Cap dev-runner output buffering

Co-Authored-By: Paperclip <noreply@paperclip.ing>

scripts/dev-runner-output.mjs

@@ -0,0 +1,53 @@
+const DEFAULT_CAPTURED_OUTPUT_BYTES = 256 * 1024;
+
+export function createCapturedOutputBuffer(maxBytes = DEFAULT_CAPTURED_OUTPUT_BYTES) {
+  const limit = Math.max(1, Math.trunc(maxBytes));
+  const chunks = [];
+  let bufferedBytes = 0;
+  let totalBytes = 0;
+  let truncated = false;
+
+  return {
+    append(chunk) {
+      if (chunk === null || chunk === undefined) return;
+      const buffer = Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk);
+      if (buffer.length === 0) return;
+
+      chunks.push(buffer);
+      bufferedBytes += buffer.length;
+      totalBytes += buffer.length;
+
+      while (bufferedBytes > limit && chunks.length > 0) {
+        const overflow = bufferedBytes - limit;
+        const head = chunks[0];
+        if (head.length <= overflow) {
+          chunks.shift();
+          bufferedBytes -= head.length;
+          truncated = true;
+          continue;
+        }
+
+        chunks[0] = head.subarray(overflow);
+        bufferedBytes -= overflow;
+        truncated = true;
+      }
+    },
+
+    finish() {
+      const body = Buffer.concat(chunks).toString("utf8");
+      if (!truncated) {
+        return {
+          text: body,
+          truncated,
+          totalBytes,
+        };
+      }
+
+      return {
+        text: `[output truncated to last ${limit} bytes; total ${totalBytes} bytes]\n${body}`,
+        truncated,
+        totalBytes,
+      };
+    },
+  };
+}

scripts/dev-runner-output.ts

@@ -0,0 +1,59 @@
+const DEFAULT_CAPTURED_OUTPUT_BYTES = 256 * 1024;
+
+export type CapturedOutput = {
+  text: string;
+  truncated: boolean;
+  totalBytes: number;
+};
+
+export function createCapturedOutputBuffer(maxBytes = DEFAULT_CAPTURED_OUTPUT_BYTES) {
+  const limit = Math.max(1, Math.trunc(maxBytes));
+  const chunks: Buffer[] = [];
+  let bufferedBytes = 0;
+  let totalBytes = 0;
+  let truncated = false;
+
+  return {
+    append(chunk: Buffer | string | null | undefined) {
+      if (chunk === null || chunk === undefined) return;
+      const buffer = Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk);
+      if (buffer.length === 0) return;
+
+      chunks.push(buffer);
+      bufferedBytes += buffer.length;
+      totalBytes += buffer.length;
+
+      while (bufferedBytes > limit && chunks.length > 0) {
+        const overflow = bufferedBytes - limit;
+        const head = chunks[0]!;
+        if (head.length <= overflow) {
+          chunks.shift();
+          bufferedBytes -= head.length;
+          truncated = true;
+          continue;
+        }
+
+        chunks[0] = head.subarray(overflow);
+        bufferedBytes -= overflow;
+        truncated = true;
+      }
+    },
+
+    finish(): CapturedOutput {
+      const body = Buffer.concat(chunks).toString("utf8");
+      if (!truncated) {
+        return {
+          text: body,
+          truncated,
+          totalBytes,
+        };
+      }
+
+      return {
+        text: `[output truncated to last ${limit} bytes; total ${totalBytes} bytes]\n${body}`,
+        truncated,
+        totalBytes,
+      };
+    },
+  };
+}

scripts/dev-runner.mjs

@@ -5,6 +5,7 @@ import path from "node:path";
 import { createInterface } from "node:readline/promises";
 import { stdin, stdout } from "node:process";
 import { fileURLToPath } from "node:url";
+import { createCapturedOutputBuffer } from "./dev-runner-output.mjs";
 import { shouldTrackDevServerPath } from "./dev-runner-paths.mjs";
 
 const mode = process.argv[2] === "watch" ? "watch" : "dev";
@@ -250,30 +251,33 @@ async function runPnpm(args, options = {}) {
     const spawned = spawn(pnpmBin, args, {
       stdio: options.stdio ?? ["ignore", "pipe", "pipe"],
       env: options.env ?? process.env,
+      cwd: options.cwd,
       shell: process.platform === "win32",
     });
 
