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| | # Copyright (C) all contributors <meta@public-inbox.org>
# License: GPL-3.0+ <https://www.gnu.org/licenses/gpl-3.0.txt>
# generic Plack/PSGI middleware to expose PublicInbox::Limiter, (see __END__)
package PublicInbox::PlackLimiter;
use v5.12;
use parent qw(Plack::Middleware);
use PublicInbox::OnDestroy;
sub prepare_app { # called via Plack::Component (used by Plack::Middleware)
my ($self) = @_;
$self->{match_cb} //= sub { 1 };
$self->{max} //= 2;
$self->{run_queue} = [];
$self->{running} = 0;
$self->{rejected} = 0;
$self->{message} //= "too busy\n";
}
sub r503 ($) {
my @body = ($_[0]->{message});
++$_[0]->{rejected};
[ 503, [ 'Content-Type' => 'text/plain',
'Content-Length' => length($body[0]) ], \@body ]
}
sub next_req { # on_destroy cb
my ($self) = @_;
--$self->{running};
my $env = shift @{$self->{run_queue}} or return;
my $wcb = delete $env->{'p-i.limiter.wcb'} // die 'BUG: no wcb';
my $res = eval { call($self, $env) };
return warn("W: $@") if $@;
ref($res) eq 'CODE' ? $res->($wcb) : $wcb->($res);
}
sub stats ($) {
my ($self) = @_;
my $nq = scalar @{$self->{run_queue}};
my $res = <<EOM;
running: $self->{running}
queued: $nq
rejected: $self->{rejected}
max: $self->{max}
EOM
[ 200, [ 'Content-Type' => 'text/plain',
'Content-Length' => length($res) ], [ $res ] ]
}
sub call {
my ($self, $env) = @_;
if (defined $self->{stats_match_cb}) {
return stats $self if $self->{stats_match_cb}->($env);
}
return $self->app->($env) if !$self->{match_cb}->($env);
return r503($self) if @{$self->{run_queue}} > ($self->{depth} // 32);
if ($self->{running} < $self->{max}) {
++$self->{running};
$env->{'p-i.limiter.next'} = on_destroy \&next_req, $self;
$self->app->($env);
} else { # capture write cb from PSGI server and queue up
sub {
$env->{'p-i.limiter.wcb'} = $_[0];
push @{$self->{run_queue}}, $env;
};
}
}
1;
__END__
=head1 NAME
PublicInbox::PlackLimiter - limit concurrency to parts of a PSGI app
=head1 SYNOPSIS
# In your .psgi file
use Plack::Builder;
builder {
# by default, only 2 requests may be processed at once:
enable '+PublicInbox::PlackLimiter';
# You will likely only want to limit certain expensive endpoints,
# while allowing maximum concurrency for inexpensive endpoints.
# You can do that by passing a `match_cb' parameter:
enable '+PublicInbox::PlackLimiter',
# some expensive endpoints for my public-inbox instance, YMMV
match_cb => sub {
my ($env) = @_;
$env->{PATH_INFO} =~ m!/(?:[Ttd]/|.+\.
(?:mbox\.gz|atom|html))\z!x ||
$env->{QUERY_STRING} =~ /\bx=[tA]\b/
},
# You can increase `max' and `depth' to higher numbers
max => 3, # maximum concurrent requests
depth => 128, # maximum queue depth (size)
# You can also enable a stats endpoint if you wish (optional):
stats_match_cb => sub {
my ($env) = @_;
$env->{REQUEST_URI} eq '/stats' &&
$env->{REMOTE_ADDR} eq '127.0.0.1'
};
# ...
}; # /builder
=head1 DESCRIPTION
PublicInbox::PlackLimiter lets a sysadmin limit concurrency to certain
expensive endpoints while allowing the normal concurrency level of the
server to run inexpensive requests.
=head1 SEE ALSO
L<Plack> L<Plack::Builder> L<Plack::Middleware>
=cut
|