encode
diff --git a/‎CHANGELOG.md
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diff --git a/‎README.md
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diff --git a/‎docs/async.md
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diff --git a/‎docs/extensions.md
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diff --git a/‎docs/http2.md
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diff --git a/‎docs/proxies.md
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diff --git a/‎httpcore/__init__.py
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diff --git a/‎httpcore/_backends/auto.py
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diff --git a/‎httpcore/_synchronization.py
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diff --git a/‎pyproject.toml
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@@ -4,8 +4,15 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
-## Unreleased
+## 1.0.0 (...)
 
+From version 1.0 our async support is now optional, as the package has minimal dependencies by default.
+
+For async support use either `pip install 'httpcore[asyncio]'` or `pip install 'httpcore[trio]'`.
+
+The project versioning policy is now explicitly governed by SEMVER. See https://semver.org/.
+
+- Async support becomes fully optional. (#809)
 - Add support for Python 3.12. (#807)
 
 ## 0.18.0 (September 8th, 2023)
 
@@ -35,16 +35,10 @@ For HTTP/1.1 only support, install with:
 $ pip install httpcore
 ```
 
-For HTTP/1.1 and HTTP/2 support, install with:
+There are also a number of optional extras available...
 
 ```shell
-$ pip install httpcore[http2]
-```
-
-For SOCKS proxy support, install with:
-
-```shell
-$ pip install httpcore[socks]
+$ pip install httpcore['asyncio,trio,http2,socks']
 ```
 
 # Sending requests
@@ -89,3 +83,29 @@ The motivation for `httpcore` is:
 * To provide a reusable low-level client library, that other packages can then build on top of.
 * To provide a *really clear interface split* between the networking code and client logic,
   so that each is easier to understand and reason about in isolation.
+
 ## Dependencies
+
+The `httpcore` package has the following dependencies...
+
+* `h11`
+* `certifi`
+
+And the following optional extras...
+
+* `anyio` - Required by `pip install httpcore['asyncio']`.
+* `trio` - Required by `pip install httpcore['trio']`.
+* `h2` - Required by `pip install httpcore['http2']`.
+* `socksio` - Required by `pip install httpcore['socks']`.
+
+## Versioning
+
+We use [SEMVER for our versioning policy](https://semver.org/).
+
+For changes between package versions please see our [project changelog](CHANGELOG.md).
+
+We recommend pinning your requirements either the most current major version, or a more specific version range:
+
+```python
+pip install 'httpcore==1.*'
+```
@@ -8,6 +8,22 @@ If you're working with an async web framework then you'll also want to use an as
 
 Launching concurrent async tasks is far more resource efficient than spawning multiple threads. The Python interpreter should be able to comfortably handle switching between over 1000 concurrent tasks, while a sensible number of threads in a thread pool might be to enable around 10 or 20 concurrent threads.
 
+## Enabling Async support
+
+If you're using async with [Python's stdlib `asyncio` support](https://docs.python.org/3/library/asyncio.html), install the optional dependencies using:
+
+```shell
+$ pip install 'httpcore[asyncio]'
+```
+
+Alternatively, if you're working with [the Python `trio` package](https://trio.readthedocs.io/en/stable/):
+
+```shell
+$ pip install 'httpcore[trio]'
+```
+
+We highly recommend `trio` for async support. The `trio` project [pioneered the principles of structured concurrency](https://en.wikipedia.org/wiki/Structured_concurrency), and has a more carefully constrained API against which to work from.
+
 ## API differences
 
 When using async support, you need make sure to use an async connection pool class:
 
@@ -147,6 +147,8 @@ The following event types are currently exposed...
 * `"http2.receive_response_body"`
 * `"http2.response_closed"`
 
+The exact set of trace events may be subject to change across different versions of `httpcore`. If you need to rely on a particular set of events it is recommended that you pin installation of the package to a fixed version.
+
 ### `"sni_hostname"`
 
 The server's hostname, which is used to confirm the hostname supplied by the SSL certificate.
 
@@ -15,7 +15,7 @@ When using the `httpcore` client, HTTP/2 support is not enabled by default, beca
 If you're issuing highly concurrent requests you might want to consider trying out our HTTP/2 support. You can do so by first making sure to install the optional HTTP/2 dependencies...
 
