Add support for NIP-40 - Expiration Timestamp (#193)

README.md

@@ -47,7 +47,7 @@ The following [NIPs](https://github.com/nostr-protocol/nips) are implemented:
 - [ ] [NIP-36: Sensitive Content](https://github.com/nostr-protocol/nips/blob/master/36.md)
 - [ ] [NIP-38: User Statuses](https://github.com/nostr-protocol/nips/blob/master/38.md)
 - [ ] [NIP-39: External Identities in Profiles](https://github.com/nostr-protocol/nips/blob/master/39.md)
-- [ ] [NIP-40: Expiration Timestamp](https://github.com/nostr-protocol/nips/blob/master/40.md)
+- [x] [NIP-40: Expiration Timestamp](https://github.com/nostr-protocol/nips/blob/master/40.md)
 - [ ] [NIP-42: Authentication of clients to relays](https://github.com/nostr-protocol/nips/blob/master/42.md)
 - [x] [NIP-44: Versioned Encryption](https://github.com/nostr-protocol/nips/blob/master/44.md)
 - [ ] [NIP-45: Counting results](https://github.com/nostr-protocol/nips/blob/master/45.md)

Sources/NostrSDK/Events/NostrEvent.swift

@@ -150,6 +150,26 @@ public class NostrEvent: Codable, Equatable, Hashable {
         tags.compactMap { EventCoordinates(eventCoordinatesTag: $0) }
     }
 
+    /// Unix timestamp at which the message SHOULD be considered expired (by relays and clients) and SHOULD be deleted by relays.
+    /// See [NIP-40 - Expiration Timestamp](https://github.com/nostr-protocol/nips/blob/master/40.md).
+    public var expiration: Int64? {
+        if let expiration = firstValueForTagName(.expiration) {
+            return Int64(expiration)
+        } else {
+            return nil
+        }
+    }
+
+    /// Whether the message SHOULD be considered expired (by relays and clients) and SHOULD be deleted by relays.
+    /// See [NIP-40 - Expiration Timestamp](https://github.com/nostr-protocol/nips/blob/master/40.md).
+    public var isExpired: Bool {
+        if let expiration {
+            return Int64(Date.now.timeIntervalSince1970) >= expiration
+        } else {
+            return false
+        }
+    }
+
     /// All tags with the provided name.
     public func allTags(withTagName tagName: TagName) -> [Tag] {
         tags.filter { $0.name == tagName.rawValue }
@@ -355,6 +375,14 @@ public extension NostrEvent {
             return self
         }
 
+        /// Specifies a unix timestamp at which the message SHOULD be considered expired (by relays and clients) and SHOULD be deleted by relays.
+        /// See [NIP-40 - Expiration Timestamp](https://github.com/nostr-protocol/nips/blob/master/40.md).
+        @discardableResult
+        public final func expiration(_ expiration: Int64) -> Self {
+            tags.append(Tag(name: .expiration, value: String(expiration)))
+            return self
+        }
+
         public func build(signedBy keypair: Keypair) throws -> T {
             try T(
                 kind: kind,

Sources/NostrSDK/Tag.swift

@@ -19,6 +19,10 @@ public enum TagName: String {
     /// coordinates to a replaceable event, which includes the kind number, pubkey that signed the event, and optionally the identifier (if the replaceable event is parameterized)
     case eventCoordinates = "a"
 
+    /// Specifies a unix timestamp at which the message SHOULD be considered expired (by relays and clients) and SHOULD be deleted by relays.
+    /// See [NIP-40 - Expiration Timestamp](https://github.com/nostr-protocol/nips/blob/master/40.md).
+    case expiration
+
     /// a hashtag to categorize events for easy searching
     case hashtag = "t"
 

Tests/NostrSDKTests/Events/NostrEventTests.swift

@@ -68,4 +68,24 @@ final class NostrEventTests: XCTestCase, FixtureLoading, MetadataCoding {
         XCTAssertEqual(metadata.relays?[1], relay2)
     }
 
+    func testExpiration() throws {
+        let futureExpiration = Int64(Date.now.timeIntervalSince1970 + 10000)
+        let futureExpirationEvent = try NostrEvent.Builder(kind: .textNote)
+            .expiration(futureExpiration)
+            .build(signedBy: .test)
+        XCTAssertEqual(futureExpirationEvent.expiration, futureExpiration)
+        XCTAssertFalse(futureExpirationEvent.isExpired)
+
+        let pastExpiration = Int64(Date.now.timeIntervalSince1970 - 1)
+        let pastExpirationEvent = try NostrEvent.Builder(kind: .textNote)
+            .expiration(pastExpiration)
+            .build(signedBy: .test)
+        XCTAssertEqual(pastExpirationEvent.expiration, pastExpiration)
+        XCTAssertTrue(pastExpirationEvent.isExpired)
+
+        let decodedExpiredEvent: NostrEvent = try decodeFixture(filename: "test_event_expired")
+        XCTAssertEqual(decodedExpiredEvent.expiration, 1697090842)
+        XCTAssertTrue(decodedExpiredEvent.isExpired)
+    }
+
 }

Tests/NostrSDKTests/Fixtures/test_event_expired.json

@@ -0,0 +1,9 @@
+{
+  "content": "This is a test message.",
+  "created_at": 1687090842,
+  "id": "b7fbbb4d473db3b3a671ad995f1248d56e9a2ed7f145c1e5f74308e60db2eba7",
+  "kind": 1,
+  "pubkey": "9947f9659dd80c3682402b612f5447e28249997fb3709500c32a585eb0977340",
+  "sig": "09a1dcace3cec8cd9934b544cede6955c9876e385d73491f1ca5354a0baecda834c43ac9510ef779f8c8c7543b3faccd821e40e0a52dde8527d071cb0d53230c",
+  "tags": [["expiration","1697090842"]]
+}