Added topic support

Fixes #21

Author: dimitribouniol

Sources/WebPush/Topic.swift

@@ -0,0 +1,85 @@
+//
+//  Topic.swift
+//  swift-webpush
+//
+//  Created by Dimitri Bouniol on 2024-12-24.
+//  Copyright © 2024 Mochi Development, Inc. All rights reserved.
+//
+
+@preconcurrency import Crypto
+import Foundation
+
+/// Topics are used to de-duplicate and overwrite messages on push services before they are delivered to a subscriber.
+///
+/// The topic is never delivered to your service worker, though is seen in plain text by the Push Service, so this type encodes it first to prevent leaking any information about the messages you are sending or your subscribers.
+///
+/// - Important: Since topics are sent in the clear to push services, they must be securely hashed. You must use a stable random value for this, such as the subscriber's ``UserAgentKeyMaterial/authenticationSecret``. This is fine for most applications, though you may wish to use a different key if your application requires it.
+///
+/// - SeeAlso: [RFC 8030 Generic Event Delivery Using HTTP §5.4. Replacing Push Messages](https://datatracker.ietf.org/doc/html/rfc8030#section-5.4)
+public struct Topic: Hashable, Sendable, CustomStringConvertible {
+    /// The topic value to use.
+    public let topic: String
+    
+    /// Create a new topic from encodable data and a salt.
+    /// 
+    /// - Important: Since topics are sent in the clear to push services, they must be securely hashed. You must use a stable random value for this, such as the subscriber's ``UserAgentKeyMaterial/authenticationSecret``. This is fine for most applications, though you may wish to use a different key if your application requires it.
+    ///
+    /// - Parameters:
+    ///   - encodableTopic: The encodable data that represents a stable topic. This can be a string, identifier, or any other token that can be encoded.
+    ///   - salt: The salt that should be used when encoding the topic.
+    public init(
+        encodableTopic: some Encodable,
+        salt: some DataProtocol
+    ) throws {
+        /// First, turn the topic into a byte stream.
+        let encoder = JSONEncoder()
+        encoder.outputFormatting = [.sortedKeys]
+        let encodedTopic = try encoder.encode(encodableTopic)
+        
+        /// Next, hash the topic using the provided salt, some info, and cut to length at 24 bytes.
+        let hashedTopic = HKDF<SHA256>.deriveKey(
+            inputKeyMaterial: SymmetricKey(data: encodedTopic),
+            salt: salt,
+            info: "WebPush Topic".utf8Bytes,
+            outputByteCount: 24
+        )
+        
+        /// Transform these 24 bytes into 32 Base64 URL-safe characters.
+        self.topic = hashedTopic.base64URLEncodedString()
+    }
+    
+    /// Create a new random topic.
+    ///
+    /// Create a topic with a random identifier to save it in your own data stores, and re-use it as needed.
+    public init() {
+        /// Generate a 24-byte topic.
+        var topicBytes: [UInt8] = Array(repeating: 0, count: 24)
+        for index in topicBytes.indices { topicBytes[index] = .random(in: .min ... .max) }
+        self.topic = topicBytes.base64URLEncodedString()
+    }
+    
+    /// Initialize a topic with an unchecked string.
+    ///
+    /// Prefer to use ``init(encodableTopic:salt:)`` when possible.
+    ///
+    /// - Warning: This may be rejected by a Push Service if it is not 32 Base64 URL-safe characters, and will not be encrypted. Expect to handle a ``PushServiceError`` with a ``PushServiceError/response`` status code of `400 Bad Request` when it does.
+    public init(unsafeTopic: String) {
+        topic = unsafeTopic
+    }
+    
+    public var description: String {
+        topic
+    }
+}
+
+extension Topic: Codable {
+    public init(from decoder: any Decoder) throws {
+        let container = try decoder.singleValueContainer()
+        topic = try container.decode(String.self)
+    }
+    
+    public func encode(to encoder: any Encoder) throws {
+        var container = encoder.singleValueContainer()
+        try container.encode(topic)
+    }
+}

