Added dedicated error for payloads that are too large

Sources/WebPush/Errors/MessageTooLargeError.swift

@@ -0,0 +1,20 @@
+//
+//  MessageTooLargeError.swift
+//  swift-webpush
+//
+//  Created by Dimitri Bouniol on 2024-12-13.
+//  Copyright © 2024 Mochi Development, Inc. All rights reserved.
+//
+
+import Foundation
+
+/// The message was too large, and could not be delivered to the push service.
+///
+/// - SeeAlso: ``WebPushManager/maximumMessageSize``
+public struct MessageTooLargeError: LocalizedError, Hashable {
+    public init() {}
+
+    public var errorDescription: String? {
+        "The message was too large, and could not be delivered to the push service."
+    }
+}

Sources/WebPush/WebPushManager.swift

@@ -494,7 +494,9 @@ public actor WebPushManager: Sendable {
         switch response.status {
         case .created: break
         case .notFound, .gone: throw BadSubscriberError()
-        // TODO: 413 payload too large - log.error and throw error
+        case .payloadTooLarge:
+            logger.error("The encrypted payload was too large and was rejected by the push service.")
+            throw MessageTooLargeError()
         // TODO: 429 too many requests, 500 internal server error, 503 server shutting down - check config and perform a retry after a delay?
         default: throw HTTPError(response: response)
         }

Tests/WebPushTests/WebPushManagerTests.swift

@@ -508,6 +508,35 @@ struct WebPushManagerTests {
             }
         }
 
+        @Test func sendExtraLargeMessageFails() async throws {
+            await confirmation { requestWasMade in
+                let vapidConfiguration = VAPID.Configuration.makeTesting()
+
+                let subscriberPrivateKey = P256.KeyAgreement.PrivateKey(compactRepresentable: false)
+                var authenticationSecret: [UInt8] = Array(repeating: 0, count: 16)
+                for index in authenticationSecret.indices { authenticationSecret[index] = .random(in: .min ... .max) }
+
+                let subscriber = Subscriber(
+                    endpoint: URL(string: "https://example.com/subscriber")!,
+                    userAgentKeyMaterial: UserAgentKeyMaterial(publicKey: subscriberPrivateKey.publicKey, authenticationSecret: Data(authenticationSecret)),
+                    vapidKeyID: vapidConfiguration.primaryKey!.id
+                )
+
+                let manager = WebPushManager(
+                    vapidConfiguration: vapidConfiguration,
+                    backgroundActivityLogger: Logger(label: "WebPushManagerTests", factory: { PrintLogHandler(label: $0, metadataProvider: $1) }),
+                    executor: .httpClient(MockHTTPClient({ request in
+                        requestWasMade()
+                        return HTTPClientResponse(status: .payloadTooLarge)
+                    }))
+                )
+
+                await #expect(throws: MessageTooLargeError()) {
+                    try await manager.send(data: Array(repeating: 0, count: 3994), to: subscriber)
+                }
+            }
+        }
+
         @Test func sendMessageToNotFoundPushServerError() async throws {
             await confirmation { requestWasMade in
                 let vapidConfiguration = VAPID.Configuration.mockedConfiguration