Tools: Check the last modified date in make-tls-ct-logids.py

In "update" mode, exclude the last modified time when comparing against
the current code block.

tools/make-tls-ct-logids.py

@@ -9,7 +9,9 @@
 
 import argparse
 from base64 import b64decode, b64encode
+from enum import Enum
 import itertools
+import os
 import requests
 from hashlib import sha256
 
@@ -19,12 +21,18 @@ HEADER = "/* Generated by tools/make-tls-ct-logids.py\n"
 # See also https://www.certificate-transparency.org/known-logs
 CT_JSON_URL = 'https://www.gstatic.com/ct/log_list/v3/all_logs_list.json'
 # File to be patched
-SOURCE_FILE = "epan/dissectors/packet-tls-utils.c"
+SOURCE_FILE = os.path.join('epan', 'dissectors', 'packet-tls-utils.c')
 
 # Maximum elements per line in the value array. 11 is chosen because it results
 # in output consistent with clang-format.
 BYTES_PER_LINE = 11
 
+class SourceStage(Enum):
+    BEGIN = 1
+    IN_METAINFO = 2
+    IN_BLOCK = 3
+    END = 4
+
 
 def escape_c(s):
     return s.replace('\\', '\\\\').replace('"', '\\"')
@@ -36,47 +44,55 @@ def byteshex(b):
 
 def process_json(obj, lastmod):
     logs = list(itertools.chain(*[op['logs'] for op in obj['operators']]))
-    lines = HEADER
-    lines += " * Last-Modified %s, %s entries. */\n" % (lastmod, len(logs))
-    lines += "static const bytes_string ct_logids[] = {\n"
+    metainfo, block = HEADER, ''
+    metainfo += " * Last-Modified %s, %s entries. */\n" % (lastmod, len(logs))
+    block += "static const bytes_string ct_logids[] = {\n"
     for entry in logs:
         desc = entry["description"]
         pubkey_der = b64decode(entry["key"])
         key_id = sha256(pubkey_der).digest()
-        lines += '    { (const guint8[]){\n'
+        block += '    { (const guint8[]){\n'
         for offset in range(0, len(key_id), BYTES_PER_LINE):
-            lines += '          %s\n' % \
+            block += '          %s\n' % \
                 byteshex(key_id[offset:offset+BYTES_PER_LINE])
-        lines += '      },\n'
-        lines += '      %d, "%s" },\n' % (len(key_id), escape_c(desc))
-    lines += "    { NULL, 0, NULL }\n"
-    lines += "};\n"
-    return lines
+        block += '      },\n'
+        block += '      %d, "%s" },\n' % (len(key_id), escape_c(desc))
+    block += "    { NULL, 0, NULL }\n"
+    block += "};\n"
+    return metainfo, block
 
 
-def parse_source():
+def parse_source(source_path):
     """
     Reads the source file and tries to split it in the parts before, inside and
     after the block.
     """
-    begin, block, end = '', '', ''
-    # Stages: 1 (before block), 2 (in block, skip), 3 (after block)
-    stage = 1
-    with open(SOURCE_FILE) as f:
+    begin, metainfo, block, end = '', '', '', ''
+    # Stages: BEGIN (before block), IN_METAINFO, IN_BLOCK (skip), END
+    stage = SourceStage.BEGIN
+    with open(source_path) as f:
         for line in f:
-            if line == HEADER:
-                stage = 2   # Begin of block
-            if stage == 1:
+            if line.startswith('/* Generated by '):
+                stage = SourceStage.IN_METAINFO
+
+
+            if stage == SourceStage.BEGIN:
                 begin += line
-            elif stage == 2:
+            elif stage == SourceStage.IN_METAINFO:
+                metainfo += line
+            elif stage == SourceStage.IN_BLOCK:
                 block += line
                 if line.startswith('}'):
-                    stage = 3   # End of block reached
-            elif stage == 3:
+                    stage = SourceStage.END
+            elif stage == SourceStage.END:
                 end += line
-    if stage != 3:
-        raise RuntimeError("Could not parse file (in stage %d)" % stage)
-    return begin, block, end
+
+            if line.startswith(' * Last-Modified '):
+                stage = SourceStage.IN_BLOCK
+
+    if stage != SourceStage.END:
+        raise RuntimeError("Could not parse file (in stage %s)" % stage.name)
+    return begin, metainfo, block, end
 
 
 parser = argparse.ArgumentParser()
@@ -86,21 +102,24 @@ parser.add_argument("--update", action="store_true",
 
 def main():
     args = parser.parse_args()
+    this_dir = os.path.dirname(__file__)
     r = requests.get(CT_JSON_URL)
-    code = process_json(r.json(), lastmod=r.headers['Last-Modified'])
+    j_metainfo, j_block = process_json(r.json(), lastmod=r.headers['Last-Modified'])
+    source_path = os.path.join(this_dir, '..', SOURCE_FILE)
 
     if args.update:
-        begin, block, end = parse_source()
-        if block == code:
+        s_begin, _, s_block, s_end = parse_source(source_path)
+        if s_block == j_block:
             print("File is up-to-date")
         else:
-            with open(SOURCE_FILE, "w") as f:
-                f.write(begin)
-                f.write(code)
-                f.write(end)
-            print("Updated %s" % SOURCE_FILE)
+            with open(source_path, "w") as f:
+                f.write(s_begin)
+                f.write(j_metainfo)
+                f.write(j_block)
+                f.write(s_end)
+            print("Updated %s" % source_path)
     else:
-        print(code)
+        print(j_metainfo, j_block)
 
 
 if __name__ == '__main__':