AnyEvent-MP/MP/Intro.pod

=head1 Message Passing for the Non-Blocked Mind

=head1 Introduction and Terminology

This is a tutorial about how to get the swing of the new L<AnyEvent::MP>
module. Which allows us to transparently pass messages to our own process
and to other processes on another or the same host.

What kind of messages? Well, basically a message here means a list of
Perl strings, numbers, hashes and arrays, mostly everything that can be
expressed as a L<JSON> text (as JSON is used by default in the protocol).

And next you might ask: between which entities are those messages
being "passed"? Basically between C<nodes>: a nodes is basically a
process/program that use L<AnyEvent::MP> and can run either on the same or
different hosts.

In this tutorial I'll show you how to write a simple chat server based on
L<AnyEvent::MP>.

=head1 System Requirements

Before we can start we have to make sure some things work on your
system.

You should of course also make sure that L<AnyEvent> and L<AnyEvent::MP>
are installed. But how to do that is out of scope of this tutorial.

Then we have to setup a I<shared secret>. For two L<AnyEvent::MP> nodes to
be able to communicate with each other and authenticate each other it is
necessary to setup the same I<shared secret> for both of them. For testing
you can write a random string into the file C<.aemp-secret> in your home
directory:

   mcookie > ~/.aemp-secret

   # or something more predictable
   echo "secret123#4blabla_please_pick_your_own" > ~/.aemp-secret

Connections will only be successful when the nodes that want to connect
to each other have the same I<shared secret>. For more security, you can
put a self-signed SSL/TLS key/certificate pair into the file (or a normal
key/certificate and it's CA certificate).

B<If something does not work as expected, and for example tcpdump shows
that the connections are closed almost immediatly, you should make sure
that F<~/.aemp-secret> is the same on all hosts/user accounts that you try
to connect with each other!>

=head1 The Chat Client

OK, lets start by implementing the "frontend" of the client. We will
develop the client first and postpone the server for later, as the most
complex things actually happen in the client.

We will use L<AnyEvent::Handle> to do non-blocking IO read on standard
input (all of this code deals with actually handling user input, no
message passing yet):

   #!perl

   use AnyEvent;
   use AnyEvent::Handle;

   sub send_message {
      die "This is where we will send the messages to the server"
         . "in the next step of this tutorial.\n"
   }

   # make an AnyEvent condition variable for the 'quit' condition
   # (when we want to exit the client).
   my $quit_cv = AnyEvent->condvar;

   my $stdin_hdl = AnyEvent::Handle->new (
      fh       => *STDIN,
      on_error => sub { $quit_cv->send },
      on_read  => sub {
         my ($hdl) = @_;

         $hdl->push_read (line => sub {
            my ($hdl, $line) = @_;

            if ($line =~ /^\/quit/) { # /quit will end the client
               $quit_cv->send;
            } else {
               send_message ($line);
            }
         });
      }
   );

   $quit_cv->recv;

This is now a very basic client. Explaining explicitly what
L<AnyEvent::Handle> does or what a I<condvar> is all about is out of scope
of this document, please consult L<AnyEvent::Intro> or the manual pages
for L<AnyEvent> and L<AnyEvent::Handle>.

=head1 First Step Into Messaging

To supply the C<send_message> function we now take a look at
L<AnyEvent::MP>. This is an example of how it might look like:

   ... # the use lines from the above snippet

   use AnyEvent::MP;

   sub send_message {
      my ($msg) = @_;

      snd $server_port, message => $msg;
   }

   ... # the rest of the above script

The C<snd> function is exported by L<AnyEvent::MP>, it stands for 'send
a message'. The first argument is the I<port> (a I<port> is something
that can receive messages, represented by a printable string) of the
server which will receive the message. How we get this port will be
explained in the next step.

The remaining arguments of C<snd> are C<message> and C<$msg>, the first
two elements of the I<message> (a I<message> in L<AnyEvent::MP> is a
simple list of values, which can be sent to a I<port>).

So all the function does is send the two values C<message> (a constant
string to tell the server what to expect) and the actual message string.

Thats all fine and simple so far, but where do we get the
C<$server_port>? Well, we need to get the unique I<port id> of the
server's port where it wants to receive all the incoming chat messages. A
I<port id> is unfortunately a very unique string, which we are unable
to know in advance. But L<AnyEvent::MP> supports the concept of 'well
known ports', which is basically a port on the server side registered
under a well known name. For example, the server has a port for receiving
chat messages with a unique I<port id> and registered it under the name
C<chatter>.

