package AnyEvent::STOMP::Client;
use strict;
use warnings;
use parent 'Object::Event';
use Carp;
use AnyEvent;
use AnyEvent::Handle;
use List::Util 'max';
our $VERSION = '0.38';
my $EOL = chr(10);
my $NULL = chr(0);
my %ENCODE_MAP = (
"\r" => "\\r",
"\n" => "\\n",
":" => "\\c",
"\\" => "\\\\",
);
my %DECODE_MAP = reverse %ENCODE_MAP;
sub new {
my $class = shift;
my $self = $class->SUPER::new;
$self->{connection_timeout_margin} = 250;
$self->{connected} = 0;
$self->{counter} = 0;
$self->{host} = shift || 'localhost';
$self->{port} = shift || 61613;
my $connect_headers = shift || {};
$self->{connect_headers} = {
'accept-version' => '1.2',
'host' => $self->{host},
'heart-beat' => '0,0'
};
if (defined $connect_headers->{'virtual-host'}) {
$self->{connect_headers}{host} = $connect_headers->{'virtual-host'};
}
if (defined $connect_headers->{'heart-beat'}) {
$self->{connect_headers}{'heart-beat'} = $connect_headers->{'heart-beat'};
}
if (defined $connect_headers->{'login'}
and defined $connect_headers->{'passcode'}
) {
$self->{connect_headers}{'login'} = $connect_headers->{'login'};
$self->{connect_headers}{'passcode'} = $connect_headers->{'passcode'};
}
my $tls_ctx = shift;
if (defined $tls_ctx) {
$self->{tls_hash}{tls} = 'connect';
$self->{tls_hash}{tls_ctx} = $tls_ctx;
if ($tls_ctx->{verify}) {
foreach my $key (keys %$tls_ctx) {
if ($key =~ m/_file$/ && not -r $tls_ctx->{$key}) {
die "ERROR: Cannot access $key at $tls_ctx->{$key}.\n";
}
}
}
}
return bless $self, $class;
}
sub connect {
my $self = shift;
croak "You already have established a connection." if $self->is_connected;
$self->{subscriptions} = {};
$self->{handle} = AnyEvent::Handle->new(
connect => [$self->{host}, $self->{port}],
keep_alive => 1,
no_delay => 1,
on_eof => sub {
undef $self->{handle};
$self->{connected} = 0;
$self->event('TRANSPORT_DISCONNECTED', $self->{host}, $self->{port});
},
on_connect => sub {
$self->event('TRANSPORT_CONNECTED', $self->{host}, $self->{port});
$self->send_frame('CONNECT', $self->{connect_headers});
},
on_connect_error => sub {
shift->destroy;
undef $self->{handle};
$self->{connected} = 0;
$self->event('TRANSPORT_CONNECT_ERROR', $self->{host}, $self->{port}, $!);
},
on_error => sub {
shift->destroy;
undef $self->{handle};
$self->{connected} = 0;
$self->event('CONNECTION_LOST', $self->{host}, $self->{port}, $!);
},
on_read => sub {
$self->read_frame;
},
%{$self->{tls_hash}},
);
}
sub disconnect {
my $self = shift;
my $ungraceful = shift;
unless ($self->is_connected) {
if (defined $self->{handle}) {
$self->{handle}->destroy;
}
$self->event('DISCONNECTED', $self->{host}, $self->{port}, $ungraceful);
return;
}
if (defined $ungraceful and $ungraceful) {
$self->send_frame('DISCONNECT');