 ```shell
-$ pip install httpcore[http2]
+$ pip install 'httpcore[http2]'
 ```
 
 And then instantiating a connection pool with HTTP/2 support enabled:
 
@@ -83,7 +83,7 @@ If you use proxies, keep in mind that the `httpcore` package only supports proxi
 
 The `httpcore` package also supports proxies using the SOCKS5 protocol.
 
-Make sure to install the optional dependancy using `pip install httpcore[socks]`.
+Make sure to install the optional dependancy using `pip install 'httpcore[socks]'`.
 
 The `SOCKSProxy` class should be using instead of a standard connection pool:
 
 
@@ -130,7 +130,7 @@ def __init__(self, *args, **kwargs):  # type: ignore
     "WriteError",
 ]
 
-__version__ = "0.18.0"
+__version__ = "1.0.0"
 
 
 __locals = locals()
 
@@ -1,15 +1,14 @@
 import typing
 from typing import Optional
 
-import sniffio
-
+from .._synchronization import current_async_library
 from .base import SOCKET_OPTION, AsyncNetworkBackend, AsyncNetworkStream
 
 
 class AutoBackend(AsyncNetworkBackend):
     async def _init_backend(self) -> None:
         if not (hasattr(self, "_backend")):
-            backend = sniffio.current_async_library()
+            backend = current_async_library()
             if backend == "trio":
                 from .trio import TrioBackend
 
 
@@ -2,8 +2,6 @@
 from types import TracebackType
 from typing import Optional, Type
 
-import sniffio
-
 from ._exceptions import ExceptionMapping, PoolTimeout, map_exceptions
 
 # Our async synchronization primatives use either 'anyio' or 'trio' depending
@@ -20,6 +18,22 @@
     anyio = None  # type: ignore
 
 
+def current_async_library() -> str:
+    # Determine if we're running under trio or asyncio.
+    # See https://sniffio.readthedocs.io/en/latest/
+    try:
+        import sniffio
+    except ImportError:  # pragma: nocover
+        return "asyncio"
+
+    environment = sniffio.current_async_library()
+
+    if environment not in ("asyncio", "trio"):  # pragma: nocover
+        raise RuntimeError("Running under an unsupported async environment.")
+
+    return environment
+
+
 class AsyncLock:
     def __init__(self) -> None:
         self._backend = ""
@@ -29,17 +43,17 @@ def setup(self) -> None:
         Detect if we're running under 'asyncio' or 'trio' and create
         a lock with the correct implementation.
         """
-        self._backend = sniffio.current_async_library()
+        self._backend = current_async_library()
         if self._backend == "trio":
             if trio is None:  # pragma: nocover
                 raise RuntimeError(
-                    "Running under trio, requires the 'trio' package to be installed."
+                    "Running with trio requires installation of 'httpcore[trio]'."
                 )
             self._trio_lock = trio.Lock()
         else:
             if anyio is None:  # pragma: nocover
                 raise RuntimeError(
-                    "Running under asyncio requires the 'anyio' package to be installed."
+                    "Running with asyncio requires installation of 'httpcore[asyncio]'."
                 )
             self._anyio_lock = anyio.Lock()
 
@@ -75,17 +89,17 @@ def setup(self) -> None:
         Detect if we're running under 'asyncio' or 'trio' and create
         a lock with the correct implementation.
         """
-        self._backend = sniffio.current_async_library()
+        self._backend = current_async_library()
         if self._backend == "trio":
             if trio is None:  # pragma: nocover
                 raise RuntimeError(
-                    "Running under trio requires the 'trio' package to be installed."
+                    "Running with trio requires installation of 'httpcore[trio]'."
                 )
             self._trio_event = trio.Event()
         else:
             if anyio is None:  # pragma: nocover
                 raise RuntimeError(
-                    "Running under asyncio requires the 'anyio' package to be installed."
