make ELF.cascade accept an optional promise (#757)

* Make EventLoopFuture.cascade and cascadeFailure accept an optional promise

Motivation:

fixes #756

Modifications:

Change EventLoopFuture.cascade to func cascade(promise: EventLoopPromise<T>?)

Result:

EventLoopFuture.cascade can be called without needing to check if the promise is nil

Sources/NIO/BaseSocketChannel.swift

@@ -802,9 +802,7 @@ class BaseSocketChannel<T: BaseSocket>: SelectableChannel, ChannelCore {
         registerPromise.futureResult.whenFailure { (_: Error) in
             self.close(promise: nil)
         }
-        if let promise = promise {
         registerPromise.futureResult.cascadeFailure(promise: promise)
-        }
 
         if self.lifecycleManager.isPreRegistered {
             // we expect kqueue/epoll registration to always succeed which is basically true, except for errors that

Sources/NIO/ChannelPipeline.swift

@@ -395,10 +395,8 @@ public final class ChannelPipeline: ChannelInvoker {
             self.remove0(ctx: ctx, promise: promise)
         }
 
-        if let promise = promise {
         contextFuture.cascadeFailure(promise: promise)
     }
-    }
 
     /// Remove a `ChannelHandler` from the `ChannelPipeline`.
     ///
@@ -412,10 +410,8 @@ public final class ChannelPipeline: ChannelInvoker {
             self.remove0(ctx: ctx, promise: promise)
         }
 
-        if let promise = promise {
         contextFuture.cascadeFailure(promise: promise)
     }
-    }
 
     /// Remove a `ChannelHandler` from the `ChannelPipeline`.
     ///

Sources/NIO/EventLoopFuture.swift

@@ -749,7 +749,8 @@ extension EventLoopFuture {
     ///
     /// - parameters:
     ///     - promise: The `EventLoopPromise` to fulfill with the results of this future.
-    public func cascade(promise: EventLoopPromise<T>) {
+    public func cascade(promise: EventLoopPromise<T>?) {
+        guard let promise = promise else { return }
         _whenCompleteWithValue { v in
             switch v {
             case .failure(let err):
@@ -769,7 +770,8 @@ extension EventLoopFuture {
     ///
     /// - parameters:
     ///     - promise: The `EventLoopPromise` to fulfill with the results of this future.
-    public func cascadeFailure<U>(promise: EventLoopPromise<U>) {
+    public func cascadeFailure<U>(promise: EventLoopPromise<U>?) {
+        guard let promise = promise else { return }
         self.whenFailure { err in
             promise.fail(error: err)
         }

Sources/NIOHTTP1/HTTPResponseCompressor.swift

@@ -124,11 +124,11 @@ public final class HTTPResponseCompressor: ChannelDuplexHandler {
             responseHead.headers.replaceOrAdd(name: "Content-Encoding", value: algorithm!.rawValue)
             initializeEncoder(encoding: algorithm!)
             pendingResponse.bufferResponseHead(responseHead)
-            chainPromise(promise)
+            pendingWritePromise.futureResult.cascade(promise: promise)
         case .body(let body):
             if algorithm != nil {
                 pendingResponse.bufferBodyPart(body)
-                chainPromise(promise)
+                pendingWritePromise.futureResult.cascade(promise: promise)
             } else {
                 ctx.write(data, promise: promise)
             }
@@ -141,7 +141,7 @@ public final class HTTPResponseCompressor: ChannelDuplexHandler {
             }
 
             pendingResponse.bufferResponseEnd(httpData)
-            chainPromise(promise)
+            pendingWritePromise.futureResult.cascade(promise: promise)
             emitPendingWrites(ctx: ctx)
             algorithm = nil
             deinitializeEncoder()
@@ -212,12 +212,6 @@ public final class HTTPResponseCompressor: ChannelDuplexHandler {
         deflateEnd(&stream)
     }
 
-    private func chainPromise(_ promise: EventLoopPromise<Void>?) {
-        if let promise = promise {
-            pendingWritePromise.futureResult.cascade(promise: promise)
-        }
-    }
-
     /// Emits all pending buffered writes to the network, optionally compressing the
     /// data. Resets the pending write buffer and promise.
     ///

Sources/NIOHTTP1/HTTPServerPipelineHandler.swift

@@ -315,7 +315,7 @@ public final class HTTPServerPipelineHandler: ChannelDuplexHandler {
             case .quiescingLastRequestEndReceived:
                 ctx.write(data).then {
                     ctx.close()
-                }.cascade(promise: promise ?? ctx.channel.eventLoop.makePromise())
+                }.cascade(promise: promise)
             case .acceptingEvents, .quiescingWaitingForRequestEnd:
                 ctx.write(data, promise: promise)
             }