align structure more with underlying chunk layout

src/decoders/chunk.ts

@@ -1,19 +1,29 @@
 import { Chunk } from '../models/chunk';
 
-export default (buffer: Uint8Array, dataDecoder: Function): Chunk => {
+export default (buffer: Uint8Array): Chunk => {
   let offset = 0;
   const view = new DataView(buffer.buffer, buffer.byteOffset, buffer.byteLength);
-  const chunk: Chunk = {};
-  chunk.id = view.getUint16(offset, true);
+  const id = view.getUint16(offset, true);
   offset += 2;
 
   // NOTE(jwetzell): this data is split up as 1 bit for has_subchunks and 15 bits for the data_len
   const combinedLengthAndFlag = view.getUint16(offset, true);
-  chunk.has_subchunks = combinedLengthAndFlag > 32768;
-  chunk.data_len = chunk.has_subchunks ? combinedLengthAndFlag - 32768 : combinedLengthAndFlag;
+  const hasSubchunks = combinedLengthAndFlag > 32768;
+  const dataLen = hasSubchunks ? combinedLengthAndFlag - 32768 : combinedLengthAndFlag;
   offset += 2;
-  chunk.chunk_data = buffer.slice(offset, offset + chunk.data_len);
 
-  dataDecoder(chunk);
+  const header = {
+    id,
+    dataLen,
+    hasSubchunks,
+  };
+
+  const chunkData = buffer.subarray(offset, offset + header.dataLen);
+
+  const chunk = {
+    chunkData,
+    header,
+  };
+
   return chunk;
 };