fix(stdin): retry transient nonblocking reads

plugins/codex/scripts/lib/fs.mjs

@@ -32,9 +32,54 @@ export function isProbablyText(buffer) {
   return true;
 }
 
-export function readStdinIfPiped() {
-  if (process.stdin.isTTY) {
+const stdinRetryWaitArray = new Int32Array(new SharedArrayBuffer(Int32Array.BYTES_PER_ELEMENT));
+const STDIN_CHUNK_SIZE = 64 * 1024;
+
+function waitForStdinRetry(delayMs) {
+  Atomics.wait(stdinRetryWaitArray, 0, 0, delayMs);
+}
+
+function isTransientReadError(error) {
+  return error?.code === "EAGAIN" || error?.code === "EWOULDBLOCK";
+}
+
+export function readStdinIfPiped({
+  stdin = process.stdin,
+  readSync = fs.readSync,
+  waitForRetry = waitForStdinRetry,
+  maxAttempts = 8,
+  initialRetryDelayMs = 10,
+  maxRetryDelayMs = 500,
+  chunkSize = STDIN_CHUNK_SIZE
+} = {}) {
+  if (stdin.isTTY) {
     return "";
   }
-  return fs.readFileSync(0, "utf8");
+
+  try {
+    Reflect.get(stdin, "_handle")?.setBlocking?.(true);
+  } catch {
+    // Some stdin handle types do not support changing blocking mode.
+  }
+
+  const chunks = [];
+  let transientAttempts = 0;
+  let retryDelayMs = initialRetryDelayMs;
+  while (true) {
+    const chunk = Buffer.allocUnsafe(chunkSize);
+    try {
+      const bytesRead = readSync(0, chunk, 0, chunk.length, null);
+      if (bytesRead === 0) {
+        return Buffer.concat(chunks).toString("utf8");
+      }
+      chunks.push(chunk.subarray(0, bytesRead));
+    } catch (error) {
+      transientAttempts += 1;
+      if (!isTransientReadError(error) || transientAttempts >= maxAttempts) {
+        throw error;
+      }
+      waitForRetry(retryDelayMs);
+      retryDelayMs = Math.min(retryDelayMs * 2, maxRetryDelayMs);
+    }
+  }
 }

tests/fs.test.mjs

@@ -0,0 +1,77 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+
+import { readStdinIfPiped } from "../plugins/codex/scripts/lib/fs.mjs";
+
+function scriptedRead(steps, events = []) {
+  return (fd, buffer, offset, length, position) => {
+    events.push(["read", fd, offset, length, position]);
+    const step = steps.shift();
+    if (step instanceof Error) throw step;
+    if (step == null) return 0;
+    const bytes = Buffer.from(step);
+    bytes.copy(buffer, offset);
+    return bytes.length;
+  };
+}
+
+function transient(code = "EAGAIN") {
+  return Object.assign(new Error("resource temporarily unavailable"), { code });
+}
+
+test("readStdinIfPiped preserves bytes consumed before a transient read failure", () => {
+  const events = [];
+  const input = readStdinIfPiped({
+    stdin: { isTTY: false, _handle: { setBlocking: (value) => events.push(["blocking", value]) } },
+    readSync: scriptedRead(["first-", transient(), "second\n", null], events),
+    waitForRetry: (delay) => events.push(["wait", delay]),
+    chunkSize: 32
+  });
+  assert.equal(input, "first-second\n");
+  assert.deepEqual(events[0], ["blocking", true]);
+  assert.deepEqual(events.filter((event) => event[0] === "wait"), [["wait", 10]]);
+});
+
+test("readStdinIfPiped treats EWOULDBLOCK as transient and bounds backoff", () => {
+  const error = transient("EWOULDBLOCK");
+  const waits = [];
+  assert.throws(() => readStdinIfPiped({
+    stdin: { isTTY: false },
+    readSync() { throw error; },
+    waitForRetry: (delay) => waits.push(delay),
+    maxAttempts: 5,
+    initialRetryDelayMs: 10,
+    maxRetryDelayMs: 25
+  }), (actual) => actual === error);
+  assert.deepEqual(waits, [10, 20, 25, 25]);
+});
+
+test("readStdinIfPiped surfaces non-transient read errors without retrying", () => {
+  const error = Object.assign(new Error("bad descriptor"), { code: "EBADF" });
+  let waits = 0;
+  assert.throws(() => readStdinIfPiped({
+    stdin: { isTTY: false },
+    readSync() { throw error; },
+    waitForRetry() { waits += 1; }
+  }), (actual) => actual === error);
+  assert.equal(waits, 0);
+});
+
+test("readStdinIfPiped ignores unsupported blocking mode and reads all chunks", () => {
+  const input = readStdinIfPiped({
+    stdin: { isTTY: false, _handle: { setBlocking() { throw new Error("unsupported"); } } },
+    readSync: scriptedRead(["ordinary ", "pipe", null]),
+    waitForRetry() { throw new Error("unexpected retry"); }
+  });
+  assert.equal(input, "ordinary pipe");
+});
+
+test("readStdinIfPiped returns empty input for a TTY without touching fd 0", () => {
+  let reads = 0;
+  const input = readStdinIfPiped({
+    stdin: { isTTY: true },
+    readSync() { reads += 1; return 0; }
+  });
+  assert.equal(input, "");
+  assert.equal(reads, 0);
+});