# Copyright (C) 2016-2018 all contributors <meta@public-inbox.org>
# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
#
# XXX This is a totally unstable API for public-inbox internal use only
# This is exposed via the 'pi-httpd.async' key in the PSGI env hash.
# The name of this key is not even stable!
# Currently is is intended for use with read-only pipes.
package PublicInbox::HTTPD::Async;
use strict;
use warnings;
use base qw(PublicInbox::DS);
use fields qw(cb cleanup);
require PublicInbox::EvCleanup;
use Errno qw(EAGAIN);

sub new {
	my ($class, $io, $cb, $cleanup) = @_;

	# no $io? call $cb at the top of the next event loop to
	# avoid recursion:
	unless (defined($io)) {
		PublicInbox::EvCleanup::asap($cb) if $cb;
		PublicInbox::EvCleanup::next_tick($cleanup) if $cleanup;
		return;
	}

	my $self = fields::new($class);
	IO::Handle::blocking($io, 0);
	$self->SUPER::new($io, PublicInbox::DS::EPOLLIN());
	$self->{cb} = $cb;
	$self->{cleanup} = $cleanup;
	$self;
}

sub restart_read ($) { $_[0]->watch(PublicInbox::DS::EPOLLIN()) }

sub main_cb ($$$) {
	my ($http, $fh, $bref) = @_;
	sub {
		my ($self) = @_;
		my $r = sysread($self->{sock}, $$bref, 8192);
		if ($r) {
			$fh->write($$bref); # may call $http->close

			if ($http->{sock}) { # !closed
				if ($http->{wbuf}) {
					# HTTP client could not keep up, so
					# stop reading and buffering.
					$self->watch(0);

					# Tell the HTTP socket to restart us
					# when HTTP client is done draining
					# $http->{wbuf}:
					$http->enqueue_restart_pass;
				}
				# stay in EPOLLIN, but let other clients
				# get some work done, too.
				return;
			}
			# fall through to close below...
		} elsif (!defined $r) {
			return restart_read($self) if $! == EAGAIN;
		}

		# Done! Error handling will happen in $fh->close
		# called by the {cleanup} handler
		delete $http->{forward};
		$self->close;
	}
}

sub async_pass {
	my ($self, $http, $fh, $bref) = @_;
	# In case the client HTTP connection ($http) dies, it
	# will automatically close this ($self) object.
	$http->{forward} = $self;
	$fh->write($$bref); # PublicInbox:HTTP::{chunked,identity}_wcb
	$self->{cb} = main_cb($http, $fh, $bref);
}

sub event_step { $_[0]->{cb}->(@_) }

sub close {
	my $self = $_[0];
	delete $self->{cb};
	$self->SUPER::close;

	# we defer this to the next timer loop since close is deferred
	if (my $cleanup = delete $self->{cleanup}) {
		PublicInbox::EvCleanup::next_tick($cleanup);
	}
}

1;