Improve error thrown when port binding is not possible

Author: odrobnik

.gitignore

@@ -11,3 +11,4 @@ DerivedData/
 .env.*
 !.env.example
 Package.resolved
+.swiftpm

Sources/SwiftMCP/Transport/HTTPSSETransport.swift

@@ -115,15 +115,29 @@ public final class HTTPSSETransport: Transport, @unchecked Sendable {
 
 			self.channel?.closeFuture.whenComplete { [logger] result in
 				switch result {
-				case .success:
-					logger.info("Server channel closed normally")
-				case .failure(let error):
-					logger.error("Server channel closed with error: \(error)")
+					case .success:
+						logger.info("Server channel closed normally")
+					case .failure(let error):
+						logger.error("Server channel closed with error: \(error)")
 				}
 			}
+		} catch let error as IOError {
+			let errorMessage: String
+			switch error.errnoCode {
+				case EADDRINUSE:
+					errorMessage = "Port \(port) is already in use. Please choose a different port or ensure no other service is using this port."
+				case EACCES:
+					errorMessage = "Permission denied to bind to port \(port). This port may require elevated privileges."
+				case EADDRNOTAVAIL:
+					errorMessage = "The address \(host) is not available for binding."
+				default:
+					errorMessage = "Failed to bind to \(host):\(port). Error: \(error.localizedDescription)"
+			}
+			logger.error("\(errorMessage)")
+			throw TransportError.bindingFailed(errorMessage)
 		} catch {
 			logger.error("Server error: \(error)")
-			throw error
+			throw TransportError.bindingFailed(error.localizedDescription)
 		}
 	}
 

Sources/SwiftMCP/Transport/TransportError.swift

@@ -0,0 +1,36 @@
+//
+//  TransportError.swift
+//  SwiftMCP
+//
+//  Created by Oliver Drobnik on 21.03.25.
+//
+
+import Foundation
+
+/**
+ Errors that can occur during transport operations in SwiftMCP.
+ 
+ This enum provides specific error types and localized descriptions for various
+ transport-related failures, such as binding failures when starting a server.
+ */
+public enum TransportError: LocalizedError {
+	/**
+	 Indicates that the transport failed to bind to a specific address and port.
+	 
+	 - Parameter message: A human-readable description of the binding failure,
+	   including details about the specific cause (e.g., port in use, permission denied).
+	 */
+	case bindingFailed(String)
+	
+	/**
+	 Provides a localized description of the error.
+	 
+	 - Returns: A human-readable string describing the error.
+	 */
+	public var errorDescription: String? {
+		switch self {
+			case .bindingFailed(let message):
+				return message
+		}
+	}
+}