fix(sns): support SubscriptionConfirmation and UnsubscribeConfirmation message types

The SnsMessage and SnsMessageObj structs were failing to deserialize
SubscriptionConfirmation and UnsubscribeConfirmation SNS messages because:

1. `unsubscribe_url` was required (String) but these message types don't have it
2. `subscribe_url` and `token` fields were missing entirely

This fix:
- Makes `unsubscribe_url` optional (Option<String>) since it's only present
  in Notification messages
- Adds `subscribe_url` field (Option<String>) for confirmation messages
- Adds `token` field (Option<String>) for confirmation messages

All fields use #[serde(default)] to handle missing fields gracefully.

Fixes #966

Signed-off-by: abhu85 <151518127+abhu85@users.noreply.github.com>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: abhu85

lambda-events/src/event/sns/mod.rs

@@ -94,8 +94,24 @@ pub struct SnsMessage {
     pub signing_cert_url: String,
 
     /// A URL that you can use to unsubscribe the endpoint from this topic. If you visit this URL, Amazon SNS unsubscribes the endpoint and stops sending notifications to this endpoint.
+    ///
+    /// Note: This field is only present in Notification messages. It is not present in SubscriptionConfirmation or UnsubscribeConfirmation messages.
     #[serde(alias = "UnsubscribeURL")]
-    pub unsubscribe_url: String,
+    #[serde(default)]
+    pub unsubscribe_url: Option<String>,
+
+    /// A URL that you can visit to re-confirm the subscription or confirm the unsubscription.
+    ///
+    /// Note: This field is only present in SubscriptionConfirmation and UnsubscribeConfirmation messages.
+    #[serde(alias = "SubscribeURL")]
+    #[serde(default)]
+    pub subscribe_url: Option<String>,
+
+    /// A value you can use with the ConfirmSubscription action to re-confirm the subscription.
+    ///
+    /// Note: This field is only present in SubscriptionConfirmation and UnsubscribeConfirmation messages.
+    #[serde(default)]
+    pub token: Option<String>,
 
     /// The Message value specified when the notification was published to the topic.
     pub message: String,
@@ -205,8 +221,24 @@ pub struct SnsMessageObj<T: Serialize> {
     pub signing_cert_url: String,
 
     /// A URL that you can use to unsubscribe the endpoint from this topic. If you visit this URL, Amazon SNS unsubscribes the endpoint and stops sending notifications to this endpoint.
+    ///
+    /// Note: This field is only present in Notification messages. It is not present in SubscriptionConfirmation or UnsubscribeConfirmation messages.
     #[serde(alias = "UnsubscribeURL")]
-    pub unsubscribe_url: String,
+    #[serde(default)]
+    pub unsubscribe_url: Option<String>,
+
+    /// A URL that you can visit to re-confirm the subscription or confirm the unsubscription.
+    ///
+    /// Note: This field is only present in SubscriptionConfirmation and UnsubscribeConfirmation messages.
+    #[serde(alias = "SubscribeURL")]
+    #[serde(default)]
+    pub subscribe_url: Option<String>,
+
+    /// A value you can use with the ConfirmSubscription action to re-confirm the subscription.
+    ///
+    /// Note: This field is only present in SubscriptionConfirmation and UnsubscribeConfirmation messages.
+    #[serde(default)]
+    pub token: Option<String>,
 
