Subject

The problem is after version 2.0.0, if you have control characters in your request body, urllib3 will count/treat them differently than previous version.

For control characters like '\x08', '\x01', urllib3 after version 2.0.0 and before will count them into different bytes, which might cause the Content-Length mismatch in some cases.

Environment

The environment I have is Python3.10, and I found this bug exists in all 2.0.* versions.

Steps to Reproduce

This bug is easy to be reproduced. Here is a sample code I used:

import urllib3

poolmanager = urllib3.PoolManager(num_pools=10, maxsize=3, block=False)
conn = poolmanager.connection_from_url("https://httpbin.org")
resp = conn.urlopen(method="POST", url="/post", body='test\x80\x80\x01\x01\x81',  headers={
                                 'User-Agent': 'python-api/2', 'Accept-Encoding': 'gzip, deflate', 'Accept': '*/*', 'Connection': 'keep-alive'})
print(resp._body)

Run this code under different version of urllib3 (in my case, I used ver 1.26.6 and 2.0.2 for testing) you will find the 'Content-Length' of the response is totally different.

Expected Behavior

The response body of the request under two different versions of urllib3 should be the same.

Actual Behavior

The 'Content-Length' for ver 1.26.6 is 9 bytes, but for ver 2.0.2, it is 12 bytes.