Implement Basic Metrics (#40)

Motivation:

End users will want to capture some baseline performance metrics that can only be accurately gathered at this level of the stack.

Modifications:

Added new `RedisMetrics` struct that retains all SwiftMetrics objects used throughout the system lifecycle, and appropriate code to track desired metrics.

Result:

Users now have a way to peek into the system's performance to understand what NIORedis is being asked to do from their usage.

Sources/NIORedis/ChannelHandlers/RedisCommandHandler.swift

@@ -62,6 +62,7 @@ extension RedisCommandHandler: ChannelInboundHandler {
             return assertionFailure("Received unexpected error while idle: \(error.localizedDescription)")
         }
         leadPromise.fail(error)
+        RedisMetrics.commandFailureCount.increment()
     }
 
     /// Invoked by NIO when a read has been fired from earlier in the response chain. This forwards the unwrapped
@@ -81,8 +82,13 @@ extension RedisCommandHandler: ChannelInboundHandler {
         assert(popped != nil)
 
         switch value {
-        case .error(let e): leadPromise.fail(e)
-        default: leadPromise.succeed(value)
+        case .error(let e):
+            leadPromise.fail(e)
+            RedisMetrics.commandFailureCount.increment()
+
+        default:
+            leadPromise.succeed(value)
+            RedisMetrics.commandSuccessCount.increment()
         }
     }
 }

Sources/NIORedis/RedisClient.swift

@@ -13,7 +13,9 @@
 //===----------------------------------------------------------------------===//
 
 import struct Foundation.UUID
+import struct Dispatch.DispatchTime
 import Logging
+import Metrics
 import NIO
 import NIOConcurrencyHelpers
 
@@ -107,6 +109,8 @@ public final class RedisConnection: RedisClient {
         self.logger[metadataKey: loggingKeyID] = "\(UUID())"
         self.logger.debug("Connection created.")
         self._state = .open
+        RedisMetrics.activeConnectionCount += 1
+        RedisMetrics.totalConnectionCount.increment()
     }
 
     /// Sends a `QUIT` command, then closes the `Channel` this instance was initialized with.
@@ -126,7 +130,10 @@ public final class RedisConnection: RedisClient {
                 self.channel.close(promise: promise)
                 return promise.futureResult
             }
-            .map { self.logger.debug("Connection closed.") }
+            .map {
+                self.logger.debug("Connection closed.")
+                RedisMetrics.activeConnectionCount -= 1
+            }
             .recover {
                 self.logger.error("Encountered error during close(): \($0)")
                 self.state = .open
@@ -162,7 +169,10 @@ public final class RedisConnection: RedisClient {
             promise: promise
         )
 
+        let startTime = DispatchTime.now().uptimeNanoseconds
         promise.futureResult.whenComplete { result in
+            let duration = DispatchTime.now().uptimeNanoseconds - startTime
+            RedisMetrics.commandRoundTripTime.recordNanoseconds(duration)
             guard case let .failure(error) = result else { return }
             self.logger.error("\(error.localizedDescription)")
         }

Sources/NIORedis/RedisMetrics.swift

@@ -0,0 +1,83 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the NIORedis open source project
+//
+// Copyright (c) 2019 NIORedis project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of NIORedis project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import Metrics
+
+/// The system funnel for all `Metrics` interactions from the Redis library.
+///
+/// It is highly recommended to not interact with this directly, and to let the library
+/// use it how it sees fit.
+///
+/// There is a nested enum type of `RedisMetrics.Label` that is available to query, match, etc. the
+/// labels used for all of the `Metrics` types created by the Redis library.
+public struct RedisMetrics {
+    /// An enumeration of all the labels used by the Redis library for various `Metrics` data points.
+    ///
+    /// Each is backed by a raw string, and this type is `CustomStringConvertible` to receive a
+    /// namespaced description in the form of `"NIORedis.<rawValue>"`.
+    public enum Label: String, CustomStringConvertible {
+        case totalConnectionCount
+        case activeConnectionCount
+        case commandSuccessCount
+        case commandFailureCount
+        case commandRoundTripTime
+
+        public var description: String {
+            return "NIORedis.\(self.rawValue)"
+        }
+    }
+
+    private static let activeConnectionCountGauge = Gauge(label: .activeConnectionCount)
+    /// The current number of connections this library has active.
+    /// - Note: Changing this number will update the `Metrics.Gauge` stored for recording the new value.
+    public static var activeConnectionCount: Int = 0 {
+        didSet {
+            activeConnectionCountGauge.record(activeConnectionCount)
+        }
+    }
+    /// The `Metrics.Counter` that retains the number of connections made since application startup.
+    public static let totalConnectionCount = Counter(label: .totalConnectionCount)
+    /// The `Metrics.Counter` that retains the number of commands that successfully returned from Redis
+    /// since application startup.
+    public static let commandSuccessCount = Counter(label: .commandSuccessCount)
+    /// The `Metrics.Counter` that retains the number of commands that failed from errors returned
+    /// by Redis since application startup.
+    public static let commandFailureCount = Counter(label: .commandFailureCount)
+    /// The `Metrics.Timer` that receives command response times in nanoseconds from when a command
+    /// is first sent through the `NIO.Channel`, to when the response is first resolved.
+    public static let commandRoundTripTime = Timer(label: .commandRoundTripTime)
+
+    private init() { }
+}
+
+extension Metrics.Counter {
+    @inline(__always)
+    convenience init(label: RedisMetrics.Label) {
+        self.init(label: label.description)
+    }
+}
+
+extension Metrics.Gauge {
+    @inline(__always)
+    convenience init(label: RedisMetrics.Label) {
+        self.init(label: label.description)
+    }
+}
+
+extension Metrics.Timer {
+    @inline(__always)
+    convenience init(label: RedisMetrics.Label) {
+        self.init(label: label.description)
+    }
+}