Extract image MIME type detection to shared utility

Move BASE64_IMAGE_PREFIXES mapping and detect_image_mime_type() function
to openhands/tools/utils/image.py to eliminate code duplication.
Update browser_use to import from shared utility module.
Add comprehensive test coverage for the utility function.

Co-authored-by: openhands <[email protected]>

Author: openhands-agent

openhands-tools/openhands/tools/browser_use/definition.py

@@ -14,6 +14,7 @@
     register_tool,
 )
 from openhands.sdk.utils import maybe_truncate
+from openhands.tools.utils.image import detect_image_mime_type
 
 
 # Lazy import to avoid hanging during module import
@@ -24,29 +25,6 @@
 # Maximum output size for browser observations
 MAX_BROWSER_OUTPUT_SIZE = 50000
 
-# Mapping of base64 prefixes to MIME types for image detection
-BASE64_IMAGE_PREFIXES = {
-    "/9j/": "image/jpeg",
-    "iVBORw0KGgo": "image/png",
-    "R0lGODlh": "image/gif",
-    "UklGR": "image/webp",
-}
-
-
-def detect_image_mime_type(base64_data: str) -> str:
-    """Detect MIME type from base64-encoded image data.
-
-    Args:
-        base64_data: Base64-encoded image data
-
-    Returns:
-        Detected MIME type, defaults to "image/png" if not detected
-    """
-    for prefix, mime_type in BASE64_IMAGE_PREFIXES.items():
-        if base64_data.startswith(prefix):
-            return mime_type
-    return "image/png"
-
 
 class BrowserObservation(Observation):
     """Base observation for browser operations."""

openhands-tools/openhands/tools/utils/image.py

@@ -0,0 +1,24 @@
+"""Image-related utility functions."""
+
+# Mapping of base64 prefixes to MIME types for image detection
+BASE64_IMAGE_PREFIXES = {
+    "/9j/": "image/jpeg",
+    "iVBORw0KGgo": "image/png",
+    "R0lGODlh": "image/gif",
+    "UklGR": "image/webp",
+}
+
+
+def detect_image_mime_type(base64_data: str) -> str:
+    """Detect MIME type from base64-encoded image data.
+
+    Args:
+        base64_data: Base64-encoded image data
+
+    Returns:
+        Detected MIME type, defaults to "image/png" if not detected
+    """
+    for prefix, mime_type in BASE64_IMAGE_PREFIXES.items():
+        if base64_data.startswith(prefix):
+            return mime_type
+    return "image/png"

tests/tools/utils/__init__.py

@@ -0,0 +1 @@
+"""Tests for tool utilities."""

tests/tools/utils/test_image.py

@@ -0,0 +1,78 @@
+"""Tests for image utility functions."""
+
+import pytest
+
+from openhands.tools.utils.image import (
+    BASE64_IMAGE_PREFIXES,
+    detect_image_mime_type,
+)
+
+
+def test_base64_image_prefixes_mapping():
+    """Test that BASE64_IMAGE_PREFIXES contains expected mappings."""
+    assert BASE64_IMAGE_PREFIXES["/9j/"] == "image/jpeg"
+    assert BASE64_IMAGE_PREFIXES["iVBORw0KGgo"] == "image/png"
+    assert BASE64_IMAGE_PREFIXES["R0lGODlh"] == "image/gif"
+    assert BASE64_IMAGE_PREFIXES["UklGR"] == "image/webp"
+
+
+def test_detect_image_mime_type_jpeg():
+    """Test JPEG detection."""
+    jpeg_base64 = "/9j/4AAQSkZJRg..."
+    assert detect_image_mime_type(jpeg_base64) == "image/jpeg"
+
+
+def test_detect_image_mime_type_png():
+    """Test PNG detection."""
+    png_base64 = "iVBORw0KGgoAAAANSUhEUg..."
+    assert detect_image_mime_type(png_base64) == "image/png"
+
+
+def test_detect_image_mime_type_gif():
+    """Test GIF detection."""
+    gif_base64 = "R0lGODlhAQABAIAAAP..."
+    assert detect_image_mime_type(gif_base64) == "image/gif"
+
+
+def test_detect_image_mime_type_webp():
+    """Test WebP detection."""
+    webp_base64 = "UklGRiQAAABXRUJQ..."
+    assert detect_image_mime_type(webp_base64) == "image/webp"
+
+
+def test_detect_image_mime_type_unknown():
+    """Test unknown format defaults to PNG."""
+    unknown_base64 = "UNKNOWN_FORMAT_DATA"
+    assert detect_image_mime_type(unknown_base64) == "image/png"
+
+
+def test_detect_image_mime_type_empty_string():
+    """Test empty string defaults to PNG."""
+    assert detect_image_mime_type("") == "image/png"
+
+
+@pytest.mark.parametrize(
+    "base64_data,expected_mime",
+    [
+        (
+            "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mNk+M9QDwADhgGAWjR9awAAAABJRU5ErkJggg==",  # noqa: E501
+            "image/png",
+        ),
+        (
+            "/9j/4AAQSkZJRgABAQAAAQABAAD/2wBDAAEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQH/2wBDAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQH/wAARCAABAAEDASIAAhEBAxEB/8QAFQABAQAAAAAAAAAAAAAAAAAAAAv/xAAUEAEAAAAAAAAAAAAAAAAAAAAA/8QAFQEBAQAAAAAAAAAAAAAAAAAAAAX/xAAUEQEAAAAAAAAAAAAAAAAAAAAA/9oADAMBAAIRAxEAPwA/",  # noqa: E501
+            "image/jpeg",
+        ),
+        (
+            "R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7",
+            "image/gif",
+        ),
+        (
+            "UklGRiQAAABXRUJQVlA4IBgAAAAwAQCdASoBAAEAAQAcJaQAA3AA/v3AgAA=",
+            "image/webp",
+        ),
+        ("AAAABBBBCCCC", "image/png"),  # Unknown format
+    ],
+)
+def test_detect_image_mime_type_parametrized(base64_data, expected_mime):
+    """Test MIME type detection with various real base64 samples."""
+    assert detect_image_mime_type(base64_data) == expected_mime