fix(cli): gemini command stuck in git bash (#6397)

Co-authored-by: Arya Gummadi <aryagummadi@google.com>

packages/cli/src/gemini.tsx

@@ -342,7 +342,9 @@ export async function main() {
     }
   }
   if (!input) {
-    console.error('No input provided via stdin.');
+    console.error(
+      `No input provided via stdin. Input can be provided by piping data into gemini or using the --prompt option.`,
+    );
     process.exit(1);
   }
 

packages/cli/src/utils/readStdin.test.ts

@@ -0,0 +1,112 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { vi, describe, expect, it, beforeEach, afterEach } from 'vitest';
+import { readStdin } from './readStdin.js';
+
+// Mock process.stdin
+const mockStdin = {
+  setEncoding: vi.fn(),
+  read: vi.fn(),
+  on: vi.fn(),
+  removeListener: vi.fn(),
+  destroy: vi.fn(),
+};
+
+describe('readStdin', () => {
+  let originalStdin: typeof process.stdin;
+  let onReadableHandler: () => void;
+  let onEndHandler: () => void;
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+    originalStdin = process.stdin;
+
+    // Replace process.stdin with our mock
+    Object.defineProperty(process, 'stdin', {
+      value: mockStdin,
+      writable: true,
+      configurable: true,
+    });
+
+    // Capture event handlers
+    mockStdin.on.mockImplementation((event: string, handler: () => void) => {
+      if (event === 'readable') onReadableHandler = handler;
+      if (event === 'end') onEndHandler = handler;
+    });
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+    Object.defineProperty(process, 'stdin', {
+      value: originalStdin,
+      writable: true,
+      configurable: true,
+    });
+  });
+
+  it('should read and accumulate data from stdin', async () => {
+    mockStdin.read
+      .mockReturnValueOnce('I love ')
+      .mockReturnValueOnce('Gemini!')
+      .mockReturnValueOnce(null);
+
+    const promise = readStdin();
+
+    // Trigger readable event
+    onReadableHandler();
+
+    // Trigger end to resolve
+    onEndHandler();
+
+    await expect(promise).resolves.toBe('I love Gemini!');
+  });
+
+  it('should handle empty stdin input', async () => {
+    mockStdin.read.mockReturnValue(null);
+
+    const promise = readStdin();
+
+    // Trigger end immediately
+    onEndHandler();
+
+    await expect(promise).resolves.toBe('');
+  });
+
+  // Emulate terminals where stdin is not TTY (eg: git bash)
+  it('should timeout and resolve with empty string when no input is available', async () => {
+    vi.useFakeTimers();
+
+    const promise = readStdin();
+
+    // Fast-forward past the timeout (to run test faster)
+    vi.advanceTimersByTime(500);
+
+    await expect(promise).resolves.toBe('');
+
+    vi.useRealTimers();
+  });
+
+  it('should clear timeout once when data is received and resolve with data', async () => {
+    const clearTimeoutSpy = vi.spyOn(global, 'clearTimeout');
+    mockStdin.read
+      .mockReturnValueOnce('chunk1')
+      .mockReturnValueOnce('chunk2')
+      .mockReturnValueOnce(null);
+
+    const promise = readStdin();
+
+    // Trigger readable event
+    onReadableHandler();
+
+    expect(clearTimeoutSpy).toHaveBeenCalledOnce();
+
+    // Trigger end to resolve
+    onEndHandler();
+
+    await expect(promise).resolves.toBe('chunk1chunk2');
+  });
+});

packages/cli/src/utils/readStdin.ts

@@ -9,86 +9,57 @@ export async function readStdin(): Promise<string> {
   return new Promise((resolve, reject) => {
     let data = '';
     let totalSize = 0;
-    let hasReceivedData = false;
-
     process.stdin.setEncoding('utf8');
 
-    function cleanup() {
-      clearTimeout(timeout);
+    const pipedInputShouldBeAvailableInMs = 500;
+    let pipedInputTimerId: null | NodeJS.Timeout = setTimeout(() => {
+      // stop reading if input is not available yet, this is needed
+      // in terminals where stdin is never TTY and nothing's piped
+      // which causes the program to get stuck expecting data from stdin
+      onEnd();
+    }, pipedInputShouldBeAvailableInMs);
+
+    const onReadable = () => {
+      let chunk;
+      while ((chunk = process.stdin.read()) !== null) {
+        if (pipedInputTimerId) {
+          clearTimeout(pipedInputTimerId);
+          pipedInputTimerId = null;
+        }
+
+        if (totalSize + chunk.length > MAX_STDIN_SIZE) {
+          const remainingSize = MAX_STDIN_SIZE - totalSize;
+          data += chunk.slice(0, remainingSize);
+          console.warn(
+            `Warning: stdin input truncated to ${MAX_STDIN_SIZE} bytes.`,
+          );
+          process.stdin.destroy(); // Stop reading further
+          break;
+        }
+        data += chunk;
+        totalSize += chunk.length;
+      }
+    };
+
+    const onEnd = () => {
+      cleanup();
+      resolve(data);
+    };
+
+    const onError = (err: Error) => {
+      cleanup();
+      reject(err);
+    };
+
+    const cleanup = () => {
+      if (pipedInputTimerId) {
+        clearTimeout(pipedInputTimerId);
+        pipedInputTimerId = null;
+      }
       process.stdin.removeListener('readable', onReadable);
       process.stdin.removeListener('end', onEnd);
       process.stdin.removeListener('error', onError);
-    }
-
-    function processChunk(chunk: string): boolean {
-      hasReceivedData = true;
-      if (totalSize + chunk.length > MAX_STDIN_SIZE) {
-        const remainingSize = MAX_STDIN_SIZE - totalSize;
-        data += chunk.slice(0, remainingSize);
-        console.warn(
-          `Warning: stdin input truncated to ${MAX_STDIN_SIZE} bytes.`,
-        );
-        process.stdin.destroy();
-        return true; // Indicates truncation occurred
-      } else {
-        data += chunk;
-        totalSize += chunk.length;
-        return false;
-      }
-    }
-
-    function checkInitialState(): boolean {
-      if (process.stdin.destroyed || process.stdin.readableEnded) {
-        cleanup();
-        resolve('');
-        return true;
-      }
-
-      const chunk = process.stdin.read();
-      if (chunk !== null) {
-        processChunk(chunk);
-        return false;
-      }
-
-      if (!process.stdin.readable) {
-        cleanup();
-        resolve('');
-        return true;
-      }
-
-      return false;
-    }
-
-    if (checkInitialState()) {
-      return;
-    }
-
-    function onReadable() {
-      let chunk;
-      while ((chunk = process.stdin.read()) !== null) {
-        const truncated = processChunk(chunk);
-        if (truncated) {
-          break;
-        }
-      }
-    }
-
-    function onEnd() {
-      cleanup();
-      resolve(data);
-    }
-
-    function onError(err: Error) {
-      cleanup();
-      reject(err);
-    }
-
-    const timeout = setTimeout(() => {
-      if (!hasReceivedData) {
-        cleanup();
-        resolve('');
-      }
-    }, 50);
+    };
 
     process.stdin.on('readable', onReadable);
     process.stdin.on('end', onEnd);