$self->{connected} = 0;
if (defined $self->{handle}) {
$self->{handle}->push_shutdown;
$self->{handle}->destroy;
}
$self->event('DISCONNECTED', $self->{host}, $self->{port}, $ungraceful);
}
else {
my $receipt_id = $self->get_uuid;
$self->send_frame('DISCONNECT', {receipt => $receipt_id,});
$self->before_receipt(
sub {
my ($self, $header) = @_;
if ($header->{'receipt-id'} eq $receipt_id) {
$self->{connected} = 0;
$self->stop_event;
$self->unreg_me;
if (defined $self->{handle}) {
$self->{handle}->push_shutdown;
$self->{handle}->destroy;
}
$self->event('DISCONNECTED', $self->{host}, $self->{port}, $ungraceful);
}
}
);
}
}
sub DESTROY {
my $self = shift;
$self->disconnect(1) if $self->is_connected;
}
sub is_connected {
my $self = shift;
return defined $self->{handle} && $self->{connected};
}
sub set_connection_timeout_margin {
my ($self, $new_connection_timeout_margin) = @_;
if ($new_connection_timeout_margin =~ m/^\d+$/) {
$self->{connection_timeout_margin} = $new_connection_timeout_margin;
}
}
sub get_connection_timeout_margin {
return shift->{connection_timeout_margin};
}
sub set_heartbeat_intervals {
my $self = shift;
my ($cx, $cy) = split ',', $self->{connect_headers}{'heart-beat'};
my ($sx, $sy) = split ',', shift;
if ($cx == 0 or $sy == 0) {
$self->{heartbeat}{interval}{client} = 0;
}
else {
$self->{heartbeat}{interval}{client} = max($cx, $sy);
}
if ($sx == 0 or $cy == 0) {
$self->{heartbeat}{interval}{server} = 0;
}
else {
$self->{heartbeat}{interval}{server} = max($sx, $cy);
}
}
sub reset_client_heartbeat_timer {
my $self = shift;
my $interval = $self->{heartbeat}{interval}{client};
unless (defined $interval and $interval > 0) {
return;
}
$self->{heartbeat}{timer}{client} = AnyEvent->timer(
after => ($interval/1000),
cb => sub {
$self->send_heartbeat;
}
);
}
sub reset_server_heartbeat_timer {
my $self = shift;
my $interval = $self->{heartbeat}{interval}{server};
unless (defined $interval and $interval > 0) {
return;
}
$self->{heartbeat}{timer}{server} = AnyEvent->timer(
after => (($interval+$self->get_connection_timeout_margin)/1000),
cb => sub {
if ($self->{connected}) {
$self->{connected} = 0;
if (defined $self->{handle}) {
$self->{handle}->push_shutdown;
$self->{handle}->destroy;
undef $self->{handle};
}
$self->event('CONNECTION_LOST', $self->{host}, $self->{port}, 'Missed server heartbeat');
}
}
);
}
sub get_uuid {
my $self = shift;
return int(time).$self->{counter}++;
}
sub subscribe {
my $self = shift;
my $destination = shift;
my $ack_mode = shift || 'auto';
my $additional_headers = shift || {};
unless ($ack_mode =~ m/(?:auto|client|client-individual)/) {
croak "Invalid acknowledgement mode '$ack_mode'. "
."Valid modes are 'auto', 'client' and 'client-individual'."
