Added _PackageBoundObject.get_static_file_options.

This method receives the name of a static file that is going to be served
up and generates a dict of options to use when serving the file.  The
default set is empty so code will fall back to the existing behavior if
the method is not overridden.

I needed this method to adjust the cache control headers for .js files that
one of my applications was statically serving.  The default expiration is
buried in an argument to send_file and is set to 12 hours.  There was no
good way to adjust this value previously.

flask/helpers.py

@@ -495,7 +495,8 @@ def send_from_directory(directory, filename, **options):
     filename = safe_join(directory, filename)
     if not os.path.isfile(filename):
         raise NotFound()
-    return send_file(filename, conditional=True, **options)
+    options.setdefault('conditional', True)
+    return send_file(filename, **options)
 
 
 def get_root_path(import_name):
@@ -651,6 +652,11 @@ class _PackageBoundObject(object):
             return FileSystemLoader(os.path.join(self.root_path,
                                                  self.template_folder))
 
+    def get_static_file_options(self, filename):
+        """Function used internally to determine what keyword arguments
+        to send to :func:`send_from_directory` for a specific file."""
+        return {}
+
     def send_static_file(self, filename):
         """Function used internally to send static files from the static
         folder to the browser.
@@ -659,7 +665,8 @@ class _PackageBoundObject(object):
         """
         if not self.has_static_folder:
             raise RuntimeError('No static folder for this object')
-        return send_from_directory(self.static_folder, filename)
+        return send_from_directory(self.static_folder, filename,
+                **self.get_static_file_options(filename))
 
     def open_resource(self, resource, mode='rb'):
         """Opens a resource from the application's resource folder.  To see

flask/testsuite/helpers.py

@@ -17,7 +17,7 @@ import unittest
 from logging import StreamHandler
 from StringIO import StringIO
 from flask.testsuite import FlaskTestCase, catch_warnings, catch_stderr
-from werkzeug.http import parse_options_header
+from werkzeug.http import parse_cache_control_header, parse_options_header
 
 
 def has_encoding(name):
@@ -204,6 +204,30 @@ class SendfileTestCase(FlaskTestCase):
             self.assert_equal(value, 'attachment')
             self.assert_equal(options['filename'], 'index.txt')
 
+    def test_static_file(self):
+        app = flask.Flask(__name__)
+        # default cache timeout is 12 hours (hard-coded)
+        with app.test_request_context():
+            rv = app.send_static_file('index.html')
+            cc = parse_cache_control_header(rv.headers['Cache-Control'])
+            self.assert_equal(cc.max_age, 12 * 60 * 60)
+        # override get_static_file_options with some new values and check them
+        class StaticFileApp(flask.Flask):
+            def __init__(self):
+                super(StaticFileApp, self).__init__(__name__)
+            def get_static_file_options(self, filename):
+                opts = super(StaticFileApp, self).get_static_file_options(filename)
+                opts['cache_timeout'] = 10
+                # this test catches explicit inclusion of the conditional
+                # keyword arg in the guts
+                opts['conditional'] = True
+                return opts
+        app = StaticFileApp()
+        with app.test_request_context():
+            rv = app.send_static_file('index.html')
+            cc = parse_cache_control_header(rv.headers['Cache-Control'])
+            self.assert_equal(cc.max_age, 10)
+
 
 class LoggingTestCase(FlaskTestCase):