Feature: expose librdkafka statistics as swift metrics

Package.swift

@@ -49,6 +49,7 @@ let package = Package(
         .package(url: "https://github.com/apple/swift-nio-ssl", from: "2.25.0"),
         .package(url: "https://github.com/swift-server/swift-service-lifecycle.git", from: "2.1.0"),
         .package(url: "https://github.com/apple/swift-log.git", from: "1.0.0"),
+        .package(url: "https://github.com/apple/swift-metrics", from: "2.4.1"),
         // The zstd Swift package produces warnings that we cannot resolve:
         // https://github.com/facebook/zstd/issues/3328
         .package(url: "https://github.com/facebook/zstd.git", from: "1.5.0"),
@@ -83,6 +84,7 @@ let package = Package(
                 .product(name: "NIOCore", package: "swift-nio"),
                 .product(name: "ServiceLifecycle", package: "swift-service-lifecycle"),
                 .product(name: "Logging", package: "swift-log"),
+                .product(name: "Metrics", package: "swift-metrics"),
             ]
         ),
         .target(
@@ -93,7 +95,10 @@ let package = Package(
         ),
         .testTarget(
             name: "KafkaTests",
-            dependencies: ["Kafka"]
+            dependencies: [
+                "Kafka",
+                .product(name: "MetricsTestKit", package: "swift-metrics")
+            ]
         ),
         .testTarget(
             name: "IntegrationTests",