}
unless (defined $destination) {
croak "Would you mind supplying me with a destination?";
}
if (defined $self->{subscriptions}{$destination}) {
carp "You already subscribed to '$destination'.";
if ($self->handles('SUBSCRIBED')) {
$self->event('SUBSCRIBED', $destination);
}
}
else {
my $subscription_id = shift || $self->get_uuid;
$self->{subscriptions}{$destination} = $subscription_id;
my $header = {
destination => $destination,
id => $subscription_id,
ack => $ack_mode,
%$additional_headers,
};
if ($self->handles('SUBSCRIBED')) {
unless (defined $header->{receipt}) {
$header->{receipt} = $self->get_uuid;
}
$self->before_receipt(
sub {
my ($self, $receipt_header) = @_;
if ($receipt_header->{'receipt-id'} eq $header->{receipt}) {
$self->event('SUBSCRIBED', $header->{destination});
$self->stop_event;
$self->unreg_me;
}
}
);
}
$self->send_frame('SUBSCRIBE', $header);
}
return $self->{subscriptions}{$destination};
}
sub unsubscribe {
my $self = shift;
my $destination = shift;
my $additional_headers = shift || {};
unless (defined $destination) {
croak "Would you mind supplying me with a destination?";
}
unless ($self->{subscriptions}{$destination}) {
croak "You've never subscribed to '$destination', have you?";
}
my $header = {
id => $self->{subscriptions}{$destination},
%$additional_headers,
};
if ($self->handles('UNSUBSCRIBED')) {
$header->{receipt} = $self->get_uuid unless defined $header->{receipt};
$self->before_receipt(
sub {
my ($self, $receipt_header) = @_;
if ($receipt_header->{'receipt-id'} eq $header->{receipt}) {
$self->event('UNSUBSCRIBED', $destination);
$self->stop_event;
$self->unreg_me;
}
}
);
}
$self->send_frame('UNSUBSCRIBE', $header);
delete $self->{subscriptions}{$destination};
}
sub header_hash2string {
my $header_hashref = shift;
return join($EOL, map { "$_:$header_hashref->{$_}" } keys %$header_hashref);
}
sub header_string2hash {
my $header_string = shift;
my $result_hashref = {};
foreach (split /\n/, $header_string) {
if (m/([^\r\n:]+):([^\r\n:]*)/) {
# Repeated Header Entries: Do not replace if it already exists
$result_hashref->{$1} = $2 unless defined $result_hashref->{$1};
}
}
return $result_hashref;
}
sub encode_header {
my $header_hashref = shift;
my $result_hashref = {};
my $ENCODE_KEYS = '['.join('', map(sprintf('\\x%02x', ord($_)), keys(%ENCODE_MAP))).']';
while (my ($k, $v) = each(%$header_hashref)) {
$v =~ s/($ENCODE_KEYS)/$ENCODE_MAP{$1}/ego;
$k =~ s/($ENCODE_KEYS)/$ENCODE_MAP{$1}/ego;
$result_hashref->{$k} = $v;
}
return $result_hashref;
}
sub decode_header {
my $header_hashref = shift;
my $result_hashref = {};
while (my ($k, $v) = each(%$header_hashref)) {
if ($v =~ m/(\\.)/) {
$v =~ s/(\\.)/$DECODE_MAP{$1}/eg || croak "Invalid header value.";
}
if ($k =~ m/(\\.)/) {
$k =~ s/(\\.)/$DECODE_MAP{$1}/eg || croak "Invalid header key.";
}
$result_hashref->{$k} = $v;
}
return $result_hashref;
}
sub send_frame {
my ($self, $command, $header_hashref, $body) = @_;
unless ($self->is_connected or $command eq 'CONNECT') {
croak "Have you considered connecting to a STOMP broker first before "
."trying to send something?";
}
utf8::encode($command);
my $header;
if ($command eq 'CONNECT') {
$header = header_hash2string($header_hashref);
}
else {
$header = header_hash2string(encode_header($header_hashref));
}
utf8::encode($header);
my $frame;
if ($command eq 'SEND') {
$body = '' unless defined $body;
$frame = $command.$EOL.$header.$EOL.$EOL.$body.$NULL;
}
else {
$frame = $command.$EOL.$header.$EOL.$EOL.$NULL;
}
$self->event('SEND_FRAME', $frame);
$self->event($command, $frame) if ($command =~ m/SEND|ACK|NACK|/);
$self->{handle}->push_write($frame);
$self->reset_client_heartbeat_timer;
}
sub send {
