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1.4 |
=head1 Message Passing for the Non-Blocked Mind |
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elmex |
1.1 |
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root |
1.8 |
=head1 Introduction and Terminology |
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elmex |
1.1 |
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root |
1.4 |
This is a tutorial about how to get the swing of the new L<AnyEvent::MP> |
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root |
1.14 |
module, which allows us to transparently pass messages to our own process |
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root |
1.8 |
and to other processes on another or the same host. |
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elmex |
1.1 |
|
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root |
1.15 |
What kind of messages? Well, basically a message here means a list of Perl |
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strings, numbers, hashes and arrays, anything that can be expressed as a |
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L<JSON> text (as JSON is used by default in the protocol). |
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elmex |
1.1 |
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elmex |
1.17 |
It's custom in L<AnyEvent::MP> to have a string which describes the type of the |
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message as first element (this is called a I<tag> in L<AnyEvent::MP>), as some |
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API functions (C<rcv>) support matching it directly. So supposedly you want to |
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send a ping message with your current time to something, this is how such a |
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message might look like (in Perl syntax): |
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1.1 |
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elmex |
1.17 |
['ping', 1251381636] |
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1.7 |
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1.17 |
And next you might ask: between which entities are those messages being |
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I<passed>? They are I<passed> between I<ports>. I<ports> are just sources and |
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destinations for messages. How do these ports relate to things you know? Well, |
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each I<port> belongs to a I<node>, and a I<node> is just the UNIX process that |
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runs your L<AnyEvent::MP> application. |
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Each I<node> is distinguished from other I<nodes> running on the same host or |
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multiple hosts in a network by it's I<node ID>. A I<node ID> can be manually |
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assigned or L<AnyEvent::MP> will assign one it self for you. |
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elmex |
1.18 |
So, you might want to visualize it like this (setup is two nodes (more are of |
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course possible): Node C<A> (in UNIX process 7066) with ports C<ABC> and C<DEF> |
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and C<B> (in UNIX process 8321) with ports C<FOO> and C<BAR>). |
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1.17 |
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|- PID: 7066 -| |- PID: 8321 -| |
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| | | | |
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| Node ID: A | | Node ID: B | |
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| | | | |
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| Port ABC =|= <----\ /-----> =|= Port FOO | |
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| | X | | |
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| Port DEF =|= <----/ \-----> =|= Port BAR | |
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| | | | |
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|-------------| |-------------| |
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The strings for the ports here are just for illustrative purposes. Even if in |
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reality I<ports> in L<AnyEvent::MP> are also identified by strings they can't |
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be choosen manually and are assigned randomly. These I<port ids> should also |
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1.18 |
not be used directly for other purposes than referring to an endpoint for |
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1.17 |
messages. |
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The next sections will explain the API of L<AnyEvent::MP>. First the API is |
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1.18 |
laid out by simple examples. Later some more complex idioms are introduced, |
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which are maybe useful to solve some real world purposes. |
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1.17 |
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# In this tutorial I'll show you how to write a simple chat server based on |
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# L<AnyEvent::MP>. This example is used because it nicely shows how to organise a |
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# simple application, but keep in mind that every node trusts any other, so this |
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# chat cannot be used to implement a real public chat server and client system, |
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# but it can be used to implement a distributed chat server for example. |
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1.8 |
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1.16 |
=head1 Passing Your First Message |
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As start lets have a look at the messaging API. The next example is just a |
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demo to show the basic elements of message passing with L<AnyEvent::MP>. |
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It shout just print: "Ending with: 123". So here the code: |
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use AnyEvent; |
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use AnyEvent::MP; |
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my $end_cv = AnyEvent->condvar; |
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my $port = port; |
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rcv $port, test => sub { |
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my ($data) = @_; |
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$end_cv->send ($data); |
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}; |
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snd $port, test => 123; |
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print "Ending with: " . $end_cv->recv . "\n"; |
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elmex |
1.17 |
It already contains most functions of the essential L<AnyEvent::MP> API. |
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First there is the C<port> function which will create a I<port> and will return |
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it's I<port id>. |
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That I<port id> can be used to send and receive messages. That I<port id> is a |
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simple string and can be safely passed to other I<nodes> in the network to |
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refer to that specific port (usually used for RPC, where you need to |
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tell the other end which I<port> to send the reply to). |
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Next function is C<rcv>: |
