config: add ssh_backend config, and default to libssh

refs: #1014

config/src/lib.rs

@@ -898,6 +898,9 @@ pub struct Config {
     #[serde(default)]
     pub ssh_domains: Vec<SshDomain>,
 
+    #[serde(default)]
+    pub ssh_backend: SshBackend,
+
     /// When running in server mode, defines configuration for
     /// each of the endpoints that we'll listen for connections
     #[serde(default)]

config/src/ssh.rs

@@ -2,6 +2,19 @@ use crate::*;
 use std::fmt::Display;
 use std::str::FromStr;
 
+#[derive(Debug, Clone, Copy, Deserialize, Serialize)]
+pub enum SshBackend {
+    Ssh2,
+    LibSsh,
+}
+impl_lua_conversion!(SshBackend);
+
+impl Default for SshBackend {
+    fn default() -> Self {
+        Self::LibSsh
+    }
+}
+
 #[derive(Default, Debug, Clone, Deserialize, Serialize)]
 pub struct SshDomain {
     /// The name of this specific domain.  Must be unique amongst
@@ -27,6 +40,8 @@ pub struct SshDomain {
 
     /// The path to the wezterm binary on the remote host
     pub remote_wezterm_path: Option<String>,
+
+    pub ssh_backend: Option<SshBackend>,
 }
 impl_lua_conversion!(SshDomain);
 

docs/changelog.md

@@ -26,6 +26,7 @@ As features stabilize some brief notes about them will accumulate here.
 * [wezterm.background_child_process](config/lua/wezterm/background_child_process.md) function to spawn a process without waiting.
 * [mux_env_remove](config/lua/config/mux_env_remove.md) setting to control which environment variables should be cleared prior to spawning processes in the multiplexer server [#1225](https://github.com/wez/wezterm/issues/1225)
 * [canonicalize_pasted_newlines](config/lua/config/canonicalize_pasted_newlines.md) option to help Windows users manage newlines in pastes [#1213](https://github.com/wez/wezterm/issues/1213)
+* SSH client now uses `libssh` by default. [ssh_backend](config/lua/config/ssh_backend.md) can be used to change this.
 
 #### Changed
 

docs/config/lua/config/ssh_backend.md

@@ -0,0 +1,18 @@
+# ssh_backend = "libssh"
+
+*Since: nightly builds only*
+
+Sets which ssh backend should be used by default for the integrated ssh client.
+
+Possible values are:
+
+* `"Ssh2"` - use libssh2
+* `"LibSsh"` - use libssh
+
+Despite the naming, `libssh2` is not a newer version of `libssh`, they are
+completely separate ssh implementations.
+
+In prior releases, `"Ssh2"` was the only option.  `"LibSsh"` is the default
+as it has broader support for newer keys and cryptography, and has clearer
+feedback about authentication events that require entering a passphrase.
+

wezterm-client/src/client.rs

@@ -5,7 +5,7 @@ use anyhow::{anyhow, bail, Context};
 use async_ossl::AsyncSslStream;
 use async_trait::async_trait;
 use codec::*;
-use config::{configuration, SshDomain, TlsDomainClient, UnixDomain};
+use config::{configuration, SshBackend, SshDomain, TlsDomainClient, UnixDomain};
 use filedescriptor::FileDescriptor;
 use futures::FutureExt;
 use mux::connui::ConnectionUI;
@@ -446,6 +446,18 @@ impl Reconnectable {
         };
 
         let mut ssh_config = ssh_config.for_host(&remote_host_name);
+        ssh_config.insert(
+            "wezterm_ssh_backend".to_string(),
+            match ssh_dom
+                .ssh_backend
+                .unwrap_or_else(|| configuration().ssh_backend)
+            {
+                SshBackend::Ssh2 => "ssh2",
+                SshBackend::LibSsh => "libssh",
+            }
+            .to_string(),
+        );
+
         if let Some(username) = &ssh_dom.username {
             ssh_config.insert("user".to_string(), username.to_string());
         }

wezterm-gui/src/main.rs

@@ -4,6 +4,7 @@
 use crate::frontend::front_end;
 use ::window::*;
 use anyhow::anyhow;
+use config::SshBackend;
 use mux::activity::Activity;
 use mux::domain::{Domain, LocalDomain};
 use mux::Mux;
@@ -94,6 +95,8 @@ enum SubCommand {
 }
 
 async fn async_run_ssh(opts: SshCommand) -> anyhow::Result<()> {
+    let config = config::configuration();
+
     let mut ssh_config = Config::new();
     ssh_config.add_default_config_files();
 
@@ -104,6 +107,15 @@ async fn async_run_ssh(opts: SshCommand) -> anyhow::Result<()> {
     let port = fields.next();
 
     let mut ssh_config = ssh_config.for_host(host);
+    ssh_config.insert(
+        "wezterm_ssh_backend".to_string(),
+        match config.ssh_backend {
+            SshBackend::Ssh2 => "ssh2",
+            SshBackend::LibSsh => "libssh",
+        }
+        .to_string(),
+    );
+
     if let Some(username) = &opts.user_at_host_and_port.username {
         ssh_config.insert("user".to_string(), username.to_string());
     }
@@ -123,7 +135,6 @@ async fn async_run_ssh(opts: SshCommand) -> anyhow::Result<()> {
         None
     };
 
-    let config = config::configuration();
     let domain: Arc<dyn Domain> = Arc::new(mux::ssh::RemoteSshDomain::with_ssh_config(
         &opts.user_at_host_and_port.to_string(),
         ssh_config,