MCP/Client/JSONL.pm

=head1 NAME

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

=head1 SYNOPSIS

   use AnyEvent::MCP::Client::JSONL;

   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
on a conventional stdio transport must contain protocol messages only.
The C<command> mode here connects the child's stdin and stdout to a
socketpair; diagnostic output belongs on stderr. A stray banner or log
message on the protocol stream 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

=over

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

Accepts the common L<AnyEvent::MCP::Client> options and these transport
options:

=over

=item command => [$program, $arg...]

=item command => $shell_command

Argument array for direct execution, or a string run through C</bin/sh -c>.
The child inherits stderr. No command runs until connecting.
Omit this option when using C<attach> instead.

=item env => { %environment }

Child environment overrides. Unspecified variables are inherited from
the parent; the parent environment is unchanged.

=item handle => { %handle }

L<AnyEvent::Handle> options. The filehandle and read/error/EOF callbacks
are managed by this transport.

=item max_size => $bytes

Bounds a buffered incoming JSON line, defaulting to 16 MiB.

=back

C<name> does not load transport defaults. The library does not infer a
subprocess command or environment.

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

Uses existing handles instead of a command. C<$fh_in> may also be an
L<AnyEvent::Handle>, whose buffered input is preserved. C<$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.

=back

=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 blessed);

