From 57e12faca966f5ea63d77cd83323e67cc2328b0d Mon Sep 17 00:00:00 2001
From: Ethan Dalool <git@voussoir.net>
Date: Fri, 2 Apr 2021 18:24:40 -0700
Subject: [PATCH] Add flasktools.py.

---
 voussoirkit/flasktools.py | 46 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100644 voussoirkit/flasktools.py

diff --git a/voussoirkit/flasktools.py b/voussoirkit/flasktools.py
new file mode 100644
index 0000000..268a56c
--- /dev/null
+++ b/voussoirkit/flasktools.py
@@ -0,0 +1,46 @@
+import gzip
+import io
+
+from voussoirkit import bytestring
+
+GZIP_MINIMUM_SIZE = 500 * bytestring.BYTE
+GZIP_MAXIMUM_SIZE = 5 * bytestring.MIBIBYTE
+GZIP_LEVEL = 3
+
+def gzip_response(request, response):
+    if response.direct_passthrough:
+        return response
+
+    accept_encoding = request.headers.get('Accept-Encoding', '')
+    if 'gzip' not in accept_encoding.lower():
+        return response
+
+    if 'Content-Encoding' in response.headers:
+        return response
+
+    content_type = response.headers.get('Content-Type', '')
+    if not (content_type.startswith('application/json') or content_type.startswith('text/')):
+        return response
+
+    if response.status_code < 200:
+        return response
+
+    if response.status_code >= 300:
+        return response
+
+    content_length = response.headers.get('Content-Length', None)
+    if content_length is not None and int(content_length) > GZIP_MAXIMUM_SIZE:
+        return response
+
+    if content_length is not None and int(content_length) < GZIP_MINIMUM_SIZE:
+        return response
+
+    gzip_buffer = io.BytesIO()
+    gzip_file = gzip.GzipFile(mode='wb', compresslevel=GZIP_LEVEL, fileobj=gzip_buffer)
+    gzip_file.write(response.get_data())
+    gzip_file.close()
+    response.set_data(gzip_buffer.getvalue())
+    response.headers['Content-Encoding'] = 'gzip'
+    response.headers['Content-Length'] = len(response.get_data())
+
+    return response