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1.16 |
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rcv $port, test => sub { ... }; |
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1.16 |
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1.17 |
It sets up a receiver callback on a specific I<port> which needs to be |
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specified as the first argument. The next argument, in this example C<test>, is |
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a I<tag> match. This means that whenever a message, with the first element |
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being the string C<tag>, is received the callback is called with the remaining |
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parts of that message. |
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Messages can be send with the C<snd> function, which looks like this in the |
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example above: |
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snd $port, test => 123; |
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This will send the message C<['test', 123]> to the I<port> with the I<port id> |
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in C<$port>. The receiver got a I<tag> match on C<test> and will call the |
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callback with the first argument being the number C<123>. |
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That callback then just passes that number on to the I<condition variable> |
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C<$end_cv> which will then pass the value to the print. But I<condition |
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variables> are out of the scope of this tutorial. So please consult the |
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L<AnyEvent::Intro> about them. |
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But passing messages inside one process is boring, but before we can continue |
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and take the next step to interprocess message passing we first have to make |
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sure some things have been setup. |
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=head1 System Requirements and System Setup |
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Before we can start with real IPC we have to make sure some things work on your |
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system. |
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First we have to setup a I<shared secret>: for two L<AnyEvent::MP> I<nodes> to |
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be able to communicate with each other and authenticate each other it is |
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necessary to setup the same I<shared secret> for both of them (or use TLS |
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certificates). |
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The easiest way is to set this up is to use the F<aemp> utility: |
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aemp gensecret |
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This creates a F<$HOME/.perl-anyevent-mp> config file and generates a random |
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shared secret. You can copy this file to any other system and then communicate |
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over the network (via TCP) with it. You can also select your own shared secret |
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(F<aemp setsecret>) and for increased security requirements you can even create |
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a TLS certificate (F<aemp gencert>), causing connections to not just be |
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authenticated, but also to be encrypted. |
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Connections will only be successful when the I<nodes> that want to connect to |
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each other have the same I<shared secret> (or successfully verify the TLS |
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certificate of the other side). |
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B<If something does not work as expected, and for example tcpdump shows |
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that the connections are closed almost immediately, you should make sure |
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that F<~/.perl-anyevent-mp> is the same on all hosts/user accounts that |
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you try to connect with each other!> |
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elmex |
1.16 |
|
152 |
elmex |
1.18 |
Thats all for now, there is more fiddling around with the C<aemp> utility |
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later. |
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155 |
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=head1 Passing Messages Between Processes |
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157 |
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=head2 The Receiver |
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Lets split the previous example up into two small programs. First the |
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receiver application: |
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#!/opt/perl/bin/perl |
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use AnyEvent; |
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use AnyEvent::MP; |
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use AnyEvent::MP::Global; |
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initialise_node "eg_simple_receiver"; |
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my $port = port; |
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AnyEvent::MP::Global::register $port, "eg_receivers"; |
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rcv $port, test => sub { |
174 |
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my ($data, $reply_port) = @_; |
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176 |
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print "Received data: " . $data . "\n"; |
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}; |
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AnyEvent->condvar->recv; |
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=head3 AnyEvent::MP::Global |
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Now, that wasn't too bad, was it? Ok, lets step through the new functions |
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and modules that have been used. For starters there is now an additional |
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module loaded: L<AnyEvent::MP::Global>. |
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That module provides us with a I<global registry>, which lets us share data |
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among all I<nodes> in a network. Why do we need it you might ask? |
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190 |
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The I<port ids> are just random strings, assigned by L<AnyEvent::MP>. We can't |
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know those I<port ids> in advance, so we don't know which I<port id> to send |
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messages to if the message is to be passed between I<nodes> (or UNIX |
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processes). To find the right I<port> of another I<node> in the network we will |
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need to communicate that somehow to the sender. And exactly that is what |
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L<AnyEvent::MP::Global> provides. |
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197 |
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=head3 initialise_node And The Network |
