tonic
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hyperium
Support layers in generated server codes.
Feature Request
Crates
tonic, tonic-build
Motivation
Servers generated by tonic-build have with_interceptor method, so that users can inject some layers before underlying service. However, async/await is unavailable in an interceptor.
Although the document and examples suggest to use Server::layer for such demand, there are some limitations.
- Users cannot choose services to be wrapped.
- Layers cannot access
tonic::Request(http::Requestis available instead) .
Proposal
Make tonic-build to generate layer method for each server.
Server::builder()
.add_service(ServerA::new(service_a).layer(MyLayer))
.add_service(ServerB::new(service_b))
.serve()
.await?
struct MyLayer {
..
}
impl Layer<S> for MyLayer {
type Service = MyService<S>;
..
}
struct MyService<S> {
..
}
impl<S, T, U> Service<tonic::Request<T>> for MyService<S>
where
S: Service<tonic::Request<T>, Response = tonic::Response<U>, Error = tonic::Status>,
..
{
type Response = tonic::Response<U>;
type Error = tonic::Status;
..
}
Alternatives
A workaround is to conduct routing and type conversion (http::Request/Response <-> tonic::Request/Response) in layers of Server::layer. This is redundant since generated servers do routing and type conversion in them.
You can use tower's ServiceBuilder for this.
let service_a = ServiceBuilder::new()
.layer(MyLayer)
.service(
MyService::new(...).start()
);
Server::builder()
.add_service(service_a)
.serve()
.await?
You can use tower's ServiceBuilder for this.
No, ServiceBuilder cannot inject layers that handles tonic::Request and tonic::Response .
I tried with examples/src/helloworld/server.rs
#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
let addr = "[::1]:50051".parse().unwrap();
let greeter = MyGreeter::default();
println!("GreeterServer listening on {}", addr);
let service = tower::ServiceBuilder::new()
.layer(MyLayer {})
.service(GreeterServer::new(greeter));
Server::builder().add_service(service).serve(addr).await?;
Ok(())
}
#[derive(Clone)]
struct MyLayer {}
impl<S> tower::Layer<S> for MyLayer {
type Service = MyService<S>;
fn layer(&self, inner: S) -> Self::Service {
MyService { inner }
}
}
#[derive(Clone)]
struct MyService<S> {
inner: S,
}
impl<S, T, U> tower::Service<tonic::Request<T>> for MyService<S>
where
S: tower::Service<tonic::Request<T>, Response = tonic::Response<U>>,
{
type Response = tonic::Response<U>;
type Error = S::Error;
type Future = S::Future;
fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
self.inner.poll_ready(cx)
}
fn call(&mut self, request: tonic::Request<T>) -> Self::Future {
self.inner.call(request)
}
}
This code raises the following errors.
error[E0277]: the trait bound `MyService<GreeterServer<MyGreeter>>: Service<request::Request<tonic::transport::Body>>` is not satisfied
--> examples/src/helloworld/server.rs:41:35
|
41 | Server::builder().add_service(service).serve(addr).await?;
| ----------- ^^^^^^^ the trait `Service<request::Request<tonic::transport::Body>>` is not implemented for `MyService<GreeterServer<MyGreeter>>`
| |
| required by a bound introduced by this call
|
= help: the trait `Service<tonic::Request<T>>` is implemented for `MyService<S>`
note: required by a bound in `Server::<L>::add_service`
--> /home/admin/github.com/hyperium/tonic/tonic/src/transport/server/mod.rs:364:12
|
362 | pub fn add_service<S>(&mut self, svc: S) -> Router<L>
| ----------- required by a bound in this associated function
363 | where
364 | S: Service<Request<Body>, Response = Response<BoxBody>, Error = Infallible>
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Server::<L>::add_service`
error[E0277]: the trait bound `MyService<GreeterServer<MyGreeter>>: NamedService` is not satisfied
--> examples/src/helloworld/server.rs:41:35
|
41 | Server::builder().add_service(service).serve(addr).await?;
| ----------- ^^^^^^^ the trait `NamedService` is not implemented for `MyService<GreeterServer<MyGreeter>>`
| |
| required by a bound introduced by this call
|
= help: the following other types implement trait `NamedService`:
GreeterServer<T>
tonic::service::interceptor::InterceptedService<S, F>
Either<S, T>
note: required by a bound in `Server::<L>::add_service`
--> /home/admin/github.com/hyperium/tonic/tonic/src/transport/server/mod.rs:365:15
|
362 | pub fn add_service<S>(&mut self, svc: S) -> Router<L>
| ----------- required by a bound in this associated function
...
365 | + NamedService
| ^^^^^^^^^^^^ required by this bound in `Server::<L>::add_service`
For more information about this error, try `rustc --explain E0277`.
error: could not compile `examples` (bin "helloworld-server") due to 2 previous errors
Why do you need it to use tonic::Request and tonic::Response? You should be using hyper::Request and hyper::Response. To resolve the error about the missing NamedService bound, you can implement the trait on your layer.
impl<S> Service<hyper::Request<Body>> for MyService<S>
where
S: Service<hyper::Request<Body>, Response = hyper::Response<BoxBody>> + Clone + Send + 'static,
S::Future: Send + 'static,
{
type Response = S::Response;
type Error = S::Error;
type Future = BoxFuture<'static, Result<Self::Response, Self::Error>>;
fn poll_ready(
&mut self,
cx: &mut std::task::Context<'_>,
) -> std::task::Poll<Result<(), Self::Error>> {
self.inner.poll_ready(cx)
}
fn call(&mut self, mut request: hyper::Request<Body>) -> Self::Future {
// This is necessary because tonic internally uses `tower::buffer::Buffer`.
// See https://github.com/tower-rs/tower/issues/547#issuecomment-767629149
// for details on why this is necessary
let clone = self.inner.clone();
let mut inner = std::mem::replace(&mut self.inner, clone);
Box::pin(async move {
Ok(inner.call(req).await?)
})
}
}
// Required by the server builder when converted into a [tonic::transport::server::Router]
impl<S> NamedService for MyService<S>
where
S: NamedService,
{
const NAME: &'static str = S::NAME;
}
There is an example here https://github.com/hyperium/tonic/blob/master/examples/src/tower/server.rs
Why do you need it to use tonic::Request and tonic::Response?
In my case, I'd like to access remote_addr in my layer. tonic::Request also provides some useful fields.
You should be using hyper::Request and hyper::Response. To resolve the error about the missing NamedService bound, you can implement the trait on your layer.
I know I can make my code work as I mentioned in Alternatives above.
I'm asking to add a new helper so that I can write it easily.