Added UserAgentKeyMaterial Error type

Author: dimitribouniol

Sources/WebPush/Errors/Base64URLDecodingError.swift

@@ -0,0 +1,18 @@
+//
+//  Base64URLDecodingError.swift
+//  swift-webpush
+//
+//  Created by Dimitri Bouniol on 2024-12-13.
+//  Copyright © 2024 Mochi Development, Inc. All rights reserved.
+//
+
+import Foundation
+
+/// An error encountered while decoding Base64 data.
+public struct Base64URLDecodingError: LocalizedError, Hashable {
+    public init() {}
+    
+    public var errorDescription: String? {
+        "The Base64 data could not be decoded."
+    }
+}

Sources/WebPush/Errors/UserAgentKeyMaterialError.swift

@@ -0,0 +1,39 @@
+//
+//  UserAgentKeyMaterialError.swift
+//  swift-webpush
+//
+//  Created by Dimitri Bouniol on 2024-12-13.
+//  Copyright © 2024 Mochi Development, Inc. All rights reserved.
+//
+
+import Foundation
+
+/// An error encountered during ``VAPID/Configuration`` initialization or decoding.
+public struct UserAgentKeyMaterialError: LocalizedError {
+    enum Kind {
+        case invalidPublicKey
+        case invalidAuthenticationSecret
+    }
+    
+    var kind: Kind
+    var underlyingError: any Error
+    
+    /// The public key was invalid.
+    public static func invalidPublicKey(underlyingError: Error) -> Self {
+        Self(kind: .invalidPublicKey, underlyingError: underlyingError)
+    }
+    
+    /// The authentication secret was invalid.
+    public static func invalidAuthenticationSecret(underlyingError: Error) -> Self {
+        Self(kind: .invalidAuthenticationSecret, underlyingError: underlyingError)
+    }
+    
+    public var errorDescription: String? {
+        switch kind {
+        case .invalidPublicKey:
+            "Subscriber Public Key (`\(UserAgentKeyMaterial.CodingKeys.publicKey)`) was invalid: \(underlyingError.localizedDescription)."
+        case .invalidAuthenticationSecret:
+            "Subscriber Authentication Secret (`\(UserAgentKeyMaterial.CodingKeys.authenticationSecret)`) was invalid: \(underlyingError.localizedDescription)."
+        }
+    }
+}

Sources/WebPush/Subscriber.swift

@@ -67,15 +67,15 @@ public struct UserAgentKeyMaterial: Sendable {
     public init(
         publicKey: String,
         authenticationSecret: String
-    ) throws {
+    ) throws(UserAgentKeyMaterialError) {
         guard let publicKeyData = Data(base64URLEncoded: publicKey)
-        else { throw CancellationError() } // invalid public key error (underlying error = URLDecoding error)
+        else { throw .invalidPublicKey(underlyingError: Base64URLDecodingError()) }
         do {
             self.publicKey = try P256.KeyAgreement.PublicKey(x963Representation: publicKeyData)
-        } catch { throw CancellationError() }  // invalid public key error (underlying error = error)
+        } catch { throw .invalidPublicKey(underlyingError: error) }
 
         guard let authenticationSecretData = Data(base64URLEncoded: authenticationSecret)
-        else { throw CancellationError() } // invalid authentication secret error (underlying error = URLDecoding error)
+        else { throw .invalidAuthenticationSecret(underlyingError: Base64URLDecodingError()) }
 
         self.authenticationSecret = authenticationSecretData
     }
@@ -190,5 +190,6 @@ public struct Subscriber: SubscriberProtocol, Codable, Hashable, Sendable {
 }
 
 extension Subscriber: Identifiable {
+    /// A safe identifier to use for the subscriber without exposing key material.
     public var id: String { endpoint.absoluteString }
 }