my ($self, $destination, $headers, $body) = @_;
if (defined $destination) {
$headers->{destination} = $destination;
}
else {
croak "Would you mind supplying me with a destination?";
}
unless (defined $headers->{'content-length'}) {
$headers->{'content-length'} = length $body || 0;
}
unless (defined $headers->{'content-type'}) {
carp "It is strongly recommended to set the 'content-type' header.";
}
$self->send_frame('SEND', $headers, $body);
}
sub ack {
my ($self, $ack_id, $transaction) = @_;
unless ($ack_id) {
croak "I do really need the message's ack header to ACK it.";
}
my $header = {id => $ack_id,};
$header->{transaction} = $transaction if (defined $transaction);
$self->send_frame('ACK', $header);
}
sub nack {
my ($self, $ack_id, $transaction) = @_;
unless ($ack_id) {
croak "I do really need the message's ack header to NACK it.";
}
my $header = {id => $ack_id,};
$header->{transaction} = $transaction if (defined $transaction);
$self->send_frame('NACK', $header);
}
sub send_heartbeat {
my $self = shift;
if ($self->is_connected) {
$self->{handle}->push_write($EOL);
$self->reset_client_heartbeat_timer;
}
}
sub begin_transaction {
my $self = shift;
my $id = shift;
my $additional_headers = shift || {};
croak "I really need a transaction identifier here!" unless (defined $id);
if (defined $self->{transactions}{$id}) {
carp "You've already begun transaction '$id'";
}
else {
$self->send_frame('BEGIN', {transaction => $id, %$additional_headers,});
$self->{transactions}{$id} = 1;
}
}
sub commit_transaction {
my $self = shift;
my $id = shift;
my $additional_headers = shift || {};
croak "I really need a transaction identifier here!" unless (defined $id);
unless (defined $self->{transactions}{$id}) {
carp "You've already commited transaction '$id'";
}
$self->send_frame('COMMIT', {transaction => $id, %$additional_headers,});
delete $self->{transactions}{$id};
}
sub abort_transaction {
my $self = shift;
my $id = shift;
my $additional_headers = shift || {};
croak "I really need a transaction identifier here!" unless (defined $id);
unless (defined $self->{transactions}{$id}) {
carp "You've already commited transaction '$id'";
}
$self->send_frame('ABORT', {transaction => $id, %$additional_headers,});
delete $self->{transactions}{$id};
}
sub read_frame {
my $self = shift;
$self->{handle}->unshift_read(
line => sub {
my ($handle, $command, $eol) = @_;
$self->reset_server_heartbeat_timer;
if ($command =~ /(CONNECTED|MESSAGE|RECEIPT|ERROR)/) {
$command = $1;
}
else {
return;
}
$self->{handle}->unshift_read(
regex => qr<\r?\n\r?\n>,
cb => sub {
my ($handle, $header_string) = @_;
my $header_hashref = header_string2hash($header_string);
my $args;
# The headers of the CONNECTED frame are not en-/decoded
# for backwards compatibility with STOMP 1.0
unless ($command eq 'CONNECTED') {
$header_hashref = decode_header($header_hashref);
}
if ($command =~ m/MESSAGE|ERROR/) {
if (defined $header_hashref->{'content-length'}) {
$args->{chunk} = $header_hashref->{'content-length'};
}
else {
$args->{regex} = qr<[^\000]*\000>;
}
$self->{handle}->unshift_read(
%$args,
cb => sub {
my ($handle, $body) = @_;
$self->event('READ_FRAME', $command, $header_hashref, $body);
$self->event($command, $header_hashref, $body);
if (defined $header_hashref->{subscription}) {
$self->event(
$command.'-'.$header_hashref->{subscription},
$header_hashref,
$body
);
}
}
);
}
else {
if ($command eq 'CONNECTED') {
$self->{connected} = 1;
$self->{session} = $header_hashref->{session};
$self->{version} = $header_hashref->{version};
$self->{server} = $header_hashref->{server};
$self->set_heartbeat_intervals($header_hashref->{'heart-beat'});
}
$self->event('READ_FRAME', $command, $header_hashref);