Sources/Kafka/Configuration/KafkaConfiguration+Metrics.swift

@@ -0,0 +1,146 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the swift-kafka-client open source project
+//
+// Copyright (c) 2023 Apple Inc. and the swift-kafka-client project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of swift-kafka-client project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import Metrics
+
+extension KafkaConfiguration {
+    // MARK: - Metrics
+
+    /// Configuration for the consumer metrics emitted by `SwiftKafka`.
+    public struct ConsumerMetrics: Sendable {
+        internal var enabled: Bool {
+            self.updateInterval != nil &&
+                (self.queuedOperation != nil ||
+                    self.totalKafkaBrokerRequests != nil ||
+                    self.totalKafkaBrokerBytesSent != nil ||
+                    self.totalKafkaBrokerResponses != nil ||
+                    self.totalKafkaBrokerResponsesSize != nil ||
+                    self.totalKafkaBrokerMessagesBytesRecieved != nil ||
+                    self.topicsInMetadataCache != nil)
+        }
+
+        /// Update interval for statistics.
+        public var updateInterval: Duration?
+
+        /// Number of operations (callbacks, events, etc) waiting in the queue.
+        public var queuedOperation: Gauge?
+
+        /// Total number of requests sent to Kafka brokers.
+        public var totalKafkaBrokerRequests: Gauge?
+        /// Total number of bytes transmitted to Kafka brokers.
+        public var totalKafkaBrokerBytesSent: Gauge?
+        /// Total number of responses received from Kafka brokers.
+        public var totalKafkaBrokerResponses: Gauge?
+        /// Total number of bytes received from Kafka brokers.
+        public var totalKafkaBrokerResponsesSize: Gauge?
+
+        /// Total number of messages consumed, not including ignored messages (due to offset, etc), from Kafka brokers.
+        public var totalKafkaBrokerMessagesRecieved: Gauge?
+        /// Total number of message bytes (including framing) received from Kafka brokers.
+        public var totalKafkaBrokerMessagesBytesRecieved: Gauge?
+
+        /// Number of topics in the metadata cache.
+        public var topicsInMetadataCache: Gauge?
+
+        private static func record<T: BinaryInteger>(_ value: T?, to: Gauge?) {
+            guard let value,
+                  let to else {
+                return
+            }
+            to.record(value)
+        }
+
+        internal func update(with rdKafkaStatistics: RDKafkaStatistics) {
+            Self.record(rdKafkaStatistics.queuedOperation, to: self.queuedOperation)
+
+            Self.record(rdKafkaStatistics.totalKafkaBrokerRequests, to: self.totalKafkaBrokerRequests)
+            Self.record(rdKafkaStatistics.totalKafkaBrokerBytesSent, to: self.totalKafkaBrokerBytesSent)
+            Self.record(rdKafkaStatistics.totalKafkaBrokerResponses, to: self.totalKafkaBrokerResponses)
+            Self.record(rdKafkaStatistics.totalKafkaBrokerResponsesSize, to: self.totalKafkaBrokerResponsesSize)
+
+            Self.record(rdKafkaStatistics.totalKafkaBrokerMessagesRecieved, to: self.totalKafkaBrokerMessagesRecieved)
+            Self.record(rdKafkaStatistics.totalKafkaBrokerMessagesBytesRecieved, to: self.totalKafkaBrokerMessagesBytesRecieved)
+
+            Self.record(rdKafkaStatistics.topicsInMetadataCache, to: self.topicsInMetadataCache)
+        }
+    }
+
+    /// Configuration for the producer metrics emitted by `SwiftKafka`.
+    public struct ProducerMetrics: Sendable {
+        internal var enabled: Bool {
+            self.updateInterval != nil &&
+                (self.queuedOperation != nil ||
+                    self.queuedProducerMessages != nil ||
+                    self.queuedProducerMessagesSize != nil ||
+                    self.totalKafkaBrokerRequests != nil ||
+                    self.totalKafkaBrokerBytesSent != nil ||
+                    self.totalKafkaBrokerResponses != nil ||
+                    self.totalKafkaBrokerResponsesSize != nil ||
+                    self.totalKafkaBrokerMessagesSent != nil ||
+                    self.totalKafkaBrokerMessagesBytesSent != nil ||
+                    self.topicsInMetadataCache != nil)
+        }
+
+        /// Update interval for statistics.
+        public var updateInterval: Duration?
+
+        /// Number of operations (callbacks, events, etc) waiting in the queue.
+        public var queuedOperation: Gauge?
+        /// Current number of queued producer messages.
+        public var queuedProducerMessages: Gauge?
+        /// Current total size in bytes of queued producer messages.
+        public var queuedProducerMessagesSize: Gauge?
+
+        /// Total number of requests sent to Kafka brokers.
+        public var totalKafkaBrokerRequests: Gauge?
+        /// Total number of bytes transmitted to Kafka brokers.
+        public var totalKafkaBrokerBytesSent: Gauge?
+        /// Total number of responses received from Kafka brokers.
+        public var totalKafkaBrokerResponses: Gauge?
+        /// Total number of bytes received from Kafka brokers.
+        public var totalKafkaBrokerResponsesSize: Gauge?
+
+        /// Total number of messages transmitted (produced) to Kafka brokers.
+        public var totalKafkaBrokerMessagesSent: Gauge?
+        /// Total number of message bytes (including framing, such as per-Message framing and MessageSet/batch framing) transmitted to Kafka brokers.
+        public var totalKafkaBrokerMessagesBytesSent: Gauge?
+
+        /// Number of topics in the metadata cache.
+        public var topicsInMetadataCache: Gauge?
+
+        private static func record<T: BinaryInteger>(_ value: T?, to: Gauge?) {
+            guard let value,
+                  let to else {
+                return
+            }
+            to.record(value)
+        }
+
+        internal func update(with rdKafkaStatistics: RDKafkaStatistics) {
+            Self.record(rdKafkaStatistics.queuedOperation, to: self.queuedOperation)
+            Self.record(rdKafkaStatistics.queuedProducerMessages, to: self.queuedProducerMessages)
+            Self.record(rdKafkaStatistics.queuedProducerMessagesSize, to: self.queuedProducerMessagesSize)
+
+            Self.record(rdKafkaStatistics.totalKafkaBrokerRequests, to: self.totalKafkaBrokerRequests)
+            Self.record(rdKafkaStatistics.totalKafkaBrokerBytesSent, to: self.totalKafkaBrokerBytesSent)
+            Self.record(rdKafkaStatistics.totalKafkaBrokerResponses, to: self.totalKafkaBrokerResponses)
+            Self.record(rdKafkaStatistics.totalKafkaBrokerResponsesSize, to: self.totalKafkaBrokerResponsesSize)
+
+            Self.record(rdKafkaStatistics.totalKafkaBrokerMessagesSent, to: self.totalKafkaBrokerMessagesSent)
+            Self.record(rdKafkaStatistics.totalKafkaBrokerMessagesBytesSent, to: self.totalKafkaBrokerMessagesBytesSent)
+
+            Self.record(rdKafkaStatistics.topicsInMetadataCache, to: self.topicsInMetadataCache)
+        }
+    }
+}

Sources/Kafka/Configuration/KafkaConsumerConfiguration.swift

@@ -207,6 +207,9 @@ public struct KafkaConsumerConfiguration {
     /// Reconnect options.
     public var reconnect: KafkaConfiguration.ReconnectOptions = .init()
 