Sources/WebPush/WebPushManager.swift

@@ -250,12 +250,14 @@ public actor WebPushManager: Sendable {
     /// - Parameters:
     ///   - message: The message to send as raw data.
     ///   - subscriber: The subscriber to send the push message to.
+    ///   - deduplicationTopic: The topic to use when deduplicating messages stored on a Push Service.
     ///   - expiration: The expiration of the push message, after wich delivery will no longer be attempted.
     ///   - urgency: The urgency of the delivery of the push message.
     ///   - logger: The logger to use for status updates. If not provided, the background activity logger will be used instead. When running in a server environment, your contextual logger should be used instead giving you full control of logging and metadata.
     public func send(
         data message: some DataProtocol,
         to subscriber: some SubscriberProtocol,
+        deduplicationTopic topic: Topic? = nil,
         expiration: Expiration = .recommendedMaximum,
         urgency: Urgency = .high,
         logger: Logger? = nil
@@ -269,12 +271,13 @@ public actor WebPushManager: Sendable {
                 privateKeyProvider: privateKeyProvider,
                 data: message,
                 subscriber: subscriber,
+                deduplicationTopic: topic,
                 expiration: expiration,
                 urgency: urgency,
                 logger: logger
             )
         case .handler(let handler):
-            try await handler(.data(Data(message)), Subscriber(subscriber), expiration, urgency)
+            try await handler(.data(Data(message)), Subscriber(subscriber), topic, expiration, urgency)
         }
     }
 
@@ -285,19 +288,22 @@ public actor WebPushManager: Sendable {
     /// - Parameters:
     ///   - message: The message to send as a string.
     ///   - subscriber: The subscriber to send the push message to.
+    ///   - deduplicationTopic: The topic to use when deduplicating messages stored on a Push Service.
     ///   - expiration: The expiration of the push message, after wich delivery will no longer be attempted.
     ///   - urgency: The urgency of the delivery of the push message.
     ///   - logger: The logger to use for status updates. If not provided, the background activity logger will be used instead. When running in a server environment, your contextual logger should be used instead giving you full control of logging and metadata.
     public func send(
         string message: some StringProtocol,
         to subscriber: some SubscriberProtocol,
+        deduplicationTopic topic: Topic? = nil,
         expiration: Expiration = .recommendedMaximum,
         urgency: Urgency = .high,
         logger: Logger? = nil
     ) async throws {
         try await routeMessage(
             message: .string(String(message)),
             to: subscriber,
+            deduplicationTopic: topic,
             expiration: expiration,
             urgency: urgency,
             logger: logger ?? backgroundActivityLogger
@@ -311,19 +317,22 @@ public actor WebPushManager: Sendable {
     /// - Parameters:
     ///   - message: The message to send as JSON.
     ///   - subscriber: The subscriber to send the push message to.
+    ///   - deduplicationTopic: The topic to use when deduplicating messages stored on a Push Service.
     ///   - expiration: The expiration of the push message, after wich delivery will no longer be attempted.
     ///   - urgency: The urgency of the delivery of the push message.
