Add descriptions to ASGI flow errors

src/asgi/conversion.rs

@@ -56,7 +56,7 @@ pub(crate) fn ws_message_into_py(py: Python, message: Message) -> PyResult<Bound
         }
         v => {
             log::warn!("Unsupported websocket message received {v:?}");
-            error_flow!()
+            error_flow!("Transport misbehaving")
         }
     }
 }

src/asgi/errors.rs

@@ -1,12 +1,12 @@
 use pyo3::exceptions::PyRuntimeError;
 use pyo3::prelude::*;
-use std::{error, fmt};
+use std::{error, fmt, rc::Rc};
 
 #[derive(Debug)]
 pub(crate) struct UnsupportedASGIMessage;
 
 #[derive(Debug)]
-pub(crate) struct ASGIFlowError;
+pub(crate) struct ASGIFlowError(pub Option<Rc<str>>);
 
 #[derive(Debug)]
 pub(crate) struct ASGITransportError;
@@ -23,7 +23,10 @@ impl fmt::Display for UnsupportedASGIMessage {
 
 impl fmt::Display for ASGIFlowError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "ASGI flow error")
+        match &self.0 {
+            Some(msg) => write!(f, "ASGI flow error: {msg}"),
+            None => write!(f, "ASGI flow error"),
+        }
     }
 }
 
@@ -47,7 +50,7 @@ impl std::convert::From<PyErr> for UnsupportedASGIMessage {
 
 impl std::convert::From<PyErr> for ASGIFlowError {
     fn from(_pyerr: PyErr) -> ASGIFlowError {
-        ASGIFlowError
+        ASGIFlowError(None)
     }
 }
 
@@ -71,7 +74,10 @@ impl std::convert::From<ASGITransportError> for PyErr {
 
 macro_rules! error_flow {
     () => {
-        Err(super::errors::ASGIFlowError.into())
+        Err(super::errors::ASGIFlowError(None).into())
+    };
+    ($msg:expr) => {
+        Err(super::errors::ASGIFlowError(Some($msg.into())).into())
     };
 }
 

src/asgi/io.rs

@@ -183,7 +183,7 @@ impl ASGIHTTPProtocol {
                     .compare_exchange(false, true, atomic::Ordering::Relaxed, atomic::Ordering::Relaxed)
                     .is_err()
                 {
-                    return error_flow!();
+                    return error_flow!("Response already started");
                 }
 
                 // NOTE: we could definitely avoid this check, and always start a streamed response
@@ -244,7 +244,7 @@ impl ASGIHTTPProtocol {
                     }
                     (true, true, true) => match &*self.body_tx.lock().unwrap() {
                         Some(tx) => self.send_body(py, tx, body, false),
-                        _ => error_flow!(),
+                        _ => error_flow!("Transport not initialized or closed"),
                     },
                     (true, false, true) => match self.body_tx.lock().unwrap().take() {
                         Some(tx) => match body.is_empty() {
@@ -254,9 +254,9 @@ impl ASGIHTTPProtocol {
                                 empty_future_into_py(py)
                             }
                         },
-                        _ => error_flow!(),
+                        _ => error_flow!("Transport not initialized or closed"),
                     },
-                    _ => error_flow!(),
+                    _ => error_flow!("Response not started"),
                 }
             }
             Ok(ASGIMessageType::HTTPResponseFile(file_path)) => match (
@@ -288,7 +288,7 @@ impl ASGIHTTPProtocol {
                     });
                     empty_future_into_py(py)
                 }
-                _ => error_flow!(),
+                _ => error_flow!("Response not started"),
             },
             Err(err) => Err(err.into()),
             _ => error_message!(),
@@ -388,7 +388,7 @@ impl ASGIWebsocketProtocol {
                     }
                 }
             }
-            FutureResultToPy::Err(error_flow!())
+            FutureResultToPy::Err(error_flow!("Connection already upgraded"))
         })
     }
 
@@ -409,7 +409,7 @@ impl ASGIWebsocketProtocol {
                     }
                 }
             }
-            FutureResultToPy::Err(error_flow!())
+            FutureResultToPy::Err(error_flow!("Transport not initialized or closed"))
         })
     }
 
@@ -492,7 +492,7 @@ impl ASGIWebsocketProtocol {
                     }
                 }
             }
-            FutureResultToPy::Err(error_flow!())
+            FutureResultToPy::Err(error_flow!("Transport not initialized or closed"))
         })
     }
 
@@ -579,7 +579,7 @@ fn adapt_body(py: Python, message: &Bound<PyDict>) -> (Box<[u8]>, bool) {
 fn adapt_file(py: Python, message: &Bound<PyDict>) -> PyResult<String> {
     match message.get_item(pyo3::intern!(py, "path"))? {
         Some(item) => item.extract(),
-        _ => error_flow!(),
+        _ => error_message!(),
     }
 }