feat: add subarray method.

Author: ghosind

src/dynamicBuffer.ts

@@ -837,6 +837,33 @@ export class DynamicBuffer {
     return this;
   }
 
+  /**
+   * Returns a new Buffer that references the same memory as the original, but offset and cropped
+   * by the start and end indices.
+   *
+   * ```ts
+   * const buf = new DynamicBuffer('ABCD');
+   * const sub = buf.subarray(1, 3);
+   * sub[0] = 67;
+   * sub[1] = 66;
+   * console.log(buf.toString());
+   * // ACBD
+   * ```
+   *
+   * @param start Where the new `Buffer` will start, default 0.
+   * @param end Where the new `Buffer` will end (not inclusive), default the length of this buffer.
+   * @returns The new buffer.
+   */
+  subarray(start: number = 0, end: number = this.length): Buffer {
+    const { startOffset, endOffset } = this.calculateOffsets(start, end);
+
+    if (!this.buffer || this.length === 0) {
+      return Buffer.alloc(0);
+    }
+
+    return this.buffer?.subarray(startOffset, endOffset);
+  }
+
   /**
    * Write data into internal buffer with the specified offset.
    *

test/dynamicBuffer.spec.ts

@@ -111,6 +111,26 @@ describe('Resize tests', () => {
   });
 });
 
+describe('Subarray test', () => {
+  it('Test subarray', () => {
+    const buf = new DynamicBuffer('ABCDEF');
+    const sub = buf.subarray(1, 3);
+    sub[0] = 67;
+    sub[1] = 66;
+
+    assert.equal(buf.toString(), 'ACBDEF');
+  });
+
+  it('Test subarray with empty buffer', () => {
+    const buf = new DynamicBuffer();
+    const sub = buf.subarray(1, 3);
+    sub[0] = 67;
+    sub[1] = 66;
+
+    assert.equal(buf.toString(), '');
+  });
+});
+
 describe('Tools methods test', () => {
   it('Test isDynamicBuffer util method', () => {
     assert.equal(isDynamicBuffer(Buffer.from('')), false);