Method writeSync

lib/internal/vfs/file_handle.js:510–552

* Writes data to the file synchronously. * @param {Buffer} buffer The buffer to write from * @param {number} offset The offset in the buffer to start reading * @param {number} length The number of bytes to write * @param {number|null} position The position to write to (null uses current

(buffer, offset, length, position)

   * @returns {number} The number of bytes written
   */
  writeSync(buffer, offset, length, position) {
    this.#checkClosed('write');
    this.#checkWritable();

    // In append mode, always write at the end
    const writePos = this.#isAppend() ?
      this.#size :
      (position !== null && position !== undefined ?
        Number(position) : this.position);
    const data = buffer.subarray(offset, offset + length);

    // Expand buffer if needed (geometric doubling for amortized O(1) appends)
    const neededSize = writePos + length;
    if (neededSize > this.#content.length) {
      const newCapacity = MathMax(neededSize, this.#content.length * 2);
      const newContent = Buffer.alloc(newCapacity);
      this.#content.copy(newContent, 0, 0, this.#size);
      this.#content = newContent;
    }

    // Write the data
    data.copy(this.#content, writePos);

    // Update actual content size
    if (neededSize > this.#size) {
      this.#size = neededSize;
    }

    // Update the entry's content, mtime, and ctime
    if (this.#entry) {
      const now = DateNow();
      this.#entry.content = this.#content.subarray(0, this.#size);
      this.#entry.mtime = now;
      this.#entry.ctime = now;
    }

    // Update position if not using explicit position
    if (position === null || position === undefined) {
      this.position = writePos + length;
    }

    return length;
  }

  /**
   * Writes data to the file.