Building Robust ASGI Applications with asgi-lifespan
Asynchronous Server Gateway Interface (ASGI) applications have gained immense popularity due to their ability to handle high traffic and provide excellent performance. To enhance the development and testing experience of ASGI apps, asgi-lifespan has emerged as a powerful library. In this article, we will explore how to build robust ASGI applications using asgi-lifespan.
Features of asgi-lifespan
asgi-lifespan offers several features that simplify the development and testing of ASGI applications:
- Sending lifespan events to an ASGI app using the LifespanManager class.
- Support for asyncio and trio, the popular Python libraries for asynchronous programming.
- Full type annotations for improved code quality.
- Excellent test coverage to ensure reliability.
Installation
To get started with asgi-lifespan, install it using pip:
bash
pip install 'asgi-lifespan==2.*'
Basic Usage
asgi-lifespan provides the LifespanManager class to programmatically send ASGI lifespan events into an ASGI app. This allows you to startup and shutdown an ASGI app without the need for an ASGI server.
Here’s a basic example showcasing the usage of LifespanManager:
from contextlib import asynccontextmanager
from asgi_lifespan import LifespanManager
from starlette.applications import Starlette
@asynccontextmanager
async def lifespan(app):
print("Starting up!")
yield
print("Shutting down!")
app = Starlette(lifespan=lifespan)
async def main():
async with LifespanManager(app) as manager:
print("We're in!")
# On asyncio:
import asyncio
asyncio.run(main())
# On trio:
import trio
trio.run(main)
In this example, we define a simple lifespan-capable ASGI app using the Starlette framework. The lifespan context manager, lifespan, is responsible for printing messages during the startup and shutdown phases. The LifespanManager is then used to manage the lifecycle of the app. Running the example displays the startup, “We’re in!”, and shutdown messages.
Sending Lifespan Events for Testing
asgi-lifespan is especially useful for testing ASGI applications. Let’s see how it can be used in conjunction with HTTPX and pytest to send test requests into an ASGI app.
First, install the required dependencies:
bash
pip install asgi-lifespan httpx starlette pytest pytest-asyncio
Next, create a test script:
Running the test suite produces the expected output, verifying that the ASGI app is properly handling requests.
Accessing State
lifespan-manager also provides a lifespan state that persists data throughout the lifespan of the app. To access this state, use manager.app instead of app within the context manager.
For example, when using HTTPX as an async test client:
async with LifespanManager(app) as manager:
async with httpx.AsyncClient(app=manager.app) as client:
...Conclusion
asgi-lifespan is a powerful library that simplifies the development and testing of ASGI applications. By leveraging the LifespanManager class, developers can programmatically send startup and shutdown events without the need for an ASGI server. This improves the efficiency and agility of application development and testing.
Remember to follow best practices for API documentation, security, scalability, and performance when building ASGI applications. With asgi-lifespan, you can create robust and reliable ASGI apps that provide an excellent user experience.
If you have any questions or want to explore more about asgi-lifespan, feel free to ask during the Q&A session.
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