BTW, these "well known port names" should follow similar rules as Perl
identifiers, so you should prefix them with your package/module name to
make them unique, unless you use them in the main program.

As I<messages> can only be sent to a I<port id> and not just to a name we have
to ask the server I<node> what I<port id> has the well known port with the
name C<chatter>.

Another new term, what is a I<node>: The messaging network that can be created with
L<AnyEvent::MP> consists of I<nodes>. A I<node> handles all the connection and
low level message sending logic for its application. The application in this
case is the server. Also every client has/is a I<node>.

=head1 Getting The Chatter Port

Ok, lots of talk, now some code. Now we will actually get the C<$server_port>
from the backend:

   ...

   use AnyEvent::MP;

   my $resolved_cv = AnyEvent->condvar;

   my $client_port = create_port;

   my $server_node = "localhost:1299#";

   snd $server_node, wkp => "chatter", "$client_port", "resolved";

   my $server_port;

   # setup a receiver callback for the 'resolved' message:
   $client_port->rcv (resolved => sub {
      my ($client_port, $type, $chatter_port_id) = @_;

      print "Resolved the server port 'chatter' to $chatter_port_id\n";
      $server_port = $chatter_port_id;

      $resolved_cv->send;
      1
   });

   # lets block the client until we resolved the server port.
   $resolved_cv->recv;

   # now setup another receiver callback for the chat messages:
   $client_port->rcv (message => sub {
      my ($client_port, $type, $msg) = @_;

      print "chat> $msg\n";
      0
   });

   # send the server a 'join' message:
   snd $server_port, join => "$client_port";

   sub send_message { ...

Now that was a lot of new stuff. In order to ask the server and receive an
answer we need to have a I<port> where we can receive the answer.
This is what C<create_port> will do for us, it just creates a new local
port and returns us an object (that will btw. stringify to the I<port id>),
that we can use to receive messages.

Next thing is the C<$server_node>. In order to refer to another node we need
some kind of string to reference it. The I<noderef> is basically a comma
separated list of C<host:port> pairs. We assume in this tutorial that the
server runs on your localhost at port 1299, this gives us the noderef
C<localhost:1299>.

Now you might ask what the C<#> at the end in C<$server_node> the above
example is about. Well, what I didn't tell you yet is that each I<node> has a
default I<port> to receive messages. The default port is the empty string
C<"">. The I<default port> of a I<node> also provides some special services for
us, for example resolving a well known port to a I<port id>.

Now to this line:

   snd $server_node, wkp => "chatter", "$client_port", "resolved";

We send a message with first element being C<wkp> (standing for 'well known
port'). Then the well known port name that we want to resolve to a I<port id>:
C<chatter>. And in order for the server node to be able to send us back the
resolved I<port id> we have to tell it where to send the result message: The
result message will have as it's first argument the string C<resolved> and
will be sent to C<$client_port> (the I<port id> of our own just created
port).

Next comes the receiver for this C<wkp> request.

   $client_port->rcv (resolved => sub {
      my ($client_port, $type, $chatter_port_id) = @_;
      ...
      1
   });

This sets up a receiver on our own port for the result message with the first
argument being the string C<resolved>. Receivers can match the contents of
the messages before actually 'sending' it to the given callback.

B<Please note> that the given callback has to return either a true or a false
value for indicating whether it is B<done> (true value) or still wants to
B<continue> (false value) receiving messages.

In this case we tell the C<$client_port> to look into the received messages and
look for the string C<resolved> in the first element of the message. If it is
found, the given callback will be called with the C<$client_port> as first
argument, and the message as the remaining arguments.

We name the first element of the message C<$type> in this case. It's a common
idiom to code the 'type' of a message into it's first element, this allows for
simple matching.

The result message will contain the I<port id> of the well known port C<chatter>
as next element, and will be put in C<$chatter_port_id>.

Next we just assign C<$server_port> and return a 1 (a true value)
from the callback. It indicates that we are done and don't want to receive
further C<resolved> messages with this callback.

Now we continue to the rest of the client by calling C<send> on
C<$resolved_cv>.

First new step after this is setting up the chat message receiver callback.

