tor-guardmgr: Add an error variant for when the vanguard mode is unsuitable.

2 files changed, 25 insertions, 8 deletions

diff --git a/crates/tor-guardmgr/src/vanguards.rs b/crates/tor-guardmgr/src/vanguards.rs
index e4c1b7445..ad1cd3c15 100644
--- a/crates/tor-guardmgr/src/vanguards.rs
+++ b/crates/tor-guardmgr/src/vanguards.rs
@@ -291,13 +291,11 @@ impl<R: Runtime> VanguardMgr<R> {
                         .l3()
                         .pick_relay(rng, netdir, neighbor_exclusion)
                 }
-                // TODO HS-VANGUARDS: perhaps we need a dedicated error variant for this
                 _ => {
-                    return Err(internal!(
-                        "vanguards for layer {layer} are not supported in mode {})",
-                        inner.mode
-                    )
-                    .into());
+                    return Err(VanguardMgrError::LayerNotSupported {
+                        layer,
+                        mode: inner.mode,
+                    });
                 }
             };
 
@@ -750,7 +748,16 @@ mod test {
             let err = vanguardmgr
                 .select_vanguard(&mut rng, &netdir, Layer3, &exclusion)
                 .unwrap_err();
-            assert!(matches!(err, VanguardMgrError::Bug(_)), "{err:?}");
+            assert!(
+                matches!(
+                    err,
+                    VanguardMgrError::LayerNotSupported {
+                        layer: Layer::Layer3,
+                        mode: VanguardMode::Lite
+                    }
+                ),
+                "{err}"
+            );
         });
     }
 
diff --git a/crates/tor-guardmgr/src/vanguards/err.rs b/crates/tor-guardmgr/src/vanguards/err.rs
index b89b1311d..6563d479f 100644
--- a/crates/tor-guardmgr/src/vanguards/err.rs
+++ b/crates/tor-guardmgr/src/vanguards/err.rs
@@ -5,7 +5,7 @@ use std::sync::Arc;
 use futures::task::SpawnError;
 use tor_error::{ErrorKind, HasKind};
 
-use crate::vanguards::Layer;
+use crate::vanguards::{Layer, VanguardMode};
 
 /// An error coming from the vanguards subsystem.
 #[derive(Clone, Debug, thiserror::Error)]
@@ -19,6 +19,15 @@ pub enum VanguardMgrError {
         action: &'static str,
     },
 
+    /// Attempted to select a vanguard layer that is not supported in the current [`VanguardMode`],
+    #[error("{layer} vanguards are not supported in {mode} mode")]
+    LayerNotSupported {
+        /// The layer we tried to select a vanguard for.
+        layer: Layer,
+        /// The [`VanguardMode`] we are in.
+        mode: VanguardMode,
+    },
+
     /// Could not find a suitable relay to use for the specifier layer.
     #[error("No suitable relays")]
     NoSuitableRelay(Layer),
@@ -44,6 +53,7 @@ impl HasKind for VanguardMgrError {
     fn kind(&self) -> ErrorKind {
         match self {
             VanguardMgrError::BootstrapRequired { .. } => ErrorKind::BootstrapRequired,
+            VanguardMgrError::LayerNotSupported { .. } => ErrorKind::BadApiUsage,
             // TODO HS-VANGUARDS: this is not right
             VanguardMgrError::NoSuitableRelay(_) => ErrorKind::Other,
             VanguardMgrError::NetDir(e) => e.kind(),