Add sni hostname extension (#696)

* Add `sni_hostname` extension

* Fix linting

* Add 'sni_hostname' to `CHANGELOG.md` and `extensions.md`

* Typo

* Update CHANGELOG.md

* Update docs/extensions.md

* Fix changelog

---------

Co-authored-by: Tom Christie <tom@tomchristie.com>

Author: karpetrosyan

CHANGELOG.md

@@ -9,6 +9,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Improve logging with per-module logger names. (#690)
 - Resolve race condition during import of `anyio` package. (#692)
 - Enable TCP_NODELAY for all synchronous sockets. (#651)
+- Add `sni_hostname` request extension. (#696)
 
 ## 0.17.1 (May 17th, 2023)
 

docs/extensions.md

@@ -147,6 +147,23 @@ The following event types are currently exposed...
 * `"http2.receive_response_body"`
 * `"http2.response_closed"`
 
+### `"sni_hostname"`
+
+The server's hostname, which is used to confirm the hostname supplied by the SSL certificate.
+
+For example:
+
+``` python
+headers = {"Host": "www.encode.io"}
+extensions = {"sni_hostname": "www.encode.io"}
+response = httpcore.request(
+    "GET",
+    "https://185.199.108.153",
+    headers=headers,
+    extensions=extensions
+)
+```
+
 ## Response Extensions
 
 ### `"http_version"`

httpcore/_async/connection.py

@@ -95,6 +95,7 @@ async def handle_async_request(self, request: Request) -> Response:
 
     async def _connect(self, request: Request) -> AsyncNetworkStream:
         timeouts = request.extensions.get("timeout", {})
+        sni_hostname = request.extensions.get("sni_hostname", None)
         timeout = timeouts.get("connect", None)
 
         retries_left = self._retries
@@ -136,7 +137,8 @@ async def _connect(self, request: Request) -> AsyncNetworkStream:
 
                     kwargs = {
                         "ssl_context": ssl_context,
-                        "server_hostname": self._origin.host.decode("ascii"),
+                        "server_hostname": sni_hostname
+                        or self._origin.host.decode("ascii"),
                         "timeout": timeout,
                     }
                     async with Trace("start_tls", logger, request, kwargs) as trace:

httpcore/_sync/connection.py

@@ -95,6 +95,7 @@ def handle_request(self, request: Request) -> Response:
 
     def _connect(self, request: Request) -> NetworkStream:
         timeouts = request.extensions.get("timeout", {})
+        sni_hostname = request.extensions.get("sni_hostname", None)
         timeout = timeouts.get("connect", None)
 
         retries_left = self._retries
@@ -136,7 +137,8 @@ def _connect(self, request: Request) -> NetworkStream:
 
                     kwargs = {
                         "ssl_context": ssl_context,
-                        "server_hostname": self._origin.host.decode("ascii"),
+                        "server_hostname": sni_hostname
+                        or self._origin.host.decode("ascii"),
                         "timeout": timeout,
                     }
                     with Trace("start_tls", logger, request, kwargs) as trace: