Introduce SendableOpaquePointer

[Unsafe pointers are no longer `Sendable`](swiftlang/swift#70396 (comment)) starting with Swift 5.10, while a warning in
earlier versions. This PR introduces `SendableOpaquePointer` to wrap `OpaquePointer` and
marks it as `@unchecked Sendable`.

Resolves #159

Sources/Kafka/RDKafka/RDKafkaClient.swift

@@ -31,30 +31,30 @@ public final class RDKafkaClient: Sendable {
     }
 
     /// Handle for the C library's Kafka instance.
-    private let kafkaHandle: OpaquePointer
+    private let kafkaHandle: SendableOpaquePointer
     /// A logger.
     private let logger: Logger
 
     /// `librdkafka`'s `rd_kafka_queue_t` that events are received on.
-    private let queue: OpaquePointer
+    private let queueHandle: SendableOpaquePointer
 
     // Use factory method to initialize
     private init(
         type: ClientType,
-        kafkaHandle: OpaquePointer,
+        kafkaHandle: SendableOpaquePointer,
         logger: Logger
     ) {
         self.kafkaHandle = kafkaHandle
         self.logger = logger
-        self.queue = rd_kafka_queue_get_main(self.kafkaHandle)
+        self.queueHandle = .init(rd_kafka_queue_get_main(self.kafkaHandle.pointer))
 
-        rd_kafka_set_log_queue(self.kafkaHandle, self.queue)
+        rd_kafka_set_log_queue(self.kafkaHandle.pointer, self.queueHandle.pointer)
     }
 
     deinit {
         // Loose reference to librdkafka's event queue
-        rd_kafka_queue_destroy(self.queue)
-        rd_kafka_destroy(kafkaHandle)
+        rd_kafka_queue_destroy(self.queueHandle.pointer)
+        rd_kafka_destroy(kafkaHandle.pointer)
     }
 
     /// Factory method creating a new instance of a ``RDKafkaClient``.
@@ -87,7 +87,8 @@ public final class RDKafkaClient: Sendable {
             throw KafkaError.client(reason: errorString)
         }
 
-        return RDKafkaClient(type: type, kafkaHandle: handle, logger: logger)
+        let kafkaHandle = SendableOpaquePointer(handle)
+        return RDKafkaClient(type: type, kafkaHandle: kafkaHandle, logger: logger)
     }
 
     /// Produce a message to the Kafka cluster.
@@ -212,7 +213,7 @@ public final class RDKafkaClient: Sendable {
         assert(arguments.count == size)
 
         return rd_kafka_produceva(
-            self.kafkaHandle,
+            self.kafkaHandle.pointer,
             arguments,
             arguments.count
         )
@@ -304,7 +305,7 @@ public final class RDKafkaClient: Sendable {
         events.reserveCapacity(maxEvents)
 
         for _ in 0..<maxEvents {
-            let event = rd_kafka_queue_poll(self.queue, 0)
+            let event = rd_kafka_queue_poll(self.queueHandle.pointer, 0)
             defer { rd_kafka_event_destroy(event) }
 
             let rdEventType = rd_kafka_event_type(event)
@@ -437,7 +438,7 @@ public final class RDKafkaClient: Sendable {
     /// - Returns: A ``KafkaConsumerMessage`` or `nil` if there are no new messages.
     /// - Throws: A ``KafkaError`` if the received message is an error message or malformed.
     func consumerPoll() throws -> KafkaConsumerMessage? {
-        guard let messagePointer = rd_kafka_consumer_poll(self.kafkaHandle, 0) else {
+        guard let messagePointer = rd_kafka_consumer_poll(self.kafkaHandle.pointer, 0) else {
             // No error, there might be no more messages
             return nil
         }
@@ -460,7 +461,7 @@ public final class RDKafkaClient: Sendable {
     /// - Parameter topicPartitionList: Pointer to a list of topics + partition pairs.
     func subscribe(topicPartitionList: RDKafkaTopicPartitionList) throws {
         try topicPartitionList.withListPointer { pointer in
-            let result = rd_kafka_subscribe(self.kafkaHandle, pointer)
+            let result = rd_kafka_subscribe(self.kafkaHandle.pointer, pointer)
             if result != RD_KAFKA_RESP_ERR_NO_ERROR {
                 throw KafkaError.rdKafkaError(wrapping: result)
             }
@@ -471,7 +472,7 @@ public final class RDKafkaClient: Sendable {
     /// - Parameter topicPartitionList: Pointer to a list of topics + partition pairs.
     func assign(topicPartitionList: RDKafkaTopicPartitionList) throws {
         try topicPartitionList.withListPointer { pointer in
-            let result = rd_kafka_assign(self.kafkaHandle, pointer)
+            let result = rd_kafka_assign(self.kafkaHandle.pointer, pointer)
             if result != RD_KAFKA_RESP_ERR_NO_ERROR {
                 throw KafkaError.rdKafkaError(wrapping: result)
             }
@@ -508,7 +509,7 @@ public final class RDKafkaClient: Sendable {
 