+                    "Running with asyncio requires installation of 'httpcore[asyncio]'."
                 )
             self._anyio_event = anyio.Event()
 
@@ -105,7 +119,7 @@ async def wait(self, timeout: Optional[float] = None) -> None:
         if self._backend == "trio":
             if trio is None:  # pragma: nocover
                 raise RuntimeError(
-                    "Running under trio requires the 'trio' package to be installed."
+                    "Running with trio requires installation of 'httpcore[trio]'."
                 )
 
             trio_exc_map: ExceptionMapping = {trio.TooSlowError: PoolTimeout}
@@ -116,7 +130,7 @@ async def wait(self, timeout: Optional[float] = None) -> None:
         else:
             if anyio is None:  # pragma: nocover
                 raise RuntimeError(
-                    "Running under asyncio requires the 'anyio' package to be installed."
                     "Running with asyncio requires installation of 'httpcore[asyncio]'."
                 )
 
             anyio_exc_map: ExceptionMapping = {TimeoutError: PoolTimeout}
@@ -135,11 +149,11 @@ def setup(self) -> None:
         Detect if we're running under 'asyncio' or 'trio' and create
         a semaphore with the correct implementation.
         """
-        self._backend = sniffio.current_async_library()
+        self._backend = current_async_library()
         if self._backend == "trio":
             if trio is None:  # pragma: nocover
                 raise RuntimeError(
-                    "Running under trio requires the 'trio' package to be installed."
+                    "Running with trio requires installation of 'httpcore[trio]'."
                 )
 
             self._trio_semaphore = trio.Semaphore(
@@ -148,7 +162,7 @@ def setup(self) -> None:
         else:
             if anyio is None:  # pragma: nocover
                 raise RuntimeError(
-                    "Running under asyncio requires the 'anyio' package to be installed."
+                    "Running with asyncio requires installation of 'httpcore[asyncio]'."
                 )
 
             self._anyio_semaphore = anyio.Semaphore(
@@ -184,19 +198,19 @@ def __init__(self) -> None:
         Detect if we're running under 'asyncio' or 'trio' and create
         a shielded scope with the correct implementation.
         """
-        self._backend = sniffio.current_async_library()
+        self._backend = current_async_library()
 
         if self._backend == "trio":
             if trio is None:  # pragma: nocover
                 raise RuntimeError(
-                    "Running under trio requires the 'trio' package to be installed."
+                    "Running with trio requires installation of 'httpcore[trio]'."
                 )
 
             self._trio_shield = trio.CancelScope(shield=True)
         else:
             if anyio is None:  # pragma: nocover
                 raise RuntimeError(
-                    "Running under asyncio requires the 'anyio' package to be installed."
+                    "Running with asyncio requires installation of 'httpcore[asyncio]'."
                 )
 
             self._anyio_shield = anyio.CancelScope(shield=True)
 
@@ -29,10 +29,8 @@ classifiers = [
     "Topic :: Internet :: WWW/HTTP",
 ]
 dependencies = [
-    "anyio>=3.0,<5.0",
     "certifi",
     "h11>=0.13,<0.15",
-    "sniffio==1.*",
 ]
 
 [project.optional-dependencies]
@@ -42,6 +40,12 @@ http2 = [
 socks = [
     "socksio==1.*",
 ]
+trio = [
+    "trio>=0.22.0,<0.23.0",
+]
+asyncio = [
+    "anyio>=4.0,<5.0",
+]
 
 [project.urls]
 Documentation = "https://www.encode.io/httpcore"
Original file line number	Diff line number	Diff line change
`@@ -130,7 +130,7 @@ def __init__(self, args, *kwargs): # type: ignore`
`130`	`130`	`"WriteError",`
`131`	`131`	`]`
`132`	`132`
`133`		`-__version__ = "0.18.0"`
	`133`	`+__version__ = "1.0.0"`
`134`	`134`
`135`	`135`
`136`	`136`	`__locals = locals()`