Fix crash when writablity becomes false and races against finishing t…

…he http request (#768)

### Motivation

If the channel's writability changed to false just before we finished a
request, we currently run into a precondition.

### Changes

- Remove the precondition and handle the case appropiatly

### Result

A crash less.

Sources/AsyncHTTPClient/ConnectionPool/HTTP1/HTTP1ClientChannelHandler.swift

@@ -665,7 +665,8 @@ struct IdleWriteStateMachine {
  self.state = .requestEndSent
  return .clearIdleWriteTimeoutTimer
  case .waitingForWritabilityEnabled:
- preconditionFailure("If the channel is not writable, we can't have sent the request end.")
+ self.state = .requestEndSent
+ return .none
  case .requestEndSent:
  return .none
  }

Tests/AsyncHTTPClientTests/HTTP1ClientChannelHandlerTests.swift

@@ -376,6 +376,56 @@ class HTTP1ClientChannelHandlerTests: XCTestCase {
  }
  }
 
+ func testIdleWriteTimeoutRaceToEnd() {
+ let embedded = EmbeddedChannel()
+ var maybeTestUtils: HTTP1TestTools?
+ XCTAssertNoThrow(maybeTestUtils = try embedded.setupHTTP1Connection())
+ guard let testUtils = maybeTestUtils else { return XCTFail("Expected connection setup works") }
+
+ var maybeRequest: HTTPClient.Request?
+ XCTAssertNoThrow(maybeRequest = try HTTPClient.Request(url: "http://localhost/", method: .POST, body: .stream { _ in
+ // Advance time by more than the idle write timeout (that's 1 millisecond) to trigger the timeout.
+ let scheduled = embedded.embeddedEventLoop.flatScheduleTask(in: .milliseconds(2)) {
+ embedded.embeddedEventLoop.makeSucceededVoidFuture()
+ }
+ return scheduled.futureResult
+ }))
+
+ guard let request = maybeRequest else { return XCTFail("Expected to be able to create a request") }
+
+ let delegate = ResponseAccumulator(request: request)
+ var maybeRequestBag: RequestBag<ResponseAccumulator>?
+ XCTAssertNoThrow(maybeRequestBag = try RequestBag(
+ request: request,
+ eventLoopPreference: .delegate(on: embedded.eventLoop),
+ task: .init(eventLoop: embedded.eventLoop, logger: testUtils.logger),
+ redirectHandler: nil,
+ connectionDeadline: .now() + .seconds(30),
+ requestOptions: .forTests(idleWriteTimeout: .milliseconds(5)),
+ delegate: delegate
+ ))
+ guard let requestBag = maybeRequestBag else { return XCTFail("Expected to be able to create a request bag") }
+
+ embedded.isWritable = true
+ embedded.pipeline.fireChannelWritabilityChanged()
+ testUtils.connection.executeRequest(requestBag)
+ let expectedHeaders: HTTPHeaders = ["host": "localhost", "Transfer-Encoding": "chunked"]
+ XCTAssertEqual(
+ try embedded.readOutbound(as: HTTPClientRequestPart.self),
+ .head(HTTPRequestHead(version: .http1_1, method: .POST, uri: "/", headers: expectedHeaders))
+ )
+
+ // change the writability to false.
+ embedded.isWritable = false
+ embedded.pipeline.fireChannelWritabilityChanged()
+ embedded.embeddedEventLoop.run()
+
+ // let the writer, write an end (while writability is false)
+ embedded.embeddedEventLoop.advanceTime(by: .milliseconds(2))
+
+ XCTAssertEqual(try embedded.readOutbound(as: HTTPClientRequestPart.self), .end(nil))
+ }
+
  func testIdleWriteTimeoutWritabilityChanged() {
  let embedded = EmbeddedChannel()
  let testWriter = TestBackpressureWriter(eventLoop: embedded.eventLoop, parts: 5)