Add old state and diff logging on fuzzer update (google#5184)

Logs currently include only the fuzzer name. Previous state and diff
information can help identify issues with any updates to fuzzers.

---------

Co-authored-by: Titouan Rigoudy <titouan.rigoudy@gmail.com>

Author: tbantikyan

src/appengine/handlers/fuzzers.py

@@ -34,6 +34,10 @@
 from libs import helpers
 
 ARCHIVE_READ_SIZE_LIMIT = 16 * 1024 * 1024
+FUZZER_FIELDS_EXCLUDED_FROM_LOG = [
+    'result', 'result_timestamp', 'console_output', 'return_code',
+    'sample_testcase', 'stats_columns', 'stats_column_descriptions'
+]
 
 
 class Handler(base_handler.Handler):
@@ -139,6 +143,10 @@ def _get_integer_value(self, key):
 
     return value
 
+  def _get_fuzzer_state_str(self, fuzzer: data_types.Fuzzer) -> str:
+    fuzzer_dict = fuzzer.to_dict(exclude=FUZZER_FIELDS_EXCLUDED_FROM_LOG)
+    return '\n'.join(f"{key}: {val}" for key, val in fuzzer_dict.items())
+
   def apply_fuzzer_changes(self, fuzzer, upload_info):
     """Apply changes to a fuzzer."""
     if upload_info and not archive.is_archive(upload_info.filename):
@@ -160,6 +168,8 @@ def apply_fuzzer_changes(self, fuzzer, upload_info):
             'uploaded is less than 16MB, ensure that the executable file has '
             '"run" in its name.', 400)
 
+    existing_fuzzer_info = self._get_fuzzer_state_str(fuzzer)
+
     jobs = request.get('jobs', [])
     timeout = self._get_integer_value('timeout')
     max_testcases = self._get_integer_value('max_testcases')
@@ -201,7 +211,14 @@ def apply_fuzzer_changes(self, fuzzer, upload_info):
 
     fuzzer_selection.update_mappings_for_fuzzer(fuzzer)
 
-    helpers.log('Uploaded fuzzer %s.' % fuzzer.name, helpers.MODIFY_OPERATION)
+    new_fuzzer_info = self._get_fuzzer_state_str(fuzzer)
+    fuzzer_diff = helpers.diff(existing_fuzzer_info, new_fuzzer_info)
+    fuzzer_update_message = (f"\n--- Updated fuzzer {fuzzer.name} ---\n"
+                             f"{new_fuzzer_info}\n"
+                             f"--- Changes (Diff) ---\n"
+                             f"{fuzzer_diff}")
+    helpers.log(fuzzer_update_message, helpers.MODIFY_OPERATION)
+
     return self.redirect('/fuzzers')
 
 

src/appengine/libs/helpers.py

@@ -14,6 +14,7 @@
 """helper.py is a kitchen sink. It contains static methods that are used by
    multiple handlers."""
 
+import difflib
 import logging
 import sys
 import traceback
@@ -165,3 +166,17 @@ def log(message, operation_type):
   """Logs operation being carried by current logged-in user."""
   logging.info('ClusterFuzz: %s (%s): %s.', operation_type, get_user_email(),
                message)
+
+
+def diff(old_str: str, new_str: str) -> str:
+  """Generates the diff between the two provided strings."""
+  old_lines = old_str.splitlines(keepends=True)
+  new_lines = new_str.splitlines(keepends=True)
+
+  diff_generator = difflib.ndiff(old_lines, new_lines)
+  clean_diff = [
+      line for line in diff_generator
+      if line.startswith('- ') or line.startswith('+ ')
+  ]
+
+  return "".join(clean_diff)

src/clusterfuzz/_internal/tests/appengine/handlers/fuzzers_test.py

@@ -0,0 +1,58 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Tests for fuzzers handler."""
+# pylint: disable=protected-access
+
+import datetime
+import unittest
+
+from clusterfuzz._internal.datastore import data_types
+from handlers import fuzzers
+
+
+class BaseEditHandlerTest(unittest.TestCase):
+  """Test BaseEditHandler."""
+
+  def setUp(self):
+    self.handler = fuzzers.BaseEditHandler()
+
+  def test_get_fuzzer_state_str(self):
+    """Test that fuzzer state str excludes specific fields."""
+    fuzzer = data_types.Fuzzer(
+        name='test_fuzzer',
+        revision=1,
+        timeout=10,
+        result='bad',
+        console_output='some output',
+        result_timestamp=datetime.datetime(2021, 1, 1),
+        return_code=1,
+        sample_testcase='testcase',
+        stats_columns='cols',
+        stats_column_descriptions='desc',
+    )
+
+    state_str = self.handler._get_fuzzer_state_str(fuzzer)
+
+    self.assertIn('name: test_fuzzer', state_str)
+    self.assertIn('revision: 1', state_str)
+    self.assertIn('timeout: 10', state_str)
+
+    # Explicitly excluded fields
+    self.assertNotIn('result:', state_str)
+    self.assertNotIn('result_timestamp', state_str)
+    self.assertNotIn('console_output:', state_str)
+    self.assertNotIn('return_code:', state_str)
+    self.assertNotIn('sample_testcase:', state_str)
+    self.assertNotIn('stats_columns:', state_str)
+    self.assertNotIn('stats_column_descriptions:', state_str)

src/clusterfuzz/_internal/tests/appengine/libs/helpers_test.py

@@ -159,3 +159,27 @@ def test_view(self):
     helpers.log('message', helpers.VIEW_OPERATION)
     self.mock.info.assert_called_once_with(
         'ClusterFuzz: %s (%s): %s.', helpers.VIEW_OPERATION, 'email', 'message')
+
+
+class DiffTest(unittest.TestCase):
+  """Test diff."""
+
+  def test_diff_empty(self):
+    """Test diff with empty strings."""
+    self.assertEqual(helpers.diff('', ''), '')
+
+  def test_diff_no_change(self):
+    """Test diff with no changes."""
+    self.assertEqual(helpers.diff('a\nb\n', 'a\nb\n'), '')
+
+  def test_diff_addition(self):
+    """Test diff with addition."""
+    self.assertEqual(helpers.diff('a\nb\n', 'a\nb\nc\n'), '+ c\n')
+
+  def test_diff_deletion(self):
+    """Test diff with deletion."""
+    self.assertEqual(helpers.diff('a\nb\nc\n', 'a\nc\n'), '- b\n')
+
+  def test_diff_modification(self):
+    """Test diff with modification."""
+    self.assertEqual(helpers.diff('a\nb\nc\n', 'a\nd\nc\n'), '- b\n+ d\n')