Fixes for previews in SwiftUI

Author: sroebert

Sources/MQTTNIO/Handlers/MQTTErrorHandler.swift

@@ -20,7 +20,8 @@ final class MQTTErrorHandler: ChannelInboundHandler {
     }
 
     func errorCaught(context: ChannelHandlerContext, error: Error) {
-        #if canImport(NIOSSL)
+        // This should use `canImport(NIOSSL)`, will change when it works with SwiftUI previews.
+        #if os(macOS) || os(Linux)
         // We ignore unclean shutdowns, which could be caused by servers not sending `close_notify`
         if let sslError = error as? NIOSSLError, case .uncleanShutdown = sslError {
             return

Sources/MQTTNIO/MQTTConfiguration.swift

@@ -541,7 +541,8 @@ extension MQTTConfiguration {
     }
 }
 
-#if canImport(NIOSSL)
+// This should use `canImport(NIOSSL)`, will change when it works with SwiftUI previews.
+#if os(macOS) || os(Linux)
 extension MQTTConfiguration {
     /// Creates an `MQTTConfiguration`.
     /// - Parameters:

Tests/MQTTNIOTests/Core/MQTTNIOTestCase.swift

@@ -117,7 +117,8 @@ class MQTTNIOTestCase: XCTestCase {
         ), eventLoopGroupProvider: .shared(tlsGroup))
     }
 
-    #if canImport(NIOSSL)
+    // This should use `canImport(NIOSSL)`, will change when it works with SwiftUI previews.
+    #if os(macOS) || os(Linux)
     var nioSSLTLSClient: MQTTClient {
         get throws {
             let rootDir = URL(fileURLWithPath: #file)