Middleware API

httpx/__init__.py

@@ -32,6 +32,7 @@
     WriteError,
     WriteTimeout,
 )
+from ._middleware import AsyncMiddleware, Middleware
 from ._models import URL, Cookies, Headers, QueryParams, Request, Response
 from ._status_codes import StatusCode, codes
 from ._transports.asgi import ASGITransport
@@ -55,6 +56,8 @@
     "codes",
     "ASGITransport",
     "AsyncClient",
+    "AsyncMiddleware",
+    "Middleware",
     "Auth",
     "BasicAuth",
     "Client",

httpx/_client.py

@@ -25,6 +25,7 @@
     TooManyRedirects,
     map_exceptions,
 )
+from ._middleware import AsyncMiddleware, Middleware
 from ._models import URL, Cookies, Headers, QueryParams, Request, Response
 from ._status_codes import codes
 from ._transports.asgi import ASGITransport
@@ -452,6 +453,7 @@ def __init__(
         max_redirects: int = DEFAULT_MAX_REDIRECTS,
         base_url: URLTypes = None,
         transport: httpcore.SyncHTTPTransport = None,
+        middleware: typing.Sequence[Middleware] = (),
         app: typing.Callable = None,
         trust_env: bool = True,
     ):
@@ -502,6 +504,8 @@ def __init__(
         }
         self._proxies = dict(sorted(self._proxies.items()))
 
+        self._middleware = middleware
+
     def _init_transport(
         self,
         verify: VerifyTypes = True,
@@ -610,9 +614,16 @@ def send(
 
         auth = self._build_auth(request, auth)
 
-        response = self._send_handling_redirects(
-            request, auth=auth, timeout=timeout, allow_redirects=allow_redirects,
+        call_next = functools.partial(
+            self._send_handling_redirects,
+            auth=auth,
+            allow_redirects=allow_redirects,
+            timeout=timeout,
         )
+        for middleware in self._middleware:
+            call_next = functools.partial(middleware.send, call_next=call_next)
+
+        response = call_next(request)
 
         if not stream:
             try:
@@ -983,6 +994,7 @@ def __init__(
         max_redirects: int = DEFAULT_MAX_REDIRECTS,
         base_url: URLTypes = None,
         transport: httpcore.AsyncHTTPTransport = None,
+        middleware: typing.Sequence[AsyncMiddleware] = (),
         app: typing.Callable = None,
         trust_env: bool = True,
     ):
@@ -1033,6 +1045,8 @@ def __init__(
         }
         self._proxies = dict(sorted(self._proxies.items()))
 
+        self._middleware = middleware
+
     def _init_transport(
         self,
         verify: VerifyTypes = True,
@@ -1138,9 +1152,16 @@ async def send(
 
         auth = self._build_auth(request, auth)
 
-        response = await self._send_handling_redirects(
-            request, auth=auth, timeout=timeout, allow_redirects=allow_redirects,
+        call_next = functools.partial(
+            self._send_handling_redirects,
+            auth=auth,
+            allow_redirects=allow_redirects,
+            timeout=timeout,
         )
+        for middleware in self._middleware:
+            call_next = functools.partial(middleware.asend, call_next=call_next)
+
+        response = await call_next(request)
 
         if not stream:
             try:

httpx/_middleware.py

@@ -0,0 +1,17 @@
+from typing import Awaitable, Callable
+
+from ._models import Request, Response
+
+
+class Middleware:
+    def send(
+        self, request: Request, call_next: Callable[[Request], Response]
+    ) -> Response:
+        raise NotImplementedError  # pragma: no cover
+
+
+class AsyncMiddleware:
+    async def asend(
+        self, request: Request, call_next: Callable[[Request], Awaitable[Response]]
+    ) -> Response:
+        raise NotImplementedError  # pragma: no cover