Panic protection in Tonic (more generally for tower-based services) #885

EarvinKayonga · 2022-01-10T17:19:34Z

EarvinKayonga
Jan 10, 2022

So I am looking for a way to handle panics gracefully. This doesn't work. Do you have other suggestions ?

use tonic::{body::BoxBody,transport::Server, Request, Response, Status};

use crate::contract::provider_server::{Provider, ProviderServer};
use contract::{UserRequest, UserResponse};
use futures::FutureExt;

use hyper::Body;
use tower::{Layer, Service};
use std::{
    task::{Context, Poll},
    time::Duration,
};

pub mod contract {
    tonic::include_proto!("provider");
}

#[derive(Debug, Default)]
pub struct GRPCProvider {}

#[tonic::async_trait]
impl Provider for GRPCProvider {
    async fn userdetails(
        &self,
        request: Request<UserRequest>,
    ) -> Result<Response<UserResponse>, Status> {
        let user = request.into_inner();

        log_user(&user);

        Ok(Response::new(UserResponse { message: true }))
    }
}

fn log_user(user: &UserRequest) {
    println!(
        "user request: email = {email}, name = {name}",
        email = user.useremail,
        name = user.username
    );
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let addr = "[::1]:50051".parse()?;
    let greeter = GRPCProvider::default();

    let layer = tower::ServiceBuilder::new()
        // Apply middleware from tower
        .timeout(Duration::from_secs(30))
        // Apply our own middleware
        .layer(PanicProtectionLayer::default())
        .into_inner();

    Server::builder()
        .layer(layer)
        .add_service(ProviderServer::new(greeter))
        .serve(addr)
        .await?;

    Ok(())
}

#[derive(Debug, Clone, Default)]
struct PanicProtectionLayer;

impl<S> Layer<S> for PanicProtectionLayer {
    type Service = PanicProtection<S>;

    fn layer(&self, service: S) -> Self::Service {
        PanicProtection { inner: service }
    }
}

#[derive(Debug, Clone)]
struct PanicProtection<S> {
    inner: S,
}

impl<S> Service<hyper::Request<Body>> for PanicProtection<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 = futures::future::BoxFuture<'static, Result<Self::Response, Self::Error>>;

    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        self.inner.poll_ready(cx)
    }

    fn call(&mut self, req: hyper::Request<Body>) -> Self::Future {
        let clone = self.inner.clone();
        let mut inner = std::mem::replace(&mut self.inner, clone);

        Box::pin(async move {
            let response = async {
               inner.call(req).await?
            }.catch_unwind().await?; // doesnot work

            Ok(response)
        })
    }
}

Answered by LucioFranco

Jan 12, 2022

We tend to just have a panic handler for the entire application (usually to print the message to our logging system). Panics should not be used for regular error handling like this. In tokio the panic will catch and just cancel the task.

View full answer

LucioFranco · 2022-01-12T21:05:44Z

LucioFranco
Jan 12, 2022
Maintainer

We tend to just have a panic handler for the entire application (usually to print the message to our logging system). Panics should not be used for regular error handling like this. In tokio the panic will catch and just cancel the task.

1 reply

EarvinKayonga Jan 14, 2022
Author

Thanks for the answer @LucioFranco.

I was also looking for a way to capture, then report the panic details (à la Sentry or Datadog).
And, I had the impression the task wasn't dropped because my clients never received a response. I'll look into it.

Cheers

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Panic protection in Tonic (more generally for tower-based services) #885

EarvinKayonga Jan 10, 2022

Replies: 1 comment · 1 reply

LucioFranco Jan 12, 2022 Maintainer

EarvinKayonga Jan 14, 2022 Author

EarvinKayonga
Jan 10, 2022

Replies: 1 comment 1 reply

LucioFranco
Jan 12, 2022
Maintainer

EarvinKayonga Jan 14, 2022
Author