Remove heap allocations from SshId (#656)

Co-authored-by: Eugene <inbox@null.page>

Author: kpcyrd

russh/src/client/mod.rs

@@ -34,6 +34,7 @@
 //!
 //! [Session]: client::Session
 
+use std::borrow::Cow;
 use std::collections::{HashMap, VecDeque};
 use std::convert::TryInto;
 use std::num::Wrapping;
@@ -1701,11 +1702,12 @@ pub struct Config {
 impl Default for Config {
     fn default() -> Config {
         Config {
-            client_id: SshId::Standard(format!(
-                "SSH-2.0-{}_{}",
+            client_id: SshId::Standard(Cow::Borrowed(concat!(
+                "SSH-2.0-",
                 env!("CARGO_PKG_NAME"),
+                "_",
                 env!("CARGO_PKG_VERSION")
-            )),
+            ))),
             limits: Limits::default(),
             window_size: 2097152,
             maximum_packet_size: 32768,

russh/src/client/test.rs

@@ -87,7 +87,7 @@ mod tests {
         // Configure the server
         let mut config = server::Config::default();
         config.auth_rejection_time = std::time::Duration::from_secs(1);
-        config.server_id = SshId::Standard("SSH-1.99-CustomServer_1.0".to_string());
+        config.server_id = SshId::Standard("SSH-1.99-CustomServer_1.0".into());
         config.inactivity_timeout = None;
         config
             .keys

russh/src/server/mod.rs

@@ -102,11 +102,12 @@ pub struct Config {
 impl Default for Config {
     fn default() -> Config {
         Config {
-            server_id: SshId::Standard(format!(
-                "SSH-2.0-{}_{}",
+            server_id: SshId::Standard(Cow::Borrowed(concat!(
+                "SSH-2.0-",
                 env!("CARGO_PKG_NAME"),
+                "_",
                 env!("CARGO_PKG_VERSION")
-            )),
+            ))),
             methods: auth::MethodSet::all(),
             auth_rejection_time: std::time::Duration::from_secs(1),
             auth_rejection_time_initial: None,

russh/src/sshbuffer.rs

@@ -14,6 +14,7 @@
 //
 
 use core::fmt;
+use std::borrow::Cow;
 use std::num::Wrapping;
 
 use cipher::SealingKey;
@@ -26,9 +27,9 @@ use super::*;
 #[derive(Debug)]
 pub enum SshId {
     /// When sending the id, append RFC standard `\r\n`. Example: `SshId::Standard("SSH-2.0-acme")`
-    Standard(String),
+    Standard(Cow<'static, str>),
     /// When sending the id, use this buffer as it is and do not append additional line terminators.
-    Raw(String),
+    Raw(Cow<'static, str>),
 }
 
 impl SshId {
@@ -52,19 +53,19 @@ impl SshId {
 #[test]
 fn test_ssh_id() {
     let mut buffer = Vec::new();
-    SshId::Standard("SSH-2.0-acme".to_string()).write(&mut buffer);
+    SshId::Standard("SSH-2.0-acme".into()).write(&mut buffer);
     assert_eq!(&buffer[..], b"SSH-2.0-acme\r\n");
 
     let mut buffer = Vec::new();
-    SshId::Raw("SSH-2.0-raw\n".to_string()).write(&mut buffer);
+    SshId::Raw("SSH-2.0-raw\n".into()).write(&mut buffer);
     assert_eq!(&buffer[..], b"SSH-2.0-raw\n");
 
     assert_eq!(
-        SshId::Standard("SSH-2.0-acme".to_string()).as_kex_hash_bytes(),
+        SshId::Standard("SSH-2.0-acme".into()).as_kex_hash_bytes(),
         b"SSH-2.0-acme"
     );
     assert_eq!(
-        SshId::Raw("SSH-2.0-raw\n".to_string()).as_kex_hash_bytes(),
+        SshId::Raw("SSH-2.0-raw\n".into()).as_kex_hash_bytes(),
         b"SSH-2.0-raw"
     );
 }