     ///   - logger: The logger to use for status updates. If not provided, the background activity logger will be used instead. When running in a server environment, your contextual logger should be used instead giving you full control of logging and metadata.
     public func send(
         json message: some Encodable&Sendable,
         to subscriber: some SubscriberProtocol,
+        deduplicationTopic topic: Topic? = nil,
         expiration: Expiration = .recommendedMaximum,
         urgency: Urgency = .high,
         logger: Logger? = nil
     ) async throws {
         try await routeMessage(
             message: .json(message),
             to: subscriber,
+            deduplicationTopic: topic,
             expiration: expiration,
             urgency: urgency,
             logger: logger ?? backgroundActivityLogger
@@ -334,12 +343,14 @@ public actor WebPushManager: Sendable {
     /// - Parameters:
     ///   - message: The message to send.
     ///   - subscriber: The subscriber to sign the message against.
+    ///   - deduplicationTopic: The topic to use when deduplicating messages stored on a Push Service.
     ///   - expiration: The expiration of the message.
     ///   - urgency: The urgency of the message.
     ///   - logger: The logger to use for status updates.
     func routeMessage(
         message: _Message,
         to subscriber: some SubscriberProtocol,
+        deduplicationTopic topic: Topic?,
         expiration: Expiration,
         urgency: Urgency,
         logger: Logger
@@ -353,6 +364,7 @@ public actor WebPushManager: Sendable {
                 privateKeyProvider: privateKeyProvider,
                 data: message.data,
                 subscriber: subscriber,
+                deduplicationTopic: topic,
                 expiration: expiration,
                 urgency: urgency,
                 logger: logger
@@ -361,6 +373,7 @@ public actor WebPushManager: Sendable {
             try await handler(
                 message,
                 Subscriber(subscriber),
+                topic,
                 expiration,
                 urgency
             )
@@ -373,6 +386,7 @@ public actor WebPushManager: Sendable {
     ///   - applicationServerECDHPrivateKey: The private key to use for the key exchange. If nil, one will be generated.
     ///   - message: The message to send as raw data.
     ///   - subscriber: The subscriber to sign the message against.
+    ///   - deduplicationTopic: The topic to use when deduplicating messages stored on a Push Service.
     ///   - expiration: The expiration of the message.
     ///   - urgency: The urgency of the message.
     ///   - logger: The logger to use for status updates.
@@ -381,6 +395,7 @@ public actor WebPushManager: Sendable {
         privateKeyProvider: Executor.KeyProvider,
         data message: some DataProtocol,
         subscriber: some SubscriberProtocol,
+        deduplicationTopic topic: Topic?,
         expiration: Expiration,
         urgency: Urgency,
         logger: Logger
@@ -483,6 +498,9 @@ public actor WebPushManager: Sendable {
         request.headers.add(name: "Content-Type", value: "application/octet-stream")
         request.headers.add(name: "TTL", value: "\(max(expiration, .dropIfUndeliverable).seconds)")
         request.headers.add(name: "Urgency", value: "\(urgency)")
+        if let topic {
+            request.headers.add(name: "Topic", value: "\(topic)")
+        }
         request.body = .bytes(ByteBuffer(bytes: requestContent))
 
