Modifying request.url impacted request.host

[xuboying]

mitmdump version:latest

I run the proxy with following command:

mitmdump -s proxy.py -U http://upstreamproxy

The proxy.py is like following:

#!/usr/bin/mitmdump
from __future__ import print_function
import re

def request(context, flow):
    print("DEBUG")
    oldhost = flow.request.host
    flow.request.url = re.sub(r"www.verycd.com",r"115.182.66.26",flow.request.url)
    # flow.request.host = oldhost   #<---This will modify the url also
    print("DEBUG")

What I expect is to change the www.verycd.com to IP in url but keep the host field still using www.verycd.com, like following:

GET http://115.182.66.26/ HTTP/1.1
...
Host: www.verycd.com
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:43.0) Gecko/20100101 Firefox/43.0

But the mitmproxy always change the url and host at the same time I got following which the server does not accept

GET http://115.182.66.26/ HTTP/1.1
...
Host: 115.182.66.26
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:43.0) Gecko/20100101 Firefox/43.0

[mhils]

Hi there,

this is currently done intentional - usually you want to modify both and people forget about the header. You can accomplish what you want by modifying the underlying data object directly (flow.request.data.host).

There are a few similar things in the request and response classes - for example, if you modify the message body, the content-length header will be adjusted accordingly. I'm not sure what's the best way for us to handle this.
@ALL: If you have any opinions on this behaviour, we'd love to hear them in the comments below.

[xuboying]

Thanks a lot for the tip, it's working!!!
IMHO, content-length can be changed in the last step, or it will be reset by other changes.