Memory cache off-by-one error (#396)

* Fixes an off by one in the handling of the in memory cache, which also caused it to blow up if cache size == 0

* Fixed InfoCache getter bypassing size restrictions of the RAM cache and actually remedied the issues with the RAM cache size == 0 case, as I thought I had in the previous commit. Added tests for these cases.

* Minor effeciency improvement - only read from disk once in the case where none of the info is cached in RAM. Still does two disk reads in all cases where RAM cache size > 0

* per conversation with @bcail in #396 - Avoiding writing to disk on every get()

loris/img_info.py

@@ -372,8 +372,7 @@ def get(self, request):
                 info_and_lastmod = (info, lastmod)
                 logger.debug('Info for %s read from file system', request)
                 # into mem:
-                self._dict[request.url] = info_and_lastmod
-
+                self.__setitem__(request, info, _to_fs=False)
         return info_and_lastmod
 
     def has_key(self, request):
@@ -389,31 +388,37 @@ def __getitem__(self, request):
         else:
             return info_lastmod
 
-    def __setitem__(self, request, info):
-        # to fs
-        logger.debug('request passed to __setitem__: %s', request)
+    def __setitem__(self, request, info, _to_fs=True):
         info_fp = self._get_info_fp(request)
-        dp = os.path.dirname(info_fp)
-        mkdir_p(dp)
-        logger.debug('Created %s', dp)
+        if _to_fs:
+            # to fs
+            logger.debug('request passed to __setitem__: %s', request)
+            dp = os.path.dirname(info_fp)
+            mkdir_p(dp)
+            logger.debug('Created %s', dp)
 
-        with open(info_fp, 'w') as f:
-            f.write(info.to_full_info_json())
-        logger.debug('Created %s', info_fp)
+            with open(info_fp, 'w') as f:
+                f.write(info.to_full_info_json())
+            logger.debug('Created %s', info_fp)
 
 
-        if info.color_profile_bytes:
-            icc_fp = self._get_color_profile_fp(request)
-            with open(icc_fp, 'wb') as f:
-                f.write(info.color_profile_bytes)
-            logger.debug('Created %s', icc_fp)
+            if info.color_profile_bytes:
+                icc_fp = self._get_color_profile_fp(request)
+                with open(icc_fp, 'wb') as f:
+                    f.write(info.color_profile_bytes)
+                logger.debug('Created %s', icc_fp)
 
         # into mem
-        lastmod = datetime.utcfromtimestamp(os.path.getmtime(info_fp))
-        with self._lock:
-            while len(self._dict) >= self.size:
-                self._dict.popitem(last=False)
-            self._dict[request.url] = (info,lastmod)
+        # The info file cache on disk must already exist before
+        # this is called - it's where the mtime gets drawn from.
+        # aka, nothing outside of this class should be using
+        # to_fs=False
+        if self.size > 0:
+            lastmod = datetime.utcfromtimestamp(os.path.getmtime(info_fp))
+            with self._lock:
+                self._dict[request.url] = (info,lastmod)
+                while len(self._dict) > self.size:
+                    self._dict.popitem(last=False)
 
     def __delitem__(self, request):
         with self._lock:

tests/img_info_t.py

@@ -7,6 +7,7 @@
 from os import path
 import json
 import tempfile
+from datetime import datetime
 
 try:
     from urllib.parse import unquote
@@ -505,6 +506,29 @@ def test_info_goes_to_http_fs_cache(self):
         )
         self.assertTrue(path.exists(expected_path))
 
+    def test_just_ram_cache_update(self):
+        # Cache size of one, so it's easy to manipulate
+        cache = img_info.InfoCache(root=self.SRC_IMAGE_CACHE, size=1)
+        self.app.info_cache = cache
+        # First request
+        request_uri = '/%s/%s' % (self.test_jp2_color_id,'info.json')
+        resp = self.client.get(request_uri)
+        expected_path = path.join(
+            self.app.info_cache.http_root,
+            unquote(self.test_jp2_color_id),
+            'info.json'
+        )
+        fs_first_time = datetime.utcfromtimestamp(os.path.getmtime(expected_path))
+        # Push this entry out of the RAM cache with another
+        push_request_uri = '/%s/%s' % (self.test_jp2_gray_id,'info.json')
+        resp = self.client.get(push_request_uri)
+        # Request the first file again
+        # It should now exist on disk, but not in RAM, so it shouldn't
+        # have been rewritten by the second get.
+        resp = self.client.get(request_uri)
+        fs_second_time = datetime.utcfromtimestamp(os.path.getmtime(expected_path))
+        self.assertTrue(fs_first_time == fs_second_time)
+
     def test_can_delete_items_from_infocache(self):
         cache, req = self._cache_with_request()
         del cache[req]
@@ -513,6 +537,29 @@ def test_empty_cache_has_zero_size(self):
         cache = img_info.InfoCache(root=self.SRC_IMAGE_CACHE)
         assert len(cache) == 0
 
+    def test_cache_limit(self):
+        cache = img_info.InfoCache(root=self.SRC_IMAGE_CACHE, size=2)
+        self.app.info_cache = cache
+        request_uris = [
+            '/%s/%s' % (self.test_jp2_color_id,'info.json'),
+            '/%s/%s' % (self.test_jpeg_id,'info.json'),
+            '/%s/%s' % (self.test_png_id,'info.json'),
+            '/%s/%s' % (self.test_jp2_gray_id,'info.json')
+        ]
+        for x in request_uris:
+            resp = self.client.get(x)
+
+        # Check we only cache two
+        assert len(self.app.info_cache) == 2
+
+    def test_no_cache(self):
+        cache = img_info.InfoCache(root=self.SRC_IMAGE_CACHE, size=0)
+        self.app.info_cache = cache
+        request_uri = '/%s/%s' % (self.test_jp2_color_id,'info.json')
+        resp = self.client.get(request_uri)
+
+        assert len(self.app.info_cache) == 0
+
     def test_deleting_cache_item_removes_color_profile_fp(self):
         # First assemble the cache
         cache, req = self._cache_with_request()