lz4.ts

import type { Codec, CodecConstructor } from "./types.js";

type WasmModule = typeof import("../pkg/rumcodecs-wasm-node/rumcodecs_wasm.js");

const DEFAULT_ACCELERATION = 1;
const MAX_BUFFER_SIZE = 0x7e000000;

let wasmModule: Promise<WasmModule> | null = null;

async function getModule(): Promise<WasmModule> {
  if (!wasmModule) {
    wasmModule = import("../pkg/rumcodecs-wasm-node/rumcodecs_wasm.js");
  }
  return wasmModule;
}

interface LZ4Config {
  acceleration?: number;
}

const LZ4: CodecConstructor<LZ4Config> = class LZ4 implements Codec {
  public static codecId = "lz4";
  public static DEFAULT_ACCELERATION = DEFAULT_ACCELERATION;
  public static max_buffer_size = MAX_BUFFER_SIZE;
  public max_buffer_size = MAX_BUFFER_SIZE;
  public acceleration: number;

  constructor(acceleration = DEFAULT_ACCELERATION) {
    if (!Number.isInteger(acceleration)) {
      throw Error(`Invalid acceleration "${acceleration}". Must be a positive integer.`);
    }
    this.acceleration = acceleration <= 0 ? DEFAULT_ACCELERATION : acceleration;
  }

  static fromConfig({ acceleration }: LZ4Config): LZ4 {
    return new LZ4(acceleration);
  }

  async encode(data: Uint8Array): Promise<Uint8Array> {
    if (data.length > MAX_BUFFER_SIZE) {
      throw Error(`Codec does not support buffers of > ${MAX_BUFFER_SIZE} bytes.`);
    }
    const m = await getModule();
    return m.lz4_compress(data, this.acceleration);
  }

  async decode(data: Uint8Array, out?: Uint8Array): Promise<Uint8Array> {
    if (data.length > MAX_BUFFER_SIZE) {
      throw Error(`Codec does not support buffers of > ${MAX_BUFFER_SIZE} bytes.`);
    }
    // The header is the numcodecs framing: a 4-byte LE original size. It gives
    // us the exact length a successful decode has to produce, which is what
    // separates a genuine empty payload from the empty Vec the WASM side
    // returns on failure. Without this check a corrupt chunk decodes to a
    // zero-filled `out` and reaches the caller as data.
    if (data.length < 4) {
      throw new Error("LZ4 decompression failed: input is shorter than the size header");
    }
    const declared = new DataView(data.buffer, data.byteOffset, 4).getUint32(0, true);
    const m = await getModule();
    const result = m.lz4_decompress(data);
    if (result.length !== declared) {
      throw new Error("LZ4 decompression failed");
    }
    if (out !== undefined) {
      out.set(result);
      return out;
    }
    return result;
  }
};

export default LZ4;