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

   $self->close if $self->{read_handle};
   weaken $self;
   $self->{read_handle} = blessed $fh_in && $fh_in->isa ("AnyEvent::Handle")
      ? $fh_in : AnyEvent::Handle->new (%{$self->{handle} || {}}, fh => $fh_in);
   $self->{read_handle}{rbuf_max} = $self->{max_size} || 16 * 1024 * 1024;
   $self->{read_handle}->on_read (undef);
   $self->{read_handle}->on_error (sub { $self->close ($_[2]) if $self });
   $self->{read_handle}->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:	1.7
Committed:	Thu Oct 15 05:48:13 2026 UTC (12 days, 8 hours ago) by root
Branch:	MAIN
Changes since 1.6:	+9 -10 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	root	1.6	use AnyEvent::MCP::Client::JSONL;
8
9	root	1.1	my $client = AnyEvent::MCP::Client::JSONL->new (
10			command => [$program, @args],
11			env => { PERL_ANYEVENT_MCP_MULTIBROKER_PROTOCOL => "stdio" },
12			);
13
14	root	1.2	=head1 DESCRIPTION
15
16			Use this transport when the MCP server is a subprocess or an already
17			connected byte stream. It reads one JSON-RPC message per line, so stdout
18	root	1.5	on a conventional stdio transport must contain protocol messages only.
19			The C<command> mode here connects the child's stdin and stdout to a
20			socketpair; diagnostic output belongs on stderr. A stray banner or log
21			message on the protocol stream can break the connection.
22	root	1.2
23			An argument array executes the program directly; a command string runs
24			through a shell. Prefer the array form when no shell syntax is needed.
25			The process starts on the first connection, not when the client object
26			is constructed.
27
28	root	1.1	=head1 METHODS
29
30	root	1.6	=over
31
32			=item $client = AnyEvent::MCP::Client::JSONL->new (%config)
33
34			Accepts the common L<AnyEvent::MCP::Client> options and these transport
35			options:
36
37			=over
38
39			=item command => [$program, $arg...]
40
41			=item command => $shell_command
42
43			Argument array for direct execution, or a string run through C</bin/sh -c>.
44			The child inherits stderr. No command runs until connecting.
45			Omit this option when using C<attach> instead.
46	root	1.1
47	root	1.6	=item env => { %environment }
48	root	1.1
49	root	1.6	Child environment overrides. Unspecified variables are inherited from
50			the parent; the parent environment is unchanged.
51	root	1.1
52	root	1.6	=item handle => { %handle }
53	root	1.1
54	root	1.6	L<AnyEvent::Handle> options. The filehandle and read/error/EOF callbacks
55			are managed by this transport.
56
57			=item max_size => $bytes
58
59			Bounds a buffered incoming JSON line, defaulting to 16 MiB.
60
61			=back
62
63			C<name> does not load transport defaults. The library does not infer a
64			subprocess command or environment.
65
66			=item $client->attach ($fh_in, $fh_out)
67	root	1.1
68	root	1.7	Uses existing handles instead of a command. C<$fh_in> may also be an
69			L<AnyEvent::Handle>, whose buffered input is preserved. C<$fh_out> defaults to C<$fh_in>
70	root	1.1	for a bidirectional socket. The client takes ownership. Attach before sending
71			requests. Closing an attached connection requires attaching new handles before
72			reconnecting.
73
74			Closing a subprocess connection sends SIGTERM and keeps its child watcher
75			alive until the child has been reaped. It does not restart an outstanding call.
76	root	1.3	An accepted multibroker idle shutdown is the exception: its child can exit
77			and perform cleanup without receiving SIGTERM.
78	root	1.1
79	root	1.6	=back
80
81	root	1.1	=cut
82
83			package AnyEvent::MCP::Client::JSONL;
84
85			use common::sense;
86			use parent "AnyEvent::MCP::Client";
87			use AnyEvent::Handle ();
88			use AnyEvent::Util ();
89			use JSON::XS ();
90	root	1.7	use Scalar::Util qw(weaken blessed);
91	root	1.1
92			sub attach {
93			my ($self, $fh_in, $fh_out) = @_;
94
95			$self->close if $self->{read_handle};
96			weaken $self;
97	root	1.7	$self->{read_handle} = blessed $fh_in && $fh_in->isa ("AnyEvent::Handle")
98			? $fh_in : AnyEvent::Handle->new (%{$self->{handle} \|\| {}}, fh => $fh_in);
99			$self->{read_handle}{rbuf_max} = $self->{max_size} \|\| 16 * 1024 * 1024;
100			$self->{read_handle}->on_read (undef);
101			$self->{read_handle}->on_error (sub { $self->close ($_[2]) if $self });
102			$self->{read_handle}->on_eof (sub { $self->close ("MCP stream closed") if $self });
103	root	1.1	$self->{write_handle} = $fh_out ? AnyEvent::Handle->new (
104			%{$self->{handle} \|\| {}},
105	root	1.4	fh => $fh_out,
106			on_read => undef,
107	root	1.1	on_error => sub { $self->close ($_[2]) if $self },
108	root	1.4	on_eof => sub { $self->close ("MCP output closed") if $self },
109	root	1.1	) : $self->{read_handle};
110			$self->_read;
111			}
112
113			sub _open {
114			my ($self, $done) = @_;
115
116			return $done->(1, undef) if $self->{read_handle};
117			return $done->(0, { transport => 1, message => "No command or attached stream" })
118			unless $self->{command};
119
120			my $ok = eval {
121			local %ENV = (%ENV, %{$self->{env} \|\| {}});
122			my ($parent, $child) = AnyEvent::Util::portable_socketpair;
123			die "Cannot create MCP socketpair: $!\n" unless defined $parent && defined $child;
124
125			my $pid;
126			my $cv = AnyEvent::Util::run_cmd (
127			ref $self->{command} eq "ARRAY" ? $self->{command} : ["/bin/sh", "-c", $self->{command}],
128			"<" => $child, ">" => $child, '$$' => \$pid, close_all => 1,
129			);
130			close $child;
131			$self->{pid} = $pid;
132			$self->attach ($parent);
133
134			weaken $self;
135			$cv->cb (sub {
136			my $status = $_[0]->recv;
137			if ($self && $self->{pid} == $pid) {
138			delete $self->{pid};
139			delete $self->{child};
140			$self->close ("MCP child exited (status $status)");
141			}
142			});
143			$self->{child} = $cv;
144			1
145			};
146			$done->($ok ? (1, undef) : (0, { transport => 1, message => "$@" }));
147			}
148
149			sub _read {
150			my ($self) = @_;
151	root	1.4
152	root	1.1	weaken $self;
153
154			$self->{read_handle}->push_read (line => sub {
155			my ($handle, $line) = @_;
156	root	1.4
157	root	1.1	return unless $self;
158			my $ok = eval {
159			$self->_receive (JSON::XS::decode_json $line);
160			1
161			};
162			return $self->close ("$@") unless $ok;
163			$self->_read if $self->{read_handle} && !$handle->destroyed;
164			});
165			}
166
167			sub _send {
168			my ($self, $message, $done) = @_;
169
170			my $ok = eval {
171			my $handle = $self->{write_handle} or die "MCP stream is not connected\n";
172			$handle->push_write (JSON::XS::encode_json ($message) . "\n");
173			1
174			};
175			$done->($ok ? (1, undef) : (0, { transport => 1, message => "$@" }));
176			}
177
178			sub _shutdown {
179			my ($self) = @_;
180
181			my $read = delete $self->{read_handle};
182			my $write = delete $self->{write_handle};
183			$read->destroy if $read;
184			$write->destroy if $write && $write != $read;
185			if (my $pid = delete $self->{pid}) {
186	root	1.3	kill TERM => $pid unless $self->{idle_shutdown_expected};
187	root	1.1	}
188			delete $self->{child};
189			}
190
191			1