Client connections leaked with long-poll GETs

[mthebridge]

I'm not sure if this is a hyper, tokio_timer or general futures issue, it seems similar to #1353 - but that suggests this is fixed by using no_proto on the Client, and I see the same problem whether or not I use no_proto .

Originally raised as jimmycuadra/rust-etcd#20, but managed to isolate it to hyper.

The trigger seems to be using tokio_timer::Timeout on a Client.get() that has returned the headers with Chunked-Encoding but no chunks received yet.

Nothing obvious in trace-level logs.

Repro instructions (on Linux - not tried on any other platforms), mostly cribbed from the rust-etcd repo:

• Start an etcd instance running locally (assuming you have docker, docker run --net=host -d quay.io/coreos/etcd:v2.2.0 works)
• Run this simple etcd client code (below) that loops watching for changes to a key.
• Observe leaking TCP connections - I view through sudo netstat - plant | grep 2379 (and eventually you'll run out of ports).

extern crate hyper;
extern crate tokio_core;
#[macro_use]
extern crate log;
extern crate env_logger;
extern crate futures;
extern crate tokio_timer;

use std::time::Duration;
use futures::future::Future;
use futures::Stream;
use tokio_core::reactor;
use tokio_timer::{Timer, TimeoutError};
use hyper::{Client, Uri};
use std::error::Error;

// Dummy error type to handle this
#[derive(Debug)]
enum MyError {
    Timeout,
    Other(String),
}

impl std::fmt::Display for MyError {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
        write!(f, "{}", self.description())
    }
}

impl Error for MyError {
    fn description(&self) -> &str {
        match *self {
            MyError::Timeout => "Timeout",
            MyError::Other(ref s) => s,
        }
    }
}

impl<T> From<TimeoutError<T>> for MyError {
    fn from(_error: TimeoutError<T>) -> MyError {
        MyError::Timeout
    }
}

impl From<hyper::Error> for MyError {
    fn from(error: hyper::Error) -> MyError {
        MyError::Other(error.description().to_string())
    }
}

fn main() {
    env_logger::init().unwrap();

    let mut core = reactor::Core::new().unwrap();

    let client = Client::new(&core.handle());

    let mut idx = 0;
    loop {
        let url_str = format!(
            "http://localhost:2379/v2/keys/foo?waitIndex={}&wait=true&recursive=true",
            idx
        );
        let url = url_str.parse::<Uri>().unwrap();
        debug!("Kicking off watch for index: {}", idx);
        let timer = Timer::default();
        let cur_idx = idx;
        let work: Box<Future<Item = (), Error = MyError>> = Box::new(
            timer.timeout(
                client
                    .get(url)
                    .map_err(|e| MyError::Other(e.description().to_string()))
                    .and_then(|response| {
                        let status = response.status();
                        response
                            .body()
                            .concat2()
                            .map_err(|e| MyError::Other(format!("Body parse error: {}", e)))
                            .and_then(move |ref _body| if status == hyper::StatusCode::Ok {
                                idx += 1;
                                Ok(())
                            } else {
                                Err(MyError::Other("Bad response from etcd".to_string()))
                            })
                    })
                    .map(|_| {
                        debug!("Completed watch for index {}", cur_idx);
                    }),
                Duration::from_secs(3),
            ),
        );
        let res = core.run(work);

        match res {
            Ok(_) => debug!("Spotted change from etcd"),
            Err(MyError::Timeout) => info!("Timeout"),
            Err(MyError::Other(e)) => error!(" error from etcd: {}", e),
        }
    }
}

[sfackler]

no_proto isn't the default.

[mthebridge]

Ah - apologies, so it isn't (double negatives confused me!). Just tried enabling no_proto() and makes no difference.

[seanmonstar]

Does the response that comes back include a response body?

[seanmonstar]

PS, don't call Timer::default() in a loop. That is creating a worker thread every single time. Create it once outside the loop.

[mthebridge]

@seanmonstar No, no body at all - it's a polling GET that returns when a change is detected (see under "Waiting for a change" at https://coreos.com/etcd/docs/latest/v2/api.html), and it's expected in our real use case that most of the time it would time out with no body.

Thanks for the performance tip on Timer::default(), though that isn't the cause.

I've tried doing some code reading and debugging but I'm finding the hyper code quite tricky to get my head around!

[seanmonstar]

This has been fixed when the no_proto config is set on the Client. The new dispatcher will soon be the default, fixing this for everyone.

[mthebridge]

Sorry to dispute - but pulling from the latest master (8f6931b), and switching to use no_proto(), I still see the same problem with the above script. So there must be another bug..

Would you prefer this reopened or a new issue?

[mthebridge]

In fact, I can repro on master by patching your new test as follows. The key is to return a chunked-encoding with no content-length and no body. With this code, the drop_client_closes_idle_connections test hangs forever (because the connection never drops).

--- a/tests/client.rs
+++ b/tests/client.rs
@@ -673,8 +673,9 @@ mod dispatch_impl {
             sock.set_write_timeout(Some(Duration::from_secs(5))).unwrap();
             let mut buf = [0; 4096];
             sock.read(&mut buf).expect("read 1");
-            let body =[b'x'; 64];
-            write!(sock, "HTTP/1.1 200 OK\r\nContent-Length: {}\r\n\r\n", body.len()).expect("write head");
+            // let body =[b'x'; 64];
+            let body = vec![];
+            write!(sock, "HTTP/1.1 200 OK\r\nTransfer-Encoding: chunked\r\n\r\n").expect("write head");
             let _ = sock.write_all(&body);
             let _ = tx1.send(());

[seanmonstar]

Ah yes, this is different! Not idle connections, but rather an active connection when the Response or the Body related to it has been dropped.

[seanmonstar]

Ok, new patch fixes the test case you provided.

[mthebridge]

Yes, that works! Thanks so much for the speedy fixes.