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199 |
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Now, lets have a look at the next new thing, the C<initialise_node>: |
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201 |
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initialise_node "eg_simple_receiver"; |
202 |
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203 |
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Before we are able to send messages to other nodes we have to initialise |
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ourself. The first argument, the string C<"eg_simple_receiver">, is called the |
205 |
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I<profile> of this node. A profile holds some information about the application |
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that is going to be a node in an L<AnyEvent::MP> network. |
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Most importantly the profile allows you to set the I<node id> that your |
209 |
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application will use. You can also set I<binds> in the profile, meaning that |
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you can define TCP ports that the application will listen on for incoming |
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connections from other nodes of the network. |
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Next you can configure I<seeds> in profile. A I<seed> is just a TCP endpoint |
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which tells the application where to find other nodes of it's network. To |
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explain this a bit more detailed we have to look at the topology of an |
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L<AnyEvent::MP> network. The topology is called a I<fully connected mesh>, here |
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an example with 4 nodes: |
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N1--N2 |
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| \/ | |
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| /\ | |
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N3--N4 |
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Now imagine another I<node> C<N5>. wants to connect itself to that network: |
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N1--N2 |
227 |
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| \/ | N5 |
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| /\ | |
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N3--N4 |
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The new node needs to know the I<binds> of all of those 4 already connected |
232 |
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nodes. And exactly this is what the I<seeds> are for. Now lets assume that |
233 |
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the new node C<N5> has as I<seed> the TCP endpoint of the node C<N2>. |
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It then connects to C<N2>: |
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N1--N2____ |
237 |
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| \/ | N5 |
238 |
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| /\ | |
239 |
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N3--N4 |
240 |
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C<N2> then tells C<N5> the I<binds> of the other nodes it is connected to, |
242 |
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and C<N5> builds up the rest of the connections: |
243 |
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244 |
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/--------\ |
245 |
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N1--N2____| |
246 |
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| \/ | N5 |
247 |
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| /\ | /| |
248 |
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N3--N4--- | |
249 |
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\________/ |
250 |
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Finished. C<N5> is now happily connected to the rest of the network. |
252 |
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253 |
elmex |
1.19 |
=head3 Setting Up The Profiles |
254 |
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255 |
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Ok, so much to the profile. Now lets setup the C<eg_simple_receiver> I<profile> |
256 |
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for later. For the receiver we just give the receiver a I<bind>: |
257 |
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258 |
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aemp profile eg_simple_receiver setbinds localhost:12266 |
259 |
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260 |
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And while we are at it, just setup the I<profile> for the sender in the second |
261 |
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part of this example too. We will call the sender I<profile> |
262 |
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C<eg_simple_sender>. For the sender we will just setup a I<seed> to the |
263 |
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receiver: |
264 |
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265 |
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aemp profile eg_simple_sender setseeds localhost:12266 |
266 |
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267 |
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You might wonder why we don't setup a I<bind> here. Well, there can be |
268 |
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exceptions to the I<fully> in the I<fully connected mesh> in L<AnyEvent::MP>. |
269 |
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If you don't configure a I<bind> for a node's profile it won't bind itself |
270 |
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somewhere. These kinds of I<nodes> will not be able to send messages to other |
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I<nodes> that also didn't I<bind> them self to some TCP address. For this |
272 |
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example, as well as some cases in the real world, we can live with this |
273 |
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limitation. |
274 |
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275 |
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=head3 Registering The Receiver |
276 |
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277 |
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Ok, where were we. We now discussed the basic purpose of L<AnyEvent::MP::Global> |
278 |
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and initialise_node with it's relations to profiles. We also setup our profiles |
279 |
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for later use and now have to continue talking about the receiver example. |
280 |
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281 |
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Lets look at the next undiscussed line(s) of code: |
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283 |
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my $port = port; |
284 |
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AnyEvent::MP::Global::register $port, "eg_receivers"; |
285 |
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286 |
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The C<port> function already has been discussed. It just creates a new I<port> |
287 |
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and gives us the I<port id>. Now to the C<register> function of |
288 |
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L<AnyEvent::MP::Global>: The first argument is a I<port id> that we want to add |
289 |
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to a I<global group>, and it's second argument is the name of that I<global |
290 |
