feat: add copy method.

Author: ghosind

src/dynamicBuffer.ts

@@ -719,6 +719,44 @@ export class DynamicBuffer {
     return this;
   }
 
+  /**
+   * Copies data from a region of `buf` to a region in `target`.
+   *
+   * @param target A buffer to copy into.
+   * @param targetStart The offset within `target` at which to be begin writing, default 0.
+   * @param sourceStart The offset within `buf` from which to begin copying, default 0.
+   * @param sourceEnd The offset within `buf` at which to stop copying (not inclusive),
+   * default `buf.length`.
+   * @returns The number of bytes copied.
+   */
+  copy(
+    target: DynamicBuffer | Buffer | Uint8Array,
+    targetStart: number = 0,
+    sourceStart: number = 0,
+    sourceEnd: number = this.length,
+  ): number {
+    if (targetStart < 0) {
+      throw new RangeError(`The value of 'targetStart' is out of range. It must be >=0. Received ${targetStart}`);
+    }
+    if (sourceStart < 0) {
+      throw new RangeError(`The value of 'sourceStart' is out of range. It must be >=0. Received ${sourceStart}`);
+    }
+    if (sourceEnd > this.length) {
+      // eslint-disable-next-line no-param-reassign
+      sourceEnd = this.length;
+    }
+
+    if (target instanceof DynamicBuffer) {
+      return target.write(this.toString(this.encoding, sourceStart, sourceEnd), targetStart);
+    }
+
+    if (!this.buffer || this.length === 0) {
+      return 0;
+    }
+
+    return this.buffer.copy(target, targetStart, sourceStart, sourceEnd);
+  }
+
   /**
    * Write data into internal buffer with the specified offset.
    *

test/export.spec.ts

@@ -113,3 +113,69 @@ describe('Exports to JSON object', () => {
     assert.equal(JSON.stringify(buf), '{"type":"Buffer","data":[72,101,108,108,111]}');
   });
 });
+
+describe('Copy to another storage', () => {
+  it('Test copy()', () => {
+    const str = 'hello world';
+    const buf1 = new DynamicBuffer(str);
+    const buf2 = new DynamicBuffer();
+
+    assert.equal(buf1.copy(buf2), str.length);
+    assert.equal(buf2.toString(), 'hello world');
+  });
+
+  it('Test copy() with builtin Buffer', () => {
+    const str = 'hello world';
+    const buf1 = new DynamicBuffer(str);
+    const buf2 = Buffer.alloc(15, '.');
+
+    assert.equal(buf1.copy(buf2), str.length);
+    assert.equal(buf2.toString(), 'hello world....');
+  });
+
+  it('Test copy() with builtin Uint8Array', () => {
+    const str = 'hello world';
+    const buf1 = new DynamicBuffer(str);
+    const buf2 = new Uint8Array(str.length);
+
+    assert.equal(buf1.copy(buf2), str.length);
+    for (let i = 0; i < buf2.length; i += 1) {
+      assert.equal(buf2[i], str.charCodeAt(i));
+    }
+  });
+
+  it('Test copy() with invalid target start', () => {
+    const buf1 = new DynamicBuffer('hello world');
+    const buf2 = new DynamicBuffer();
+
+    assert.throws(() => {
+      buf1.copy(buf2, -1);
+    });
+  });
+
+  it('Test copy() with invalid source start', () => {
+    const buf1 = new DynamicBuffer('hello world');
+    const buf2 = new DynamicBuffer();
+
+    assert.throws(() => {
+      buf1.copy(buf2, 0, -1);
+    });
+  });
+
+  it('Test copy() with big source end', () => {
+    const str = '!hello world';
+    const buf1 = new DynamicBuffer(str);
+    const buf2 = new DynamicBuffer('...');
+
+    assert.equal(buf1.copy(buf2, 1, 1, 100), str.length - 1);
+    assert.equal(buf2.toString(), '.hello world');
+  });
+
+  it('Test copy() with empty buffer', () => {
+    const buf1 = new DynamicBuffer();
+    const buf2 = Buffer.alloc(5, '.');
+
+    assert.equal(buf1.copy(buf2), 0);
+    assert.equal(buf2.toString(), '.....');
+  });
+});