Synchronous TLS-in-TLS doesn't work

[karpetrosyan]

Discussed in #833

^{Originally posted by mborsetti November 1, 2023}
Executing the following using HTTPX:

import httpx

response = httpx.get('https://api.ipify.org', proxies='https://proxyname.com')
print(response.status_code)

Throws a RuntimeError ("not supported by httpcore package"):

Traceback (most recent call last):
 File "C:\Program Files\JetBrains\PyCharm Community Edition 2023.1.3\plugins\python-ce\helpers\pydev\pydevd.py", line 1500, in _exec
 pydev_imports.execfile(file, globals, locals) # execute the script
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "C:\Program Files\JetBrains\PyCharm Community Edition 2023.1.3\plugins\python-ce\helpers\pydev\_pydev_imps\_pydev_execfile.py", line 18, in execfile
 exec(compile(contents+"\n", file, 'exec'), glob, loc)
 File "C:\Users\anonymous\AppData\Roaming\JetBrains\PyCharmCE2023.2\scratches\scratch_2.py", line 4, in <module>
 response = httpx.get('https://api.ipify.org', proxies='https://proxyname.com')
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "C:\Program Files\Python\Python312\Lib\site-packages\httpx\_api.py", line 189, in get
 return request(
 ^^^^^^^^
 File "C:\Program Files\Python\Python312\Lib\site-packages\httpx\_api.py", line 100, in request
 return client.request(
 ^^^^^^^^^^^^^^^
 File "C:\Program Files\Python\Python312\Lib\site-packages\httpx\_client.py", line 814, in request
 return self.send(request, auth=auth, follow_redirects=follow_redirects)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "C:\Program Files\Python\Python312\Lib\site-packages\httpx\_client.py", line 901, in send
 response = self._send_handling_auth(
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 File "C:\Program Files\Python\Python312\Lib\site-packages\httpx\_client.py", line 929, in _send_handling_auth
 response = self._send_handling_redirects(
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "C:\Program Files\Python\Python312\Lib\site-packages\httpx\_client.py", line 966, in _send_handling_redirects
 response = self._send_single_request(request)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "C:\Program Files\Python\Python312\Lib\site-packages\httpx\_client.py", line 1002, in _send_single_request
 response = transport.handle_request(request)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "C:\Program Files\Python\Python312\Lib\site-packages\httpx\_transports\default.py", line 228, in handle_request
 resp = self._pool.handle_request(req)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "C:\Program Files\Python\Python312\Lib\site-packages\httpcore\_sync\connection_pool.py", line 262, in handle_request
 raise exc
 File "C:\Program Files\Python\Python312\Lib\site-packages\httpcore\_sync\connection_pool.py", line 245, in handle_request
 response = connection.handle_request(request)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "C:\Program Files\Python\Python312\Lib\site-packages\httpcore\_sync\http_proxy.py", line 317, in handle_request
 stream = stream.start_tls(**kwargs)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "C:\Program Files\Python\Python312\Lib\site-packages\httpcore\_backends\sync.py", line 149, in start_tls
 raise RuntimeError(
RuntimeError: Attempted to add a TLS layer on top of the existing TLS stream, which is not supported by httpcore package

Similar code using requests works just fine:

import requests

response = requests.get('https://api.ipify.org', proxies={'https': 'https://proxyname.com'})
print(response.status_code)

Result:

200
```</div>