+    /// Options for librdkafka metrics updates
+    public var metrics: KafkaConfiguration.ConsumerMetrics = .init()
+
     /// Security protocol to use (plaintext, ssl, sasl_plaintext, sasl_ssl).
     /// Default: `.plaintext`
     public var securityProtocol: KafkaConfiguration.SecurityProtocol = .plaintext
@@ -271,6 +274,11 @@ extension KafkaConsumerConfiguration {
         resultDict["reconnect.backoff.ms"] = String(reconnect.backoff.rawValue)
         resultDict["reconnect.backoff.max.ms"] = String(reconnect.maximumBackoff.inMilliseconds)
 
+        if self.metrics.enabled,
+           let updateInterval = self.metrics.updateInterval {
+            resultDict["statistics.interval.ms"] = String(updateInterval.inMilliseconds)
+        }
+
         // Merge with SecurityProtocol configuration dictionary
         resultDict.merge(securityProtocol.dictionary) { _, _ in
             fatalError("securityProtocol and \(#file) should not have duplicate keys")

Sources/Kafka/Configuration/KafkaProducerConfiguration.swift

@@ -161,6 +161,9 @@ public struct KafkaProducerConfiguration {
     /// Reconnect options.
     public var reconnect: KafkaConfiguration.ReconnectOptions = .init()
 
+    /// Options for librdkafka metrics updates
+    public var metrics: KafkaConfiguration.ProducerMetrics = .init()
+
     /// Security protocol to use (plaintext, ssl, sasl_plaintext, sasl_ssl).
     /// Default: `.plaintext`
     public var securityProtocol: KafkaConfiguration.SecurityProtocol = .plaintext
@@ -212,6 +215,11 @@ extension KafkaProducerConfiguration {
         resultDict["reconnect.backoff.ms"] = String(self.reconnect.backoff.rawValue)
         resultDict["reconnect.backoff.max.ms"] = String(self.reconnect.maximumBackoff.inMilliseconds)
 
+        if self.metrics.enabled,
+           let updateInterval = self.metrics.updateInterval {
+            resultDict["statistics.interval.ms"] = String(updateInterval.inMilliseconds)
+        }
+
         // Merge with SecurityProtocol configuration dictionary
         resultDict.merge(self.securityProtocol.dictionary) { _, _ in
             fatalError("securityProtocol and \(#file) should not have duplicate keys")

Sources/Kafka/KafkaConsumer.swift

@@ -130,6 +130,7 @@ public final class KafkaConsumer: Sendable, Service {
         NIOAsyncSequenceProducerBackPressureStrategies.NoBackPressure,
         KafkaConsumerCloseOnTerminate
     >
+
     /// The configuration object of the consumer client.
     private let configuration: KafkaConsumerConfiguration
     /// A logger.
@@ -203,6 +204,9 @@ public final class KafkaConsumer: Sendable, Service {
         if configuration.isAutoCommitEnabled == false {
             subscribedEvents.append(.offsetCommit)
         }
+        if configuration.metrics.enabled {
+            subscribedEvents.append(.statistics)
+        }
 
         let client = try RDKafkaClient.makeClient(
             type: .consumer,
@@ -243,6 +247,9 @@ public final class KafkaConsumer: Sendable, Service {
         if configuration.isAutoCommitEnabled == false {
             subscribedEvents.append(.offsetCommit)
         }
+        if configuration.metrics.enabled {
+            subscribedEvents.append(.statistics)
+        }
 
         let client = try RDKafkaClient.makeClient(
             type: .consumer,
@@ -341,6 +348,8 @@ public final class KafkaConsumer: Sendable, Service {
                     case .consumerMessages(let result):
                         // We do not support back pressure, we can ignore the yield result
                         _ = source.yield(result)
+                    case .statistics(let statistics):
+                        self.configuration.metrics.update(with: statistics)
                     default:
                         break // Ignore
                     }

Sources/Kafka/KafkaConsumerEvent.swift

@@ -19,6 +19,8 @@ public enum KafkaConsumerEvent: Sendable, Hashable {
 
     internal init(_ event: RDKafkaClient.KafkaEvent) {
         switch event {
+        case .statistics:
+            fatalError("Cannot cast \(event) to KafkaConsumerEvent")
         case .deliveryReport:
             fatalError("Cannot cast \(event) to KafkaConsumerEvent")
         case .consumerMessages:

Sources/Kafka/KafkaProducer.swift

@@ -116,10 +116,16 @@ public final class KafkaProducer: Service, Sendable {
     ) throws {
         let stateMachine = NIOLockedValueBox(StateMachine(logger: logger))
 