   $client_port->rcv (message => sub {
      my ($client_port, $type, $msg) = @_;

      print "chat> $msg\n";
      0
   });

We assume that all messages that are broadcast to all clients by the server
will contain the string C<message> as first element, and the actual message as
second element. The callback returns a false value this time, to indicate that
it wants to continue receiving messages.

Last but not least we actually tell the server to send us
the new chat messages from other clients. We do so by sending the
message type C<join> followed by our own I<port id>.

   # send the server a 'join' message:
   snd $server_port, join => "$client_port";

Then the server knows where to send all the new messages to.

=head1 The Completed Client

This is the complete client script:

   #!perl

   use AnyEvent;
   use AnyEvent::Handle;
   use AnyEvent::MP;

   my $resolved_cv = AnyEvent->condvar;

   my $client_port = create_port;

   my $server_node = "localhost:1299#";

   snd $server_node, wkp => "chatter", "$client_port", "resolved";

   my $server_port;

   # setup a receiver callback for the 'resolved' message:
   $client_port->rcv (resolved => sub {
      my ($client_port, $type, $chatter_port_id) = @_;

      print "Resolved the server port 'chatter' to $chatter_port_id\n";
      $server_port = $chatter_port_id;

      $resolved_cv->send;
      1
   });

   # lets block the client until we resolved the server port.
   $resolved_cv->recv;

   # now setup another receiver callback for the chat messages:
   $client_port->rcv (message => sub {
      my ($client_port, $type, $msg) = @_;

      print "chat> $msg\n";
      0
   });

   # send the server a 'join' message:
   snd $server_port, join => "$client_port";

   sub send_message {
      my ($msg) = @_;

      snd $server_port, message => $msg;
   }

   # make an AnyEvent condition variable for the 'quit' condition
   # (when we want to exit the client).
   my $quit_cv = AnyEvent->condvar;

   my $stdin_hdl = AnyEvent::Handle->new (
      fh      => \*STDIN,
      on_read => sub {
         my ($hdl) = @_;

         $hdl->push_read (line => sub {
            my ($hdl, $line) = @_;

            if ($line =~ /^\/quit/) { # /quit will end the client
               $quit_cv->send;

            } else {
               send_message ($line);
            }
         });
      }
   );

   $quit_cv->recv;

=head1 The Server

Ok, now finally to the server. What do we need? Well, we need to setup
the well known port C<chatter> where all clients send their messages to.

Up and into code right now:

   #!perl

   use AnyEvent;
   use AnyEvent::MP;

   become_public "localhost:1299";

   my $chatter_port = create_port;
   $chatter_port->register ("chatter");

   my %client_ports;

   $chatter_port->rcv (join => sub {
      my ($chatter_port, $type, $client_port) = @_;

      print "got new client port: $client_port\n";

      $client_ports{$client_port} = 1;
      0
   });

   $chatter_port->rcv (message => sub {
      my ($chatter_port, $type, $msg) = @_;

      print "message> $msg\n";

      snd $_, message => $msg for keys %client_ports;
      0
   });

   AnyEvent->condvar->recv;

This is all. Looks much easier, doesn't it? I'll explain it only shortly, as
we had the discussion of the C<rcv> method in the client part of this tutorial
above.

First this:

   become_public "localhost:1299";

This will tell our I<node> to become a I<public> node, which means that it can
be contacted via TCP. The first argument should be the I<noderef> the server
wants to be reachable at. In this case it's the TCP port 1299 on localhost.

Next we basically setup two receivers, one for the C<join> messages and
another one for the actual messages of type C<messsage>.

In the C<join> message we get the client's port, which we just remember in the
C<%client_ports> hash. In the receiver for the message type C<message> we will
just iterate through all known C<%client_ports> and relay the message to them.

And thats it.

=head1 The Remaining Problems

The shown implementation still has some bugs. For instance: How does the
server know that the client isn't there anymore, and can cleanup the
C<%client_ports> hash? And also the chat messages have no originator,
so we don't know who actually sent the message (which would be quite useful
for human-to-human interaction: to know who the other one is :).

But aside from these issues I hope this tutorial got you the swing of
L<AnyEvent::MP> and explained some common idioms.

How to solve the reliability and C<%client_ports> cleanup problem will
be explained later in this tutorial (TODO).

