feat(PoC): terrors crate usage

server/Cargo.lock

@@ -761,6 +761,13 @@ dependencies = [
  "zeroize",
 ]
 
+[[package]]
+name = "arbiter-terrors-poc"
+version = "0.1.0"
+dependencies = [
+ "terrors",
+]
+
 [[package]]
 name = "arbiter-tokens-registry"
 version = "0.1.0"
@@ -4856,6 +4863,12 @@ dependencies = [
  "windows-sys 0.60.2",
 ]
 
+[[package]]
+name = "terrors"
+version = "0.3.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "987fd8c678ca950df2a18b2c6e9da6ca511d449278fab3565efe0d49c0c07a5d"
+
 [[package]]
 name = "test-log"
 version = "0.2.19"

server/crates/arbiter-terrors-poc/src/auth.rs

@@ -1,5 +1,35 @@
+use crate::errors::{InternalError1, InternalError2, InvalidSignature, NotRegistered};
 use terrors::OneOf;
-use crate::errors::{Internal, InvalidSignature, NotRegistered};
+
+use crate::errors::ProtoError;
+
+// Each sub-call's error type already implements DrainInto<ProtoError>, so we convert
+// directly to ProtoError without broaden — no turbofish needed anywhere.
+//
+// Call chain:
+//   load_config()  → OneOf<(InternalError2,)>          → ProtoError::from
+//   get_nonce()    → OneOf<(InternalError1, InternalError2)> → ProtoError::from
+//   verify_sig()   → OneOf<(InvalidSignature,)>         → ProtoError::from
+pub fn process_request(id: u32, sig: &str) -> Result<String, ProtoError> {
+    if id == 0 {
+        return Err(ProtoError::NotRegistered);
+    }
+
+    let config = load_config(id).map_err(ProtoError::from)?;
+    let nonce = crate::db::get_nonce(id).map_err(ProtoError::from)?;
+    verify_signature(nonce, sig).map_err(ProtoError::from)?;
+
+    Ok(format!("config={config} nonce={nonce} sig={sig}"))
+}
+
+// Simulates loading a config value.
+// id=97 triggers InternalError2 ("config read failed").
+fn load_config(id: u32) -> Result<String, OneOf<(InternalError2,)>> {
+    if id == 97 {
+        return Err(OneOf::new(InternalError2("config read failed".to_owned())));
+    }
+    Ok(format!("cfg-{id}"))
+}
 
 pub fn verify_signature(_nonce: u32, sig: &str) -> Result<(), OneOf<(InvalidSignature,)>> {
     if sig != "ok" {
@@ -8,18 +38,21 @@ pub fn verify_signature(_nonce: u32, sig: &str) -> Result<(), OneOf<(InvalidSign
     Ok(())
 }
 
-pub fn authenticate(
-    id: u32,
-    sig: &str,
-) -> Result<u32, OneOf<(NotRegistered, InvalidSignature, Internal)>> {
+type AuthError = OneOf<(
+    NotRegistered,
+    InvalidSignature,
+    InternalError1,
+    InternalError2,
+)>;
+
+pub fn authenticate(id: u32, sig: &str) -> Result<u32, AuthError> {
     if id == 0 {
         return Err(OneOf::new(NotRegistered));
     }
 
-    let nonce = crate::db::get_nonce(id)
-        .map_err(|e| e.broaden::<(NotRegistered, InvalidSignature, Internal), _>())?;
-    verify_signature(nonce, sig)
-        .map_err(|e| e.broaden::<(NotRegistered, InvalidSignature, Internal), _>())?;
+    // Return type AuthError lets the compiler infer the broaden target.
+    let nonce = crate::db::get_nonce(id).map_err(OneOf::broaden)?;
+    verify_signature(nonce, sig).map_err(OneOf::broaden)?;
 
