From 4241f8c8c0761344eeccf219d125324b0b232f6f Mon Sep 17 00:00:00 2001
From: Ankush Menat <ankush@frappe.io>
Date: Sun, 21 Aug 2022 18:30:14 +0530
Subject: [PATCH] perf: simpler/faster preload header computation

We parse entire response to find preload headers, instead just use
include_style and include_script to include assets directly into preload
headers. This shaves off ~13% overhead in response.
---
 frappe/__init__.py            |  1 +
 frappe/utils/jinja_globals.py | 24 ++++++++++++++++++++++--
 frappe/website/utils.py       | 30 ++++++++++--------------------
 3 files changed, 33 insertions(+), 22 deletions(-)

diff --git a/frappe/__init__.py b/frappe/__init__.py
index a796db9a83..53bc1018da 100644
--- a/frappe/__init__.py
+++ b/frappe/__init__.py
@@ -240,6 +240,7 @@ def init(site: str, sites_path: str = ".", new_site: bool = False) -> None:
 	local.document_cache = {}
 	local.meta_cache = {}
 	local.form_dict = _dict()
+	local.preload_assets = {"style": [], "script": []}
 	local.session = _dict()
 	local.dev_server = _dev_server
 	local.qb = get_query_builder(local.conf.db_type or "mariadb")
diff --git a/frappe/utils/jinja_globals.py b/frappe/utils/jinja_globals.py
index 44835be352..1265bd4d42 100644
--- a/frappe/utils/jinja_globals.py
+++ b/frappe/utils/jinja_globals.py
@@ -95,13 +95,33 @@ def get_dom_id(seed=None):
 	return "id-" + generate_hash(seed, 12)
 
 
-def include_script(path):
+def include_script(path, preload=True):
+	"""Get path of bundled script files.
+
+	If preload is specified the path will be added to preload headers so browsers can prefetch
+	assets."""
 	path = bundled_asset(path)
+
+	if preload:
+		import frappe
+
+		frappe.local.preload_assets["script"].append(path)
+
 	return f'<script type="text/javascript" src="{path}"></script>'
 
 
-def include_style(path, rtl=None):
+def include_style(path, rtl=None, preload=True):
+	"""Get path of bundled style files.
+
+	If preload is specified the path will be added to preload headers so browsers can prefetch
+	assets."""
 	path = bundled_asset(path)
+
+	if preload:
+		import frappe
+
+		frappe.local.preload_assets["style"].append(path)
+
 	return f'<link type="text/css" rel="stylesheet" href="{path}">'
 
 
diff --git a/frappe/website/utils.py b/frappe/website/utils.py
index 508026f064..bfb600a8c4 100644
--- a/frappe/website/utils.py
+++ b/frappe/website/utils.py
@@ -527,7 +527,8 @@ def build_response(path, data, http_status_code, headers: dict | None = None):
 	response.headers["X-Page-Name"] = path.encode("ascii", errors="xmlcharrefreplace")
 	response.headers["X-From-Cache"] = frappe.local.response.from_cache or False
 
-	add_preload_headers(response)
+	add_preload_for_bundled_assets(response)
+
 	if headers:
 		for key, val in headers.items():
 			response.headers[key] = val.encode("ascii", errors="xmlcharrefreplace")
@@ -557,29 +558,18 @@ def set_content_type(response, data, path):
 	return data
 
 
-def add_preload_headers(response):
-	from bs4 import BeautifulSoup, SoupStrainer
+def add_preload_for_bundled_assets(response):
 
-	try:
-		preload = []
-		strainer = SoupStrainer(re.compile("script|link"))
-		soup = BeautifulSoup(response.data, "html.parser", parse_only=strainer)
-		for elem in soup.find_all("script", src=re.compile(".*")):
-			preload.append(("script", elem.get("src")))
+	links = []
 
-		for elem in soup.find_all("link", rel="stylesheet"):
-			preload.append(("style", elem.get("href")))
+	for css in frappe.local.preload_assets["style"]:
+		links.append(f"<{css}>; rel=preload; as=style")
 
-		links = []
-		for _type, link in preload:
-			links.append(f"<{link}>; rel=preload; as={_type}")
+	for js in frappe.local.preload_assets["script"]:
+		links.append(f"<{js}>; rel=preload; as=script")
 
-		if links:
-			response.headers["Link"] = ",".join(links)
-	except Exception:
-		import traceback
-
-		traceback.print_exc()
+	if links:
+		response.headers["Link"] = ",".join(links)
 
 
 @lru_cache