aiofastnet provides drop-in optimized replacements for asyncio's:

• loop.create_connection()
• loop.open_connection()
• loop.create_server()
• loop.start_server()
• loop.start_tls()
• loop.sendfile()

If your library or application already uses the asyncio streams or transport/protocol model, aiofastnet lets you keep the same architecture while replacing one of the most expensive layers underneath it.

The benchmark below compares echo round-trips over loopback for TCP and SSL. The exact gains depend on workload, message sizes, CPU, OpenSSL version, and how much of your total runtime is spent in transport/SSL plumbing.

Source: examples/benchmark.py

In these benchmarks, aiofastnet is up to 2.2x faster than standard asyncio.

aiofastnet is fully compatible with free-threaded Python builds and scales as expected when multiple event loops run in parallel across multiple threads.

Source: examples/benchmark_threaded.py

• Faster hot path. Transport and SSL internals are reimplemented in Cython/C to reduce overhead on long-lived connections.
• Drop-in API. Keep using the standard asyncio streams or transport/protocol model and familiar loop-level networking operations.
• Works with the event loop you already use. aiofastnet works with stock asyncio loops, uvloop, and winloop.
• Particularly strong for SSL-heavy workloads. aiofastnet uses OpenSSL more directly and avoids extra copies in the data path.
• Safer transport write() / writelines() behavior. If the socket cannot accept everything immediately, only bytes and memoryview objects backed by bytes are retained without copying. Other objects, including bytearray and non-bytes exporters, are copied before being queued. Unlike standard asyncio transports, this avoids sending corrupted data if application code modifies the underlying buffer after write() / writelines() returns.
• Better SSL backpressure semantics. Buffer sizes and write limits reflect what is actually queued across the stack.
• Works for library authors. WebSocket, HTTP, RPC, proxy, database, broker, and custom protocol libraries can expose the same API while giving users a faster transport layer.

Install from PyPI:

$ pip install aiofastnet

aiofastnet requires Python 3.9 or greater.

The API mirrors stdlib asyncio. Pass the running loop and use your existing protocol factory:

import asyncio
import aiofastnet

class EchoClientProtocol(asyncio.Protocol):
    def connection_made(self, transport):
        self.transport = transport
        self.transport.write(b"hello")

    def data_received(self, data):
        print("received:", data)
        self.transport.close()

async def main():
    loop = asyncio.get_running_loop()

    transport, protocol = await aiofastnet.create_connection(
        loop,
        EchoClientProtocol,
        "127.0.0.1",
        9000,
    )

    await asyncio.sleep(0.1)

asyncio.run(main())

For servers, replace loop.create_server(...) with aiofastnet.create_server(loop, ...) in the same way.

aiofastnet also exposes start_tls and sendfile:

transport = await aiofastnet.start_tls(
    loop,
    transport,
    protocol,
    ssl_context,
    server_side=False,
    server_hostname="example.com",
)

await aiofastnet.sendfile(transport, fileobj)

aiofastnet is most attractive when you already rely on asyncio's transport/protocol APIs and one or more of these are true:

• You have long-lived TCP or TLS connections.
• You run protocol-heavy services where transport overhead is visible in CPU profiles.
• You maintain a library and want better performance without changing your public API.
• You care about consistent write() / writelines() buffer behavior.
• You want SSL flow control to reflect the whole buffered stack, not only part of it.

aiofastnet is not the right default for every networking project:

• If your workload is dominated by very short-lived connections, you should expect little or no gain. aiofastnet focuses on optimizing the data path after connection establishment.

aiofastnet is built and tested on Linux, macOS, and Windows. It works with the standard asyncio event loop, uvloop, and winloop.

On Windows it works with SelectorEventLoop and winloop. With ProactorEventLoop it falls back to asyncio's native connection and server implementation, because the proactor loop does not provide the add_reader() / add_writer() hooks required by aiofastnet's custom transport implementation. For transports created through aiofastnet, a compatibility wrapper preserves the documented write() / writelines() buffer-safety behavior.

aiofastnet is compatible with free-threaded Python builds such as python3.14t. The extension modules are built to work without forcing the legacy GIL back on, so separate event loops may run in separate threads.

The repository includes several free-threading examples:

• examples/benchmark_threaded.py runs multiple echo client/server pairs in parallel to compare single-loop and multi-threaded execution.
• examples/echo_server_threaded.py starts one listening echo server per thread on the same port with reuse_port=True so the kernel can distribute incoming connections across worker threads.
• examples/echo_client_threaded.py starts one echo client per thread and drives them in parallel against the shared server port.

Transport objects remain thread-affine. Methods such as write(), writelines(), close(), pause_reading(), and similar transport operations must be called from the same thread that established the connection. Calling transport methods directly from a different thread raises RuntimeError.

This matches the general asyncio model: loops and loop-owned objects are not meant to be used concurrently from arbitrary threads. aiofastnet does not add internal transport locking for cross-thread access.

To use aiofastnet correctly with multithreading:

• Create a separate event loop in each worker thread.
• Create connections and servers inside the loop thread that will own them.
• Keep all direct transport interaction on that same thread.
• If another thread needs to send data or close a transport, schedule that work onto the owning loop with loop.call_soon_threadsafe(...) instead of touching the transport directly.

In other words, free-threaded Python lets multiple loops make progress in parallel, but each individual connection is still owned by exactly one loop and one thread.

1. Clone the repository:

   $ git clone git@github.com:tarasko/aiofastnet.git
   $ cd aiofastnet
   

2. Create and activate a virtual environment:

   $ python3 -m venv aiofn-dev
   $ source aiofn-dev/bin/activate
   

3. Install test dependencies:

   $ pip install -r requirements-test.txt
   

4. Build extensions in place and run tests:

   $ python setup.py build_ext --inplace
   $ pytest -s -v
   

5. Run the benchmark:

   $ python -m examples.benchmark
   

Contributions are welcome.