=head1 Inside The Protocol

Now, for the interested parties, let me explain some details about the protocol
that L<AnyEvent::MP> nodes use to communicate to each other. If you are not
interested you can skip this section.

Usually TCP is used for communication. Each I<node>, if configured to be a
I<public> node with the C<become_public> function will listen on the configured
TCP port (default is usually 4040).

If now one I<node> wants to send a message to another I<node> it will connect
to the host and port given in the I<port id>.

Then some handshaking occurs to check whether both I<nodes> have the same
I<shared secret> configured. Optionally even TLS can be enabled (about how to
do this exactly please consult the L<AnyEvent::MP> man pages, just a hint: It
should be enough to put the private key and (self signed) certificate in the
C<~/.aemp-secret> file of all nodes).

Now the serialized (usually L<JSON> is used for this, but it is also possible
to use other serialization formats, like L<Storable>) messages are sent over
the wire using a simple framing protocol.

=head1 SEE ALSO

L<AnyEvent>

L<AnyEvent::Handle>

L<AnyEvent::MP>

=head1 AUTHOR

  Robin Redeker <elmex@ta-sa.org>

Revision:	1.8
Committed:	Tue Aug 4 20:00:00 2009 UTC (14 years, 9 months ago) by root
Branch:	MAIN
Changes since 1.7:	+69 -55 lines
Log Message:	* empty log message *
#	Content
1	=head1 Message Passing for the Non-Blocked Mind
2
3	=head1 Introduction and Terminology
4
5	This is a tutorial about how to get the swing of the new L<AnyEvent::MP>
6	module. Which allows us to transparently pass messages to our own process
7	and to other processes on another or the same host.
8
9	What kind of messages? Well, basically a message here means a list of
10	Perl strings, numbers, hashes and arrays, mostly everything that can be
11	expressed as a L<JSON> text (as JSON is used by default in the protocol).
12
13	And next you might ask: between which entities are those messages
14	being "passed"? Basically between C<nodes>: a nodes is basically a
15	process/program that use L<AnyEvent::MP> and can run either on the same or
16	different hosts.
17
18	In this tutorial I'll show you how to write a simple chat server based on
19	L<AnyEvent::MP>.
20
21	=head1 System Requirements
22
23	Before we can start we have to make sure some things work on your
24	system.
25
26	You should of course also make sure that L<AnyEvent> and L<AnyEvent::MP>
27	are installed. But how to do that is out of scope of this tutorial.
28
29	Then we have to setup a I<shared secret>. For two L<AnyEvent::MP> nodes to
30	be able to communicate with each other and authenticate each other it is
31	necessary to setup the same I<shared secret> for both of them. For testing
32	you can write a random string into the file C<.aemp-secret> in your home
33	directory:
34
35	mcookie > ~/.aemp-secret
36
37	# or something more predictable
38	echo "secret123#4blabla_please_pick_your_own" > ~/.aemp-secret
39
40	Connections will only be successful when the nodes that want to connect
41	to each other have the same I<shared secret>. For more security, you can
42	put a self-signed SSL/TLS key/certificate pair into the file (or a normal
43	key/certificate and it's CA certificate).
44
45	B<If something does not work as expected, and for example tcpdump shows
46	that the connections are closed almost immediatly, you should make sure
47	that F<~/.aemp-secret> is the same on all hosts/user accounts that you try
48	to connect with each other!>
49
50	=head1 The Chat Client
51
52	OK, lets start by implementing the "frontend" of the client. We will
53	develop the client first and postpone the server for later, as the most
54	complex things actually happen in the client.
55
56	We will use L<AnyEvent::Handle> to do non-blocking IO read on standard
57	input (all of this code deals with actually handling user input, no
58	message passing yet):
59
60	#!perl
61
62	use AnyEvent;
63	use AnyEvent::Handle;
64
65	sub send_message {
66	die "This is where we will send the messages to the server"
67	. "in the next step of this tutorial.\n"
68	}
69
70	# make an AnyEvent condition variable for the 'quit' condition
71	# (when we want to exit the client).
72	my $quit_cv = AnyEvent->condvar;
73
74	my $stdin_hdl = AnyEvent::Handle->new (
75	fh => *STDIN,
76	on_error => sub { $quit_cv->send },
77	on_read => sub {
78	my ($hdl) = @_;
79
80	$hdl->push_read (line => sub {
81	my ($hdl, $line) = @_;
82
83	if ($line =~ /^\/quit/) { # /quit will end the client
