From b5274fefb9cb5dda5069f194161e9b683304d73b Mon Sep 17 00:00:00 2001
From: Ethan Dalool <git@voussoir.net>
Date: Sun, 18 Mar 2018 21:42:31 -0700
Subject: [PATCH] Add caching.py to enable browser caching of files.

---
 .../etiquette_flask/caching.py                | 72 +++++++++++++++++++
 .../etiquette_flask/etiquette_flask/common.py | 17 ++++-
 2 files changed, 88 insertions(+), 1 deletion(-)
 create mode 100644 frontends/etiquette_flask/etiquette_flask/caching.py

diff --git a/frontends/etiquette_flask/etiquette_flask/caching.py b/frontends/etiquette_flask/etiquette_flask/caching.py
new file mode 100644
index 0000000..1515791
--- /dev/null
+++ b/frontends/etiquette_flask/etiquette_flask/caching.py
@@ -0,0 +1,72 @@
+'''
+This file provides the FileCacheManager to serve ETag and Cache-Control headers
+for files on disk.
+
+We consider the following cases:
+
+Client does not have the file (or has disabled their cache, effectively same):
+    Server sends file, provides ETag, and tells client to save it for max-age.
+
+Client has the file, but it has been a long time, beyond the max-age:
+    Client provides the old ETag. If it's still valid, Server responds with
+    304 Not Modified and no data. Client keeps the file.
+
+Client has the file, and it is within the max-age:
+    Client does not make a request at all.
+
+This FileCacheManager uses the file's MD5 hash as the ETag, and will only
+recalculate it if the file's mtime has changed since the last request.
+'''
+
+import time
+
+import etiquette
+
+from voussoirkit import cacheclass
+from voussoirkit import pathclass
+
+class FileCacheManager:
+    def __init__(self, maxlen, max_filesize, max_age):
+        self.cache = cacheclass.Cache(maxlen=maxlen)
+        self.max_filesize = int(max_filesize)
+        self.max_age = int(max_age)
+
+    def get(self, filepath):
+        if (self.max_filesize is not None) and (filepath.size > self.max_filesize):
+            #print('I\'m not going to cache that!')
+            return None
+
+        try:
+            return self.cache[filepath]
+        except KeyError:
+            pass
+        cache_file = CacheFile(filepath, max_age=self.max_age)
+        self.cache[filepath] = cache_file
+        return cache_file
+
+class CacheFile:
+    def __init__(self, filepath, max_age):
+        self.filepath = filepath
+        self.max_age = max_age
+        self._stored_hash_time = None
+        self._stored_hash_value = None
+
+    def get_etag(self):
+        if self._stored_hash_value is None:
+            refresh = True
+        elif self.filepath.stat.st_mtime > self._stored_hash_time:
+            refresh = True
+        else:
+            refresh = False
+
+        if refresh:
+            self._stored_hash_time = self.filepath.stat.st_mtime
+            self._stored_hash_value = etiquette.helpers.hash_file_md5(self.filepath)
+        return self._stored_hash_value
+
+    def get_headers(self):
+        headers = {
+            'ETag': self.get_etag(),
+            'Cache-Control': 'max-age=%d' % self.max_age,
+        }
+        return headers
diff --git a/frontends/etiquette_flask/etiquette_flask/common.py b/frontends/etiquette_flask/etiquette_flask/common.py
index 7a46299..57fa35f 100644
--- a/frontends/etiquette_flask/etiquette_flask/common.py
+++ b/frontends/etiquette_flask/etiquette_flask/common.py
@@ -5,8 +5,10 @@ import traceback
 
 import etiquette
 
+from voussoirkit import bytestring
 from voussoirkit import pathclass
 
+from . import caching
 from . import jsonify
 from . import sessions
 
@@ -34,7 +36,11 @@ site.debug = True
 P = etiquette.photodb.PhotoDB()
 
 session_manager = sessions.SessionManager(maxlen=10000)
-
+file_cache_manager = caching.FileCacheManager(
+    maxlen=10000,
+    max_filesize=5 * bytestring.MIBIBYTE,
+    max_age=180,
+)
 
 def P_wrapper(function):
     def P_wrapped(thingid, response_type='html'):
@@ -100,6 +106,13 @@ def send_file(filepath, override_mimetype=None):
     if not filepath.is_file:
         flask.abort(404)
 
+    cache_file = file_cache_manager.get(filepath)
+    if cache_file is not None:
+        client_etag = request.headers.get('If-None-Match', None)
+        if client_etag and client_etag == cache_file.get_etag():
+            response = flask.Response(status=304, headers=cache_file.get_headers())
+            return response
+
     outgoing_headers = {}
     if override_mimetype is not None:
         mimetype = override_mimetype
@@ -147,6 +160,8 @@ def send_file(filepath, override_mimetype=None):
 
     outgoing_headers['Accept-Ranges'] = 'bytes'
     outgoing_headers['Content-Length'] = (range_max - range_min) + 1
+    if cache_file is not None:
+        outgoing_headers.update(cache_file.get_headers())
 
     if request.method == 'HEAD':
         outgoing_data = bytes()