$self->event($command, $header_hashref);
}
},
);
},
);
}
sub on_transport_connected {
return shift->reg_cb('TRANSPORT_CONNECTED', shift);
}
sub on_transport_disconnected {
return shift->reg_cb('TRANSPORT_DISCONNECTED', shift);
}
sub on_connected {
return shift->reg_cb('CONNECTED', shift);
}
sub on_disconnected {
return shift->reg_cb('DISCONNECTED', shift);
}
sub on_connection_lost {
return shift->reg_cb('CONNECTION_LOST', shift);
}
sub on_connect_error {
return shift->reg_cb('TRANSPORT_CONNECT_ERROR', shift);
}
sub on_send_frame {
return shift->reg_cb('SEND_FRAME', shift);
}
sub on_send {
return shift->reg_cb('SEND', shift);
}
sub on_ack {
return shift->reg_cb('ACK', shift);
}
sub on_nack {
return shift->reg_cb('NACK', shift);
}
sub on_read_frame {
return shift->reg_cb('READ_FRAME', shift);
}
sub on_message {
my ($self, $cb, $destination) = @_;
if (defined $destination) {
unless (defined $self->{subscriptions}{$destination}) {
carp "You haven't subscribed to '"
.$self->{subscriptions}{$destination}."' yet. This callback may never be called.";
}
return $self->reg_cb('MESSAGE-'.$self->{subscriptions}{$destination}, $cb);
}
else {
return $self->reg_cb('MESSAGE', $cb);
}
}
sub before_receipt {
return shift->reg_cb('before_RECEIPT', shift);
}
sub on_receipt {
return shift->reg_cb('RECEIPT', shift);
}
sub on_error {
return shift->reg_cb('ERROR', shift);
}
sub on_subscribed {
return shift->reg_cb('SUBSCRIBED', shift);
}
sub on_unsubscribed {
return shift->reg_cb('UNSUBSCRIBED', shift);
}
sub unregister_callback {
my ($self, $guard) = @_;
$self->unreg_cb($guard);
}
1;
__END__
=head1 NAME
AnyEvent::STOMP::Client - An event-based non-blocking STOMP 1.2 client based on
AnyEvent and Object::Event.
=head1 SYNOPSIS
use AnyEvent::STOMP::Client;
my $stomp_client = new AnyEvent::STOMP::Client()
$stomp_client->connect();
$stomp_client->on_connected(
sub {
my $self = shift;
$self->subscribe('/queue/test-destination');
$self->send(
'/queue/test-destination',
{'content-type' => 'text/plain',},
"Hello World!"
);
}
);
$stomp_client->on_message(
sub {
my ($self, $header, $body) = @_;
print "$body\n";
}
);
AnyEvent->condvar->recv;
=head1 DESCRIPTION
AnyEvent::STOMP::Client provides a STOMP (Simple Text Oriented Messaging
Protocol) client. Thanks to AnyEvent, AnyEvent::STOMP::Client is completely
non-blocking, by making extensive use of the AnyEvent::Handle and timers (and,
under the hood, AnyEvent::Socket). Building on Object::Event,
AnyEvent::STOMP::Client implements various events (e.g. the MESSAGE event, when
a STOMP MESSAGE frame is received) and offers callbacks for these (e.g.
on_message($callback)).
=head1 METHODS
=head2 $client = new $host, $port, $connect_headers, $tls_context
Create an instance of C<AnyEvent::STOMP::Client>.
=over
=item C<$host>
String, optional, defaults to C<localhost>. The host, where a STOMP-compatible
message broker is running.
=item C<$port>
Integer, optional, defaults to C<61613>. The TCP port we connect to. I.e. the
port where the message broker instance is listening.
=item C<$connect_headers>
Hash, optional, empty by default. May be used to add arbitrary headers to the
STOMP C<CONNECT> frame. STOMP login headers would, for example, be supplied
using this parameter.
=item C<$tls_context>
Hash, optional, undef by default. May be used to supply a SSL/TLS context
directly to C<AnyEvent::Handle>. See L<AnyEvent::TLS> for documentation.
=back
=head3 Example
C<< my $client = AnyEvent::STOMP::Client->new(
'127.0.0.1',
61614,
{'login' => 'guest', 'passcode' => 'guest', 'virtual-host' => 'foo'}
); >>
=head2 $client = connect
Connect to the specified STOMP message broker. Croaks if you already
established a connection.
