send starting height to peers (#4904)

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

zebra-network/src/peer/handshake.rs

@@ -27,7 +27,6 @@ use tracing::{span, Level, Span};
 use tracing_futures::Instrument;
 
 use zebra_chain::{
-    block,
     chain_tip::{ChainTip, NoChainTip},
     parameters::Network,
     serialization::SerializationError,
@@ -580,9 +579,7 @@ where
         address_from: AddrInVersion::new(our_listen_addr, our_services),
         nonce: local_nonce,
         user_agent: user_agent.clone(),
-        // The protocol works fine if we don't reveal our current block height,
-        // and not sending it means we don't need to be connected to the chain state.
-        start_height: block::Height(0),
+        start_height: minimum_peer_version.chain_tip_height(),
         relay,
     };
 

zebra-network/src/peer/minimum_peer_version.rs

@@ -1,6 +1,6 @@
 //! Watches for chain tip height updates to determine the minimum supported peer protocol version.
 
-use zebra_chain::{chain_tip::ChainTip, parameters::Network};
+use zebra_chain::{block::Height, chain_tip::ChainTip, parameters::Network};
 
 use crate::protocol::external::types::Version;
 
@@ -66,6 +66,16 @@ where
             self.has_changed = true;
         }
     }
+
+    /// Return the current chain tip height.
+    ///
+    /// If it is not available return height zero.
+    pub fn chain_tip_height(&self) -> Height {
+        match self.chain_tip.best_tip_height() {
+            Some(height) => height,
+            None => Height(0),
+        }
+    }
 }
 
 /// A custom [`Clone`] implementation to ensure that the first call to