Baileys/src/WABinary/decode.ts

import { inflateSync } from 'zlib'
import * as constants from './constants'
import { jidEncode } from './jid-utils'
import type { BinaryNode, BinaryNodeCodingOptions } from './types'

export const decompressingIfRequired = (buffer: Buffer) => {
	if(2 & buffer.readUInt8()) {
		buffer = inflateSync(buffer.slice(1))
	} else { // nodes with no compression have a 0x00 prefix, we remove that
		buffer = buffer.slice(1)
	}

	return buffer
}

export const decodeDecompressedBinaryNode = (
	buffer: Buffer,
	opts: Pick<BinaryNodeCodingOptions, 'DOUBLE_BYTE_TOKENS' | 'SINGLE_BYTE_TOKENS' | 'TAGS'>,
	indexRef: { index: number } = { index: 0 }
): BinaryNode => {
	const { DOUBLE_BYTE_TOKENS, SINGLE_BYTE_TOKENS, TAGS } = opts

	const checkEOS = (length: number) => {
		if(indexRef.index + length > buffer.length) {
			throw new Error('end of stream')
		}
	}

	const next = () => {
		const value = buffer[indexRef.index]
		indexRef.index += 1
		return value
	}

	const readByte = () => {
		checkEOS(1)
		return next()
	}

	const readBytes = (n: number) => {
		checkEOS(n)
		const value = buffer.slice(indexRef.index, indexRef.index + n)
		indexRef.index += n
		return value
	}

	const readStringFromChars = (length: number) => {
		return readBytes(length).toString('utf-8')
	}

	const readInt = (n: number, littleEndian = false) => {
		checkEOS(n)
		let val = 0
		for(let i = 0; i < n; i++) {
			const shift = littleEndian ? i : n - 1 - i
			val |= next() << (shift * 8)
		}

		return val
	}

	const readInt20 = () => {
		checkEOS(3)
		return ((next() & 15) << 16) + (next() << 8) + next()
	}

	const unpackHex = (value: number) => {
		if(value >= 0 && value < 16) {
			return value < 10 ? '0'.charCodeAt(0) + value : 'A'.charCodeAt(0) + value - 10
		}

		throw new Error('invalid hex: ' + value)
	}

	const unpackNibble = (value: number) => {
		if(value >= 0 && value <= 9) {
			return '0'.charCodeAt(0) + value
		}

		switch (value) {
		case 10:
			return '-'.charCodeAt(0)
		case 11:
			return '.'.charCodeAt(0)
		case 15:
			return '\0'.charCodeAt(0)
		default:
			throw new Error('invalid nibble: ' + value)
		}
	}

	const unpackByte = (tag: number, value: number) => {
		if(tag === TAGS.NIBBLE_8) {
			return unpackNibble(value)
		} else if(tag === TAGS.HEX_8) {
			return unpackHex(value)
		} else {
			throw new Error('unknown tag: ' + tag)
		}
	}

	const readPacked8 = (tag: number) => {
		const startByte = readByte()
		let value = ''

		for(let i = 0; i < (startByte & 127); i++) {
			const curByte = readByte()
			value += String.fromCharCode(unpackByte(tag, (curByte & 0xf0) >> 4))
			value += String.fromCharCode(unpackByte(tag, curByte & 0x0f))
		}

		if(startByte >> 7 !== 0) {
			value = value.slice(0, -1)
		}

		return value
	}

	const isListTag = (tag: number) => {
		return tag === TAGS.LIST_EMPTY || tag === TAGS.LIST_8 || tag === TAGS.LIST_16
	}

	const readListSize = (tag: number) => {
		switch (tag) {
		case TAGS.LIST_EMPTY:
			return 0
		case TAGS.LIST_8:
			return readByte()
		case TAGS.LIST_16:
			return readInt(2)
		default:
			throw new Error('invalid tag for list size: ' + tag)
		}
	}

	const readJidPair = () => {
		const i = readString(readByte())
		const j = readString(readByte())
		if(j) {
			return (i || '') + '@' + j
		}

		throw new Error('invalid jid pair: ' + i + ', ' + j)
	}

	const readAdJid = () => {
		const agent = readByte()
		const device = readByte()
		const user = readString(readByte())

		return jidEncode(user, agent === 0 ? 's.whatsapp.net' : 'lid', device)
	}

	const readString = (tag: number): string => {
		if(tag >= 1 && tag < SINGLE_BYTE_TOKENS.length) {
			return SINGLE_BYTE_TOKENS[tag] || ''
		}

		switch (tag) {
		case TAGS.DICTIONARY_0:
		case TAGS.DICTIONARY_1:
		case TAGS.DICTIONARY_2:
		case TAGS.DICTIONARY_3:
			return getTokenDouble(tag - TAGS.DICTIONARY_0, readByte())
		case TAGS.LIST_EMPTY:
			return ''
		case TAGS.BINARY_8:
			return readStringFromChars(readByte())
		case TAGS.BINARY_20:
			return readStringFromChars(readInt20())
		case TAGS.BINARY_32:
			return readStringFromChars(readInt(4))
		case TAGS.JID_PAIR:
			return readJidPair()
		case TAGS.AD_JID:
			return readAdJid()
		case TAGS.HEX_8:
		case TAGS.NIBBLE_8:
			return readPacked8(tag)
		default:
			throw new Error('invalid string with tag: ' + tag)
		}
	}

	const readList = (tag: number) => {
		const items: BinaryNode[] = []
		const size = readListSize(tag)
		for(let i = 0;i < size;i++) {
			items.push(decodeDecompressedBinaryNode(buffer, opts, indexRef))
		}

		return items
	}

	const getTokenDouble = (index1: number, index2: number) => {
		const dict = DOUBLE_BYTE_TOKENS[index1]
		if(!dict) {
			throw new Error(`Invalid double token dict (${index1})`)
		}

		const value = dict[index2]
		if(typeof value === 'undefined') {
			throw new Error(`Invalid double token (${index2})`)
		}

		return value
	}

	const listSize = readListSize(readByte())
	const header = readString(readByte())
	if(!listSize || !header.length) {
		throw new Error('invalid node')
	}

	const attrs: BinaryNode['attrs'] = { }
	let data: BinaryNode['content']
	if(listSize === 0 || !header) {
		throw new Error('invalid node')
	}

	// read the attributes in
	const attributesLength = (listSize - 1) >> 1
	for(let i = 0; i < attributesLength; i++) {
		const key = readString(readByte())
		const value = readString(readByte())

		attrs[key] = value
	}

	if(listSize % 2 === 0) {
		const tag = readByte()
		if(isListTag(tag)) {
			data = readList(tag)
		} else {
			let decoded: Buffer | string
			switch (tag) {
			case TAGS.BINARY_8:
				decoded = readBytes(readByte())
				break
			case TAGS.BINARY_20:
				decoded = readBytes(readInt20())
				break
			case TAGS.BINARY_32:
				decoded = readBytes(readInt(4))
				break
			default:
				decoded = readString(tag)
				break
			}

			data = decoded
		}
	}

	return {
		tag: header,
		attrs,
		content: data
	}
}

export const decodeBinaryNode = (buff: Buffer): BinaryNode => {
	const decompBuff = decompressingIfRequired(buff)
	return decodeDecompressedBinaryNode(decompBuff, constants)
}