Struct ChannelServer 

pub struct ChannelServer<H> { /* private fields */ }

Implementation of russh::server::Handler which provides per-channel session handlers using a parametric ChannelHandler.

Primary motivation is to support custom console or TUI sessions over tailnet SSH connections.

Authentication and authorization

Incoming connections are gated by the control-pushed Tailscale SSH policy: auth_none resolves the source IP to a known tailnet peer and evaluates the policy via Device::authorize_ssh (fail-closed — an unknown peer, an absent policy, or a non-matching policy all reject). The ssh policy block’s accept/reject rules, principal matching, and SSH-user mapping are honored; advanced features (recording, holdAndDelegate, per-session capability enforcement) are not yet implemented.

Trait Implementations

impl<H> Handler for ChannelServer<H>

where H: ChannelHandler + Send, H::Error: Send,

type Error = Box<dyn Error + Sync + Send>

async fn auth_none(&mut self, user: &str) -> Result<Auth, Self::Error>

Check authentication using the “none” method.

async fn channel_open_session( &mut self, channel: Channel<Msg>, session: &mut Session, ) -> Result<bool, Self::Error>

Called when a new session channel is created. Return value indicates whether the channel request should be granted.

async fn channel_close( &mut self, channel: ChannelId, session: &mut Session, ) -> Result<(), Self::Error>

Called when the client closes a channel.

async fn signal( &mut self, channel: ChannelId, signal: Sig, session: &mut Session, ) -> Result<(), Self::Error>

The client is sending a signal (usually to pass to the currently running process).

async fn data( &mut self, channel: ChannelId, data: &[u8], session: &mut Session, ) -> Result<(), Self::Error>

Called when a data packet is received. A response can be written to the response argument.

async fn channel_eof( &mut self, channel: ChannelId, session: &mut Session, ) -> Result<(), Self::Error>

Called when the client sends EOF to a channel.

async fn window_change_request( &mut self, channel: ChannelId, col_width: u32, row_height: u32, _: u32, _: u32, session: &mut Session, ) -> Result<(), Self::Error>

The client’s pseudo-terminal window size has changed.

async fn pty_request( &mut self, channel: ChannelId, _: &str, col_width: u32, row_height: u32, _: u32, _: u32, _: &[(Pty, u32)], session: &mut Session, ) -> Result<(), Self::Error>

The client requests a pseudo-terminal with the given specifications.

fn auth_password( &mut self, user: &str, password: &str, ) -> impl Future<Output = Result<Auth, Self::Error>> + Send

Check authentication using the “password” method.

fn auth_publickey_offered( &mut self, user: &str, public_key: &PublicKey, ) -> impl Future<Output = Result<Auth, Self::Error>> + Send

Pre-authentication callback for public key authentication. This method is called when a client is:

fn auth_publickey( &mut self, user: &str, public_key: &PublicKey, ) -> impl Future<Output = Result<Auth, Self::Error>> + Send

Check authentication using the “publickey” method. This method is called after the signature has been verified and key ownership has been confirmed.

fn auth_openssh_certificate( &mut self, user: &str, certificate: &Certificate, ) -> impl Future<Output = Result<Auth, Self::Error>> + Send

Check authentication using an OpenSSH certificate. This method is called after the signature has been verified and key ownership has been confirmed.

fn auth_keyboard_interactive<'a>( &'a mut self, user: &str, submethods: &str, response: Option<Response<'a>>, ) -> impl Future<Output = Result<Auth, Self::Error>> + Send

Check authentication using the “keyboard-interactive” method.

fn auth_succeeded( &mut self, session: &mut Session, ) -> impl Future<Output = Result<(), Self::Error>> + Send

Called when authentication succeeds for a session.

fn authentication_banner( &mut self, ) -> impl Future<Output = Result<Option<String>, Self::Error>> + Send

Called when authentication starts but before it is successful. Return value is an authentication banner, usually a warning message shown to the client.

fn channel_open_x11( &mut self, channel: Channel<Msg>, originator_address: &str, originator_port: u32, session: &mut Session, ) -> impl Future<Output = Result<bool, Self::Error>> + Send

Called when a new X11 channel is created. Return value indicates whether the channel request should be granted.

fn channel_open_direct_tcpip( &mut self, channel: Channel<Msg>, host_to_connect: &str, port_to_connect: u32, originator_address: &str, originator_port: u32, session: &mut Session, ) -> impl Future<Output = Result<bool, Self::Error>> + Send