         let error = changesList.withListPointer { listPointer in
             return rd_kafka_commit(
-                self.kafkaHandle,
+                self.kafkaHandle.pointer,
                 listPointer,
                 1 // async = true
             )
@@ -551,9 +552,9 @@ public final class RDKafkaClient: Sendable {
 
             changesList.withListPointer { listPointer in
                 rd_kafka_commit_queue(
-                    self.kafkaHandle,
+                    self.kafkaHandle.pointer,
                     listPointer,
-                    self.queue,
+                    self.queueHandle.pointer,
                     nil,
                     opaquePointer
                 )
@@ -572,7 +573,7 @@ public final class RDKafkaClient: Sendable {
         let queue = DispatchQueue(label: "com.swift-server.swift-kafka.flush")
         try await withCheckedThrowingContinuation { (continuation: CheckedContinuation<Void, Error>) in
             queue.async {
-                let error = rd_kafka_flush(self.kafkaHandle, timeoutMilliseconds)
+                let error = rd_kafka_flush(self.kafkaHandle.pointer, timeoutMilliseconds)
                 if error != RD_KAFKA_RESP_ERR_NO_ERROR {
                     continuation.resume(throwing: KafkaError.rdKafkaError(wrapping: error))
                 } else {
@@ -587,7 +588,7 @@ public final class RDKafkaClient: Sendable {
     ///
     /// Make sure to run poll loop until ``RDKafkaClient/consumerIsClosed`` returns `true`.
     func consumerClose() throws {
-        let result = rd_kafka_consumer_close_queue(self.kafkaHandle, self.queue)
+        let result = rd_kafka_consumer_close_queue(self.kafkaHandle.pointer, self.queueHandle.pointer)
         let kafkaError = rd_kafka_error_code(result)
         if kafkaError != RD_KAFKA_RESP_ERR_NO_ERROR {
             throw KafkaError.rdKafkaError(wrapping: kafkaError)
@@ -596,14 +597,14 @@ public final class RDKafkaClient: Sendable {
 
     /// Returns `true` if the underlying `librdkafka` consumer is closed.
     var isConsumerClosed: Bool {
-        rd_kafka_consumer_closed(self.kafkaHandle) == 1
+        rd_kafka_consumer_closed(self.kafkaHandle.pointer) == 1
     }
 
     /// Scoped accessor that enables safe access to the pointer of the client's Kafka handle.
     /// - Warning: Do not escape the pointer from the closure for later use.
     /// - Parameter body: The closure will use the Kafka handle pointer.
     @discardableResult
     func withKafkaHandlePointer<T>(_ body: (OpaquePointer) throws -> T) rethrows -> T {
-        return try body(self.kafkaHandle)
+        return try body(self.kafkaHandle.pointer)
     }
 }

Sources/Kafka/RDKafka/RDKafkaTopicHandles.swift

@@ -17,7 +17,7 @@ import NIOConcurrencyHelpers
 
 /// Swift class that matches topic names with their respective `rd_kafka_topic_t` handles.
 internal final class RDKafkaTopicHandles: Sendable {
-    private let _internal: NIOLockedValueBox<[String: OpaquePointer]>
+    private let _internal: NIOLockedValueBox<[String: SendableOpaquePointer]>
 
     // Note: we retain the client to ensure it does not get
     // deinitialized before rd_kafka_topic_destroy() is invoked (required)
@@ -31,7 +31,7 @@ internal final class RDKafkaTopicHandles: Sendable {
     deinit {
         self._internal.withLockedValue { dict in
             for (_, topicHandle) in dict {
-                rd_kafka_topic_destroy(topicHandle)
+                rd_kafka_topic_destroy(topicHandle.pointer)
             }
         }
     }
@@ -59,7 +59,7 @@ internal final class RDKafkaTopicHandles: Sendable {
     ) throws -> OpaquePointer {
         try self._internal.withLockedValue { dict in
             if let handle = dict[topic] {
-                return handle
+                return handle.pointer
             } else {
                 let rdTopicConf = try RDKafkaTopicConfig.createFrom(topicConfiguration: topicConfiguration)
                 let newHandle = self.client.withKafkaHandlePointer { kafkaHandle in
@@ -76,7 +76,7 @@ internal final class RDKafkaTopicHandles: Sendable {
                     let error = KafkaError.rdKafkaError(wrapping: rd_kafka_last_error())
                     throw error
                 }
-                dict[topic] = newHandle
+                dict[topic] = .init(newHandle)
                 return newHandle
             }
         }

Sources/Kafka/Utilities/SendableOpaquePointer.swift

@@ -0,0 +1,25 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the swift-kafka-client open source project
+//
+// Copyright (c) 2024 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
+//
+//===----------------------------------------------------------------------===//
+
+/// A wrapper for the `OpaquePointer` used to represent different handles from `librdkafka`.
+///
+/// This wrapper silences `Sendable` warnings for the pointer introduced in Swift 5.10, and should
+/// only be used for handles from `librdkafka` that are known to be thread-safe.
+internal struct SendableOpaquePointer: @unchecked Sendable {
+    let pointer: OpaquePointer
+
+    init(_ pointer: OpaquePointer) {
+        self.pointer = pointer
+    }
+}