Merge branch '53-circular-buffer' into 'master'

53 -- Use `CircularBuffer` for `RedisCommandHandler` queue

Closes #53

See merge request Mordil/swift-redis-nio-client!59

Author: Mordil

Sources/RedisNIO/ChannelHandlers/RedisCommandHandler.swift

@@ -32,16 +32,16 @@ public struct RedisCommandContext {
 /// A `ChannelDuplexHandler` that works with `RedisCommandContext`s to send commands and forward responses.
 open class RedisCommandHandler {
     /// Queue of promises waiting to receive a response value from a sent command.
-    private var commandResponseQueue: [EventLoopPromise<RESPValue>]
+    private var commandResponseQueue: CircularBuffer<EventLoopPromise<RESPValue>>
     private var logger: Logger
 
     deinit {
         guard commandResponseQueue.count > 0 else { return }
         logger.warning("Command handler deinit when queue is not empty. Current size: \(commandResponseQueue.count)")
     }
 
-    public init(logger: Logger = Logger(label: "RedisNIO.CommandHandler")) {
-        self.commandResponseQueue = []
+    public init(logger: Logger = Logger(label: "RedisNIO.CommandHandler"), initialQueueCapacity: Int = 5) {
+        self.commandResponseQueue = CircularBuffer(initialCapacity: initialQueueCapacity)
         self.logger = logger
         self.logger[metadataKey: "CommandHandler"] = "\(UUID())"
     }
@@ -58,30 +58,31 @@ extension RedisCommandHandler: ChannelInboundHandler {
     ///
     /// See `ChannelInboundHandler.errorCaught(context:error:)`
     public func errorCaught(context: ChannelHandlerContext, error: Error) {
-        guard let leadPromise = commandResponseQueue.last else {
-            return assertionFailure("Received unexpected error while idle: \(error.localizedDescription)")
-        }
-        leadPromise.fail(error)
+        let queue = self.commandResponseQueue
+        
+        assert(queue.count > 0, "Received unexpected error while idle: \(error.localizedDescription)")
+        
+        self.commandResponseQueue.removeAll()
+        queue.forEach { $0.fail(error) }
+        
+        logger.critical("Error in channel pipeline.", metadata: ["error": .string(error.localizedDescription)])
+        
         context.fireErrorCaught(error)
-        RedisMetrics.commandFailureCount.increment()
     }
 
     /// Invoked by NIO when a read has been fired from earlier in the response chain. This forwards the unwrapped
     /// `RESPValue` to the promise awaiting a response at the front of the queue.
     ///
     /// See `ChannelInboundHandler.channelRead(context:data:)`
     public func channelRead(context: ChannelHandlerContext, data: NIOAny) {
-        let value = unwrapInboundIn(data)
+        let value = self.unwrapInboundIn(data)
 
-        guard let leadPromise = commandResponseQueue.last else {
+        guard let leadPromise = self.commandResponseQueue.popFirst() else {
             assertionFailure("Read triggered with an empty promise queue! Ignoring: \(value)")
             logger.critical("Read triggered with no promise waiting in the queue!")
             return
         }
 
-        let popped = commandResponseQueue.popLast()
-        assert(popped != nil)
-
         switch value {
         case .error(let e):
             leadPromise.fail(e)
@@ -108,8 +109,11 @@ extension RedisCommandHandler: ChannelOutboundHandler {
     ///
     /// See `ChannelOutboundHandler.write(context:data:promise:)`
     public func write(context: ChannelHandlerContext, data: NIOAny, promise: EventLoopPromise<Void>?) {
-        let commandContext = unwrapOutboundIn(data)
-        commandResponseQueue.insert(commandContext.responsePromise, at: 0)
-        context.write(wrapOutboundOut(commandContext.command), promise: promise)
+        let commandContext = self.unwrapOutboundIn(data)
+        self.commandResponseQueue.append(commandContext.responsePromise)
+        context.write(
+            self.wrapOutboundOut(commandContext.command),
+            promise: promise
+        )
     }
 }