Add support for swift-service-lifecycle

[aryan-25]

Motivation:

The swift-service-lifecycle library is commonly used for managing service lifetimes. We should adopt swift-service-lifecycle for NIOHTTPServer.

Modifications:

• Updated the child channel initializers for HTTP/1.1 and Secure Upgrade in NIOHTTPServer to use swift-nio-extra's ServerQuiescingHelper. The ServerQuiescingHelper is added to the channel pipeline, and propagates a ChannelShouldQuiesceEvent upon graceful shutdown being triggered.

  • For HTTP/1.1, the HTTPServerPipelineHandler handler, which is contained in the pipeline, already handles ChannelShouldQuiesceEvent events.

  • For HTTP/2, a NIOHTTP2ServerConnectionManager is added to the pipeline. This connection manager reacts to a ChannelShouldQuiesceEvent and gracefully shuts down HTTP/2 connections.

• Updated NIOHTTPServer's serve(handler:) to handle graceful shutdown (using swift-service-lifecycle's withTaskCancellationOrGracefulShutdownHandler method).

Result:

Support for swift-service-lifecycle added.

[FranzBusch]

Why do we need to let the user customize this? They can setup their own handler by wrapping this service if they wanted to.

[aryan-25]

Agreed. I hadn't thought about this. I've removed the onGracefulShutdown argument now.

[tib]

Looks very good—just two small additions, though:

1. I strongly believe you also need to use #if ServiceLifecycle checks in the Tests/NIOHTTPServerTests/NIOHTTPServer+ServiceLifecycleTests.swift file.

Also, make sure you test all trait combinations:

swift test --parallel --traits ServiceLifecycle
swift test --parallel --enable-all-traits
swift test --disable-default-traits

2. A dedicated section in the README about the available traits would be helpful, similar to the one we have for swift-configuration.

Thank you for the work. 🙏

[tib]

It'd be nice if we could also enable the ServiceLifecycle trait by default.

[aryan-25]

The ServiceLifecycle trait is now no longer needed; NIOHTTPServer depends on swift-service-lifecycle by default.

[aryan-25]

Following from #58, I've removed changes to the abstract server API in this PR and created a PR for those changes in the swift-http-api-proposal repository where the abstract server API now resides.

[aryan-25]

Based on some offline discussions, we won't be making any changes to the abstract HTTPServer API.

All HTTPServer implementations should be handling graceful shutdown directly in the serve method.

Users can use the new ClosureService that will be introduced by swift-server/swift-service-lifecycle#227 in order to use a HTTPServer conformance with ServiceGroup (example).