chore(tonic): Move TimeoutExpired out of transport (#1826)

By moving the TimeoutExpired type from the transport module
to the the tonic engine proper, the type is made available to
other transport implementations and tonic can be built without
the "server" feature while still returning a Status indicating
the timeout.

Alternative transport implementations can use the type, now that it is
moved, when they want the tonic Status error handling to recognize the
error as having been triggered by a timeout in the transport logic. The
tonic Status error will have a code of Cancelled with a message of
"Timeout expired".

There is already a test for this:

    cargo test picks_server_timeout_if_thats_sorter

which worked the original way and contines to work; but now a new
transport implementation can get the same behavior.

Addresses #1825.

tonic/src/lib.rs

@@ -120,7 +120,7 @@ pub use extensions::GrpcMethod;
 pub use http::Extensions;
 pub use request::{IntoRequest, IntoStreamingRequest, Request};
 pub use response::Response;
-pub use status::{Code, Status};
+pub use status::{Code, Status, TimeoutExpired};
 
 pub(crate) type Error = Box<dyn std::error::Error + Send + Sync>;
 

tonic/src/status.rs

@@ -606,8 +606,7 @@ fn find_status_in_source_chain(err: &(dyn Error + 'static)) -> Option<Status> {
             });
         }
 
-        #[cfg(feature = "server")]
-        if let Some(timeout) = err.downcast_ref::<crate::transport::TimeoutExpired>() {
+        if let Some(timeout) = err.downcast_ref::<TimeoutExpired>() {
             return Some(Status::cancelled(timeout.to_string()));
         }
 
@@ -1013,3 +1012,23 @@ mod tests {
         assert_eq!(status.details(), DETAILS);
     }
 }
+
+/// Error returned if a request didn't complete within the configured timeout.
+///
+/// Timeouts can be configured either with [`Endpoint::timeout`], [`Server::timeout`], or by
+/// setting the [`grpc-timeout` metadata value][spec].
+///
+/// [`Endpoint::timeout`]: crate::transport::server::Server::timeout
+/// [`Server::timeout`]: crate::transport::channel::Endpoint::timeout
+/// [spec]: https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md
+#[derive(Debug)]
+pub struct TimeoutExpired(pub ());
+
+impl fmt::Display for TimeoutExpired {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "Timeout expired")
+    }
+}
+
+// std::error::Error only requires a type to impl Debug and Display
+impl std::error::Error for TimeoutExpired {}

tonic/src/transport/mod.rs

@@ -106,8 +106,6 @@ pub use self::error::Error;
 #[doc(inline)]
 #[cfg(feature = "server")]
 pub use self::server::Server;
-#[doc(inline)]
-pub use self::service::grpc_timeout::TimeoutExpired;
 
 #[cfg(feature = "tls")]
 pub use self::tls::Certificate;

tonic/src/transport/service/grpc_timeout.rs

@@ -1,8 +1,7 @@
-use crate::metadata::GRPC_TIMEOUT_HEADER;
+use crate::{metadata::GRPC_TIMEOUT_HEADER, TimeoutExpired};
 use http::{HeaderMap, HeaderValue, Request};
 use pin_project::pin_project;
 use std::{
-    fmt,
     future::Future,
     pin::Pin,
     task::{ready, Context, Poll},
@@ -147,26 +146,6 @@ fn try_parse_grpc_timeout(
     }
 }
 
-/// Error returned if a request didn't complete within the configured timeout.
-///
-/// Timeouts can be configured either with [`Endpoint::timeout`], [`Server::timeout`], or by
-/// setting the [`grpc-timeout` metadata value][spec].
-///
-/// [`Endpoint::timeout`]: crate::transport::server::Server::timeout
-/// [`Server::timeout`]: crate::transport::channel::Endpoint::timeout
-/// [spec]: https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md
-#[derive(Debug)]
-pub struct TimeoutExpired(());
-
-impl fmt::Display for TimeoutExpired {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "Timeout expired")
-    }
-}
-
-// std::error::Error only requires a type to impl Debug and Display
-impl std::error::Error for TimeoutExpired {}
-
 #[cfg(test)]
 mod tests {
     use super::*;