Add a license-checking Python script (#123)

* Add a license-checking Python script

* Responses to CR

config/check_license.py

@@ -0,0 +1,47 @@
+# Copyright 2019 The Nomulus Authors. All Rights Reserved.
+#
+# 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.
+
+import os
+import sys
+import re
+
+license = r".*Copyright \d{4} The Nomulus Authors\. All Rights Reserved\."
+extensions = ("java", "js", "soy", "sql", "py", "sh")
+non_included_patterns = {".git", "/build/", "/generated/", "node_modules/", "JUnitBackports.java", }
+
+def should_include_path(path):
+    for pattern in non_included_patterns:
+        if pattern in path: return False
+    return path.endswith(extensions)
+
+def get_files():
+    result = []
+    for root, dirnames, filenames in os.walk("."):
+        paths = [os.path.join(root, filename) for filename in filenames]
+        result.extend(filter(should_include_path, paths))
+    return result
+
+if __name__ == "__main__":
+    all_files = get_files()
+    failed_files = []
+
+    for file in all_files:
+        with open(file, 'r') as f:
+            file_content = f.read()
+            if not re.match(license, file_content, re.DOTALL):
+                failed_files.append(file)
+
+    if failed_files:
+        print("The following files did not match the license header: " + str(failed_files))
+        sys.exit(1)