84	$quit_cv->send;
85	} else {
86	send_message ($line);
87	}
88	});
89	}
90	);
91
92	$quit_cv->recv;
93
94	This is now a very basic client. Explaining explicitly what
95	L<AnyEvent::Handle> does or what a I<condvar> is all about is out of scope
96	of this document, please consult L<AnyEvent::Intro> or the manual pages
97	for L<AnyEvent> and L<AnyEvent::Handle>.
98
99	=head1 First Step Into Messaging
100
101	To supply the C<send_message> function we now take a look at
102	L<AnyEvent::MP>. This is an example of how it might look like:
103
104	... # the use lines from the above snippet
105
106	use AnyEvent::MP;
107
108	sub send_message {
109	my ($msg) = @_;
110
111	snd $server_port, message => $msg;
112	}
113
114	... # the rest of the above script
115
116	The C<snd> function is exported by L<AnyEvent::MP>, it stands for 'send
117	a message'. The first argument is the I<port> (a I<port> is something
118	that can receive messages, represented by a printable string) of the
119	server which will receive the message. How we get this port will be
120	explained in the next step.
121
122	The remaining arguments of C<snd> are C<message> and C<$msg>, the first
123	two elements of the I<message> (a I<message> in L<AnyEvent::MP> is a
124	simple list of values, which can be sent to a I<port>).
125
126	So all the function does is send the two values C<message> (a constant
127	string to tell the server what to expect) and the actual message string.
128
129	Thats all fine and simple so far, but where do we get the
130	C<$server_port>? Well, we need to get the unique I<port id> of the
131	server's port where it wants to receive all the incoming chat messages. A
132	I<port id> is unfortunately a very unique string, which we are unable
133	to know in advance. But L<AnyEvent::MP> supports the concept of 'well
134	known ports', which is basically a port on the server side registered
135	under a well known name. For example, the server has a port for receiving
136	chat messages with a unique I<port id> and registered it under the name
137	C<chatter>.
138
139	BTW, these "well known port names" should follow similar rules as Perl
140	identifiers, so you should prefix them with your package/module name to
141	make them unique, unless you use them in the main program.
142
143	As I<messages> can only be sent to a I<port id> and not just to a name we have
144	to ask the server I<node> what I<port id> has the well known port with the
145	name C<chatter>.
146
147	Another new term, what is a I<node>: The messaging network that can be created with
148	L<AnyEvent::MP> consists of I<nodes>. A I<node> handles all the connection and
149	low level message sending logic for its application. The application in this
150	case is the server. Also every client has/is a I<node>.
151
152	=head1 Getting The Chatter Port
153
154	Ok, lots of talk, now some code. Now we will actually get the C<$server_port>
155	from the backend:
156
157	...
158
159	use AnyEvent::MP;
160
161	my $resolved_cv = AnyEvent->condvar;
162
163	my $client_port = create_port;
164
165	my $server_node = "localhost:1299#";
166
167	snd $server_node, wkp => "chatter", "$client_port", "resolved";
168
169	my $server_port;
170
171	# setup a receiver callback for the 'resolved' message:
172	$client_port->rcv (resolved => sub {
173	my ($client_port, $type, $chatter_port_id) = @_;
174
175	print "Resolved the server port 'chatter' to $chatter_port_id\n";
176	$server_port = $chatter_port_id;
177
178	$resolved_cv->send;
179	1
180	});
181
182	# lets block the client until we resolved the server port.
183	$resolved_cv->recv;
184
185	# now setup another receiver callback for the chat messages:
186	$client_port->rcv (message => sub {
187	my ($client_port, $type, $msg) = @_;
188
189	print "chat> $msg\n";
190	0
191	});
192
193	# send the server a 'join' message:
194	snd $server_port, join => "$client_port";
195
196	sub send_message { ...
197
198	Now that was a lot of new stuff. In order to ask the server and receive an
199	answer we need to have a I<port> where we can receive the answer.
200	This is what C<create_port> will do for us, it just creates a new local
201	port and returns us an object (that will btw. stringify to the I<port id>),
202	that we can use to receive messages.
203
204	Next thing is the C<$server_node>. In order to refer to another node we need
205	some kind of string to reference it. The I<noderef> is basically a comma