     Ok(nonce)
 }
@@ -57,8 +90,50 @@ mod tests {
     }
 
     #[test]
-    fn authenticate_internal_error() {
+    fn authenticate_internal_error1() {
         let err = authenticate(99, "ok").unwrap_err();
-        assert!(err.narrow::<crate::errors::Internal, _>().is_ok());
+        assert!(err.narrow::<crate::errors::InternalError1, _>().is_ok());
+    }
+
+    #[test]
+    fn authenticate_internal_error2() {
+        let err = authenticate(98, "ok").unwrap_err();
+        assert!(err.narrow::<crate::errors::InternalError2, _>().is_ok());
+    }
+
+    #[test]
+    fn process_request_success() {
+        let result = process_request(1, "ok").unwrap();
+        assert!(result.contains("nonce=42"));
+    }
+
+    #[test]
+    fn process_request_not_registered() {
+        let err = process_request(0, "ok").unwrap_err();
+        assert!(matches!(err, crate::errors::ProtoError::NotRegistered));
+    }
+
+    #[test]
+    fn process_request_invalid_signature() {
+        let err = process_request(1, "bad").unwrap_err();
+        assert!(matches!(err, crate::errors::ProtoError::InvalidSignature));
+    }
+
+    #[test]
+    fn process_request_internal_from_config() {
+        // id=97 → load_config returns InternalError2
+        let err = process_request(97, "ok").unwrap_err();
+        assert!(
+            matches!(err, crate::errors::ProtoError::Internal(ref msg) if msg == "config read failed")
+        );
+    }
+
+    #[test]
+    fn process_request_internal_from_db() {
+        // id=99 → get_nonce returns InternalError1
+        let err = process_request(99, "ok").unwrap_err();
+        assert!(
+            matches!(err, crate::errors::ProtoError::Internal(ref msg) if msg == "db pool unavailable")
+        );
     }
 }

server/crates/arbiter-terrors-poc/src/db.rs

@@ -1,13 +1,15 @@
+use crate::errors::{InternalError1, InternalError2};
 use terrors::OneOf;
-use crate::errors::Internal;
 
 // Simulates fetching a nonce from a database.
-// id=99 is a sentinel that triggers an Internal error.
-pub fn get_nonce(id: u32) -> Result<u32, OneOf<(Internal,)>> {
-    if id == 99 {
-        return Err(OneOf::new(Internal("db pool unavailable".into())));
+// id=99 → InternalError1 (pool unavailable)
+// id=98 → InternalError2 (query timeout)
+pub fn get_nonce(id: u32) -> Result<u32, OneOf<(InternalError1, InternalError2)>> {
+    match id {
+        99 => Err(OneOf::new(InternalError1("db pool unavailable".to_owned()))),
+        98 => Err(OneOf::new(InternalError2("query timeout".to_owned()))),
+        _ => Ok(42),
     }
-    Ok(42)
 }
 
 #[cfg(test)]
@@ -20,9 +22,17 @@ mod tests {
     }
 
     #[test]
-    fn get_nonce_returns_internal_error_for_sentinel() {
+    fn get_nonce_returns_internal_error1_for_sentinel() {
         let err = get_nonce(99).unwrap_err();
-        let internal = err.take::<crate::errors::Internal>();
+        let internal = err.narrow::<crate::errors::InternalError1, _>().unwrap();
         assert_eq!(internal.0, "db pool unavailable");
     }
+
+    #[test]
+    fn get_nonce_returns_internal_error2_for_sentinel() {
+        let err = get_nonce(98).unwrap_err();
+        let e = err.narrow::<crate::errors::InternalError1, _>().unwrap_err();
+        let internal = e.take::<crate::errors::InternalError2>();
+        assert_eq!(internal.0, "query timeout");
+    }
 }

server/crates/arbiter-terrors-poc/src/errors.rs

@@ -5,7 +5,7 @@ use terrors::OneOf;
 pub enum ProtoError {
     NotRegistered,
     InvalidSignature,
-    Internal(String),
+    Internal(String), // Or Box<dyn Error>, who cares?
 }
 
 // Internal terrors types
@@ -14,8 +14,11 @@ pub struct NotRegistered;
 #[derive(Debug)]
 pub struct InvalidSignature;
 #[derive(Debug)]
-pub struct Internal(pub String);
+pub struct InternalError1(pub String);
+#[derive(Debug)]
+pub struct InternalError2(pub String);
 
+// Errors can be scattered across the codebase as long as they implement Into<ProtoError>
 impl From<NotRegistered> for ProtoError {
     fn from(_: NotRegistered) -> Self {
         ProtoError::NotRegistered
@@ -28,22 +31,61 @@ impl From<InvalidSignature> for ProtoError {
     }
 }
 
-impl From<Internal> for ProtoError {
-    fn from(e: Internal) -> Self {
+impl From<InternalError1> for ProtoError {
+    fn from(e: InternalError1) -> Self {
+        ProtoError::Internal(e.0)
+    }
+}
+impl From<InternalError2> for ProtoError {
+    fn from(e: InternalError2) -> Self {
         ProtoError::Internal(e.0)
     }
 }
 
