
* Decompress a compressed payload.
* @param {Buffer} chunk Compressed data
* @param {boolean} fin Final fragment flag
* @param {Function} callback Callback function
*/
decompress (chunk, fin, callback) {
// An endpoint uses the following algorithm to decompress a message.
// 1. Append 4 octets of 0x00 0x00 0xff 0xff to the tail end of the
// payload of the message.
// 2. Decompress the resulting data using DEFLATE.
if (!this.#inflate) {
let windowBits = Z_DEFAULT_WINDOWBITS
if (this.#options.serverMaxWindowBits) { // empty values default to Z_DEFAULT_WINDOWBITS
if (!isValidClientWindowBits(this.#options.serverMaxWindowBits)) {
callback(new Error('Invalid server_max_window_bits'))
return
}
windowBits = Number.parseInt(this.#options.serverMaxWindowBits)
}
try {
this.#inflate = createInflateRaw({ windowBits })
} catch (err) {
callback(err)
return
}
this.#inflate[kBuffer] = []
this.#inflate[kLength] = 0
this.#inflate.on('data', (data) => {
this.#inflate[kLength] += data.length
if (this.#maxPayloadSize > 0 && this.#inflate[kLength] > this.#maxPayloadSize) {
callback(new MessageSizeExceededError())
this.#inflate.removeAllListeners()
this.#inflate = null
return
}
this.#inflate[kBuffer].push(data)
})
this.#inflate.on('error', (err) => {
this.#inflate = null
callback(err)
})
}
this.#inflate.write(chunk)
if (fin) {
this.#inflate.write(tail)
}
this.#inflate.flush(() => {
if (!this.#inflate) {
return
}
const full = Buffer.concat(this.#inflate[kBuffer], this.#inflate[kLength])
this.#inflate[kBuffer].length = 0
this.#inflate[kLength] = 0
callback(null, full)
})
}
}
module.exports = { PerMessageDeflate }
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