206	separated list of C<host:port> pairs. We assume in this tutorial that the
207	server runs on your localhost at port 1299, this gives us the noderef
208	C<localhost:1299>.
209
210	Now you might ask what the C<#> at the end in C<$server_node> the above
211	example is about. Well, what I didn't tell you yet is that each I<node> has a
212	default I<port> to receive messages. The default port is the empty string
213	C<"">. The I<default port> of a I<node> also provides some special services for
214	us, for example resolving a well known port to a I<port id>.
215
216	Now to this line:
217
218	snd $server_node, wkp => "chatter", "$client_port", "resolved";
219
220	We send a message with first element being C<wkp> (standing for 'well known
221	port'). Then the well known port name that we want to resolve to a I<port id>:
222	C<chatter>. And in order for the server node to be able to send us back the
223	resolved I<port id> we have to tell it where to send the result message: The
224	result message will have as it's first argument the string C<resolved> and
225	will be sent to C<$client_port> (the I<port id> of our own just created
226	port).
227
228	Next comes the receiver for this C<wkp> request.
229
230	$client_port->rcv (resolved => sub {
231	my ($client_port, $type, $chatter_port_id) = @_;
232	...
233	1
234	});
235
236	This sets up a receiver on our own port for the result message with the first
237	argument being the string C<resolved>. Receivers can match the contents of
238	the messages before actually 'sending' it to the given callback.
239
240	B<Please note> that the given callback has to return either a true or a false
241	value for indicating whether it is B<done> (true value) or still wants to
242	B<continue> (false value) receiving messages.
243
244	In this case we tell the C<$client_port> to look into the received messages and
245	look for the string C<resolved> in the first element of the message. If it is
246	found, the given callback will be called with the C<$client_port> as first
247	argument, and the message as the remaining arguments.
248
249	We name the first element of the message C<$type> in this case. It's a common
250	idiom to code the 'type' of a message into it's first element, this allows for
251	simple matching.
252
253	The result message will contain the I<port id> of the well known port C<chatter>
254	as next element, and will be put in C<$chatter_port_id>.
255
256	Next we just assign C<$server_port> and return a 1 (a true value)
257	from the callback. It indicates that we are done and don't want to receive
258	further C<resolved> messages with this callback.
259
260	Now we continue to the rest of the client by calling C<send> on
261	C<$resolved_cv>.
262
263	First new step after this is setting up the chat message receiver callback.
264
265	$client_port->rcv (message => sub {
266	my ($client_port, $type, $msg) = @_;
267
268	print "chat> $msg\n";
269	0
270	});
271
272	We assume that all messages that are broadcast to all clients by the server
273	will contain the string C<message> as first element, and the actual message as
274	second element. The callback returns a false value this time, to indicate that
275	it wants to continue receiving messages.
276
277	Last but not least we actually tell the server to send us
278	the new chat messages from other clients. We do so by sending the
279	message type C<join> followed by our own I<port id>.
280
281	# send the server a 'join' message:
282	snd $server_port, join => "$client_port";
283
284	Then the server knows where to send all the new messages to.
285
286	=head1 The Completed Client
287
288	This is the complete client script:
289
290	#!perl
291
292	use AnyEvent;
293	use AnyEvent::Handle;
294	use AnyEvent::MP;
295
296	my $resolved_cv = AnyEvent->condvar;
297
298	my $client_port = create_port;
299
300	my $server_node = "localhost:1299#";
301
302	snd $server_node, wkp => "chatter", "$client_port", "resolved";
303
304	my $server_port;
305
306	# setup a receiver callback for the 'resolved' message:
307	$client_port->rcv (resolved => sub {
308	my ($client_port, $type, $chatter_port_id) = @_;
309
310	print "Resolved the server port 'chatter' to $chatter_port_id\n";
311	$server_port = $chatter_port_id;
312
313	$resolved_cv->send;
314	1
315	});
316
317	# lets block the client until we resolved the server port.
318	$resolved_cv->recv;
319
320	# now setup another receiver callback for the chat messages:
321	$client_port->rcv (message => sub {
322	my ($client_port, $type, $msg) = @_;
