Add new XDR structs & fields for pull mode

Stellar-overlay.x

@@ -47,11 +47,20 @@ struct Hello
     uint256 nonce;
 };
 
+
+// During the roll-out phrase, pull mode will be optional.
+// Therefore, we need a way to communicate with other nodes
+// that we want/don't want pull mode.
+// However, the goal is for everyone to enable it by default,
+// so we don't want to introduce a new member variable.
+// For now, we'll use the `flags` field (originally named
+// `unused`) in `Auth`.
+// 100 is just a number that is not 0.
+const AUTH_MSG_FLAG_PULL_MODE_REQUESTED = 100;
+
 struct Auth
 {
-    // Empty message, just to confirm
-    // establishment of MAC keys.
-    int unused;
+    int flags;
 };
 
 enum IPAddrType
@@ -102,7 +111,9 @@ enum MessageType
     SURVEY_REQUEST = 14,
     SURVEY_RESPONSE = 15,
 
-    SEND_MORE = 16
+    SEND_MORE = 16,
+    FLOOD_ADVERT = 18,
+    FLOOD_DEMAND = 19
 };
 
 struct DontHave
@@ -185,6 +196,22 @@ case SURVEY_TOPOLOGY:
     TopologyResponseBody topologyResponseBody;
 };
 
+const TX_ADVERT_VECTOR_MAX_SIZE = 1000;
+typedef Hash TxAdvertVector<TX_ADVERT_VECTOR_MAX_SIZE>;
+
+struct FloodAdvert
+{
+    TxAdvertVector txHashes;
+};
+
+const TX_DEMAND_VECTOR_MAX_SIZE = 1000;
+typedef Hash TxDemandVector<TX_DEMAND_VECTOR_MAX_SIZE>;
+
+struct FloodDemand
+{
+    TxDemandVector txHashes;
+};
+
 union StellarMessage switch (MessageType type)
 {
 case ERROR_MSG:
@@ -227,6 +254,12 @@ case GET_SCP_STATE:
     uint32 getSCPLedgerSeq; // ledger seq requested ; if 0, requests the latest
 case SEND_MORE:
     SendMore sendMoreMessage;
+
+// Pull mode
+case FLOOD_ADVERT:
+     FloodAdvert floodAdvert;
+case FLOOD_DEMAND:
+     FloodDemand floodDemand;
 };
 
 union AuthenticatedMessage switch (uint32 v)