feat(rustbridge): add streaming responses and robust large-payload/backpressure handling to RustBridge

test/helpers/mock-rust-binary.mjs

@@ -2,22 +2,46 @@
 
 /**
  * Mock "Rust binary" for testing the RustBridge IPC protocol.
- * Reads JSON lines from stdin, writes JSON lines to stdout.
+ * Reads JSON lines from stdin via Buffer-based scanner, writes JSON lines to stdout.
  * Emits a ready event on startup.
  */
 
-import { createInterface } from 'readline';
-
 // Emit ready event
 const readyEvent = JSON.stringify({ event: 'ready', data: { version: '1.0.0' } });
 process.stdout.write(readyEvent + '\n');
 
-const rl = createInterface({ input: process.stdin });
+// Buffer-based newline scanner for stdin (mirrors the RustBridge approach)
+let stdinBuffer = Buffer.alloc(0);
 
-rl.on('line', (line) => {
+process.stdin.on('data', (chunk) => {
+  stdinBuffer = Buffer.concat([stdinBuffer, chunk]);
+
+  let newlineIndex;
+  while ((newlineIndex = stdinBuffer.indexOf(0x0A)) !== -1) {
+    const lineBuffer = stdinBuffer.subarray(0, newlineIndex);
+    stdinBuffer = stdinBuffer.subarray(newlineIndex + 1);
+    const line = lineBuffer.toString('utf8').trim();
+    if (line) {
+      handleLine(line);
+    }
+  }
+});
+
+/**
+ * Backpressure-aware write to stdout.
+ */
+function writeResponse(data) {
+  const json = JSON.stringify(data) + '\n';
+  if (!process.stdout.write(json)) {
+    // Wait for drain before continuing
+    process.stdout.once('drain', () => {});
+  }
+}
+
+function handleLine(line) {
   let request;
   try {
-    request = JSON.parse(line.trim());
+    request = JSON.parse(line);
   } catch {
     return;
   }
@@ -26,35 +50,53 @@ rl.on('line', (line) => {
 
   if (method === 'echo') {
     // Echo back the params as result
-    const response = JSON.stringify({ id, success: true, result: params });
-    process.stdout.write(response + '\n');
+    writeResponse({ id, success: true, result: params });
+  } else if (method === 'largeEcho') {
+    // Echo back params (same as echo, named distinctly for large payload tests)
+    writeResponse({ id, success: true, result: params });
   } else if (method === 'error') {
     // Return an error
-    const response = JSON.stringify({ id, success: false, error: 'Test error message' });
-    process.stdout.write(response + '\n');
+    writeResponse({ id, success: false, error: 'Test error message' });
   } else if (method === 'emitEvent') {
     // Emit a custom event, then respond with success
-    const event = JSON.stringify({ event: params.eventName, data: params.eventData });
-    process.stdout.write(event + '\n');
-    const response = JSON.stringify({ id, success: true, result: null });
-    process.stdout.write(response + '\n');
+    writeResponse({ event: params.eventName, data: params.eventData });
+    writeResponse({ id, success: true, result: null });
   } else if (method === 'slow') {
     // Respond after a delay
     setTimeout(() => {
-      const response = JSON.stringify({ id, success: true, result: { delayed: true } });
-      process.stdout.write(response + '\n');
+      writeResponse({ id, success: true, result: { delayed: true } });
     }, 100);
+  } else if (method === 'streamEcho') {
+    // Send params.count stream chunks, then final response
+    const count = params.count || 0;
+    let sent = 0;
+    const interval = setInterval(() => {
+      if (sent < count) {
+        writeResponse({ id, stream: true, data: { index: sent, value: `chunk_${sent}` } });
+        sent++;
+      } else {
+        clearInterval(interval);
+        writeResponse({ id, success: true, result: { totalChunks: count } });
+      }
+    }, 10);
+  } else if (method === 'streamError') {
+    // Send 1 chunk, then error
+    writeResponse({ id, stream: true, data: { index: 0, value: 'before_error' } });
+    setTimeout(() => {
+      writeResponse({ id, success: false, error: 'Stream error after chunk' });
+    }, 20);
+  } else if (method === 'streamEmpty') {
+    // Zero chunks, immediate final response
+    writeResponse({ id, success: true, result: { totalChunks: 0 } });
   } else if (method === 'exit') {
     // Graceful exit
-    const response = JSON.stringify({ id, success: true, result: null });
-    process.stdout.write(response + '\n');
+    writeResponse({ id, success: true, result: null });
     process.exit(0);
   } else {
     // Unknown command
-    const response = JSON.stringify({ id, success: false, error: `Unknown method: ${method}` });
-    process.stdout.write(response + '\n');
+    writeResponse({ id, success: false, error: `Unknown method: ${method}` });
   }
-});
+}
 
 // Handle SIGTERM gracefully
 process.on('SIGTERM', () => {