MCP/Client/JSONL.pm

=head1 NAME

AnyEvent::MCP::Client::JSONL - MCP byte streams and stdio subprocesses

=head1 SYNOPSIS

   my $client = AnyEvent::MCP::Client::JSONL->new (
      command => [$program, @args],
      env => { PERL_ANYEVENT_MCP_MULTIBROKER_PROTOCOL => "stdio" },
   );

=head1 DESCRIPTION

Use this transport when the MCP server is a subprocess or an already
connected byte stream. It reads one JSON-RPC message per line, so stdout
from a child server must contain protocol messages only. Diagnostic output
belongs on stderr. A single stray banner on stdout can break the connection.

An argument array executes the program directly; a command string runs
through a shell. Prefer the array form when no shell syntax is needed.
The process starts on the first connection, not when the client object
is constructed.

=head1 METHODS

=head2 $client = AnyEvent::MCP::Client::JSONL->new (%config)

C<command> is an argument array for direct execution, or a string explicitly
run through C</bin/sh -c>. The child inherits stderr. C<env> contains child
environment overrides. No command runs until connecting.

C<handle> contains AnyEvent::Handle options, excluding the filehandle and
read/error/EOF callbacks managed here. C<max_size> bounds an incoming JSON
line, defaulting to 16 MiB.

C<name> is available for application identification but does not load transport
defaults. The library does not infer a subprocess command or environment.

=head2 $client->attach ($fh_in, $fh_out)

Uses existing handles instead of a command. C<$fh_out> defaults to C<$fh_in>
for a bidirectional socket. The client takes ownership. Attach before sending
requests. Closing an attached connection requires attaching new handles before
reconnecting.

Closing a subprocess connection sends SIGTERM and keeps its child watcher
alive until the child has been reaped. It does not restart an outstanding call.
An accepted multibroker idle shutdown is the exception: its child can exit
and perform cleanup without receiving SIGTERM.

=cut

package AnyEvent::MCP::Client::JSONL;

use common::sense;
use parent "AnyEvent::MCP::Client";
use AnyEvent::Handle ();
use AnyEvent::Util ();
use JSON::XS ();
use Scalar::Util qw(weaken);

sub attach {
   my ($self, $fh_in, $fh_out) = @_;

   $self->close if $self->{read_handle};
   weaken $self;
   $self->{read_handle} = AnyEvent::Handle->new (
      %{$self->{handle} || {}},
      fh       => $fh_in,
      rbuf_max => $self->{max_size} || 16 * 1024 * 1024,
      on_read  => undef,
      on_error => sub { $self->close ($_[2]) if $self },
      on_eof   => sub { $self->close ("MCP stream closed") if $self },
   );
   $self->{write_handle} = $fh_out ? AnyEvent::Handle->new (
      %{$self->{handle} || {}},
      fh       => $fh_out,
      on_read  => undef,
      on_error => sub { $self->close ($_[2]) if $self },
      on_eof   => sub { $self->close ("MCP output closed") if $self },
   ) : $self->{read_handle};
   $self->_read;
}

sub _open {
   my ($self, $done) = @_;

   return $done->(1, undef) if $self->{read_handle};
   return $done->(0, { transport => 1, message => "No command or attached stream" })
      unless $self->{command};

   my $ok = eval {
      local %ENV = (%ENV, %{$self->{env} || {}});
      my ($parent, $child) = AnyEvent::Util::portable_socketpair;
      die "Cannot create MCP socketpair: $!\n" unless defined $parent && defined $child;

      my $pid;
      my $cv = AnyEvent::Util::run_cmd (
         ref $self->{command} eq "ARRAY" ? $self->{command} : ["/bin/sh", "-c", $self->{command}],
         "<" => $child, ">" => $child, '$$' => \$pid, close_all => 1,
      );
      close $child;
      $self->{pid} = $pid;
      $self->attach ($parent);

      weaken $self;
      $cv->cb (sub {
         my $status = $_[0]->recv;
         if ($self && $self->{pid} == $pid) {
            delete $self->{pid};
            delete $self->{child};
            $self->close ("MCP child exited (status $status)");
         }
      });
      $self->{child} = $cv;
      1
   };
   $done->($ok ? (1, undef) : (0, { transport => 1, message => "$@" }));
}

sub _read {
   my ($self) = @_;

   weaken $self;