         /// Send the request to the push endpoint.
@@ -778,6 +796,7 @@ extension WebPushManager {
         case handler(@Sendable (
             _ message: _Message,
             _ subscriber: Subscriber,
+            _ topic: Topic?,
             _ expiration: Expiration,
             _ urgency: Urgency
         ) async throws -> Void)

Sources/WebPushTesting/WebPushManager+Testing.swift

@@ -30,6 +30,7 @@ extension WebPushManager {
         messageHandler: @escaping @Sendable (
             _ message: Message,
             _ subscriber: Subscriber,
+            _ topic: Topic?,
             _ expiration: Expiration,
             _ urgency: Urgency
         ) async throws -> Void

Tests/WebPushTests/TopicTests.swift

@@ -0,0 +1,98 @@
+//
+//  TopicTests.swift
+//  swift-webpush
+//
+//  Created by Dimitri Bouniol on 2024-12-24.
+//  Copyright © 2024 Mochi Development, Inc. All rights reserved.
+//
+
+
+import Crypto
+import Foundation
+import Testing
+@testable import WebPush
+
+extension Character {
+    var isBase64URLSafe: Bool {
+        self.isASCII && (
+            self.isLetter
+            || self.isNumber
+            || self == "-"
+            || self == "_"
+        )
+    }
+}
+
+@Suite struct TopicTests {
+    @Test func topicIsValid() throws {
+        func checkValidity(_ topic: String) {
+            #expect(topic.count == 32)
+            let allSafeCharacters = topic.allSatisfy(\.isBase64URLSafe)
+            #expect(allSafeCharacters)
+        }
+        checkValidity(try Topic(encodableTopic: "Hello", salt: "Salty".utf8Bytes).topic)
+        checkValidity(try Topic(encodableTopic: "", salt: "Salty".utf8Bytes).topic)
+        checkValidity(try Topic(encodableTopic: "", salt: "".utf8Bytes).topic)
+        checkValidity(try Topic(encodableTopic: ["A", "B", "C"], salt: "SecretSalt".utf8Bytes).topic)
+        checkValidity(try Topic(encodableTopic: ["a" : "b"], salt: "SecretSalt".utf8Bytes).topic)
+        checkValidity(try Topic(encodableTopic: UUID(), salt: "SecretSalt".utf8Bytes).topic)
+        checkValidity(Topic().topic)
+        
+        struct ComplexTopic: Codable {
+            var user = "Dimitri"
+            var app = "Jiiiii"
+            var id = UUID()
+            var secretNumber = 42
+        }
+        checkValidity(try Topic(encodableTopic: ComplexTopic(), salt: "SecretSalt".utf8Bytes).topic)
+        
+        do {
+            let unsafeTopic = Topic(unsafeTopic: "test")
+            #expect(unsafeTopic.topic.count != 32)
+            let allSafeCharacters = unsafeTopic.topic.allSatisfy(\.isBase64URLSafe)
+            #expect(allSafeCharacters)
+        }
+        do {
+            let unsafeTopic = Topic(unsafeTopic: "()")
+            #expect(unsafeTopic.topic.count != 32)
+            let allSafeCharacters = unsafeTopic.topic.allSatisfy(\.isBase64URLSafe)
+            #expect(!allSafeCharacters)
+        }
+    }
+    
+    @Test func topicIsTransformed() throws {
+        #expect(try Topic(encodableTopic: "Hello", salt: "Salty".utf8Bytes).topic == "mwgQxrwapKl47ipX1F8Rc84rcd2ve3M-")
+        #expect(Topic(unsafeTopic: "test").topic == "test")
+        #expect(Topic(unsafeTopic: "A really long test (with unsafe characters to boot ふふふ!)").topic == "A really long test (with unsafe characters to boot ふふふ!)")
+    }
+    
+    @Test func topicIsDescribable() throws {
+        #expect("\(try Topic(encodableTopic: "Hello", salt: "Salty".utf8Bytes))" == "mwgQxrwapKl47ipX1F8Rc84rcd2ve3M-")
+        #expect("\(Topic(unsafeTopic: "test"))" == "test")
+        #expect("\(Topic(unsafeTopic: "A really long test (with unsafe characters to boot ふふふ!)"))" == "A really long test (with unsafe characters to boot ふふふ!)")
+    }
+    
+    @Test func transformsDeterministically() throws {
+        #expect(try Topic(encodableTopic: "Hello", salt: "Salty".utf8Bytes) == Topic(encodableTopic: "Hello", salt: "Salty".utf8Bytes))
+        #expect(try Topic(encodableTopic: "Hello", salt: "Salty".utf8Bytes) != Topic(encodableTopic: "Hello", salt: "NotSalty".utf8Bytes))
+        #expect(try Topic(encodableTopic: "Hello", salt: "Salty".utf8Bytes) != Topic(encodableTopic: "Hello, World", salt: "Salty".utf8Bytes))
+    }
+    
+    @Suite struct Coding {
+        @Test func encoding() throws {
+            #expect(String(decoding: try JSONEncoder().encode(Topic(encodableTopic: "Hello", salt: "Salty".utf8Bytes)), as: UTF8.self) == "\"mwgQxrwapKl47ipX1F8Rc84rcd2ve3M-\"")
+        }
+        
+        @Test func decoding() throws {
+            #expect(try JSONDecoder().decode(Topic.self, from: Data("\"mwgQxrwapKl47ipX1F8Rc84rcd2ve3M-\"".utf8)) == Topic(encodableTopic: "Hello", salt: "Salty".utf8Bytes))
+            
+            #expect(try JSONDecoder().decode(Topic.self, from: Data("\"test\"".utf8)) == Topic(unsafeTopic: "test"))
+            
+            #expect(try JSONDecoder().decode(Topic.self, from: Data("\"A really long test (with unsafe characters to boot ふふふ!)\"".utf8)) == Topic(unsafeTopic: "A really long test (with unsafe characters to boot ふふふ!)"))
+            
+            #expect(throws: DecodingError.self) {
+                try JSONDecoder().decode(Topic.self, from: Data("{}".utf8))
+            }
+        }
+    }
+}