fix: parse lsp content length by byte

steipete · steipete · commit 0d66710539ca · 2026-05-28T12:29:45.000-04:00
diff --git a/src/agents/agent-bundle-lsp-runtime.test.ts b/src/agents/agent-bundle-lsp-runtime.test.ts
@@ -46,7 +46,7 @@ class MockChildProcess extends EventEmitter {
   readonly stderr = new PassThrough();
   readonly stdin: Writable;
 
-  constructor() {
+  constructor(private readonly initializeResponsePrefix = "") {
     super();
     this.stdin = new Writable({
       write: (chunk, _encoding, callback) => {
@@ -71,7 +71,9 @@ class MockChildProcess extends EventEmitter {
     }
     const result = body.method === "initialize" ? { capabilities: { hoverProvider: true } } : null;
     queueMicrotask(() => {
-      this.stdout.write(encodeLspMessage({ jsonrpc: "2.0", id: body.id, result }));
+      this.stdout.write(
+        `${this.initializeResponsePrefix}${encodeLspMessage({ jsonrpc: "2.0", id: body.id, result })}`,
+      );
     });
   }
 }
@@ -119,6 +121,23 @@ describe("bundle LSP runtime", () => {
     expect(killProcessTreeMock).toHaveBeenCalledWith(4321, { graceMs: 1000 });
   });
 
+  it("keeps LSP framing aligned after multibyte messages in the same chunk", async () => {
+    configureSingleLspServer();
+    const prefix = encodeLspMessage({
+      jsonrpc: "2.0",
+      method: "window/logMessage",
+      params: { message: "ready té" },
+    });
+    const child = new MockChildProcess(prefix);
+    spawnMock.mockReturnValue(child);
+    const { createBundleLspToolRuntime } = await import("./agent-bundle-lsp-runtime.js");
+
+    const runtime = await createBundleLspToolRuntime({ workspaceDir: "/tmp/workspace" });
+
+    expect(runtime.tools.map((tool) => tool.name)).toContain("lsp_hover_typescript");
+    await runtime.dispose();
+  });
+
   it("disposes active LSP sessions from the global shutdown sweep", async () => {
     configureSingleLspServer();
     const child = new MockChildProcess();
diff --git a/src/agents/agent-bundle-lsp-runtime.ts b/src/agents/agent-bundle-lsp-runtime.ts
@@ -25,7 +25,7 @@ type LspSession = {
   process: ChildProcess;
   requestId: number;
   pendingRequests: Map<number, PendingLspRequest>;
-  buffer: string;
+  buffer: Buffer;
   initialized: boolean;
   capabilities: LspServerCapabilities;
   disposed: boolean;
@@ -93,7 +93,7 @@ function createLspSession(serverName: string, child: ChildProcess): LspSession {
     process: child,
     requestId: 0,
     pendingRequests: new Map(),
-    buffer: "",
+    buffer: Buffer.alloc(0),
     initialized: false,
     capabilities: {},
     disposed: false,
@@ -105,8 +105,9 @@ function registerActiveLspSession(session: LspSession): void {
 }
 
 function attachLspProcessHandlers(session: LspSession): void {
-  session.process.stdout?.setEncoding("utf-8");
-  session.process.stdout?.on("data", (chunk: string) => handleIncomingData(session, chunk));
+  session.process.stdout?.on("data", (chunk: Buffer | string) =>
+    handleIncomingData(session, chunk),
+  );
   session.process.stderr?.setEncoding("utf-8");
   session.process.stderr?.on("data", (chunk: string) => {
     for (const line of chunk.split(/\r?\n/).filter(Boolean)) {
@@ -120,38 +121,39 @@ function encodeLspMessage(body: unknown): string {
   return `Content-Length: ${Buffer.byteLength(json, "utf-8")}\r\n\r\n${json}`;
 }
 
-function parseLspMessages(buffer: string): { messages: unknown[]; remaining: string } {
+function parseLspMessages(buffer: Buffer): { messages: unknown[]; remaining: Buffer } {
   const messages: unknown[] = [];
   let remaining = buffer;
+  const headerSeparator = Buffer.from("\r\n\r\n", "ascii");
 
   while (true) {
-    const headerEnd = remaining.indexOf("\r\n\r\n");
+    const headerEnd = remaining.indexOf(headerSeparator);
     if (headerEnd === -1) {
       break;
     }
 
-    const header = remaining.slice(0, headerEnd);
+    const header = remaining.subarray(0, headerEnd).toString("ascii");
     const match = header.match(/Content-Length:\s*(\d+)/i);
     if (!match) {
-      remaining = remaining.slice(headerEnd + 4);
+      remaining = remaining.subarray(headerEnd + headerSeparator.length);
       continue;
     }
 
     const contentLength = Number.parseInt(match[1], 10);
-    const bodyStart = headerEnd + 4;
+    const bodyStart = headerEnd + headerSeparator.length;
     const bodyEnd = bodyStart + contentLength;
 
-    if (Buffer.byteLength(remaining.slice(bodyStart), "utf-8") < contentLength) {
+    if (remaining.length < bodyEnd) {
       break;
     }
 
     try {
-      const body = remaining.slice(bodyStart, bodyStart + contentLength);
+      const body = remaining.subarray(bodyStart, bodyEnd).toString("utf8");
       messages.push(JSON.parse(body));
     } catch {
       // skip malformed
     }
-    remaining = remaining.slice(bodyEnd);
+    remaining = remaining.subarray(bodyEnd);
   }
 
   return { messages, remaining };
@@ -174,10 +176,13 @@ function sendRequest(session: LspSession, method: string, params?: unknown): Pro
   });
 }
 
-function handleIncomingData(session: LspSession, chunk: string) {
-  session.buffer += chunk;
+function handleIncomingData(session: LspSession, chunk: Buffer | string) {
+  session.buffer = Buffer.concat([
+    session.buffer,
+    typeof chunk === "string" ? Buffer.from(chunk, "utf8") : chunk,
+  ]);
   const { messages, remaining } = parseLspMessages(session.buffer);
-  session.buffer = remaining;
+  session.buffer = remaining.length === 0 ? Buffer.alloc(0) : Buffer.from(remaining);
 
   for (const msg of messages) {
     if (typeof msg !== "object" || msg === null) {
