protocols/kad: Support multiple protocol names (#2846)

Add support for multiple Kademlia protocol names to allow
protocol name upgrades.

protocols/kad/CHANGELOG.md

@@ -1,7 +1,13 @@
 # 0.40.0 [unreleased]
 
+- Add support for multiple protocol names. Update `Kademlia`, `KademliaConfig`,
+  and `KademliaProtocolConfig` accordingly. See [Issue 2837]. See [PR 2846].
+
 - Update to `libp2p-swarm` `v0.39.0`.
 
+[Issue 2837]: https://github.com/libp2p/rust-libp2p/issues/2837
+[PR 2846]: https://github.com/libp2p/rust-libp2p/pull/2846
+
 # 0.39.0
 
 - Update prost requirement from 0.10 to 0.11 which no longer installs the protoc Protobuf compiler.

protocols/kad/src/behaviour.rs

@@ -214,14 +214,28 @@ impl Default for KademliaConfig {
 }
 
 impl KademliaConfig {
+    /// Sets custom protocol names.
+    ///
+    /// Kademlia nodes only communicate with other nodes using the same protocol
+    /// name. Using custom name(s) therefore allows to segregate the DHT from
+    /// others, if that is desired.
+    ///
+    /// More than one protocol name can be supplied. In this case the node will
+    /// be able to talk to other nodes supporting any of the provided names.
+    /// Multiple names must be used with caution to avoid network partitioning.
+    pub fn set_protocol_names(&mut self, names: Vec<Cow<'static, [u8]>>) -> &mut Self {
+        self.protocol_config.set_protocol_names(names);
+        self
+    }
+
     /// Sets a custom protocol name.
     ///
     /// Kademlia nodes only communicate with other nodes using the same protocol
     /// name. Using a custom name therefore allows to segregate the DHT from
     /// others, if that is desired.
+    #[deprecated(since = "0.40.0", note = "use `set_protocol_names()` instead")]
     pub fn set_protocol_name(&mut self, name: impl Into<Cow<'static, [u8]>>) -> &mut Self {
-        self.protocol_config.set_protocol_name(name);
-        self
+        self.set_protocol_names(std::iter::once(name.into()).collect())
     }
 
     /// Sets the timeout for a single query.
@@ -403,8 +417,8 @@ where
     }
 
     /// Get the protocol name of this kademlia instance.
-    pub fn protocol_name(&self) -> &[u8] {
-        self.protocol_config.protocol_name()
+    pub fn protocol_names(&self) -> &[Cow<'static, [u8]>] {
+        self.protocol_config.protocol_names()
     }
 
     /// Creates a new `Kademlia` network behaviour with the given configuration.

protocols/kad/src/protocol.rs

@@ -142,21 +142,28 @@ impl From<KadPeer> for proto::message::Peer {
 //       `OutboundUpgrade` to be just a single message
 #[derive(Debug, Clone)]
 pub struct KademliaProtocolConfig {
-    protocol_name: Cow<'static, [u8]>,
+    protocol_names: Vec<Cow<'static, [u8]>>,
     /// Maximum allowed size of a packet.
     max_packet_size: usize,
 }
 
 impl KademliaProtocolConfig {
     /// Returns the configured protocol name.
-    pub fn protocol_name(&self) -> &[u8] {
-        &self.protocol_name
+    pub fn protocol_names(&self) -> &[Cow<'static, [u8]>] {
+        &self.protocol_names
     }
 
-    /// Modifies the protocol name used on the wire. Can be used to create incompatibilities
+    /// Modifies the protocol names used on the wire. Can be used to create incompatibilities
     /// between networks on purpose.
+    pub fn set_protocol_names(&mut self, names: Vec<Cow<'static, [u8]>>) {
+        self.protocol_names = names;
+    }
+
+    /// Sets single protocol name used on the wire. Can be used to create incompatibilities
+    /// between networks on purpose.
+    #[deprecated(since = "0.40.0", note = "use `set_protocol_names()` instead")]
     pub fn set_protocol_name(&mut self, name: impl Into<Cow<'static, [u8]>>) {
-        self.protocol_name = name.into();
+        self.set_protocol_names(std::iter::once(name.into()).collect());
     }
 
     /// Modifies the maximum allowed size of a single Kademlia packet.
@@ -168,18 +175,18 @@ impl KademliaProtocolConfig {
 impl Default for KademliaProtocolConfig {
     fn default() -> Self {
         KademliaProtocolConfig {
-            protocol_name: Cow::Borrowed(DEFAULT_PROTO_NAME),
+            protocol_names: iter::once(Cow::Borrowed(DEFAULT_PROTO_NAME)).collect(),
             max_packet_size: DEFAULT_MAX_PACKET_SIZE,
         }
     }
 }
 
 impl UpgradeInfo for KademliaProtocolConfig {
     type Info = Cow<'static, [u8]>;
-    type InfoIter = iter::Once<Self::Info>;
+    type InfoIter = std::vec::IntoIter<Self::Info>;
 
     fn protocol_info(&self) -> Self::InfoIter {
-        iter::once(self.protocol_name.clone())
+        self.protocol_names.clone().into_iter()
     }
 }