2 files changed, 70 insertions, 0 deletions
diff --git a/packages/cli/src/ui/utils/textUtils.test.ts b/packages/cli/src/ui/utils/textUtils.test.ts
new file mode 100644
index 00000000..5dd08875
--- /dev/null
+++ b/packages/cli/src/ui/utils/textUtils.test.ts
@@ -0,0 +1,41 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { isBinary } from './textUtils';
+
+describe('textUtils', () => {
+  describe('isBinary', () => {
+    it('should return true for a buffer containing a null byte', () => {
+      const buffer = Buffer.from([
+        0x89, 0x50, 0x4e, 0x47, 0x0d, 0x1a, 0x0a, 0x00,
+      ]);
+      expect(isBinary(buffer)).toBe(true);
+    });
+
+    it('should return false for a buffer containing only text', () => {
+      const buffer = Buffer.from('This is a test string.');
+      expect(isBinary(buffer)).toBe(false);
+    });
+
+    it('should return false for an empty buffer', () => {
+      const buffer = Buffer.from([]);
+      expect(isBinary(buffer)).toBe(false);
+    });
+
+    it('should return false for a null or undefined buffer', () => {
+      expect(isBinary(null)).toBe(false);
+      expect(isBinary(undefined)).toBe(false);
+    });
+
+    it('should only check the sample size', () => {
+      const longBufferWithNullByteAtEnd = Buffer.concat([
+        Buffer.from('a'.repeat(1024)),
+        Buffer.from([0x00]),
+      ]);
+      expect(isBinary(longBufferWithNullByteAtEnd, 512)).toBe(false);
+    });
+  });
+});
diff --git a/packages/cli/src/ui/utils/textUtils.ts b/packages/cli/src/ui/utils/textUtils.ts
index 12852865..35e4c4a2 100644
--- a/packages/cli/src/ui/utils/textUtils.ts
+++ b/packages/cli/src/ui/utils/textUtils.ts
@@ -16,3 +16,32 @@ export const getAsciiArtWidth = (asciiArt: string): number => {
   const lines = asciiArt.split('\n');
   return Math.max(...lines.map((line) => line.length));
 };
+
+/**
+ * Checks if a Buffer is likely binary by testing for the presence of a NULL byte.
+ * The presence of a NULL byte is a strong indicator that the data is not plain text.
+ * @param data The Buffer to check.
+ * @param sampleSize The number of bytes from the start of the buffer to test.
+ * @returns True if a NULL byte is found, false otherwise.
+ */
+export function isBinary(
+  data: Buffer | null | undefined,
+  sampleSize = 512,
+): boolean {
+  if (!data) {
+    return false;
+  }
+
+  const sample = data.length > sampleSize ? data.subarray(0, sampleSize) : data;
+
+  for (let i = 0; i < sample.length; i++) {
+    // The presence of a NULL byte (0x00) is one of the most reliable
+    // indicators of a binary file. Text files should not contain them.
+    if (sample[i] === 0) {
+      return true;
+    }
+  }
+
+  // If no NULL bytes were found in the sample, we assume it's text.
+  return false;
+}