Called when a new direct TCP/IP (“local TCP forwarding”) channel is opened. Return value indicates whether the channel request should be granted.

fn channel_open_forwarded_tcpip( &mut self, channel: Channel<Msg>, host_to_connect: &str, port_to_connect: u32, originator_address: &str, originator_port: u32, session: &mut Session, ) -> impl Future<Output = Result<bool, Self::Error>> + Send

Called when a new remote forwarded TCP connection comes in.

fn channel_open_direct_streamlocal( &mut self, channel: Channel<Msg>, socket_path: &str, session: &mut Session, ) -> impl Future<Output = Result<bool, Self::Error>> + Send

Called when a new direct-streamlocal (“local UNIX socket forwarding”) channel is created. Return value indicates whether the channel request should be granted.

fn channel_open_confirmation( &mut self, id: ChannelId, max_packet_size: u32, window_size: u32, session: &mut Session, ) -> impl Future<Output = Result<(), Self::Error>> + Send

Called when the client confirmed our request to open a channel. A channel can only be written to after receiving this message (this library panics otherwise).

fn extended_data( &mut self, channel: ChannelId, code: u32, data: &[u8], session: &mut Session, ) -> impl Future<Output = Result<(), Self::Error>> + Send

Called when an extended data packet is received. Code 1 means that this packet comes from stderr, other codes are not defined (see RFC4254).

fn window_adjusted( &mut self, channel: ChannelId, new_size: u32, session: &mut Session, ) -> impl Future<Output = Result<(), Self::Error>> + Send

Called when the network window is adjusted, meaning that we can send more bytes.

fn adjust_window(&mut self, channel: ChannelId, current: u32) -> u32

Called when this server adjusts the network window. Return the next target window.

fn x11_request( &mut self, channel: ChannelId, single_connection: bool, x11_auth_protocol: &str, x11_auth_cookie: &str, x11_screen_number: u32, session: &mut Session, ) -> impl Future<Output = Result<(), Self::Error>> + Send

The client requests an X11 connection.

fn env_request( &mut self, channel: ChannelId, variable_name: &str, variable_value: &str, session: &mut Session, ) -> impl Future<Output = Result<(), Self::Error>> + Send

The client wants to set the given environment variable. Check these carefully, as it is dangerous to allow any variable environment to be set.

fn shell_request( &mut self, channel: ChannelId, session: &mut Session, ) -> impl Future<Output = Result<(), Self::Error>> + Send

The client requests a shell.

fn exec_request( &mut self, channel: ChannelId, data: &[u8], session: &mut Session, ) -> impl Future<Output = Result<(), Self::Error>> + Send

The client sends a command to execute, to be passed to a shell. Make sure to check the command before doing so.

fn subsystem_request( &mut self, channel: ChannelId, name: &str, session: &mut Session, ) -> impl Future<Output = Result<(), Self::Error>> + Send

The client asks to start the subsystem with the given name (such as sftp).

fn agent_request( &mut self, channel: ChannelId, session: &mut Session, ) -> impl Future<Output = Result<bool, Self::Error>> + Send

The client requests OpenSSH agent forwarding

fn tcpip_forward( &mut self, address: &str, port: &mut u32, session: &mut Session, ) -> impl Future<Output = Result<bool, Self::Error>> + Send

Used for reverse-forwarding ports, see RFC4254. If port is 0, you should set it to the allocated port number.

fn cancel_tcpip_forward( &mut self, address: &str, port: u32, session: &mut Session, ) -> impl Future<Output = Result<bool, Self::Error>> + Send

Used to stop the reverse-forwarding of a port, see RFC4254.

fn streamlocal_forward( &mut self, socket_path: &str, session: &mut Session, ) -> impl Future<Output = Result<bool, Self::Error>> + Send

fn cancel_streamlocal_forward( &mut self, socket_path: &str, session: &mut Session, ) -> impl Future<Output = Result<bool, Self::Error>> + Send

fn lookup_dh_gex_group( &mut self, gex_params: &GexParams, ) -> impl Future<Output = Result<Option<DhGroup>, Self::Error>> + Send

Override when enabling the diffie-hellman-group-exchange-* key exchange methods.

impl<H> TailnetServer for ChannelServer<H>

fn new_client(dev: Arc<Device>, addr: SocketAddr) -> Self

Construct a new handler.