Don't use SNI when host is an IP Address

Per the SNI spec we shouldn't be using SNI when the hostname is an IP address.

Just wondering — what is SNI? 😄 Also, is there any more context on how this bug was discovered?

Server Name Identification (RFC 6066 Section 3) which disallows IP addresses (see the RFC search for "Literal IPv4"). It's set via server_hostname in Trio for example.

Also I found this issue cuz I fixed it for urllib3. :)

How sure are you that this issue actually exists in httpx?

Unless I'm mistaken connections are established using asyncio.open_connection which AFAICT does the Right Thing.

I had a look with wireshark, and I only see the server_name extension in the ClientHello if I query a host name. If I connect to an IP address, the server_name extension is absent.

@sethmlarson

@sethmlarson I get the same behavior than @jlaine for the TrioBackend (#276): server_name is absent from the ClientHello if connecting to an IP address:

import trio
import httpx
from httpx.concurrency.trio import TrioBackend


async def main(url):
    async with httpx.AsyncClient(backend=TrioBackend()) as client:
        await client.get(url)


trio.run(main, "https://8.8.8.8")

Nice, then we can probably close this issue.

This would definitely need to be re-visited if we ever start using server_hostname for asyncio or trio.

So do we not send SNI for any handshakes? Because that's an issue in itself.

We do send SNI when querying an FQDN, and don't when querying an IP (at least for asyncio). If you don't force asyncio's hand by setting server_hostname it does the right thing on its own.

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Don't use SNI when host is an IP Address #278

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Don't use SNI when host is an IP Address #278

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florimondmanca commented on Aug 26, 2019

sethmlarson commented on Aug 26, 2019

jlaine commented on Aug 26, 2019

florimondmanca commented on Aug 27, 2019

sethmlarson commented on Aug 27, 2019

jlaine commented on Aug 28, 2019

sethmlarson commented on Aug 28, 2019

jlaine commented on Aug 28, 2019

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