How to modify JSON response body with mitmproxy

Question

When I send a request to a specific website API I get this as response

{
  "Tickets": [
    {
      "ticketAvailable": true,
...

How would I intercept and change ticketAvailable to false instead of true using mitmproxy?

from mitmproxy import ctx
from mitmproxy import http
import json

def response(flow: http.HTTPFlow) -> None:
    if flow.request.pretty_url == "https://example.com/api/v1/something":
        data = json.loads(flow.response.get_text())
        data["data"]["Tickets"]["ticketAvailable"] = false
        flow.response.text = json.dumps(data)

I have tried this, but it doesn't seem to work.

EDIT: Have not managed to fix it yet

from mitmproxy import ctx
from mitmproxy import http
import json

def response(flow: http.HTTPFlow) -> None:
    if flow.request.pretty_url == "https://example.com/api/v1/something":
        data = json.loads(flow.response.get_text())
        data["Tickets"][0]["ticketAvailable"] = "false"
        flow.response.text = json.dumps(data)

score 5 · Answer 1 · answered Dec 06 '21 at 18:17

I figured out a way to fix it. I simply changed flow.request.pretty_url to flow.request.pretty_url.endswith

from mitmproxy import ctx
from mitmproxy import http
import json

def response(flow: http.HTTPFlow) -> None:
    if flow.request.pretty_url.endswith("/something"):
        data = json.loads(flow.response.get_text())
        data["Tickets"][0]["ticketAvailable"] = False
        flow.response.text = json.dumps(data)

Blair Nangle · Answer 2 · 2021-12-06T17:38:21.227

0

Tickets is an array, so you'll need to access the 0th index in the array to update ticketAvailable to false. Also, there doesn't appear to be a data key in the response body, so there is no need for ["data"] when navigating the dictionary's keys.

Also note that booleans in Python are capitalised, i.e., True and False, so you should either use the native Python boolean (useful if you actually need to use data elsewhere) or wrap false in quotes (fine if you are just loading data back into JSON, which it looks like you are).

Either:

data["Tickets"][0]["ticketAvailable"] = False

Or:

data["Tickets"][0]["ticketAvailable"] = "false"

edited Dec 06 '21 at 17:38

answered Dec 06 '21 at 17:23

Blair Nangle

1,221
12
18

Thank you. I've fixed everything you've said, but it still doesn't work. I've posted my new code in an edit. I can see the script is successfully loaded into mitmproxy, but it's not doing anything as far as I can see. – riwejak558 Dec 06 '21 at 18:10
How are you checking the update step? Have you tried printing `data` before and after updating? What do you see? – Blair Nangle Dec 06 '21 at 18:14
I managed to find a way to fix it. Check my answer above. Thank you so much for your help! – riwejak558 Dec 06 '21 at 18:18

How to modify JSON response body with mitmproxy

2 Answers2