Optimise Multiaddr::append. (#549)

Append to the existing vector instead of allocating a temporary one and
copying bytes over.

misc/multiaddr/src/lib.rs

@@ -24,6 +24,7 @@ use serde::{
 };
 use std::{
     fmt,
+    io,
     iter::FromIterator,
     net::{SocketAddr, SocketAddrV4, SocketAddrV6, IpAddr, Ipv4Addr, Ipv6Addr},
     result::Result as StdResult,
@@ -180,9 +181,10 @@ impl Multiaddr {
     ///
     #[inline]
     pub fn append(&mut self, p: Protocol) {
-        let mut w = Vec::new();
-        p.write_bytes(&mut w).expect("writing to a Vec never fails");
-        self.bytes.extend_from_slice(&w);
+        let n = self.bytes.len();
+        let mut w = io::Cursor::new(&mut self.bytes);
+        w.set_position(n as u64);
+        p.write_bytes(&mut w).expect("writing to a Vec never fails")
     }
 
     /// Remove the outermost address.

misc/multiaddr/tests/lib.rs

@@ -283,3 +283,16 @@ fn ser_and_deser_bincode() {
     let deserialized: Multiaddr = bincode::deserialize(&serialized).unwrap();
     assert_eq!(addr, deserialized);
 }
+
+#[test]
+fn append() {
+    let mut a: Multiaddr = Protocol::Ip4(Ipv4Addr::new(1, 2, 3, 4)).into();
+    a.append(Protocol::Tcp(80));
+    a.append(Protocol::Http);
+
+    let mut i = a.iter();
+    assert_eq!(Some(Protocol::Ip4(Ipv4Addr::new(1, 2, 3, 4))), i.next());
+    assert_eq!(Some(Protocol::Tcp(80)), i.next());
+    assert_eq!(Some(Protocol::Http), i.next());
+    assert_eq!(None, i.next())
+}