Merge rust-bitcoin#4639: feat(p2p): create NetworkExt trait for default P2P port and Magic values

eba1204 feat(p2p): create `NetworkExt` trait for default P2P port and network `Magic` values (Luis Schwab)

Pull request description:

  Closes rust-bitcoin#4632.
  ~~Depends on rust-bitcoin#4640.~~
  
  This PR introduces the `NetworkExt` trait that extends `Network` with getters for default P2P port and network `Magic` bytes.
  
  ## Changelog
  - Create `NetworkExt` trait.
  - Implement `default_p2p_port` for `Network`.
  - Implement `default_network_magic` for `Network`.


ACKs for top commit:
  tcharding:
    ACK eba1204
  apoelstra:
    ACK eba1204; successfully ran local tests


Tree-SHA512: 83e05981b54e04f047ae6778755ba9f872634be18aedc179c86134f8ecae53d76a16c0a0caa7824f475ef83b0446acd94c3d2f2941fb5403191feb6773a30fb3

Author: apoelstra

p2p/src/lib.rs

@@ -23,6 +23,7 @@ pub mod message_bloom;
 pub mod message_compact_blocks;
 pub mod message_filter;
 pub mod message_network;
+mod network_ext;
 
 extern crate alloc;
 
@@ -38,7 +39,7 @@ use io::{BufRead, Write};
 
 #[rustfmt::skip]
 #[doc(inline)]
-pub use self::address::Address;
+pub use self::{address::Address, network_ext::NetworkExt};
 
 /// Version of the protocol as appearing in network message headers.
 ///

p2p/src/network_ext.rs

@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: CC0-1.0
+
+//! This module implements an extension trait for [`Network`]
+//! with getter methods for the default P2P port and default
+//! network [`Magic`] bytes.
+
+use bitcoin::{Network, TestnetVersion};
+
+use crate::Magic;
+
+/// Trait that extends [`Network`] by adding getter methods for the default P2P ports and [`Magic`] bytes.
+pub trait NetworkExt {
+    /// The default P2P port for a given [`Network`].
+    fn default_p2p_port(self) -> u16;
+
+    /// The default network [`Magic`] for a given [`Network`].
+    fn default_network_magic(self) -> Magic;
+}
+
+impl NetworkExt for Network {
+    /// The default P2P port for a given [`Network`].
+    ///
+    /// Note: All [`TestnetVersion`] variants >4 are treated as [`TestnetVersion::V4`].
+    /// This function will be updated as new test networks are defined.
+    fn default_p2p_port(self) -> u16 {
+        match &self {
+            Network::Bitcoin => 8333,
+            Network::Signet => 38333,
+            Network::Testnet(TestnetVersion::V3) => 18333,
+            Network::Testnet(TestnetVersion::V4) => 48333,
+            Network::Testnet(_) => 48333,
+            Network::Regtest => 18444,
+        }
+    }
+
+    /// The default network [`Magic`] for a given [`Network`].
+    ///
+    /// Note: All [`TestnetVersion`] variants >4 are treated as [`TestnetVersion::V4`].
+    /// This function will be updated as new test networks are defined.
+    fn default_network_magic(self) -> Magic {
+        match &self {
+            Network::Bitcoin => Magic::BITCOIN,
+            Network::Signet => Magic::SIGNET,
+            Network::Testnet(TestnetVersion::V3) => Magic::TESTNET3,
+            Network::Testnet(TestnetVersion::V4) => Magic::TESTNET4,
+            Network::Testnet(_) => Magic::TESTNET4,
+            Network::Regtest => Magic::REGTEST,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn default_p2p_port() {
+        let networks = [
+            Network::Bitcoin,
+            Network::Signet,
+            Network::Testnet(TestnetVersion::V3),
+            Network::Testnet(TestnetVersion::V4),
+            Network::Regtest,
+        ];
+
+        let p2p_ports = vec![8333, 38333, 18333, 48333, 18444];
+
+        for (network, p2p_port) in networks.iter().zip(p2p_ports) {
+            assert_eq!(network.default_p2p_port(), p2p_port);
+        }
+    }
+
+    #[test]
+    fn default_network_magic() {
+        let networks = [
+            Network::Bitcoin,
+            Network::Signet,
+            Network::Testnet(TestnetVersion::V3),
+            Network::Testnet(TestnetVersion::V4),
+            Network::Regtest,
+        ];
+
+        let network_magics =
+            vec![Magic::BITCOIN, Magic::SIGNET, Magic::TESTNET3, Magic::TESTNET4, Magic::REGTEST];
+
+        for (network, network_magic) in networks.iter().zip(network_magics) {
+            assert_eq!(network.default_network_magic(), network_magic);
+        }
+    }
+}