Use rand::thread_rng to impl Default for Nonce.

zebra-network/Cargo.toml

@@ -7,6 +7,7 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+rand = "0.7"
 byteorder = "1.3"
 chrono = "0.4"
 failure = "0.1"

zebra-network/src/types.rs

@@ -17,3 +17,10 @@ pub struct Services(pub u64);
 /// A nonce used in the networking layer to identify messages.
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub struct Nonce(pub u64);
+
+impl Default for Nonce {
+    fn default() -> Self {
+        use rand::{thread_rng, Rng};
+        Self(thread_rng().gen())
+    }
+}