   $self->{read_handle}->push_read (line => sub {
      my ($handle, $line) = @_;

      return unless $self;
      my $ok = eval {
         $self->_receive (JSON::XS::decode_json $line);
         1
      };
      return $self->close ("$@") unless $ok;
      $self->_read if $self->{read_handle} && !$handle->destroyed;
   });
}

sub _send {
   my ($self, $message, $done) = @_;

   my $ok = eval {
      my $handle = $self->{write_handle} or die "MCP stream is not connected\n";
      $handle->push_write (JSON::XS::encode_json ($message) . "\n");
      1
   };
   $done->($ok ? (1, undef) : (0, { transport => 1, message => "$@" }));
}

sub _shutdown {
   my ($self) = @_;

   my $read = delete $self->{read_handle};
   my $write = delete $self->{write_handle};
   $read->destroy if $read;
   $write->destroy if $write && $write != $read;
   if (my $pid = delete $self->{pid}) {
      kill TERM => $pid unless $self->{idle_shutdown_expected};
   }
   delete $self->{child};
}

1
Revision:	1.4
Committed:	Tue Oct 13 10:17:31 2026 UTC (2 weeks ago) by root
Branch:	MAIN
Changes since 1.3:	+8 -6 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3			AnyEvent::MCP::Client::JSONL - MCP byte streams and stdio subprocesses
4
5			=head1 SYNOPSIS
6
7			my $client = AnyEvent::MCP::Client::JSONL->new (
8			command => [$program, @args],
9			env => { PERL_ANYEVENT_MCP_MULTIBROKER_PROTOCOL => "stdio" },
10			);
11
12	root	1.2	=head1 DESCRIPTION
13
14			Use this transport when the MCP server is a subprocess or an already
15			connected byte stream. It reads one JSON-RPC message per line, so stdout
16			from a child server must contain protocol messages only. Diagnostic output
17			belongs on stderr. A single stray banner on stdout can break the connection.
18
19			An argument array executes the program directly; a command string runs
20			through a shell. Prefer the array form when no shell syntax is needed.
21			The process starts on the first connection, not when the client object
22			is constructed.
23
24	root	1.1	=head1 METHODS
25
26			=head2 $client = AnyEvent::MCP::Client::JSONL->new (%config)
27
28			C<command> is an argument array for direct execution, or a string explicitly
29			run through C</bin/sh -c>. The child inherits stderr. C<env> contains child
30			environment overrides. No command runs until connecting.
31
32			C<handle> contains AnyEvent::Handle options, excluding the filehandle and
33			read/error/EOF callbacks managed here. C<max_size> bounds an incoming JSON
34			line, defaulting to 16 MiB.
35
36			C<name> is available for application identification but does not load transport
37			defaults. The library does not infer a subprocess command or environment.
38
39			=head2 $client->attach ($fh_in, $fh_out)
40
41			Uses existing handles instead of a command. C<$fh_out> defaults to C<$fh_in>
42			for a bidirectional socket. The client takes ownership. Attach before sending
43			requests. Closing an attached connection requires attaching new handles before
44			reconnecting.
45
46			Closing a subprocess connection sends SIGTERM and keeps its child watcher
47			alive until the child has been reaped. It does not restart an outstanding call.
48	root	1.3	An accepted multibroker idle shutdown is the exception: its child can exit
49			and perform cleanup without receiving SIGTERM.
50	root	1.1
51			=cut
52
