mtcute/packages/tl-runtime/src/reader.ts

import Long from 'long'

import { hexEncode } from './encodings/hex.js'
import { utf8Decode } from './encodings/utf8.js'

const TWO_PWR_32_DBL = (1 << 16) * (1 << 16)

/**
 * Mapping of TL object IDs to reader functions.
 *
 * Note that these types should never be present in the map
 * and are parsed manually inside `.object()`:
 * - `0x1cb5c415` aka `vector`
 * - `0x3072cfa1` aka `gzip_packed`
 * - `0xbc799737` aka `boolFalse`
 * - `0x997275b5` aka `boolTrue`
 * - `0x3fedd339` aka `true`
 * - `0x56730bcc` aka `null`
 */
// avoid unnecessary type complexity
// eslint-disable-next-line @typescript-eslint/no-explicit-any
export type TlReaderMap = Record<number, (r: any) => unknown> & {
    // eslint-disable-next-line @typescript-eslint/no-explicit-any
    _results?: Record<string, (r: any) => unknown>
}

/**
 * Reader for TL objects.
 */
export class TlBinaryReader {
    readonly dataView: DataView
    readonly uint8View: Uint8Array

    pos = 0

    /**
     * @param objectsMap  Readers map
     * @param data  Buffer to read from
     * @param start  Position to start reading from
     */
    constructor(
        readonly objectsMap: TlReaderMap | undefined,
        data: ArrayBuffer,
        start = 0,
    ) {
        if (ArrayBuffer.isView(data)) {
            this.pos = start
            this.dataView = new DataView(data.buffer, data.byteOffset, data.byteLength)
            this.uint8View = new Uint8Array(data.buffer, data.byteOffset, data.byteLength)
        } else {
            this.pos = start
            this.dataView = new DataView(data)
            this.uint8View = new Uint8Array(data)
        }
    }

    /**
     * Create a new reader without objects map for manual usage
     *
     * @param data  Buffer to read from
     * @param start  Position to start reading from
     */
    static manual(data: ArrayBuffer, start = 0): TlBinaryReader {
        return new TlBinaryReader(undefined, data, start)
    }

    /**
     * Deserialize a single object
     *
     * @param objectsMap  Readers map
     * @param data  Buffer to read from
     * @param start  Position to start reading from
     */
    static deserializeObject<T>(objectsMap: TlReaderMap, data: Uint8Array, start = 0): T {
        return new TlBinaryReader(objectsMap, data, start).object() as T
    }

    int(): number {
        const res = this.dataView.getInt32(this.pos, true)
        this.pos += 4

        return res
    }

    uint(): number {
        const res = this.dataView.getUint32(this.pos, true)
        this.pos += 4

        return res
    }

    /**
     * Get the next {@link uint} without advancing the reader cursor
     */
    peekUint(): number {
        // e.g. for checking ctor number
        return this.dataView.getUint32(this.pos, true)
    }

    int53(): number {
        // inlined toNumber from Long
        const res =
            (this.dataView.getInt32(this.pos, true) >>> 0) + TWO_PWR_32_DBL * this.dataView.getInt32(this.pos + 4, true)
        this.pos += 8

        return res
    }

    long(unsigned = false): Long {
        const lo = this.dataView.getInt32(this.pos, true)
        const hi = this.dataView.getInt32(this.pos + 4, true)

        this.pos += 8

        return new Long(lo, hi, unsigned)
    }

    float(): number {
        const res = this.dataView.getFloat32(this.pos, true)
        this.pos += 4

        return res
    }

    double(): number {
        const res = this.dataView.getFloat64(this.pos, true)
        this.pos += 8

        return res
    }

    boolean(): boolean {
        const val = this.uint()
        if (val === 0xbc799737) return false
        if (val === 0x997275b5) return true
        throw new Error(`Expected either boolTrue or boolFalse, got 0x${val.toString(16)}`)
    }

    /**
     * Read raw bytes of the given length
     * @param bytes  Length of the buffer to read
     */
    raw(bytes = -1): Uint8Array {
        if (bytes === -1) bytes = this.uint8View.length - this.pos

        return this.uint8View.subarray(this.pos, (this.pos += bytes))
    }

    int128(): Uint8Array {
        return this.uint8View.subarray(this.pos, (this.pos += 16))
    }

    int256(): Uint8Array {
        return this.uint8View.subarray(this.pos, (this.pos += 32))
    }

    bytes(): Uint8Array {
        const firstByte = this.uint8View[this.pos++]
        let length
        let padding

        if (firstByte === 254) {
            length = this.uint8View[this.pos++] | (this.uint8View[this.pos++] << 8) | (this.uint8View[this.pos++] << 16)
            padding = length % 4
        } else {
            length = firstByte
            padding = (length + 1) % 4
        }

        const data = this.raw(length)
        if (padding > 0) this.pos += 4 - padding

        return data
    }

    string(): string {
        return utf8Decode(this.bytes())
    }

    object(id = this.uint()): unknown {
        if (id === 0x1cb5c415 /* vector */) {
            return this.vector(this.object, true)
        }
        if (id === 0xbc799737 /* boolFalse */) return false
        if (id === 0x997275b5 /* boolTrue */) return true
        // unsure if it is actually used in the wire, seems like it's only used for boolean flags
        if (id === 0x3fedd339 /* true */) return true
        // never used in the actual schema, but whatever
        if (id === 0x56730bcc /* null */) return null

        // hot path, avoid additional runtime checks

        const reader = this.objectsMap![id]

        if (!reader) {
            // unknown type. bruh moment.
            // mtproto sucks and there's no way we can just skip it
            this.seek(-4)
            const pos = this.pos
            const error = new TypeError(`Unknown object id: 0x${id.toString(16)}. Content: ${hexEncode(this.raw())}`)
            this.pos = pos
            throw error
        }

        return reader(this)
    }

    vector(reader = this.object, bare = false): unknown[] {
        if (!bare) {
            const uint = this.uint()

            if (uint !== 0x1cb5c415) {
                throw new Error(
                    `Invalid object code, expected 0x1cb5c415 (vector), got 0x${uint.toString(16)} at ${this.pos - 4}`,
                )
            }
        }

        const length = this.uint()
        const ret = []
        for (let i = 0; i < length; i++) ret.push(reader.call(this))

        return ret
    }

    /**
     * Advance the reader cursor by the given amount of bytes
     *
     * @param delta  Amount of bytes to advance (can be negative)
     */
    seek(delta: number): void {
        this.seekTo(this.pos + delta)
    }

    /**
     * Seek to the given position
     *
     * @param pos  Position to seek to
     */
    seekTo(pos: number): void {
        if (pos >= this.uint8View.length || pos < 0) {
            throw new RangeError('New position is out of range')
        }
        this.pos = pos
    }
}