pre-commit: Add license-header check inspired by Spicy

.pre-commit-config.yaml

@@ -2,6 +2,17 @@
 # See https://pre-commit.com/hooks.html for more hooks
 #
 repos:
+- repo: local
+  hooks:
+  - id: license
+    name: Check for license headers
+    entry: ./ci/license-header.py
+    language: python
+    types_or:
+      - "c"
+      - "c++"
+    exclude: '^(testing/btest/plugins/.*|testing/builtin-plugins/.*)$'
+
 - repo: https://github.com/pre-commit/mirrors-clang-format
   rev: 'v18.1.8'
   hooks:

ci/license-header.py

@@ -0,0 +1,36 @@
+#!/usr/bin/env python3
+
+import sys
+import re
+
+exit_code = 0
+
+pat1 = re.compile(r"See the file \"COPYING\" in the main distribution directory for copyright.")
+
+# This is the copyright line used within Spicy plugin and popular in
+# Spicy analyzers.
+pat2 = re.compile(r"Copyright \(c\) 2... by the Zeek Project. See COPYING for details.")
+
+
+def match_line(line):
+    for pat in [pat1, pat2]:
+        m = pat.search(line)
+        if m is not None:
+            return True
+
+    return False
+
+
+for f in sys.argv[1:]:
+    has_license_header = False
+    with open(f) as fp:
+        for line in fp:
+            line = line.strip()
+            if has_license_header := match_line(line):
+                break
+
+    if not has_license_header:
+        print(f"{f}:does not seem to contain a license header", file=sys.stderr)
+        exit_code = 1
+
+sys.exit(exit_code)