53			package AnyEvent::MCP::Client::JSONL;
54
55			use common::sense;
56			use parent "AnyEvent::MCP::Client";
57			use AnyEvent::Handle ();
58			use AnyEvent::Util ();
59			use JSON::XS ();
60			use Scalar::Util qw(weaken);
61
62			sub attach {
63			my ($self, $fh_in, $fh_out) = @_;
64
65			$self->close if $self->{read_handle};
66			weaken $self;
67			$self->{read_handle} = AnyEvent::Handle->new (
68			%{$self->{handle} \|\| {}},
69	root	1.4	fh => $fh_in,
70	root	1.1	rbuf_max => $self->{max_size} \|\| 16 * 1024 * 1024,
71	root	1.4	on_read => undef,
72	root	1.1	on_error => sub { $self->close ($_[2]) if $self },
73	root	1.4	on_eof => sub { $self->close ("MCP stream closed") if $self },
74	root	1.1	);
75			$self->{write_handle} = $fh_out ? AnyEvent::Handle->new (
76			%{$self->{handle} \|\| {}},
77	root	1.4	fh => $fh_out,
78			on_read => undef,
79	root	1.1	on_error => sub { $self->close ($_[2]) if $self },
80	root	1.4	on_eof => sub { $self->close ("MCP output closed") if $self },
81	root	1.1	) : $self->{read_handle};
82			$self->_read;
83			}
84
85			sub _open {
86			my ($self, $done) = @_;
87
88			return $done->(1, undef) if $self->{read_handle};
89			return $done->(0, { transport => 1, message => "No command or attached stream" })
90			unless $self->{command};
91
92			my $ok = eval {
93			local %ENV = (%ENV, %{$self->{env} \|\| {}});
94			my ($parent, $child) = AnyEvent::Util::portable_socketpair;
95			die "Cannot create MCP socketpair: $!\n" unless defined $parent && defined $child;
96
97			my $pid;
98			my $cv = AnyEvent::Util::run_cmd (
99			ref $self->{command} eq "ARRAY" ? $self->{command} : ["/bin/sh", "-c", $self->{command}],
100			"<" => $child, ">" => $child, '$$' => \$pid, close_all => 1,
101			);
102			close $child;
103			$self->{pid} = $pid;
104			$self->attach ($parent);
105
106			weaken $self;
107			$cv->cb (sub {
108			my $status = $_[0]->recv;
109			if ($self && $self->{pid} == $pid) {
110			delete $self->{pid};
111			delete $self->{child};
112			$self->close ("MCP child exited (status $status)");
113			}
114			});
115			$self->{child} = $cv;
116			1
117			};
118			$done->($ok ? (1, undef) : (0, { transport => 1, message => "$@" }));
119			}
120
121			sub _read {
122			my ($self) = @_;
123	root	1.4
124	root	1.1	weaken $self;
125
126			$self->{read_handle}->push_read (line => sub {
127			my ($handle, $line) = @_;
128	root	1.4
129	root	1.1	return unless $self;
130			my $ok = eval {
131			$self->_receive (JSON::XS::decode_json $line);
132			1
133			};
134			return $self->close ("$@") unless $ok;
135			$self->_read if $self->{read_handle} && !$handle->destroyed;
136			});
137			}
138
139			sub _send {
140			my ($self, $message, $done) = @_;
141
142			my $ok = eval {
143			my $handle = $self->{write_handle} or die "MCP stream is not connected\n";
144			$handle->push_write (JSON::XS::encode_json ($message) . "\n");
145			1
146			};
147			$done->($ok ? (1, undef) : (0, { transport => 1, message => "$@" }));
148			}
149
150			sub _shutdown {
151			my ($self) = @_;
152
153			my $read = delete $self->{read_handle};
154			my $write = delete $self->{write_handle};
155			$read->destroy if $read;
156			$write->destroy if $write && $write != $read;
157			if (my $pid = delete $self->{pid}) {
158	root	1.3	kill TERM => $pid unless $self->{idle_shutdown_expected};
159	root	1.1	}
160			delete $self->{child};
161			}
162
163			1