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add an optional decompression for content-type: application/zlib #8283
Description
Problem Description
I am using the transparent mode and I am receiving responses encoded with gzip (decoded normally), but the content type is also application/zlib.
Proposal
I propose to add an optional decompression for zlib content types. So, after decoded it, I will see an unformatted JSON too :v
Alternatives
1. Event Hooks (bad)
I created a addon script to decompress and spoof the content type to application/json to use the native JSON preview:
"""
mitmproxy -s zlib-hook.py
"""
import zlib
class DecodeZlib:
def response(self, flow):
if 'application/zlib' not in flow.response.headers.get('content-type', ''):
return
content = zlib.decompress(flow.response.content)
if content and (chr(content[0]) in ('[', '{') and chr(content[-1]) in ('}', ']')):
flow.response.headers['content-type'] = 'application/json'
flow.response.content = content
addons = [DecodeZlib()]It works very nice, but it modify the request data and by this side not seems so nice.
2. Custom Content View (should be good)
"""
mitmproxy -s zlib-and-json-cv.py
"""
import zlib
import json
from mitmproxy import contentviews
class ZlibAndJson(contentviews.Contentview):
name = "zlib +? JSON"
@staticmethod
def _is_json_content(content: bytes) -> bool:
if not content:
return False
starts_with_brackets = chr(content[0]) in ("[", "{")
ends_with_brackets = chr(content[-1]) in ("}", "]")
return starts_with_brackets and ends_with_brackets
def prettify(self, data: bytes, metadata: contentviews.Metadata) -> str:
data = zlib.decompress(data)
if self._is_json_content(data):
return json.dumps(json.loads(data), indent=2)
return data.decode()
def render_priority(self, data: bytes, metadata: contentviews.Metadata) -> float:
if not metadata.content_type:
return 0.0
if "application/zlib" not in metadata.content_type:
return 0.0
return 2.0
contentviews.add(ZlibAndJson)Problems:
syntax_highlightproperty cannot be dynamic based on the content, like:
@property
def syntax_highlight(self) -> SyntaxHighlight:
data = ???
return "yaml" if self._is_json_content(data) else "none"Additional context
Activity
Prinzhorn commentedon Jun 15, 2026
The content-type is
application/zlib, how should mitmproxy know it's supposed to be JSON? Your script seems to be the way to go.d3cryptofc commentedon Jun 15, 2026
For now, I think add an optional/automatic zlib decompression is sufficient to close this issue.
We could create a specific issue for JSON detection based on the content later. But manually create an add-on for this is not so bad.