-    let stdoutBuffer = "";
-    let stderrBuffer = "";
+    const stdoutBuffer = createCapturedOutputBuffer();
+    const stderrBuffer = createCapturedOutputBuffer();
 
     if (spawned.stdout) {
       spawned.stdout.on("data", (chunk) => {
-        stdoutBuffer += String(chunk);
+        stdoutBuffer.append(chunk);
       });
     }
     if (spawned.stderr) {
       spawned.stderr.on("data", (chunk) => {
-        stderrBuffer += String(chunk);
+        stderrBuffer.append(chunk);
       });
     }
 
     spawned.on("error", reject);
     spawned.on("exit", (code, signal) => {
+      const stdout = stdoutBuffer.finish();
+      const stderr = stderrBuffer.finish();
       resolve({
         code: code ?? 0,
         signal,
-        stdout: stdoutBuffer,
-        stderr: stderrBuffer,
+        stdout: stdout.text,
+        stderr: stderr.text,
       });
     });
   });

scripts/dev-runner.ts

@@ -4,6 +4,7 @@ import { existsSync, mkdirSync, readdirSync, rmSync, statSync, writeFileSync } f
 import path from "node:path";
 import { createInterface } from "node:readline/promises";
 import { stdin, stdout } from "node:process";
+import { createCapturedOutputBuffer } from "./dev-runner-output.mjs";
 import { shouldTrackDevServerPath } from "./dev-runner-paths.mjs";
 import { createDevServiceIdentity, repoRoot } from "./dev-service-profile.ts";
 import {
@@ -315,27 +316,29 @@ async function runPnpm(args: string[], options: {
       shell: process.platform === "win32",
     });
 
-    let stdoutBuffer = "";
-    let stderrBuffer = "";
+    const stdoutBuffer = createCapturedOutputBuffer();
+    const stderrBuffer = createCapturedOutputBuffer();
 
     if (spawned.stdout) {
       spawned.stdout.on("data", (chunk) => {
-        stdoutBuffer += String(chunk);
+        stdoutBuffer.append(chunk);
       });
     }
     if (spawned.stderr) {
       spawned.stderr.on("data", (chunk) => {
-        stderrBuffer += String(chunk);
+        stderrBuffer.append(chunk);
       });
     }
 
     spawned.on("error", reject);
     spawned.on("exit", (code, signal) => {
+      const stdout = stdoutBuffer.finish();
+      const stderr = stderrBuffer.finish();
       resolve({
         code: code ?? 0,
         signal,
-        stdout: stdoutBuffer,
-        stderr: stderrBuffer,
+        stdout: stdout.text,
+        stderr: stderr.text,
       });
     });
   });

server/src/__tests__/dev-runner-output.test.ts

@@ -0,0 +1,29 @@
+import { describe, expect, it } from "vitest";
+import { createCapturedOutputBuffer } from "../../../scripts/dev-runner-output.mjs";
+
+describe("createCapturedOutputBuffer", () => {
+  it("keeps small output unchanged", () => {
+    const capture = createCapturedOutputBuffer(32);
+    capture.append("hello");
+    capture.append(" world");
+
+    expect(capture.finish()).toEqual({
+      text: "hello world",
+      totalBytes: 11,
+      truncated: false,
+    });
+  });
+
+  it("retains only the bounded tail when output grows large", () => {
+    const capture = createCapturedOutputBuffer(8);
+    capture.append("abcd");
+    capture.append(Buffer.from("efgh"));
+    capture.append("ijkl");
+
+    const result = capture.finish();
+    expect(result.truncated).toBe(true);
+    expect(result.totalBytes).toBe(12);
+    expect(result.text).toContain("total 12 bytes");
+    expect(result.text.endsWith("efghijkl")).toBe(true);
+  });
+});