Add convenience function for creating a DataView (#45)

* Add convenience function for creating a DataView

* Support Node.js Buffer

src/bytes.test.ts

@@ -7,6 +7,7 @@ import {
   bytesToSignedBigInt,
   bytesToString,
   concatBytes,
+  createDataView,
   hexToBytes,
   isBytes,
   numberToBytes,
@@ -414,3 +415,83 @@ describe('concatBytes', () => {
     ).toStrictEqual(Uint8Array.from([1, 2, 3, 52, 5]));
   });
 });
+
+describe('createDataView', () => {
+  describe('Uint8Array', () => {
+    it('returns a DataView from a byte array', () => {
+      const dataView = createDataView(new Uint8Array([1, 2, 3]));
+
+      expect(dataView).toBeInstanceOf(DataView);
+      expect(dataView.getUint8(0)).toBe(1);
+      expect(dataView.getUint8(1)).toBe(2);
+      expect(dataView.getUint8(2)).toBe(3);
+    });
+
+    it('returns a DataView from a subarray of a byte array', () => {
+      const original = new Uint8Array([1, 2, 3, 4, 5]);
+      const subset = original.subarray(1, 4);
+
+      const dataView = createDataView(subset);
+
+      expect(dataView).toBeInstanceOf(DataView);
+      expect(dataView.byteOffset).toBe(1);
+      expect(dataView.byteLength).toBe(3);
+      expect(dataView.getUint8(0)).toBe(2);
+      expect(dataView.getUint8(1)).toBe(3);
+      expect(dataView.getUint8(2)).toBe(4);
+    });
+
+    it('returns a DataView from a slice of a byte array', () => {
+      const original = new Uint8Array([1, 2, 3, 4, 5]);
+      const subset = original.slice(1, 4);
+
+      const dataView = createDataView(subset);
+
+      expect(dataView).toBeInstanceOf(DataView);
+      expect(dataView.byteOffset).toBe(0);
+      expect(dataView.byteLength).toBe(3);
+      expect(dataView.getUint8(0)).toBe(2);
+      expect(dataView.getUint8(1)).toBe(3);
+      expect(dataView.getUint8(2)).toBe(4);
+    });
+  });
+
+  describe('Node.js Buffer', () => {
+    it('returns a DataView from a byte array', () => {
+      const dataView = createDataView(Buffer.from([1, 2, 3]));
+
+      expect(dataView).toBeInstanceOf(DataView);
+      expect(dataView.getUint8(0)).toBe(1);
+      expect(dataView.getUint8(1)).toBe(2);
+      expect(dataView.getUint8(2)).toBe(3);
+    });
+
+    it('returns a DataView from a subarray of a byte array', () => {
+      const original = Buffer.from([1, 2, 3, 4, 5]);
+      const subset = original.subarray(1, 4);
+
+      const dataView = createDataView(subset);
+
+      expect(dataView).toBeInstanceOf(DataView);
+      expect(dataView.byteOffset).toBe(0);
+      expect(dataView.byteLength).toBe(3);
+      expect(dataView.getUint8(0)).toBe(2);
+      expect(dataView.getUint8(1)).toBe(3);
+      expect(dataView.getUint8(2)).toBe(4);
+    });
+
+    it('returns a DataView from a slice of a byte array', () => {
+      const original = Buffer.from([1, 2, 3, 4, 5]);
+      const subset = original.slice(1, 4);
+
+      const dataView = createDataView(subset);
+
+      expect(dataView).toBeInstanceOf(DataView);
+      expect(dataView.byteOffset).toBe(0);
+      expect(dataView.byteLength).toBe(3);
+      expect(dataView.getUint8(0)).toBe(2);
+      expect(dataView.getUint8(1)).toBe(3);
+      expect(dataView.getUint8(2)).toBe(4);
+    });
+  });
+});

src/bytes.ts

@@ -393,3 +393,38 @@ export function concatBytes(values: Bytes[]): Uint8Array {
 
   return bytes;
 }
+
+/**
+ * Create a {@link DataView} from a {@link Uint8Array}. This is a convenience
+ * function that avoids having to create a {@link DataView} manually, which
+ * requires passing the `byteOffset` and `byteLength` parameters every time.
+ *
+ * Not passing the `byteOffset` and `byteLength` parameters can result in
+ * unexpected behavior when the {@link Uint8Array} is a view of a larger
+ * {@link ArrayBuffer}, e.g., when using {@link Uint8Array.subarray}.
+ *
+ * This function also supports Node.js {@link Buffer}s.
+ *
+ * @example
+ * ```typescript
+ * const bytes = new Uint8Array([1, 2, 3]);
+ *
+ * // This is equivalent to:
+ * // const dataView = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength);
+ * const dataView = createDataView(bytes);
+ * ```
+ * @param bytes - The bytes to create the {@link DataView} from.
+ * @returns The {@link DataView}.
+ */
+export function createDataView(bytes: Uint8Array): DataView {
+  if (typeof Buffer !== 'undefined' && bytes instanceof Buffer) {
+    const buffer = bytes.buffer.slice(
+      bytes.byteOffset,
+      bytes.byteOffset + bytes.byteLength,
+    );
+
+    return new DataView(buffer);
+  }
+
+  return new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength);
+}