fix(dht): check for empty body contents in initial msg validation (#5123

)

Description
---
Discards messages with empty body contents in initial message validation

Motivation and Context
---
[RFC-172 Stabalisation PR](tari-project/rfcs#88) adds a rule that routing nodes should discard a message with empty body contents.

How Has This Been Tested?
---
New unit test

comms/dht/src/inbound/decryption.rs

@@ -75,6 +75,8 @@ enum DecryptionError {
     EncryptedMessageNoDestination,
     #[error("Decryption failed: {0}")]
     DecryptionFailedMalformedCipher(#[from] DhtEncryptError),
+    #[error("Encrypted message must have a non-empty body")]
+    EncryptedMessageEmptyBody,
 }
 
 /// This layer is responsible for attempting to decrypt inbound messages.
@@ -346,6 +348,10 @@ where S: Service<DecryptedDhtMessage, Response = (), Error = PipelineError>
     /// Performs message validation that should be performed by all nodes. If an error is encountered, the message is
     /// invalid and should never have been sent.
     fn initial_validation(message: DhtInboundMessage) -> Result<ValidatedDhtInboundMessage, DecryptionError> {
+        if message.body.is_empty() {
+            return Err(DecryptionError::EncryptedMessageEmptyBody);
+        }
+
         if message.dht_header.flags.is_encrypted() {
             // Check if there is no destination specified and discard
             if message.dht_header.destination.is_unknown() {
@@ -572,6 +578,33 @@ mod test {
         assert_eq!(decrypted.decryption_result.unwrap_err(), inbound_msg.body);
     }
 
+    #[test]
+    fn decrypt_inbound_fail_empty_contents() {
+        let service = service_fn(
+            move |_msg: DecryptedDhtMessage| -> future::Ready<Result<(), PipelineError>> {
+                panic!("Should not be called")
+            },
+        );
+        let node_identity = make_node_identity();
+        let (connectivity, _) = create_connectivity_mock();
+        let mut service = DecryptionService::new(Default::default(), node_identity, connectivity, service);
+
+        let some_other_node_identity = make_node_identity();
+        let mut inbound_msg = make_dht_inbound_message(
+            &some_other_node_identity,
+            &Vec::new(),
+            DhtMessageFlags::ENCRYPTED,
+            true,
+            true,
+        )
+        .unwrap();
+        inbound_msg.body = Vec::new();
+
+        let err = block_on(service.call(inbound_msg.clone())).unwrap_err();
+        let err = err.downcast::<DecryptionError>().unwrap();
+        unpack_enum!(DecryptionError::EncryptedMessageEmptyBody = err);
+    }
+
     #[runtime::test]
     async fn decrypt_inbound_fail_destination() {
         let (connectivity, mock) = create_connectivity_mock();