feat: add read method.

- Add read method to get the byte at the position in the buffer.
- Add test cases for read method.

Author: ghosind

src/dynamicBuffer.ts

@@ -185,6 +185,31 @@ export class DynamicBuffer {
     return count;
   }
 
+  /**
+   * Reads and returns a byte at the position `offset` in this buffer.
+   *
+   * ```js
+   * buf.append('Hello world');
+   * console.log(buf.read(0));
+   * // 72
+   * ```
+   *
+   * @param offset Number of bytes to skip before starting to read, and the offset must satisfy
+   * between 0 and `this.length - `, default `0`.
+   * @returns The byte at the position in the buffer.
+   */
+  read(offset: number = 0) {
+    if (!this.buffer || offset < 0 || offset >= this.used) {
+      throw new RangeError(`The value of "offset" is out of range. It must be >= 0 and <= ${
+        this.used - 1
+      }. Received ${
+        offset
+      }`);
+    }
+
+    return this.buffer[offset];
+  }
+
   /**
    * Copies the buffer data onto a new `Buffer` instance without unused parts.
    *

test/read.spec.ts

@@ -0,0 +1,47 @@
+import assert from 'assert';
+import { constants } from 'buffer';
+import { describe, it } from 'mocha';
+
+import { DynamicBuffer } from '../src';
+
+describe('Read tests', () => {
+  it('Test read without parameter', () => {
+    const buffer = new DynamicBuffer();
+    const str = 'Hello world';
+
+    buffer.append(str);
+
+    assert.equal(buffer.read(), str.charCodeAt(0));
+  });
+
+  it('Test read with legal ranges', () => {
+    const buffer = new DynamicBuffer();
+    const str = 'Hello world';
+
+    buffer.append(str);
+
+    for (let i = 0; i < str.length; i += 1) {
+      assert.equal(buffer.read(i), str.charCodeAt(i));
+    }
+  });
+
+  it('Test read with a negative offset', () => {
+    const buffer = new DynamicBuffer();
+
+    buffer.append('Hello world');
+
+    assert.throws(() => {
+      buffer.read(-1);
+    });
+  });
+
+  it('Test read with a offset larger than buffer length', () => {
+    const buffer = new DynamicBuffer();
+
+    buffer.append('Hello world');
+
+    assert.throws(() => {
+      buffer.read(buffer.length + 1);
+    });
+  });
+});