Add cache file versioning, distrust cache with different version

ChangeLog

@@ -3,6 +3,7 @@ ChangeLog
 0.2.0dev
     * Improve automatic thumbnail and preview selection
     * `sl1s` added as sla extension gcode type
+    * Add cache file versioning, distrust cache files with a different version
 
 0.1.0
     * Initial release

gcode_metadata/metadata.py

@@ -9,6 +9,7 @@
 import zipfile
 from typing import Dict, Any, Type, Callable, List, Optional
 from logging import getLogger
+from importlib.metadata import version
 
 GCODE_EXTENSIONS = (".gcode", ".gc", ".g", ".gco")
 SLA_EXTENSIONS = ("sl1", "sl1s")
@@ -238,14 +239,46 @@ def cache_name(self):
         return new_path
 
     def is_cache_fresh(self):
-        """If cache is fresher than file, returns True"""
+        """Checks if we can use the current cache file"""
+        return self.is_cache_recent() and self.is_cache_correct_version()
+
+    def is_cache_recent(self):
+        """Checks if the cache file is newer than the source file"""
         try:
             file_time_created = os.path.getctime(self.path)
             cache_time_created = os.path.getctime(self.cache_name)
-            return file_time_created < cache_time_created
         except FileNotFoundError:
             return False
 
+        return file_time_created > cache_time_created
+
+    def is_cache_correct_version(self):
+        """Checks if the cache file was created with the same version
+        of gcode-metadata"""
+
+        def isallowed(char):
+            """Filters out dissalowed characters, used with str.filter"""
+            return char not in "\",\n} "
+
+        # This expects the first item in the json file to be the
+        # gcode-metadata version, with which the cache was created.
+        # If it's not there, or the version is different, the cache is deleted
+        with open(self.cache_name, "r", encoding="utf-8") as file:
+            for line in file:
+                if text := "".join(filter(str.isalpha, line)):
+                    if text.startswith("version"):
+                        break
+                    return False
+            else:  # didn't reach break
+                return False
+            first_pair = line.split(",", 1)[0]
+            _, version_part = first_pair.split(":", 1)
+            file_version = "".join(filter(isallowed, version_part))
+            if file_version == version('gcode-metadata'):
+                return True
+
+        return False
+
     def save_cache(self):
         """Take metadata from source file and save them as JSON to
         <file_name>.cache file.
@@ -264,6 +297,7 @@ def get_cache_data(info):
         try:
             if self.data:
                 cache = {
+                    "version": version('gcode-metadata'),
                     "metadata": self.data,
                 }
 

tests/test_metadata.py

@@ -1,7 +1,10 @@
 """Tests for gcode-metadata tool for g-code files."""
+import json
 import os
 import tempfile
 import shutil
+from importlib.metadata import version
+
 import time
 import pytest
 
@@ -23,6 +26,18 @@ def tmp_dir():
     del temp
 
 
+def give_cache_version(path, version_to_give):
+    """Modifies the cache file and adds a valid version number"""
+    with open(path, "r", encoding='utf-8') as cache_file:
+        cache = json.load(cache_file)
+    my_cache = {
+        "version": version_to_give
+    }
+    my_cache.update(cache)
+    with open(path, "w", encoding='utf-8') as cache_file:
+        json.dump(my_cache, cache_file)
+
+
 def test_get_metadata_file_does_not_exist():
     """Test get_metadata() with a non-existing file"""
     fname = '/somehwere/in/the/rainbow/my.gcode'
@@ -56,26 +71,52 @@ def test_load_cache_key_error():
         MetaData(fname).load_cache()
 
 
-def test_is_cache_fresh_fresher(tmp_dir):
-    """is_cache_fresh, when cache file is fresher, than original file"""
+def test_is_cache_recent_fresher(tmp_dir):
+    """is_cache_recent, when cache file is fresher, than original file"""
     fn_gcode = os.path.join(gcodes_dir, "fdn_filename.gcode")
     temp_gcode = shutil.copy(fn_gcode, tmp_dir)
     # Create the time difference
     time.sleep(0.01)
     fn_cache = os.path.join(gcodes_dir, ".fdn_filename.gcode.cache")
     shutil.copy(fn_cache, tmp_dir)
-    assert MetaData(temp_gcode).is_cache_fresh()
+    assert MetaData(temp_gcode).is_cache_recent()
 
 
-def test_is_cache_fresh_older(tmp_dir):
-    """is_cache_fresh, when cache file is older, than original file"""
+def test_is_cache_recent_older(tmp_dir):
+    """is_cache_recent, when cache file is older, than original file"""
     fn_cache = os.path.join(gcodes_dir, ".fdn_filename.gcode.cache")
     shutil.copy(fn_cache, tmp_dir)
     # Create the time difference
     time.sleep(0.01)
     fn_gcode = os.path.join(gcodes_dir, "fdn_filename.gcode")
     temp_gcode = shutil.copy(fn_gcode, tmp_dir)
-    assert MetaData(temp_gcode).is_cache_fresh() is False
+    assert MetaData(temp_gcode).is_cache_recent() is False
+
+
+def test_is_cache_correct_version_none():
+    """is_cache_correct_version, when cache file has no version"""
+    fn_gcode = os.path.join(gcodes_dir, "fdn_filename.gcode")
+    assert not MetaData(fn_gcode).is_cache_correct_version()
+
+
+def test_is_cache_correct_version_mismatch(tmp_dir):
+    """is_cache_correct_version, when cache file has different version"""
+    fn_cache = os.path.join(gcodes_dir, ".fdn_filename.gcode.cache")
+    fn_gcode = os.path.join(gcodes_dir, "fdn_filename.gcode")
+    temp_gcode = shutil.copy(fn_gcode, tmp_dir)
+    cache_path = shutil.copy(fn_cache, tmp_dir)
+    give_cache_version(cache_path, "0.0.0")
+    assert MetaData(temp_gcode).is_cache_correct_version() is False
+
+
+def test_is_cache_correct_version_match(tmp_dir):
+    """is_cache_correct_version, when cache file has the same version"""
+    fn_cache = os.path.join(gcodes_dir, ".fdn_filename.gcode.cache")
+    fn_gcode = os.path.join(gcodes_dir, "fdn_filename.gcode")
+    temp_gcode = shutil.copy(fn_gcode, tmp_dir)
+    cache_path = shutil.copy(fn_cache, tmp_dir)
+    give_cache_version(cache_path, version('gcode-metadata'))
+    assert MetaData(temp_gcode).is_cache_correct_version() is True
 
 
 def test_get_metadata_invalid_file():