95 -- Backport unexpected channel closure callback

This is a cherry-pick commit of ad316a9

Author: Mordil

Sources/RediStack/RedisConnection.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the RediStack open source project
 //
-// Copyright (c) 2019-2020 RediStack project authors
+// Copyright (c) 2019-2021 RediStack project authors
 // Licensed under Apache License v2.0
 //
 // See LICENSE.txt for license information
@@ -139,6 +139,10 @@ public final class RedisConnection: RedisClient, RedisClientWithUserContext {
             ], on: self.eventLoop)
         }
     }
+    /// A closure to invoke when the connection closes unexpectedly.
+    ///
+    /// An unexpected closure is when the connection is closed by any other method than by calling `close(logger:)`.
+    public var onUnexpectedClosure: (() -> Void)?
 
     internal let channel: Channel
     private let systemContext: Context
@@ -182,6 +186,7 @@ public final class RedisConnection: RedisClient, RedisClientWithUserContext {
             self.state = .closed
             self.logger.error("connection was closed unexpectedly")
             RedisMetrics.activeConnectionCount.decrement()
+            self.onUnexpectedClosure?()
         }
 
         self.logger.trace("connection created")

Tests/RediStackTests/RedisConnectionTests.swift

@@ -0,0 +1,45 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the RediStack open source project
+//
+// Copyright (c) 2021 RediStack project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of RediStack project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import Logging
+import NIO
+@testable import RediStack
+import XCTest
+
+final class RedisConnectionTests: XCTestCase {
+
+}
+
+// MARK: Unexpected Closures
+extension RedisConnectionTests {
+    func test_connectionUnexpectedlyCloses_invokesCallback() throws {
+        let loop = EmbeddedEventLoop()
+
+        let expectedClosureConnection = RedisConnection(configuredRESPChannel: EmbeddedChannel(loop: loop), context: Logger(label: ""))
+        let expectedClosureExpectation = self.expectation(description: "this should not be fulfilled")
+        expectedClosureExpectation.isInverted = true
+
+        expectedClosureConnection.onUnexpectedClosure = { expectedClosureExpectation.fulfill() }
+        _ = expectedClosureConnection.close(logger: nil)
+
+        let channel = EmbeddedChannel(loop: loop)
+        let notExpectedClosureConnection = RedisConnection(configuredRESPChannel: channel, context: Logger(label: ""))
+        let notExpectedClosureExpectation = self.expectation(description: "this should be fulfilled")
+        notExpectedClosureConnection.onUnexpectedClosure = { notExpectedClosureExpectation.fulfill() }
+
+        _ = try channel.finish(acceptAlreadyClosed: true)
+
+        self.waitForExpectations(timeout: 0.5)
+    }
+}