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I didn't wait until September to do it, this year!
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EPOLL_CTL_ADD may fail with transient ENOMEM or ENOSPC errors,
so don't tear down the process when that happens.
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There's a bunch of leftover "require" and "use" statements we no
longer need and can get rid of, along with some excessive
imports via "use".
IO::Handle usage isn't always obvious, so add comments
describing why a package loads it. Along the same lines,
document the tmpdir support as the reason we depend on
File::Temp 0.19, even though every Perl 5.10.1+ user has it.
While we're at it, favor "use" over "require", since it it gives
us extra compile-time checking.
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We need to warn when hitting file or socket memory limits
or misconfigurations which clear O_NONBLOCK to make it easier
to diagnose configuration problems. We'll also warn on
some other errors in case bugs creep in...
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For users relying on socket activation via service manager (e.g.
systemd) and running multiple service instances (@1, @2),
we need to ensure configuration of the socket is NonBlocking.
Otherwise, service managers such as systemd may clear the
O_NONBLOCK flag for a small window where accept/accept4
blocks:
public-inbox-nntpd@1 |systemd |public-inbox-nntpd@2
--------------------------+----------------+--------------------
F_SETFL,O_NONBLOCK|O_RDWR | | (not running, yet)
|F_SETFL, O_RDWR |
|fork+exec @2... |
accept(...) # blocks! | |(started by systemd)
| |F_SETFL,O_NONBLOCK|O_RDWR
| |accept(...) non-blocking
It's a very small window where O_NONBLOCK can be cleared,
but it exists, and I finally hit it after many years.
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We don't need extra wakeups from the kernel when we know a
listener is already active.
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We can avoid the EPOLL_CTL_ADD && EPOLL_CTL_MOD sequence with
a single EPOLL_CTL_ADD.
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Having separate read/write callbacks in every class is too
confusing to my easily-confused mind. Instead, give every class
an "event_step" callback which is easier to wrap my head around.
This will make future code to support IO::Socket::SSL-wrapped
sockets easier-to-digest, since SSL_write() can require waiting
on POLLIN events, and SSL_read() can require waiting on POLLOUT
events.
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Since our listen sockets are non-blocking and we may run
multiple httpd|nntpd processes; we need a way to avoid
thundering herds when there are multiple httpd|nntpd worker
processes.
EPOLLEXCLUSIVE was added just for that in Linux 4.5
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These modules are unmaintained upstream at the moment, but I'll
be able to help with the intended maintainer once/if CPAN
ownership is transferred. OTOH, we've been waiting for that
transfer for several years, now...
Changes I intend to make:
* EPOLLEXCLUSIVE for Linux
* remove unused fields wasting memory
* kqueue bugfixes e.g. https://rt.cpan.org/Ticket/Display.html?id=116615
* accept4 support
And some lower priority experiments:
* switch to EV_ONESHOT / EPOLLONESHOT (incompatible changes)
* nginx-style buffering to tmpfile instead of string array
* sendfile off tmpfile buffers
* io_uring maybe?
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Using update-copyrights from gnulib
While we're at it, use the SPDX identifier for AGPL-3.0+ to
ease mechanical processing.
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Notes for future developers (myself included) since we
can't assume people can read my mind.
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This is meant to provide an easy starting point for server admins.
It provides a basic HTTP server for admins unfamiliar with
configuring PSGI applications as well as being an identical
interface for management as our nntpd implementation.
This HTTP server may also be a generic Plack/PSGI server for
existing Plack/PSGI applications.
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We can avoid making getpeername syscalls this way.
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Hopefully this gives new hackers a better overview of
how the components relate to each other.
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We'll probably be supporting read-only IMAP, or maybe
we'll just implement a custom HTTP server so users can
manage/upgrade the same way as the nntpd while being
immune to slow clients.
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