+        var subscribedEvents: [RDKafkaEvent] = [.log] // No .deliveryReport here!
+
+        if configuration.metrics.enabled {
+            subscribedEvents.append(.statistics)
+        }
+
         let client = try RDKafkaClient.makeClient(
             type: .producer,
             configDictionary: configuration.dictionary,
-            events: [.log], // No .deliveryReport here!
+            events: subscribedEvents,
             logger: logger
         )
 
@@ -156,10 +162,16 @@ public final class KafkaProducer: Service, Sendable {
     ) throws -> (KafkaProducer, KafkaProducerEvents) {
         let stateMachine = NIOLockedValueBox(StateMachine(logger: logger))
 
+        var subscribedEvents: [RDKafkaEvent] = [.log, .deliveryReport]
+        // Listen to statistics events when statistics enabled
+        if configuration.metrics.enabled {
+            subscribedEvents.append(.statistics)
+        }
+
         let client = try RDKafkaClient.makeClient(
             type: .producer,
             configDictionary: configuration.dictionary,
-            events: [.log, .deliveryReport],
+            events: subscribedEvents,
             logger: logger
         )
 
@@ -212,9 +224,14 @@ public final class KafkaProducer: Service, Sendable {
             case .pollAndYield(let client, let source):
                 let events = client.eventPoll()
                 for event in events {
-                    let producerEvent = KafkaProducerEvent(event)
-                    // Ignore YieldResult as we don't support back pressure in KafkaProducer
-                    _ = source?.yield(producerEvent)
+                    switch event {
+                    case .statistics(let statistics):
+                        self.configuration.metrics.update(with: statistics)
+                    case .deliveryReport(let reports):
+                        _ = source?.yield(.deliveryReports(reports))
+                    case .consumerMessages:
+                        fatalError("Unexpected event for producer \(event)")
+                    }
                 }
                 try await Task.sleep(for: self.configuration.pollInterval)
             case .flushFinishSourceAndTerminatePollLoop(let client, let source):

Sources/Kafka/KafkaProducerEvent.swift

@@ -23,6 +23,8 @@ public enum KafkaProducerEvent: Sendable, Hashable {
         switch event {
         case .deliveryReport(results: let results):
             self = .deliveryReports(results)
+        case .statistics:
+            fatalError("Cannot cast \(event) to KafkaProducerEvent")
         case .consumerMessages:
             fatalError("Cannot cast \(event) to KafkaProducerEvent")
         }

Sources/Kafka/RDKafka/RDKafkaClient.swift

@@ -14,6 +14,7 @@
 
 import Crdkafka
 import Dispatch
+import class Foundation.JSONDecoder
 import Logging
 
 /// Base class for ``KafkaProducer`` and ``KafkaConsumer``,
@@ -311,6 +312,7 @@ final class RDKafkaClient: Sendable {
     enum KafkaEvent {
         case deliveryReport(results: [KafkaDeliveryReport])
         case consumerMessages(result: Result<KafkaConsumerMessage, Error>)
+        case statistics(RDKafkaStatistics)
     }
 
     /// Poll the event `rd_kafka_queue_t` for new events.
@@ -341,6 +343,10 @@ final class RDKafkaClient: Sendable {
                 self.handleLogEvent(event)
             case .offsetCommit:
                 self.handleOffsetCommitEvent(event)
+            case .statistics:
+                if let forwardEvent = self.handleStatistics(event) {
+                    events.append(forwardEvent)
+                }
             case .none:
                 // Finished reading events, return early
                 return events
@@ -392,6 +398,22 @@ final class RDKafkaClient: Sendable {
         // The returned message(s) MUST NOT be freed with rd_kafka_message_destroy().
     }
 
+    /// Handle event of type `RDKafkaEvent.statistics`.
+    ///
+    /// - Parameter event: Pointer to underlying `rd_kafka_event_t`.
+    private func handleStatistics(_ event: OpaquePointer?) -> KafkaEvent? {
+        let jsonStr = String(cString: rd_kafka_event_stats(event))
+        do {
+            if let jsonData = jsonStr.data(using: .utf8) {
+                let json = try JSONDecoder().decode(RDKafkaStatistics.self, from: jsonData)
+                return .statistics(json)
+            }
+        } catch {
+            assertionFailure("Error occurred when decoding JSON statistics: \(error) when decoding \(jsonStr)")
+        }
+        return nil
+    }
+
     /// Handle event of type `RDKafkaEvent.log`.
     ///
     /// - Parameter event: Pointer to underlying `rd_kafka_event_t`.