=head2 $client->disconnect
Sends a C<DISCONNECT> STOMP frame to the message broker (if we are still
connected). Croaks, if you are trying to disconnect without actually being
connected.
=over
=item C<$ungraceful>
Boolean, defaults to 0. If the ungraceful option is set, then simply a
C<DISCONNECT> STOMP frame is sent and the connection state is considered to be
disconnected without awaiting any response from the server.
If, however, the option is not set, then a receipt is asked for and the
connection is only considered to be no longer established upon receiving a
receipt for the C<DISCONNECT> frame.
=back
=head2 bool $client->is_connected
Check whether we are still connected to the broker. May only be accurate if
STOMP heart-beats are used.
=head2 $subscription_id = $client->subscribe $destination, $ack_mode, $additional_headers
Subscribe to a destination by sending a C<SUBSCRIBE> STOMP frame to the message
broker. Returns the subscription identifier.
=over
=item C<$destination>
String, mandatory. The destination to which we want to subscribe to.
=item C<$ack_mode>
C<auto> | C<client> | C<client-individual>, optional, defaults to C<auto>.
See the STOMP documentation for further information on acknowledgement modes.
=item C<$additional_headers>
Used to pass arbitrary headers to the C<SUBSCRIBE> STOMP frame. Broker specific
flow control parameters for example is what would want to supply here.
=back
=head2 $client->unsubscribe $destination, $additional_headers
Unsubscribe from a destination by sending an C<UNSUBSCRIBE> STOMP frame to the
message broker.
=over
=item C<$destination>
String, mandatory. The destination from which we want to unsubscribe.
=item C<$additional_headers>
Used to pass arbitrary headers to the C<UNSUBSCRIBE> STOMP frame.
=back
=head2 $client->send $destination, $headers, $body
Send a STOMP C<SEND> frame to the message broker.
=over
=item C<$destination>
String, mandatory. The destination to which to send the message to.
=item C<$header>
Hash, optional, empty by default. Arbitrary headers included in the C<SEND>
frame. See the STOMP documentation for supported headers.
=item C<$body>
String, optional, empty by default. The body of the message, according to the
content-type specified in the header.
=back
=head2 $client->ack $ack_id, $transaction_id
Send an C<ACK> frame to acknowledge a received message.
=over
=item C<$ack_id>
String, mandatory. Has to match the C<ack> header of the message that is to be
acknowledged.
=item C<$transaction_id>
String, optional. A transaction identifier, if the C<ACK> is part of a transaction.
=back
=head2 $client->nack $ack_id, $transaction_id
Send an C<NACK> frame to NOT acknowledge a received message.
=over
=item C<$ack_id>
String, mandatory. Has to match the C<ack> header of the message that is to be
nacked.
=item C<$transaction_id>
String, optional. A transaction identifier, if the C<NACK> is part of a
transaction.
=back
=head2 $client->begin_transaction $transaction_id, $additional_headers
Begin a STOMP transaction.
=over
=item C<$transaction_id>
String, mandatory. A unique identifier for the transaction.
=item C<$additional_headers>
Hash, optional, empty by default. Used to pass arbitrary headers to the STOMP
frame.
=back
=head2 $client->commit_transaction $transaction_id, $additional_headers
Commit a STOMP transaction.
=over
=item C<$transaction_id>
String, mandatory. A unique identifier for the transaction.
=item C<$additional_headers>
Hash, optional, empty by default. Used to pass arbitrary headers to the STOMP
frame.
=back
=head2 $client->abort_transaction $transaction_id, $additional_headers
Abort a STOMP transaction.
=over
=item C<$transaction_id>
String, mandatory. A unique identifier for the transaction.
=item C<$additional_headers>
Hash, optional, empty by default. Used to pass arbitrary headers to the STOMP
frame.
=back
=head2 Callbacks
In order for the C<AnyEvent::STOMP::Client> to be useful, callback subroutines
can be registered for the following events:
=head3 $guard = $client->on_connected $callback
Invoked when a CONNECTED frame is received. Parameters passed to the callback:
C<$self>, C<$header_hashref>.
