mutating func receiveGoaway()

in Sources/NIOHTTP2/ConnectionStateMachine/ConnectionStateMachine.swift [1186:1256]
57 lines of code
10 McCabe index (conditional complexity)

    mutating func receiveGoaway(lastStreamID: HTTP2StreamID) -> StateMachineResultWithEffect {
        // GOAWAY frames are some of the most subtle frames in HTTP/2, they cause a number of state transitions all at once.
        // In particular, the value of lastStreamID heavily affects the state transitions we perform here.
        // In this case, all streams initiated by us that have stream IDs higher than lastStreamID will be closed, effective
        // immediately. If this leaves us with zero streams, the connection is fullyQuiesced. Otherwise, we are quiescing.
        switch self.state {
        case .prefaceReceived(var state):
            return self.avoidingStateMachineCoW { newState in
                let result = state.receiveGoAwayFrame(lastStreamID: lastStreamID)
                let newStateData = QuiescingPrefaceReceivedState(fromPrefaceReceived: state, lastStreamID: lastStreamID)
                newState = .quiescingPrefaceReceived(newStateData)
                return result
            }

        case .active(var state):
            return self.avoidingStateMachineCoW { newState in
                let result = state.receiveGoAwayFrame(lastStreamID: lastStreamID)
                let newStateData = RemotelyQuiescedState(fromActive: state, lastLocalStreamID: lastStreamID)
                newState = .remotelyQuiesced(newStateData)
                newState.closeIfNeeded(newStateData)
                return result
            }

        case .locallyQuiesced(var state):
            return self.avoidingStateMachineCoW { newState in
                let result = state.receiveGoAwayFrame(lastStreamID: lastStreamID)
                let newStateData = BothQuiescingState(fromLocallyQuiesced: state, lastLocalStreamID: lastStreamID)
                newState = .bothQuiescing(newStateData)
                newState.closeIfNeeded(newStateData)
                return result
            }

        case .remotelyQuiesced(var state):
            return self.avoidingStateMachineCoW { newState in
                let result = state.receiveGoAwayFrame(lastStreamID: lastStreamID)
                newState = .remotelyQuiesced(state)
                newState.closeIfNeeded(state)
                return result
            }

        case .bothQuiescing(var state):
            return self.avoidingStateMachineCoW { newState in
                let result = state.receiveGoAwayFrame(lastStreamID: lastStreamID)
                newState = .bothQuiescing(state)
                newState.closeIfNeeded(state)
                return result
            }

        case .quiescingPrefaceReceived(var state):
            return self.avoidingStateMachineCoW { newState in
                let result = state.receiveGoAwayFrame(lastStreamID: lastStreamID)
                newState = .quiescingPrefaceReceived(state)
                return result
            }

        case .idle, .prefaceSent, .quiescingPrefaceSent:
            // We're waiting for the preface.
            return .init(result: .connectionError(underlyingError: NIOHTTP2Errors.missingPreface(), type: .protocolError), effect: nil)

        case .fullyQuiesced(var state):
            return self.avoidingStateMachineCoW { newState in
                // We allow duplicate GOAWAY here, so long as it ratchets correctly.
                let result = state.receiveGoAwayFrame(lastStreamID: lastStreamID)
                newState = .fullyQuiesced(state)
                return result
            }

        case .modifying:
            preconditionFailure("Must not be left in modifying state")
        }
    }