unix-fd listener should not remove sockets on deregister()

[ensc]

actix-server runs https://github.com/actix/actix-net/blob/605ec251432786b169490aac60679388aa902d95/actix-server/src/socket.rs#L74-L84

This deregister function can be called as part of flow control as response to Pause command https://github.com/actix/actix-net/blob/605ec251432786b169490aac60679388aa902d95/actix-server/src/accept.rs#L286-L292

When resuming operations, the socket file is gone and clients can not connect to the server anymore.

The cleanup should happen only when connection is closed finally (Stop command?)

[fakeshadow]

https://github.com/actix/actix-net/issues/97

[ensc]

My use case for unix fds are CI tests: Instead of listening on tcp sockets and implementing ways to find free port numbers, I use unix sockets. Then, I can call the server like

curl --unix-socket /tmp/foo http://server.example.com

While doing tests, somehow the Pause event is triggered (I am not sure why; perhaps because I use SIGSTOP on the server between test steps), and things stop to work after

1. curl --unix-socket /tmpfoo --> ok

2. actix-net removes /tmp/foo

3. curl --unix-socket /tmpfoo --> fails because file does not exist anymore

My workaround for now is to let actix-net listen on a temporary socket and rename it later to the real one.

[hommeabeil]

I got the same issue with a really simple server which listen on unix socket. Form it it when we go through the backpressure method, which deregister the socket. Here is a backtrace taken with gdb

#0  std::fs::remove_file (path=0x7ffff7787846) at /usr/src/debug/libstd-rs/1.49.0-r0/rustc-1.49.0-src/library/std/src/fs.rs:1529
#1  0x00005555558b0e0d in <actix_server::socket::SocketListener as mio::event_imp::Evented>::deregister (self=0x7fffec000d80, poll=0x7ffff7788e30)
    at /usr/src/debug/sx-sts/0.1.0-r0/cargo_home/bitbake/actix-server-1.0.4/src/socket.rs:137
#2  0x00005555558fac89 in mio::poll::Poll::deregister (self=0x7ffff7788e30, handle=0x7fffec000d80)
    at /usr/src/debug/sx-sts/0.1.0-r0/cargo_home/bitbake/mio-0.6.23/src/poll.rs:910
#3  0x00005555558a80bd in actix_server::accept::Accept::backpressure (self=0x7ffff7788e30, on=true)
    at /usr/src/debug/sx-sts/0.1.0-r0/cargo_home/bitbake/actix-server-1.0.4/src/accept.rs:383
#4  0x00005555558a86f5 in actix_server::accept::Accept::accept_one (self=0x7ffff7788e30, msg=...)
    at /usr/src/debug/sx-sts/0.1.0-r0/cargo_home/bitbake/actix-server-1.0.4/src/accept.rs:437
#5  0x00005555558a979b in actix_server::accept::Accept::accept (self=0x7ffff7788e30, token=0)
    at /usr/src/debug/sx-sts/0.1.0-r0/cargo_home/bitbake/actix-server-1.0.4/src/accept.rs:475
#6  0x00005555558a62ca in actix_server::accept::Accept::poll (self=0x7ffff7788e30)
    at /usr/src/debug/sx-sts/0.1.0-r0/cargo_home/bitbake/actix-server-1.0.4/src/accept.rs:257
#7  0x00005555558a5071 in actix_server::accept::Accept::start::{{closure}} ()
    at /usr/src/debug/sx-sts/0.1.0-r0/cargo_home/bitbake/actix-server-1.0.4/src/accept.rs:170
#8  0x00005555558cb093 in std::sys_common::backtrace::__rust_begin_short_backtrace (f=...)
    at /usr/src/debug/libstd-rs/1.49.0-r0/rustc-1.49.0-src/library/std/src/sys_common/backtrace.rs:125
#9  0x00005555558ddb95 in std::thread::Builder::spawn_unchecked::{{closure}}::{{closure}} ()
    at /usr/src/debug/libstd-rs/1.49.0-r0/rustc-1.49.0-src/library/std/src/thread/mod.rs:474
#10 0x00005555558a9e85 in <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once (self=..., _args=())
    at /usr/src/debug/libstd-rs/1.49.0-r0/rustc-1.49.0-src/library/std/src/panic.rs:322
#11 0x00005555558cdb33 in std::panicking::try::do_call (data=0x7ffff77894c8 "\000")
    at /usr/src/debug/libstd-rs/1.49.0-r0/rustc-1.49.0-src/library/std/src/panicking.rs:381
#12 0x00005555558d8cad in __rust_try ()
#13 0x00005555558cc4d4 in std::panicking::try (f=...) at /usr/src/debug/libstd-rs/1.49.0-r0/rustc-1.49.0-src/library/std/src/panicking.rs:345
#14 0x00005555558aa275 in std::panic::catch_unwind (f=...) at /usr/src/debug/libstd-rs/1.49.0-r0/rustc-1.49.0-src/library/std/src/panic.rs:396
#15 0x00005555558dd95e in std::thread::Builder::spawn_unchecked::{{closure}} ()
    at /usr/src/debug/libstd-rs/1.49.0-r0/rustc-1.49.0-src/library/std/src/thread/mod.rs:473
#16 0x000055555589a6fe in core::ops::function::FnOnce::call_once{{vtable-shim}} ()
    at /usr/src/debug/libstd-rs/1.49.0-r0/rustc-1.49.0-src/library/core/src/ops/function.rs:227
#17 0x0000555555dc728a in std::sys::unix::thread::Thread::new::thread_start ()
#18 0x00007ffff7edee24 in start_thread (arg=<optimized out>) at pthread_create.c:477
#19 0x00007ffff7cc9e9f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

What can we do about it ? Is simply removing the fs::remove_file should work ? My guess is we will be leaking the file in a clean exit ?