feature: Get the current minimum protocol version

zebra-network/src/peer/handshake.rs

@@ -199,12 +199,12 @@ where
             // For example, we could reject old peers with probability 0.5.
             //
             // At the network upgrade, we also need to disconnect from old peers.
-            // TODO: replace MIN_NETWORK_UPGRADE with
-            //       NetworkUpgrade::current(network, height) where network is
-            //       the configured network, and height is the best tip's block
+            // TODO: replace min_for_upgrade(network, MIN_NETWORK_UPGRADE) with
+            //       current_min(network, height) where network is the
+            //       configured network, and height is the best tip's block
             //       height.
 
-            if remote_version < Version::min_version(network, constants::MIN_NETWORK_UPGRADE) {
+            if remote_version < Version::min_for_upgrade(network, constants::MIN_NETWORK_UPGRADE) {
                 // Disconnect if peer is using an obsolete version.
                 return Err(HandshakeError::ObsoleteVersion(remote_version));
             }

zebra-network/src/protocol/external/types.rs

@@ -4,6 +4,7 @@ use crate::constants::magics;
 
 use std::fmt;
 
+use zebra_chain::types::BlockHeight;
 use zebra_chain::Network::{self, *};
 use zebra_consensus::parameters::NetworkUpgrade::{self, *};
 
@@ -38,7 +39,7 @@ pub struct Version(pub u32);
 impl Version {
     /// Returns the minimum network protocol version for `network` and
     /// `network_upgrade`.
-    pub fn min_version(network: Network, network_upgrade: NetworkUpgrade) -> Self {
+    pub fn min_for_upgrade(network: Network, network_upgrade: NetworkUpgrade) -> Self {
         // TODO: Should we reject earlier protocol versions during our initial
         //       sync? zcashd accepts 170_002 or later during its initial sync.
         Version(match (network, network_upgrade) {
@@ -54,6 +55,14 @@ impl Version {
             (Mainnet, Canopy) => 170_013,
         })
     }
+
+    /// Returns the current minimum protocol version for `network` and `height`.
+    ///
+    /// Returns None if the network has no branch id at this height.
+    pub fn current_min(network: Network, height: BlockHeight) -> Version {
+        let network_upgrade = NetworkUpgrade::current(network, height);
+        Version::min_for_upgrade(network, network_upgrade)
+    }
 }
 
 bitflags! {
@@ -120,3 +129,69 @@ mod proptest {
         }
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn version_extremes_mainnet() {
+        version_extremes(Mainnet)
+    }
+
+    #[test]
+    fn version_extremes_testnet() {
+        version_extremes(Testnet)
+    }
+
+    /// Test the min_for_upgrade and current_min functions for `network` with
+    /// extreme values.
+    fn version_extremes(network: Network) {
+        assert_eq!(
+            Version::current_min(network, BlockHeight(0)),
+            Version::min_for_upgrade(network, BeforeOverwinter),
+        );
+
+        // We assume that the last version we know about continues forever
+        // (even if we suspect that won't be true)
+        assert_ne!(
+            Version::current_min(network, BlockHeight::MAX),
+            Version::min_for_upgrade(network, BeforeOverwinter),
+        );
+    }
+
+    #[test]
+    fn version_consistent_mainnet() {
+        version_consistent(Mainnet)
+    }
+
+    #[test]
+    fn version_consistent_testnet() {
+        version_consistent(Testnet)
+    }
+
+    /// Check that the min_for_upgrade and current_min functions
+    /// are consistent for `network`.
+    fn version_consistent(network: Network) {
+        let highest_network_upgrade = NetworkUpgrade::current(network, BlockHeight::MAX);
+        assert!(highest_network_upgrade == Canopy || highest_network_upgrade == Heartwood,
+                "expected coverage of all network upgrades: add the new network upgrade to the list in this test");
+
+        for &network_upgrade in &[
+            BeforeOverwinter,
+            Overwinter,
+            Sapling,
+            Blossom,
+            Heartwood,
+            Canopy,
+        ] {
+            let height = network_upgrade.activation_height(network);
+            if let Some(height) = height {
+                assert_eq!(
+                    Version::min_for_upgrade(network, network_upgrade),
+                    Version::current_min(network, height)
+                );
+            }
+        }
+    }
+}