     /// Deserialized into a `T` from nested JSON inside the SNS message string. `T` must implement the `Deserialize` or `DeserializeOwned` trait.
     #[serde_as(as = "serde_with::json::JsonString")]
@@ -462,4 +494,45 @@ mod test {
         let reparsed: SnsEventObj<CustStruct> = serde_json::from_slice(output.as_bytes()).unwrap();
         assert_eq!(parsed, reparsed);
     }
+
+    #[test]
+    #[cfg(feature = "sns")]
+    fn my_example_sns_subscription_confirmation() {
+        // Test for issue #966: SnsMessage struct fails with SubscriptionConfirmation types
+        // SubscriptionConfirmation messages have SubscribeURL and Token fields instead of UnsubscribeURL
+        let data = include_bytes!("../../fixtures/example-sns-subscription-confirmation.json");
+        let parsed: SnsEvent = serde_json::from_slice(data).unwrap();
+        assert_eq!(1, parsed.records.len());
+
+        let sns_message = &parsed.records[0].sns;
+        assert_eq!("SubscriptionConfirmation", sns_message.sns_message_type);
+        assert!(sns_message.unsubscribe_url.is_none());
+        assert!(sns_message.subscribe_url.is_some());
+        assert!(sns_message.token.is_some());
+        assert_eq!(
+            "https://sns.us-east-1.amazonaws.com/?Action=ConfirmSubscription&TopicArn=arn:aws:sns:us-east-1:123456789012:MyTopic&Token=2336412f37fb687f5d51e6e2425dacbbffff",
+            sns_message.subscribe_url.as_ref().unwrap()
+        );
+        assert_eq!(
+            "2336412f37fb687f5d51e6e2425dacbbffff",
+            sns_message.token.as_ref().unwrap()
+        );
+
+        let output: String = serde_json::to_string(&parsed).unwrap();
+        let reparsed: SnsEvent = serde_json::from_slice(output.as_bytes()).unwrap();
+        assert_eq!(parsed, reparsed);
+    }
+
+    #[test]
+    #[cfg(feature = "sns")]
+    fn my_example_sns_notification_has_unsubscribe_url() {
+        // Verify that Notification messages still have unsubscribe_url
+        let data = include_bytes!("../../fixtures/example-sns-event.json");
+        let parsed: SnsEvent = serde_json::from_slice(data).unwrap();
+        let sns_message = &parsed.records[0].sns;
+        assert_eq!("Notification", sns_message.sns_message_type);
+        assert!(sns_message.unsubscribe_url.is_some());
+        assert!(sns_message.subscribe_url.is_none());
+        assert!(sns_message.token.is_none());
+    }
 }

lambda-events/src/fixtures/example-sns-subscription-confirmation.json

@@ -0,0 +1,23 @@
+{
+  "Records": [
+    {
+      "EventVersion": "1.0",
+      "EventSubscriptionArn": "arn:aws:sns:us-east-1:123456789012:MyTopic:00000000-0000-0000-0000-000000000000",
+      "EventSource": "aws:sns",
+      "Sns": {
+        "Type": "SubscriptionConfirmation",
+        "MessageId": "165545c9-2a5c-472c-8df2-7ff2be2b3b1b",
+        "TopicArn": "arn:aws:sns:us-east-1:123456789012:MyTopic",
+        "Message": "You have chosen to subscribe to the topic arn:aws:sns:us-east-1:123456789012:MyTopic.\nTo confirm the subscription, visit the SubscribeURL included in this message.",
+        "Timestamp": "2012-04-26T20:45:04.751Z",
+        "SignatureVersion": "1",
+        "Signature": "EXAMPLEpH+DcEwjAPg8O9mY8dReBSwksfg2S7WKQcikcNKWLQjwu6A4VbeS0QHVCkhRS7fUQvi2egU3N858fiTDN6bkkOxYDVrY0Ad8L10Hs3zH81mtnPk5uvvolIC1CXGu43obcgFxeL3khZl8IKvO61GWB6jI9b5+gLPoBc1Q=",
+        "SigningCertURL": "https://sns.us-east-1.amazonaws.com/SimpleNotificationService-f3ecfb7224c7233fe7bb5f59f96de52f.pem",
+        "SubscribeURL": "https://sns.us-east-1.amazonaws.com/?Action=ConfirmSubscription&TopicArn=arn:aws:sns:us-east-1:123456789012:MyTopic&Token=2336412f37fb687f5d51e6e2425dacbbffff",
+        "Token": "2336412f37fb687f5d51e6e2425dacbbffff",
+        "Subject": null,
+        "MessageAttributes": {}
+      }
+    }
+  ]
+}