backend: always send etags to make use of cache-control

backend.py

@@ -184,16 +184,19 @@ class CalibreDB:
         path = self.get_volume_filepath(volume_id)
         with ZipFile(path, 'r') as volume:
             try:
-                page_filename = volume.filelist[page_number - 1].filename
+                zip_info = volume.filelist[page_number - 1]
             except IndexError:
                 raise exceptions.NotFound()
                 return None
 
+            page_filename = zip_info.filename
+
             page_data = BytesIO()
             page_data.write(volume.read(page_filename))
             page_data.seek(0)
 
             return {
                 'data': page_data,
-                'mimetype': mimetypes[os.path.splitext(page_filename)[1]]
+                'mimetype': mimetypes[os.path.splitext(page_filename)[1]],
+                'etag': str(zip_info.CRC)
             }

mangareader.py

@@ -3,6 +3,7 @@ from backend import CalibreDB
 from flask import Flask, jsonify, send_from_directory, send_file, render_template, request
 from flask_cors import CORS
 from werkzeug.routing import BaseConverter
+from zlib import crc32
 import os
 
 
@@ -10,6 +11,13 @@ def send_from_cwd(filename):
     return send_from_directory(os.getcwd(), filename)
 
 
+def send_file_with_etag(fp, **kwargs):
+    response = send_file(fp, **kwargs)
+    response.set_etag(str(crc32(fp.read())))
+    fp.seek(0)
+    return response
+
+
 app = Flask(__name__, static_folder='frontend/dist/static', template_folder='frontend/dist')
 app.config['SEND_FILE_MAX_AGE_DEFAULT'] = 604800  # 1 week
 CORS(app)
@@ -37,7 +45,7 @@ def get_series_cover(series_id):
 @app.route('/api/series/<int:series_id>/cover/thumbnail')
 def get_series_cover_thumbnail(series_id):
     thumbnail = db.get_series_cover_thumbnail(series_id)
-    return send_file(thumbnail, mimetype='image/jpeg')
+    return send_file_with_etag(thumbnail, mimetype='image/jpeg')
 
 
 @app.route('/api/series/<int:series_id>')
@@ -53,7 +61,7 @@ def get_volume_cover(volume_id):
 @app.route('/api/volume/<int:volume_id>/cover/thumbnail')
 def get_volume_cover_thumbnail(volume_id):
     thumbnail = db.get_volume_cover_thumbnail(volume_id)
-    return send_file(thumbnail, mimetype='image/jpeg')
+    return send_file_with_etag(thumbnail, mimetype='image/jpeg')
 
 
 @app.route('/api/volume/<int:volume_id>')
@@ -64,7 +72,9 @@ def get_volume_info(volume_id):
 @app.route('/api/volume/<int:volume_id>/page/<int:page_number>')
 def get_volume_page(volume_id, page_number):
     page = db.get_volume_page(volume_id, page_number)
-    return send_file(page['data'], mimetype=page['mimetype'])
+    response = send_file(page['data'], mimetype=page['mimetype'])
+    response.set_etag(page['etag'])
+    return response
 
 
 if __name__ == '__main__':