=head3 $guard = $client->on_disconnected $callback
Invoked after having successfully disconnected from a broker. I.e. when a
callback is registered for this event and the C<disconnect> subroutine is
called, then a receipt header is included in the DISCONNECT frame and the
disconnected event is fired upon receiving the receipt for the DISCONNECT frame.
Parameters passed to the callback: C<$self>, C<$host>, C<$port>.
=head3 $guard = $client->on_connection_lost $callback
Invoked when either the C<on_error> callback specified in the
C<AnyEvent::Handle> constructor is called, or when no more
heartbeats arrive from the server.
Parameters passed to the callback: C<$self>, C<$host>, C<$port>.
=head3 $guard = $client->on_connect_error $callback
Invoked when the C<on_connect_error> callback specified in the
C<AnyEvent::Handle> constructor is called.
Parameters passed to the callback: C<$self>, C<$host>, C<$port>.
=head3 $guard = $client->on_send_frame $callback
Invoked when a STOMP frame is sent. Parameters passed to the callback:
C<$self>, C<$frame> (the sent frame as string).
=head3 $guard = $client->on_send $callback
Invoked when a STOMP SEND command is sent. Parameters passed to the callback:
C<$self>, C<$frame> (the sent frame as string).
=head3 $guard = $client->on_ack $callback
Invoked when a STOMP ACK command is sent. Parameters passed to the callback:
C<$self>, C<$frame> (the sent frame as string).
=head3 $guard = $client->on_nack $callback
Invoked when a STOMP NACK command is sent. Parameters passed to the callback:
C<$self>, C<$frame> (the sent frame as string).
=head3 $guard = $client->on_read_frame $callback
Invoked when a STOMP frame is received (irrespective of the STOMP command).
Parameters passed to the callback: C<$self>, C<$command>, C<$header_hashref>,
C<$body> (may be C<undef>, if the frame is not specified to contain a body).
=head3 $guard = $client->on_message $callback $destination
Invoked when a MESSAGE frame is received. Optionally, a C<$destination>
parameter may be specified, resulting in the callback only being invoked,
when a MESSAGE is received from that specific destination.
Parameters passed to the callback: C<$self>, C<$header_hashref>, C<$body>.
=head3 $guard = $client->on_receipt $callback
Invoked when a RECEIPT frame is received. Parameters passed to the callback:
C<$self>, C<$header_hashref>.
=head3 $guard = $client->on_error $callback
Invoked when an ERROR frame is received. Parameters passed to the callback:
C<$self>, C<$header_hashref>, C<$body>.
=head3 $guard = $client->on_subscribed $callback
Invoked after having successfully subscribed to a destination. Works behind the
scenes like the C<on_disconnected> described above. Parameters passed to the
callback: C<$self>, C<$destination>.
=head3 $guard = $client->on_unsubscribed $callback
Invoked after having successfully unsubscribed to a destination. Works behind
the scenes like the C<on_disconnected> described above. Parameters passed to the
callback: C<$self>, C<$destination>.
=head3 $client->unregister_callback $guard
To unregister a previously registered callback.
=over
=item C<$guard>
The return value of one of the above on_<xyz> subroutines, identifying the
registered callback.
=back
=head1 BUGS / LIMITATIONS
=over
=item
Currently only the most recent version of STOMP, i.e. 1.2, is supported.
=back
=head1 SEE ALSO
L<AnyEvent>, L<AnyEvent::Handle>, L<AnyEvent::TLS>, L<Object::Event>,
L<STOMP 1.2 Documentation|http://stomp.github.io/stomp-specification-1.2.html>
=head1 AUTHOR
Raphael Seebacher, E<lt>raphael@seebachers.chE<gt>
=head1 COPYRIGHT AND LICENSE
Copyright (C) 2013 by L<Open Systems AG|http://www.open.ch>. All rights reserved.
This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.
=cut