323
324	print "chat> $msg\n";
325	0
326	});
327
328	# send the server a 'join' message:
329	snd $server_port, join => "$client_port";
330
331	sub send_message {
332	my ($msg) = @_;
333
334	snd $server_port, message => $msg;
335	}
336
337	# make an AnyEvent condition variable for the 'quit' condition
338	# (when we want to exit the client).
339	my $quit_cv = AnyEvent->condvar;
340
341	my $stdin_hdl = AnyEvent::Handle->new (
342	fh => \*STDIN,
343	on_read => sub {
344	my ($hdl) = @_;
345
346	$hdl->push_read (line => sub {
347	my ($hdl, $line) = @_;
348
349	if ($line =~ /^\/quit/) { # /quit will end the client
350	$quit_cv->send;
351
352	} else {
353	send_message ($line);
354	}
355	});
356	}
357	);
358
359	$quit_cv->recv;
360
361	=head1 The Server
362
363	Ok, now finally to the server. What do we need? Well, we need to setup
364	the well known port C<chatter> where all clients send their messages to.
365
366	Up and into code right now:
367
368	#!perl
369
370	use AnyEvent;
371	use AnyEvent::MP;
372
373	become_public "localhost:1299";
374
375	my $chatter_port = create_port;
376	$chatter_port->register ("chatter");
377
378	my %client_ports;
379
380	$chatter_port->rcv (join => sub {
381	my ($chatter_port, $type, $client_port) = @_;
382
383	print "got new client port: $client_port\n";
384
385	$client_ports{$client_port} = 1;
386	0
387	});
388
389	$chatter_port->rcv (message => sub {
390	my ($chatter_port, $type, $msg) = @_;
391
392	print "message> $msg\n";
393
394	snd $_, message => $msg for keys %client_ports;
395	0
396	});
397
398	AnyEvent->condvar->recv;
399
400	This is all. Looks much easier, doesn't it? I'll explain it only shortly, as
401	we had the discussion of the C<rcv> method in the client part of this tutorial
402	above.
403
404	First this:
405
406	become_public "localhost:1299";
407
408	This will tell our I<node> to become a I<public> node, which means that it can
409	be contacted via TCP. The first argument should be the I<noderef> the server
410	wants to be reachable at. In this case it's the TCP port 1299 on localhost.
411
412	Next we basically setup two receivers, one for the C<join> messages and
413	another one for the actual messages of type C<messsage>.
414
415	In the C<join> message we get the client's port, which we just remember in the
416	C<%client_ports> hash. In the receiver for the message type C<message> we will
417	just iterate through all known C<%client_ports> and relay the message to them.
418
419	And thats it.
420
421	=head1 The Remaining Problems
422
423	The shown implementation still has some bugs. For instance: How does the
424	server know that the client isn't there anymore, and can cleanup the
425	C<%client_ports> hash? And also the chat messages have no originator,
426	so we don't know who actually sent the message (which would be quite useful
427	for human-to-human interaction: to know who the other one is :).
428
429	But aside from these issues I hope this tutorial got you the swing of
430	L<AnyEvent::MP> and explained some common idioms.
431
432	How to solve the reliability and C<%client_ports> cleanup problem will
433	be explained later in this tutorial (TODO).
434
435	=head1 Inside The Protocol
436
437	Now, for the interested parties, let me explain some details about the protocol
438	that L<AnyEvent::MP> nodes use to communicate to each other. If you are not
439	interested you can skip this section.
440
441	Usually TCP is used for communication. Each I<node>, if configured to be a
442	I<public> node with the C<become_public> function will listen on the configured
443	TCP port (default is usually 4040).
444
445	If now one I<node> wants to send a message to another I<node> it will connect
446	to the host and port given in the I<port id>.
447
448	Then some handshaking occurs to check whether both I<nodes> have the same
449	I<shared secret> configured. Optionally even TLS can be enabled (about how to
450	do this exactly please consult the L<AnyEvent::MP> man pages, just a hint: It
451	should be enough to put the private key and (self signed) certificate in the
452	C<~/.aemp-secret> file of all nodes).
453
454	Now the serialized (usually L<JSON> is used for this, but it is also possible
455	to use other serialization formats, like L<Storable>) messages are sent over
456	the wire using a simple framing protocol.
457
458	=head1 SEE ALSO
459
460	L<AnyEvent>
461
462	L<AnyEvent::Handle>
463
464	L<AnyEvent::MP>
465
466	=head1 AUTHOR
467
468	Robin Redeker <elmex@ta-sa.org>
469