diff --git a/synapse/util/templates.py b/synapse/util/templates.py
new file mode 100644
index 0000000000..7e5109d206
--- /dev/null
+++ b/synapse/util/templates.py
@@ -0,0 +1,106 @@
+# -*- coding: utf-8 -*-
+# Copyright 2021 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Utilities for dealing with jinja2 templates"""
+
+import time
+import urllib.parse
+from typing import TYPE_CHECKING, Callable, Iterable, Union
+
+import jinja2
+
+if TYPE_CHECKING:
+ from synapse.config.homeserver import HomeServerConfig
+
+
+def build_jinja_env(
+ template_search_directories: Iterable[str],
+ config: "HomeServerConfig",
+ autoescape: Union[bool, Callable[[str], bool], None] = None,
+) -> jinja2.Environment:
+ """Set up a Jinja2 environment to load templates from the given search path
+
+ The returned environment defines the following filters:
+ - format_ts: formats timestamps as strings in the server's local timezone
+ (XXX: why is that useful??)
+ - mxc_to_http: converts mxc: uris to http URIs. Args are:
+ (uri, width, height, resize_method="crop")
+
+ and the following global variables:
+ - server_name: matrix server name
+
+ Args:
+ template_search_directories: directories to search for templates
+
+ config: homeserver config, for things like `server_name` and `public_baseurl`
+
+ autoescape: whether template variables should be autoescaped. bool, or
+ a function mapping from template name to bool. Defaults to escaping templates
+ whose names end in .html, .xml or .htm.
+
+ Returns:
+ jinja environment
+ """
+
+ if autoescape is None:
+ autoescape = jinja2.select_autoescape()
+
+ loader = jinja2.FileSystemLoader(template_search_directories)
+ env = jinja2.Environment(loader=loader, autoescape=autoescape)
+
+ # Update the environment with our custom filters
+ env.filters.update(
+ {
+ "format_ts": _format_ts_filter,
+ "mxc_to_http": _create_mxc_to_http_filter(config.public_baseurl),
+ }
+ )
+
+ # common variables for all templates
+ env.globals.update({"server_name": config.server_name})
+
+ return env
+
+
+def _create_mxc_to_http_filter(public_baseurl: str) -> Callable:
+ """Create and return a jinja2 filter that converts MXC urls to HTTP
+
+ Args:
+ public_baseurl: The public, accessible base URL of the homeserver
+ """
+
+ def mxc_to_http_filter(value, width, height, resize_method="crop"):
+ if value[0:6] != "mxc://":
+ return ""
+
+ server_and_media_id = value[6:]
+ fragment = None
+ if "#" in server_and_media_id:
+ server_and_media_id, fragment = server_and_media_id.split("#", 1)
+ fragment = "#" + fragment
+
+ params = {"width": width, "height": height, "method": resize_method}
+ return "%s_matrix/media/v1/thumbnail/%s?%s%s" % (
+ public_baseurl,
+ server_and_media_id,
+ urllib.parse.urlencode(params),
+ fragment or "",
+ )
+
+ return mxc_to_http_filter
+
+
+def _format_ts_filter(value: int, format: str):
+ return time.strftime(format, time.localtime(value / 1000))
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