Tolerate shutdown message after channel is closed

Sources/AsyncHTTPClient/ConnectionPool/HTTP2/HTTP2Connection.swift

@@ -111,7 +111,7 @@ final class HTTP2Connection {
 
     deinit {
         guard case .closed = self.state else {
-            preconditionFailure("Connection must be closed, before we can deinit it")
+            preconditionFailure("Connection must be closed, before we can deinit it. Current state: \(self.state)")
         }
     }
 
@@ -164,15 +164,23 @@ final class HTTP2Connection {
         return promise.futureResult
     }
 
-    private func start() -> EventLoopFuture<Int> {
+    func start() -> EventLoopFuture<Int> {
         self.channel.eventLoop.assertInEventLoop()
 
         let readyToAcceptConnectionsPromise = self.channel.eventLoop.makePromise(of: Int.self)
 
         self.state = .starting(readyToAcceptConnectionsPromise)
         self.channel.closeFuture.whenComplete { _ in
-            self.state = .closed
-            self.delegate.http2ConnectionClosed(self)
+            switch self.state {
+            case .initialized, .closed:
+                preconditionFailure("invalid state \(self.state)")
+            case .starting(let readyToAcceptConnectionsPromise):
+                self.state = .closed
+                readyToAcceptConnectionsPromise.fail(HTTPClientError.remoteConnectionClosed)
+            case .active, .closing:
+                self.state = .closed
+                self.delegate.http2ConnectionClosed(self)
+            }
         }
 
         do {
@@ -258,16 +266,26 @@ final class HTTP2Connection {
     private func shutdown0() {
         self.channel.eventLoop.assertInEventLoop()
 
-        self.state = .closing
+        switch self.state {
+        case .active:
+            self.state = .closing
 
-        // inform all open streams, that the currently running request should be cancelled.
-        self.openStreams.forEach { box in
-            box.channel.triggerUserOutboundEvent(HTTPConnectionEvent.shutdownRequested, promise: nil)
-        }
+            // inform all open streams, that the currently running request should be cancelled.
+            self.openStreams.forEach { box in
+                box.channel.triggerUserOutboundEvent(HTTPConnectionEvent.shutdownRequested, promise: nil)
+            }
 
-        // inform the idle connection handler, that connection should be closed, once all streams
-        // are closed.
-        self.channel.triggerUserOutboundEvent(HTTPConnectionEvent.shutdownRequested, promise: nil)
+            // inform the idle connection handler, that connection should be closed, once all streams
+            // are closed.
+            self.channel.triggerUserOutboundEvent(HTTPConnectionEvent.shutdownRequested, promise: nil)
+
+        case .closed, .closing:
+            // we are already closing/closed and we need to tolerate this
+            break
+
+        case .initialized, .starting:
+            preconditionFailure("invalid state \(self.state)")
+        }
     }
 }
 

Tests/AsyncHTTPClientTests/HTTP2ConnectionTests+XCTest.swift

@@ -26,6 +26,7 @@ extension HTTP2ConnectionTests {
     static var allTests: [(String, (HTTP2ConnectionTests) -> () throws -> Void)] {
         return [
             ("testCreateNewConnectionFailureClosedIO", testCreateNewConnectionFailureClosedIO),
+            ("testConnectionToleratesShutdownEventsAfterAlreadyClosed", testConnectionToleratesShutdownEventsAfterAlreadyClosed),
             ("testSimpleGetRequest", testSimpleGetRequest),
             ("testEveryDoneRequestLeadsToAStreamAvailableCall", testEveryDoneRequestLeadsToAStreamAvailableCall),
             ("testCancelAllRunningRequests", testCancelAllRunningRequests),

Tests/AsyncHTTPClientTests/HTTP2ConnectionTests.swift

@@ -42,6 +42,28 @@ class HTTP2ConnectionTests: XCTestCase {
         ).wait())
     }
 
+    func testConnectionToleratesShutdownEventsAfterAlreadyClosed() {
+        let embedded = EmbeddedChannel()
+        XCTAssertNoThrow(try embedded.connect(to: SocketAddress(ipAddress: "127.0.0.1", port: 3000)).wait())
+
+        let logger = Logger(label: "test.http2.connection")
+        let connection = HTTP2Connection(
+            channel: embedded,
+            connectionID: 0,
+            decompression: .disabled,
+            delegate: TestHTTP2ConnectionDelegate(),
+            logger: logger
+        )
+        _ = connection.start()
+
+        XCTAssertNoThrow(try embedded.close().wait())
+        // to really destroy the channel we need to tick once
+        embedded.embeddedEventLoop.run()
+
+        // should not crash
+        connection.shutdown()
+    }
+
     func testSimpleGetRequest() {
         let eventLoopGroup = MultiThreadedEventLoopGroup(numberOfThreads: 1)
         let eventLoop = eventLoopGroup.next()