Drop urllib3 in favor of public gist

docs/advanced.md

@@ -809,6 +809,8 @@ HTTPX's `Client` also accepts a `transport` argument. This argument allows you
 to provide a custom Transport object that will be used to perform the actual
 sending of the requests.
 
+### Usage
+
 For some advanced configuration you might need to instantiate a transport
 class directly, and pass it to the client instance. The `httpcore` package
 provides a `local_address` configuration that is only available via this
@@ -850,18 +852,19 @@ do not include any default values for configuring aspects such as the
 connection pooling details, so you'll need to provide more explicit
 configuration when using this API.
 
-HTTPX also currently ships with a transport that uses the excellent
-[`urllib3` library](https://urllib3.readthedocs.io/en/latest/), which can be
-used with the sync `Client`...
+### urllib3 transport
+
+This [public gist](https://gist.github.com/florimondmanca/d56764d78d748eb9f73165da388e546e) provides a transport that uses the excellent [`urllib3` library](https://urllib3.readthedocs.io/en/latest/), and can be used with the sync `Client`...
 
 ```python
 >>> import httpx
->>> client = httpx.Client(transport=httpx.URLLib3Transport())
+>>> from urllib3_transport import URLLib3Transport
+>>> client = httpx.Client(transport=URLLib3Transport())
 >>> client.get("https://example.org")
 <Response [200 OK]>
 ```
 
-Note that you'll need to install the `urllib3` package to use `URLLib3Transport`.
+### Writing custom transports
 
 A transport instance must implement the Transport API defined by
 [`httpcore`](https://www.encode.io/httpcore/api/). You

docs/compatibility.md

@@ -81,3 +81,11 @@ Besides, `httpx.Request()` does not support the `auth`, `timeout`, `allow_redire
 ## Mocking
 
 If you need to mock HTTPX the same way that test utilities like `responses` and `requests-mock` does for `requests`, see [RESPX](https://github.com/lundberg/respx).
+
+## Networking layer
+
+`requests` defers most of its HTTP networking code to the excellent [`urllib3` library](https://urllib3.readthedocs.io/en/latest/).
+
+On the other hand, HTTPX uses [HTTPCore](https://github.com/encode/httpcore) as its core HTTP networking layer, which is a different project than `urllib3`.
+
+If you're transitioning from Requests to HTTPX, you might want to consider using HTTPX with an [`urllib3` custom transport](/advanced#urllib3-transport) at first, so that `urllib3` is retained as the underlying HTTP networking implementation, allowing you to deal with any differences in behavior as a second phase.

httpx/__init__.py

@@ -38,7 +38,6 @@
 from ._models import URL, Cookies, Headers, QueryParams, Request, Response
 from ._status_codes import StatusCode, codes
 from ._transports.asgi import ASGITransport
-from ._transports.urllib3 import URLLib3ProxyTransport, URLLib3Transport
 from ._transports.wsgi import WSGITransport
 
 __all__ = [
@@ -101,8 +100,6 @@
     "TransportError",
     "UnsupportedProtocol",
     "URL",
-    "URLLib3ProxyTransport",
-    "URLLib3Transport",
     "WriteError",
     "WriteTimeout",
     "WSGITransport",

scripts/coverage

@@ -8,4 +8,4 @@ export SOURCE_FILES="httpx tests"
 
 set -x
 
-${PREFIX}coverage report --omit=httpx/_transports/urllib3.py --show-missing --skip-covered --fail-under=100
+${PREFIX}coverage report --show-missing --skip-covered --fail-under=100