-// Converts the narrowed remainder after handling NotRegistered
-impl From<OneOf<(InvalidSignature, Internal)>> for ProtoError {
-    fn from(e: OneOf<(InvalidSignature, Internal)>) -> Self {
-        match e.narrow::<InvalidSignature, _>() {
-            Ok(_) => ProtoError::InvalidSignature,
-            Err(e) => {
-                let Internal(msg) = e.take();
-                ProtoError::Internal(msg)
+/// Private helper trait for converting from OneOf<T...> where each T can be converted
+/// into the target type `O` by recursively narrowing until a match is found.
+/// 
+/// IDK why this isn't already in terrors.
+trait DrainInto<O>: terrors::TypeSet + Sized {
+    fn drain(e: OneOf<Self>) -> O;
+}
+
+macro_rules! impl_drain_into {
+    ($head:ident) => {
+        impl<$head, O> DrainInto<O> for ($head,)
+        where
+            $head: Into<O> + 'static,
+        {
+            fn drain(e: OneOf<($head,)>) -> O {
+                e.take().into()
             }
         }
+    };
+    ($head:ident, $($tail:ident),+) => {
+        impl<$head, $($tail),+, O> DrainInto<O> for ($head, $($tail),+)
+        where
+            $head: Into<O> + 'static,
+            ($($tail,)+): DrainInto<O>,
+        {
+            fn drain(e: OneOf<($head, $($tail),+)>) -> O {
+                match e.narrow::<$head, _>() {
+                    Ok(h) => h.into(),
+                    Err(rest) => <($($tail,)+)>::drain(rest),
+                }
+            }
+        }
+        impl_drain_into!($($tail),+);
+    };
+}
+
+// Generates impls for all tuple sizes from 1 up to 7 (restricted by terrors internal impl).
+// Each invocation produces one impl then recurses on the tail.
+impl_drain_into!(A, B, C, D, E, F, G, H, I);
+
+// Blanket From impl: body delegates to the recursive drain.
+impl<E: DrainInto<ProtoError>> From<OneOf<E>> for ProtoError {
+    fn from(e: OneOf<E>) -> Self {
+        E::drain(e)
     }
 }
 
@@ -65,14 +107,14 @@ mod tests {
 
     #[test]
     fn internal_converts_to_proto() {
-        let e: ProtoError = Internal("boom".into()).into();
+        let e: ProtoError = InternalError1("boom".into()).into();
         assert!(matches!(e, ProtoError::Internal(msg) if msg == "boom"));
     }
 
     #[test]
     fn one_of_remainder_converts_to_proto_invalid_signature() {
         use terrors::OneOf;
-        let e: OneOf<(InvalidSignature, Internal)> = OneOf::new(InvalidSignature);
+        let e: OneOf<(InvalidSignature, InternalError1)> = OneOf::new(InvalidSignature);
         let proto = ProtoError::from(e);
         assert!(matches!(proto, ProtoError::InvalidSignature));
     }
@@ -80,7 +122,8 @@ mod tests {
     #[test]
     fn one_of_remainder_converts_to_proto_internal() {
         use terrors::OneOf;
-        let e: OneOf<(InvalidSignature, Internal)> = OneOf::new(Internal("db fail".into()));
+        let e: OneOf<(InvalidSignature, InternalError1)> =
+            OneOf::new(InternalError1("db fail".into()));
         let proto = ProtoError::from(e);
         assert!(matches!(proto, ProtoError::Internal(msg) if msg == "db fail"));
     }

server/crates/arbiter-terrors-poc/src/main.rs

@@ -18,9 +18,26 @@ fn run(id: u32, sig: &str) {
     }
 }
 
+fn run_process(id: u32, sig: &str) {
+    print!("process_request(id={id}, sig={sig:?}) => ");
+    match auth::process_request(id, sig) {
+        Ok(s) => println!("Ok({s})"),
+        Err(e) => println!("Err(ProtoError::{e:?})"),
+    }
+}
+
 fn main() {
+    println!("=== authenticate ===");
     run(0, "ok");   // NotRegistered
     run(1, "bad");  // InvalidSignature
-    run(99, "ok");         // Internal
+    run(99, "ok");  // InternalError1
+    run(98, "ok");  // InternalError2
     run(1, "ok");   // success
+
+    println!("\n=== process_request (Try chain) ===");
+    run_process(0, "ok");   // NotRegistered (guard, no I/O)
+    run_process(97, "ok");  // InternalError2 from load_config
+    run_process(99, "ok");  // InternalError1 from get_nonce
+    run_process(1, "bad");  // InvalidSignature from verify_signature
+    run_process(1, "ok");   // success
 }