When decoding a payload that has no recipients, return an empty list

without further inspection of the byte buffer.

This reduces the need to calling methods to determine ahead of time
which of the decode methods should be called.

tessera-core/src/main/java/com/quorum/tessera/transaction/PayloadEncoderImpl.java

@@ -127,6 +127,11 @@ public EncodedPayloadWithRecipients decodePayloadWithRecipients(final byte[] inp
                 new Nonce(recipientNonce)
         );
 
+        //this means there are no recipients in the payload (which we receive when we are a participant)
+        if (!buffer.hasRemaining()) {
+            return new EncodedPayloadWithRecipients(payload, emptyList());
+        }
+
         final long recipientLength = buffer.getLong();
 
         final List<byte[]> recipientKeys = new ArrayList<>();

tessera-core/src/test/java/com/quorum/tessera/transaction/PayloadEncoderTest.java

@@ -179,4 +179,29 @@ public void decodePayloadWithRecipients() {
         assertThat(result.getEncodedPayload().getRecipientBoxes()).isNotEqualTo(control.getEncodedPayload().getRecipientBoxes());
     }
 
+    @Test
+    public void decodeWithNoRecipientsGivesEmptyList() {
+
+        final byte[] input = new byte[]{0, 0, 0, 0, 0, 0, 0, 32, -51, 40, -97, 78, 121, 47, -26, -66, 10, -21, -80, -22, -33, 78, 30, 85, -61, 56, 22, -100, 70, 124, 114, -34, -41, 36, -62, 6, 109, 63, -17, 8, 0, 0, 0, 0, 0, 0, 0, 28, 120, 111, 63, -100, 97, -12, -103, 20, 2, -48, 37, -86, -115, -112, -75, -27, 55, 12, -1, 120, 13, 0, 86, 92, 52, 77, -4, 45, 0, 0, 0, 0, 0, 0, 0, 24, -115, -84, -58, 14, 82, 118, 4, -118, -53, 86, 3, 14, 112, 70, -4, 81, 121, 84, -24, -3, -73, -17, 6, 124, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 48, -87, -102, 0, 95, -13, 48, 76, -115, -115, 62, 54, -55, -78, 125, -54, -34, -71, -11, -95, -85, 78, -24, -30, 47, 65, 5, 88, 38, -111, -12, -41, -97, 103, -60, -101, 43, -57, -68, 68, -109, 36, 49, -63, -123, 62, 21, 67, -28, 0, 0, 0, 0, 0, 0, 0, 24, -63, 5, 86, 42, -85, -12, -36, 16, -108, 48, 26, 36, 44, -82, 15, -38, -19, 6, -101, 107, 110, -30, 95, 5};
+
+        final byte[] senderKey = new byte[]{-51, 40, -97, 78, 121, 47, -26, -66, 10, -21, -80, -22, -33, 78, 30, 85, -61, 56, 22, -100, 70, 124, 114, -34, -41, 36, -62, 6, 109, 63, -17, 8};
+        final byte[] ciphertext = new byte[]{120, 111, 63, -100, 97, -12, -103, 20, 2, -48, 37, -86, -115, -112, -75, -27, 55, 12, -1, 120, 13, 0, 86, 92, 52, 77, -4, 45};
+        final byte[] nonce = new byte[]{-115, -84, -58, 14, 82, 118, 4, -118, -53, 86, 3, 14, 112, 70, -4, 81, 121, 84, -24, -3, -73, -17, 6, 124};
+        final byte[] recipientnonce = new byte[]{-63, 5, 86, 42, -85, -12, -36, 16, -108, 48, 26, 36, 44, -82, 15, -38, -19, 6, -101, 107, 110, -30, 95, 5};
+        final byte[] recipient = new byte[]{-87, -102, 0, 95, -13, 48, 76, -115, -115, 62, 54, -55, -78, 125, -54, -34, -71, -11, -95, -85, 78, -24, -30, 47, 65, 5, 88, 38, -111, -12, -41, -97, 103, -60, -101, 43, -57, -68, 68, -109, 36, 49, -63, -123, 62, 21, 67, -28};
+
+        final EncodedPayloadWithRecipients encodedPayloadWithRecipients = payloadEncoder.decodePayloadWithRecipients(input);
+        final EncodedPayload encodedPayload = encodedPayloadWithRecipients.getEncodedPayload();
+
+        assertThat(encodedPayloadWithRecipients.getRecipientKeys()).isEmpty();
+
+        assertThat(encodedPayload.getSenderKey()).isEqualTo(PublicKey.from(senderKey));
+        assertThat(encodedPayload.getCipherText()).containsExactly(ciphertext);
+        assertThat(encodedPayload.getCipherTextNonce()).isEqualTo(new Nonce(nonce));
+        assertThat(encodedPayload.getRecipientNonce()).isEqualTo(new Nonce(recipientnonce));
+        assertThat(encodedPayload.getRecipientBoxes()).hasSize(1);
+        assertThat(encodedPayload.getRecipientBoxes().get(0)).containsExactly(recipient);
+
+    }
+
 }