[v1.x] fix(stdio): release consumed ReadBuffer storage

src/shared/stdio.ts

@@ -33,7 +33,8 @@ export class ReadBuffer {
         }
 
         const line = this._buffer.toString('utf8', 0, index).replace(/\r$/, '');
-        this._buffer = this._buffer.subarray(index + 1);
+        const remainder = this._buffer.subarray(index + 1);
+        this._buffer = remainder.length === 0 ? undefined : remainder;
         return deserializeMessage(line);
     }
 

test/shared/stdio.test.ts

@@ -1,3 +1,4 @@
+import { vi } from 'vitest';
 import { JSONRPCMessage } from '../../src/types.js';
 import { STDIO_DEFAULT_MAX_BUFFER_SIZE, ReadBuffer } from '../../src/shared/stdio.js';
 
@@ -34,6 +35,53 @@ test('should be reusable after clearing', () => {
     expect(readBuffer.readMessage()).toEqual(testMessage);
 });
 
+describe('consumed buffer', () => {
+    afterEach(() => {
+        vi.restoreAllMocks();
+    });
+
+    test('should release the backing allocation after the final newline', () => {
+        const readBuffer = new ReadBuffer();
+        const message = Buffer.from(JSON.stringify(testMessage) + '\n');
+        const allocation = Buffer.alloc(64 * 1024);
+        message.copy(allocation);
+        readBuffer.append(allocation.subarray(0, message.length));
+
+        expect(readBuffer.readMessage()).toEqual(testMessage);
+        expect(readBuffer).toHaveProperty('_buffer', undefined);
+        expect(readBuffer.readMessage()).toBeNull();
+    });
+
+    test('should append the next chunk without copying after draining', () => {
+        const readBuffer = new ReadBuffer();
+        readBuffer.append(Buffer.from(JSON.stringify(testMessage) + '\n'));
+        expect(readBuffer.readMessage()).toEqual(testMessage);
+
+        const nextChunk = Buffer.from(JSON.stringify(testMessage) + '\n');
+        const concatSpy = vi.spyOn(Buffer, 'concat');
+        readBuffer.append(nextChunk);
+
+        expect(concatSpy).not.toHaveBeenCalled();
+        expect(readBuffer.readMessage()).toEqual(testMessage);
+        expect(readBuffer.readMessage()).toBeNull();
+    });
+
+    test('should preserve a partial message after a complete message', () => {
+        const readBuffer = new ReadBuffer();
+        const nextMessage: JSONRPCMessage = { jsonrpc: '2.0', method: 'second' };
+        const message = JSON.stringify(nextMessage);
+        const split = Math.floor(message.length / 2);
+        readBuffer.append(Buffer.from(JSON.stringify(testMessage) + '\n' + message.slice(0, split)));
+
+        expect(readBuffer.readMessage()).toEqual(testMessage);
+        expect(readBuffer.readMessage()).toBeNull();
+
+        readBuffer.append(Buffer.from(message.slice(split) + '\r\n'));
+        expect(readBuffer.readMessage()).toEqual(nextMessage);
+        expect(readBuffer.readMessage()).toBeNull();
+    });
+});
+
 describe('buffer size limit', () => {
     test('should throw when buffer exceeds default max size', () => {
         const readBuffer = new ReadBuffer();