perf(objects): copy small Source contents out of the shared inflate buffer

scopes/scope/objects/models/source.spec.ts

@@ -0,0 +1,13 @@
+import { expect } from 'chai';
+import { deflateSync } from 'zlib';
+import { BitObject } from '../objects';
+import Source from './source';
+
+describe('Source', () => {
+  it('should not keep the whole inflated buffer when the file is small', async () => {
+    const file = Source.from(Buffer.from('const a = 1;'));
+    const parsed = (await BitObject.parseObject(deflateSync(file.serialize()))) as Source;
+    expect(parsed.contents.toString()).to.equal('const a = 1;');
+    expect(parsed.contents.buffer.byteLength).to.be.below(16 * 1024);
+  });
+});

scopes/scope/objects/models/source.ts

@@ -22,6 +22,9 @@ export default class Source extends BitObject {
   }
 
   static parse(contents: Buffer): Source {
+    // zlib returns small results as a slice of a bigger (16KB) buffer. unlike other objects, which are parsed and dropped,
+    // a Source keeps these bytes, often for long (e.g. as a component file), so it copies them instead of pinning 16KB.
+    if (contents.byteLength < contents.buffer.byteLength / 2) contents = Buffer.from(contents);
     return new Source(contents);
   }