Say which config client control could not find a profile in

Cargo.toml

@@ -10,7 +10,7 @@ default-members = [
 ]
 
 [workspace.package]
-version = "0.0.76"
+version = "0.0.77"
 edition = "2024"
 description = "SOCKS5/HTTP-proxy-over-QUIC split tunnel via iroh P2P"
 

crates/flextunnel-cli/src/tui/mod.rs

@@ -18,8 +18,8 @@
 mod form;
 mod view;
 
-use anyhow::{Context, Result};
-use std::path::PathBuf;
+use anyhow::{Context, Result, anyhow};
+use std::path::{Path, PathBuf};
 use std::time::{Duration, Instant};
 
 use flextunnel_core::config;
@@ -96,17 +96,16 @@ pub fn run(config_path: Option<PathBuf>, server_node_id: Option<String>) -> Resu
     let file = if server_node_id.is_some() && config_path.is_none() {
         None
     } else {
-        config::load_client_config(config_path.as_deref())
-            .context("client control needs a profile: -c <file>, the default config, or -n <server id>")?
+        config::load_client_config(config_path.as_deref())?
     };
     let cli = config::ClientConfig {
         server_node_id,
         ..Default::default()
     };
     let r = config::resolve_client(cli, file);
-    let server_id = r.server_node_id.context(
-        "The profile has no server node id (set server_node_id in the config or pass -n).",
-    )?;
+    let Some(server_id) = r.server_node_id else {
+        return Err(no_profile_error(config_path.as_deref()));
+    };
     let key = instance::instance_key(&server_id)?;
     let profile = r.name.unwrap_or_else(|| format!("server {key}…"));
 
@@ -127,6 +126,63 @@ pub fn run(config_path: Option<PathBuf>, server_node_id: Option<String>) -> Resu
     run_panel(app, &mut backend).context("Lost the connection to the client (did it stop?)")
 }
 
+/// The error for a `client control` that has nothing to identify a client by.
+/// The two cases read very differently and want different fixes: a config file
+/// that exists but carries no `server_node_id`, versus no config file at all —
+/// the usual shape under the systemd template (see `docs/systemd.md`), where
+/// every profile lives in its own `<instance>.toml` and there is no
+/// `client.toml` for a bare `client control` to find. In that case name the
+/// profiles that *are* there, so the fix is a copy-paste away.
+fn no_profile_error(config_path: Option<&Path>) -> anyhow::Error {
+    if let Some(path) = config_path {
+        return anyhow!(
+            "The client config {} has no server_node_id, so it does not say which client to \
+             attach to. Set server_node_id in it, or pass -n <server EndpointId>.",
+            path.display()
+        );
+    }
+    let Some(default_path) = config::default_client_config_path() else {
+        return anyhow!(
+            "Could not determine the default config directory. Pass -c <file> or \
+             -n <server EndpointId>."
+        );
+    };
+    if default_path.exists() {
+        return anyhow!(
+            "The default client config {} has no server_node_id, so it does not say which \
+             client to attach to. Set server_node_id in it, pass -c <file> for another \
+             profile, or pass -n <server EndpointId>.",
+            default_path.display()
+        );
+    }
+    let mut msg = format!(
+        "There is no client config at {}, so `client control` has no profile to attach to. \
+         Pass the profile's config with -c <file>, or attach by server id with \
+         -n <server EndpointId>.",
+        default_path.display()
+    );
+    if let Some(dir) = default_path.parent()
+        && let Some(found) = profile_configs(dir)
+    {
+        msg.push_str(&format!("\nProfiles in {}: {}", dir.display(), found.join(", ")));
+    }
+    anyhow!(msg)
+}
+
+/// Config files in the flextunnel config dir that could be a client profile,
+/// as bare file names, sorted. `None` when there are none (or the directory is
+/// unreadable) — the caller then says nothing rather than an empty list.
+fn profile_configs(dir: &Path) -> Option<Vec<String>> {
+    let mut names: Vec<String> = std::fs::read_dir(dir)
+        .ok()?
+        .flatten()
+        .map(|e| e.file_name().to_string_lossy().into_owned())
+        .filter(|n| n.ends_with(".toml") && n != "server.toml")
+        .collect();
+    names.sort();
+    (!names.is_empty()).then_some(names)
+}
+
 /// Run the self-contained control panel for `client start --quick`: the same UI
 /// as `client control`, but driving the session in this process over `tx`
 /// instead of a socket. Quitting (q/Esc/Ctrl-C) returns, dropping `tx` — which
@@ -407,3 +463,40 @@ impl App {
         Ok(())
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn profile_configs_lists_candidate_client_configs() {
+        let dir = tempfile::tempdir().unwrap();
+        for name in [
+            "macintel.toml",
+            "aws.toml",
+            "server.toml",
+            "forwards-abc.json",
+            "client.key",
+        ] {
+            std::fs::write(dir.path().join(name), "").unwrap();
+        }
+        assert_eq!(
+            profile_configs(dir.path()).unwrap(),
+            ["aws.toml", "macintel.toml"]
+        );
+    }
+
+    #[test]
+    fn no_profiles_reports_nothing_to_list() {
+        let dir = tempfile::tempdir().unwrap();
+        assert!(profile_configs(dir.path()).is_none());
+        assert!(profile_configs(&dir.path().join("missing")).is_none());
+    }
+
+    #[test]
+    fn a_named_config_without_a_server_id_names_that_file() {
+        let msg = no_profile_error(Some(Path::new("/tmp/aws.toml"))).to_string();
+        assert!(msg.contains("/tmp/aws.toml"), "{msg}");
+        assert!(msg.contains("server_node_id"), "{msg}");
+    }
+}

crates/flextunnel-core/src/config.rs

@@ -241,13 +241,20 @@ pub fn load_server_config(path: Option<&Path>, default_config: bool) -> Result<O
 pub fn load_client_config(path: Option<&Path>) -> Result<Option<ClientConfig>> {
     match path {
         Some(p) => Ok(Some(load_config(&expand_tilde(p))?)),
-        None => match default_config_path("client.toml") {
+        None => match default_client_config_path() {
             Some(p) if p.exists() => Ok(Some(load_config(&p)?)),
             _ => Ok(None),
         },
     }
 }
 
+/// Where [`load_client_config`] looks when no path is given:
+/// `~/.config/flextunnel/client.toml` (which need not exist). `None` only when
+/// the home directory is unknown. Callers use it to name the file in errors.
+pub fn default_client_config_path() -> Option<PathBuf> {
+    default_config_path("client.toml")
+}
+
 /// Merge CLI-provided values over file values over defaults for the server.
 ///
 /// `cli` carries the CLI flags as a `ServerConfig` (a field is `Some`/non-empty

docs/systemd.md

@@ -85,6 +85,12 @@ the server id — systemd isn't involved:
 flextunnel client control -c ~/.config/flextunnel/aws.toml
 ```
 
+The `-c` is not optional here: a bare `flextunnel client control` reads only
+`~/.config/flextunnel/client.toml`, which this layout deliberately does not
+have — each instance's profile is `<instance>.toml`. (Running it bare says so,
+and lists the profile files it found.) `-n <server EndpointId>` attaches
+without any config file.
+
 Detaching (`q`) never affects the tunnel. Port forwards edited there persist
 per server (`~/.config/flextunnel/forwards-<server id prefix>.json`) but
 always load **disabled**; enabling is a per-session action, so a unit restart