refactor: improve ReadBuffer internal structure & logic

Author: Sahar Shemesh

src/shared/stdio.ts

@@ -4,54 +4,43 @@ import { JSONRPCMessage, JSONRPCMessageSchema } from '../types.js';
  * Buffers a continuous stdio stream into discrete JSON-RPC messages.
  */
 export class ReadBuffer {
-    private _buffer?: Buffer;
+    private _validLines: string[] = [];
+    private _lastIncompleteLine: string = '';
 
     append(chunk: Buffer): void {
-        this._buffer = filterNonJsonLines(this._buffer ? Buffer.concat([this._buffer, chunk]) : chunk);
+        this._processChunk(chunk);
     }
 
     readMessage(): JSONRPCMessage | null {
-        if (!this._buffer) {
+        if (this._validLines.length === 0) {
             return null;
         }
-
-        const index = this._buffer.indexOf('\n');
-        if (index === -1) {
-            return null;
-        }
-
-        const line = this._buffer.toString('utf8', 0, index).replace(/\r$/, '');
-        this._buffer = this._buffer.subarray(index + 1);
+        const line = this._validLines.shift()!;
         return deserializeMessage(line);
     }
 
     clear(): void {
-        this._buffer = undefined;
+        this._validLines = [];
+        this._lastIncompleteLine = '';
+    }
+    
+    private _processChunk(newChunk: Buffer): void {
+        // Combine any previously incomplete line with the new chunk
+        const combinedText = this._lastIncompleteLine + newChunk.toString('utf8');
+        const newLines = combinedText.split('\n');
+
+        // The last element may be incomplete, so store it for the next chunk
+        this._lastIncompleteLine = newLines.pop() ?? '';
+        const completedLines = newLines.filter(looksLikeJson);
+        this._validLines.push(...completedLines);
     }
 }
 
 /**
- * Filters out any lines that are not valid JSON objects from the given buffer.
- * Retains the last line in case it is incomplete.
- * @param buffer The buffer to filter.
- * @returns A new buffer containing only valid JSON object lines and the last line.
+ *  Checks if a line looks like a JSON object.
+ * @param line  The line to check.
+ * @returns True if the line looks like a JSON object, false otherwise.
  */
-function filterNonJsonLines(buffer: Buffer): Buffer {
-    const text = buffer.toString('utf8');
-    const lines = text.split('\n');
-
-    // Pop the last line - it may be incomplete (no trailing newline yet)
-    const incompleteLine = lines.pop() ?? '';
-
-    // Filter complete lines to only keep those that look like JSON objects
-    const validLines = lines.filter(looksLikeJson);
-
-    // Reconstruct: valid JSON lines + incomplete line
-    const filteredText = validLines.length > 0 ? validLines.join('\n') + '\n' + incompleteLine : incompleteLine;
-
-    return Buffer.from(filteredText, 'utf8');
-}
-
 function looksLikeJson(line: string): boolean {
     const trimmed = line.trim();
     return trimmed.startsWith('{') && trimmed.endsWith('}');