Preserve HTTP header casing (#216)

httpcore/_async/http11.py

@@ -133,8 +133,17 @@ async def _receive_response(
             event = await self._receive_event(timeout)
             if isinstance(event, h11.Response):
                 break
+
         http_version = b"HTTP/" + event.http_version
-        return http_version, event.status_code, event.reason, event.headers
+
+        if hasattr(event.headers, "raw_items"):
+            # h11 version 0.11+ supports a `raw_items` interface to get the
+            # raw header casing, rather than the enforced lowercase headers.
+            headers = event.headers.raw_items()
+        else:
+            headers = event.headers
+
+        return http_version, event.status_code, event.reason, headers
 
     async def _receive_response_data(
         self, timeout: TimeoutDict

httpcore/_sync/http11.py

@@ -133,8 +133,17 @@ def _receive_response(
             event = self._receive_event(timeout)
             if isinstance(event, h11.Response):
                 break
+
         http_version = b"HTTP/" + event.http_version
-        return http_version, event.status_code, event.reason, event.headers
+
+        if hasattr(event.headers, "raw_items"):
+            # h11 version 0.11+ supports a `raw_items` interface to get the
+            # raw header casing, rather than the enforced lowercase headers.
+            headers = event.headers.raw_items()
+        else:
+            headers = event.headers
+
+        return http_version, event.status_code, event.reason, headers
 
     def _receive_response_data(
         self, timeout: TimeoutDict

setup.py

@@ -53,7 +53,7 @@ def get_packages(package):
     packages=get_packages("httpcore"),
     include_package_data=True,
     zip_safe=False,
-    install_requires=["h11>=0.8,<0.11", "sniffio==1.*"],
+    install_requires=["h11==0.*", "sniffio==1.*"],
     extras_require={
         "http2": ["h2>=3,<5"],
     },