Resolve SSH aliases for Dosh UDP host

src/bin/dosh-client.rs

@@ -98,17 +98,21 @@ async fn main() -> Result<()> {
     let (cols, rows) = size().unwrap_or((80, 24));
 
     let started = Instant::now();
-    let target_udp_host = args
-        .dosh_host
-        .clone()
-        .or_else(|| config.dosh_host.clone())
-        .unwrap_or_else(|| {
-            if args.local_auth {
+    let target_udp_host =
+        if let Some(host) = args.dosh_host.clone().or_else(|| config.dosh_host.clone()) {
+            host
+        } else if args.local_auth {
             "127.0.0.1".to_string()
         } else {
+            ssh_config_hostname(&server, ssh_port).unwrap_or_else(|err| {
+                log_debug(
+                    args.verbose,
+                    2,
+                    &format!("dosh could not resolve SSH config hostname, using {server}: {err:#}"),
+                );
                 ssh_destination_host(&server)
-            }
-        });
+            })
+        };
 
     let credential = if !args.no_cache {
         load_cache(&cache_path).ok()
@@ -378,6 +382,40 @@ fn ssh_destination_host(server: &str) -> String {
         .to_string()
 }
 
+fn ssh_config_hostname(server: &str, ssh_port: Option<u16>) -> Result<String> {
+    let mut command = Command::new("ssh");
+    command.arg("-G");
+    if let Some(ssh_port) = ssh_port {
+        command.arg("-p").arg(ssh_port.to_string());
+    }
+    let output = command
+        .arg(server)
+        .output()
+        .with_context(|| format!("run ssh -G {server}"))?;
+    if !output.status.success() {
+        return Err(anyhow!(
+            "ssh -G failed: {}",
+            String::from_utf8_lossy(&output.stderr)
+        ));
+    }
+    let raw = String::from_utf8(output.stdout)?;
+    parse_ssh_config_hostname(&raw).ok_or_else(|| anyhow!("ssh -G did not print hostname"))
+}
+
+fn parse_ssh_config_hostname(raw: &str) -> Option<String> {
+    raw.lines().find_map(|line| {
+        let line = line.trim();
+        let (key, value) = line.split_once(char::is_whitespace)?;
+        if key.eq_ignore_ascii_case("hostname") {
+            let value = value.trim();
+            if !value.is_empty() {
+                return Some(value.to_string());
+            }
+        }
+        None
+    })
+}
+
 fn resolve_addr(host: &str, port: u16) -> Result<SocketAddr> {
     (host, port)
         .to_socket_addrs()
@@ -407,6 +445,10 @@ async fn bootstrap_attach(
     let (n, _) = tokio::time::timeout(Duration::from_secs(5), socket.recv_from(&mut buf)).await??;
     let packet = protocol::decode(&buf[..n])?;
     if packet.header.kind != PacketKind::AttachOk {
+        if packet.header.kind == PacketKind::AttachReject {
+            let reject: AttachReject = protocol::from_body(&packet.body)?;
+            return Err(anyhow!("attach rejected: {}", reject.reason));
+        }
         return Err(anyhow!("attach rejected or unexpected response"));
     }
     let plain = protocol::decrypt_body(&packet, &bootstrap.session_key, SERVER_TO_CLIENT)?;
@@ -471,6 +513,10 @@ async fn try_ticket_attach(
         tokio::time::timeout(Duration::from_millis(700), socket.recv_from(&mut buf)).await??;
     let packet = protocol::decode(&buf[..n])?;
     if packet.header.kind != PacketKind::AttachOk {
+        if packet.header.kind == PacketKind::AttachReject {
+            let reject: AttachReject = protocol::from_body(&packet.body)?;
+            return Err(anyhow!("ticket attach rejected: {}", reject.reason));
+        }
         return Err(anyhow!("ticket attach rejected"));
     }
     let envelope: TicketAttachOkEnvelope = protocol::from_body(&packet.body)?;
@@ -533,6 +579,10 @@ async fn try_resume(
         tokio::time::timeout(Duration::from_millis(700), socket.recv_from(&mut buf)).await??;
     let packet = protocol::decode(&buf[..n])?;
     if packet.header.kind != PacketKind::ResumeOk {
+        if packet.header.kind == PacketKind::AttachReject {
+            let reject: AttachReject = protocol::from_body(&packet.body)?;
+            return Err(anyhow!("resume rejected: {}", reject.reason));
+        }
         return Err(anyhow!("resume rejected"));
     }
     let plain = protocol::decrypt_body(&packet, &cached.session_key, SERVER_TO_CLIENT)?;
@@ -866,7 +916,7 @@ const TERMINAL_CLEANUP: &[u8] = concat!(
 
 #[cfg(test)]
 mod tests {
-    use super::InputNormalizer;
+    use super::{InputNormalizer, parse_ssh_config_hostname, ssh_destination_host};
 
     #[test]
     fn normalizes_ss3_cursor_keys_to_csi() {
@@ -890,4 +940,27 @@ mod tests {
         let mut normalizer = InputNormalizer::default();
         assert_eq!(normalizer.normalize(b"\x1bOP"), b"\x1bOP");
     }
+
+    #[test]
+    fn parses_ssh_config_hostname() {
+        let raw = "user palav\nhostname palav.dev\nport 22\n";
+        assert_eq!(
+            parse_ssh_config_hostname(raw),
+            Some("palav.dev".to_string())
+        );
+    }
+
+    #[test]
+    fn parses_ssh_config_hostname_case_insensitively() {
+        let raw = "HostName 192.0.2.10\n";
+        assert_eq!(
+            parse_ssh_config_hostname(raw),
+            Some("192.0.2.10".to_string())
+        );
+    }
+
+    #[test]
+    fn strips_user_from_fallback_udp_host() {
+        assert_eq!(ssh_destination_host("palav@example.com"), "example.com");
+    }
 }