Issue 1424 - Latest flask-compress (1.6.0) breaks Dash (#1426)

CHANGELOG.md

@@ -2,6 +2,10 @@
 All notable changes to `dash` will be documented in this file.
 This project adheres to [Semantic Versioning](https://semver.org/).
 
+## Unreleased
+### Fixed
+- [#1426](https://github.com/plotly/dash/pull/1426) Fix a regression caused by `flask-compress==1.6.0` causing performance degradation on server requests
+
 ## [1.16.2] - 2020-09-25
 ### Fixed
 - [#1415](https://github.com/plotly/dash/pull/1415) Fix a regression with some layouts callbacks involving dcc.Tabs, not yet loaded dash_table.DataTable and dcc.Graph to not be called

dash/dash.py

@@ -20,6 +20,7 @@
 import flask
 from flask_compress import Compress
 from werkzeug.debug.tbtools import get_current_traceback
+from pkg_resources import get_distribution, parse_version
 
 import plotly
 import dash_renderer
@@ -49,6 +50,8 @@
 from . import _validate
 from . import _watch
 
+_flask_compress_version = parse_version(get_distribution("flask-compress").version)
+
 # Add explicit mapping for map files
 mimetypes.add_type("application/json", ".map", True)
 
@@ -283,6 +286,16 @@ def __init__(
         else:
             raise ValueError("server must be a Flask app or a boolean")
 
+        if (
+            self.server is not None
+            and not hasattr(self.server.config, "COMPRESS_ALGORITHM")
+            and _flask_compress_version >= parse_version("1.6.0")
+        ):
+            # flask-compress==1.6.0 changed default to ['br', 'gzip']
+            # and non-overridable default compression with Brotli is
+            # causing performance issues
+            self.server.config["COMPRESS_ALGORITHM"] = ["gzip"]
+
         base_prefix, routes_prefix, requests_prefix = pathname_configs(
             url_base_pathname, routes_pathname_prefix, requests_pathname_prefix
         )

requires-install.txt

@@ -1,5 +1,5 @@
 Flask>=1.0.2
-flask-compress==1.5.0
+flask-compress
 plotly
 dash_renderer==1.8.2
 dash-core-components==1.12.1