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group>. |
291 |
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You can choose that name of such a I<global group> freely, and it's purpose is |
293 |
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to store a set of I<port ids>. That set is made available throughout the whole |
294 |
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L<AnyEvent::MP> network, so that each node can see which ports belong to that |
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group. |
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297 |
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The sender will later look for the ports in that I<global group> and send |
298 |
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messages to them. |
299 |
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300 |
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Last step in the example is to setup a receiver callback for those messages |
301 |
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like we have discussed in the first example. We again match for the I<tag> |
302 |
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C<test>. The difference is just that we don't end the application after |
303 |
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receiving the first message. We just infinitely continue to look out for new |
304 |
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messages. |
305 |
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306 |
root |
1.8 |
=head1 The Chat Client |
307 |
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308 |
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OK, lets start by implementing the "frontend" of the client. We will |
309 |
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develop the client first and postpone the server for later, as the most |
310 |
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complex things actually happen in the client. |
311 |
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312 |
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We will use L<AnyEvent::Handle> to do non-blocking IO read on standard |
313 |
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input (all of this code deals with actually handling user input, no |
314 |
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message passing yet): |
315 |
elmex |
1.7 |
|
316 |
root |
1.8 |
#!perl |
317 |
elmex |
1.1 |
|
318 |
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use AnyEvent; |
319 |
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use AnyEvent::Handle; |
320 |
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321 |
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sub send_message { |
322 |
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die "This is where we will send the messages to the server" |
323 |
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. "in the next step of this tutorial.\n" |
324 |
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} |
325 |
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326 |
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# make an AnyEvent condition variable for the 'quit' condition |
327 |
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# (when we want to exit the client). |
328 |
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my $quit_cv = AnyEvent->condvar; |
329 |
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330 |
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my $stdin_hdl = AnyEvent::Handle->new ( |
331 |
root |
1.8 |
fh => *STDIN, |
332 |
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on_error => sub { $quit_cv->send }, |
333 |
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on_read => sub { |
334 |
elmex |
1.1 |
my ($hdl) = @_; |
335 |
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336 |
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$hdl->push_read (line => sub { |
337 |
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my ($hdl, $line) = @_; |
338 |
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339 |
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if ($line =~ /^\/quit/) { # /quit will end the client |
340 |
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$quit_cv->send; |
341 |
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} else { |
342 |
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send_message ($line); |
343 |
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} |
344 |
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}); |
345 |
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} |
346 |
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); |
347 |
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348 |
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$quit_cv->recv; |
349 |
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350 |
root |
1.4 |
This is now a very basic client. Explaining explicitly what |
351 |
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L<AnyEvent::Handle> does or what a I<condvar> is all about is out of scope |
352 |
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|
of this document, please consult L<AnyEvent::Intro> or the manual pages |
353 |
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for L<AnyEvent> and L<AnyEvent::Handle>. |
354 |
elmex |
1.1 |
|
355 |
root |
1.9 |
=head1 First Steps Into Messaging |
356 |
elmex |
1.1 |
|
357 |
root |
1.8 |
To supply the C<send_message> function we now take a look at |
358 |
|
|
L<AnyEvent::MP>. This is an example of how it might look like: |
359 |
elmex |
1.1 |
|
360 |
|
|
... # the use lines from the above snippet |
361 |
|
|
|
362 |
|
|
use AnyEvent::MP; |
363 |
|
|
|
364 |
|
|
sub send_message { |
365 |
|
|
my ($msg) = @_; |
366 |
|
|
|
367 |
|
|
snd $server_port, message => $msg; |
368 |
|
|
} |
369 |
|
|
|
370 |
|
|
... # the rest of the above script |
371 |
|
|
|
372 |
root |
1.8 |
The C<snd> function is exported by L<AnyEvent::MP>, it stands for 'send |
373 |
|
|
a message'. The first argument is the I<port> (a I<port> is something |
374 |
|
|
that can receive messages, represented by a printable string) of the |
375 |
|
|
server which will receive the message. How we get this port will be |
376 |
|
|
explained in the next step. |
377 |
|
|
|
378 |
|
|
The remaining arguments of C<snd> are C<message> and C<$msg>, the first |
379 |
|
|
two elements of the I<message> (a I<message> in L<AnyEvent::MP> is a |
380 |
|
|
simple list of values, which can be sent to a I<port>). |
381 |
|
|
|
382 |
|
|
So all the function does is send the two values C<message> (a constant |
383 |
|
|
string to tell the server what to expect) and the actual message string. |
384 |
|
|
|
385 |
|
|
Thats all fine and simple so far, but where do we get the |
386 |
|
|
C<$server_port>? Well, we need to get the unique I<port id> of the |
387 |
|
|
server's port where it wants to receive all the incoming chat messages. A |
388 |
root |
1.9 |
I<port id> is unfortunately a very unique string, which we are unable to |
389 |
|
|
know in advance. But L<AnyEvent::MP> supports the concept of 'registered |
390 |
|
|
ports', which is basically a port on the server side registered under |
391 |
|
|
a well known name. |
392 |
|
|
|
393 |
|
|
For example, the server has a port for receiving chat messages with a |
394 |
|
|
unique I<port id> and registers it under the name C<chatter>. |
395 |
root |
1.4 |
|
396 |
root |
1.9 |
BTW, these "registered port names" should follow similar rules as Perl |
397 |
root |
1.4 |
identifiers, so you should prefix them with your package/module name to |
398 |
|
|
make them unique, unless you use them in the main program. |
399 |
elmex |
1.1 |
|
400 |
root |
1.9 |
As I<messages> can only be sent to a I<port id> and not just to some name |
401 |
|
|
we have to ask the server node for the I<port id> of the port registered |
402 |
|
|
as C<chatter>. |
403 |
elmex |
1.1 |
|
404 |
root |
1.9 |
=head1 Finding The Chatter Port |
405 |
elmex |
1.1 |
|
406 |
root |
1.9 |
Ok, lots of talk, now some code. Now we will actually get the |
407 |
|
|
C<$server_port> from the backend: |
408 |
elmex |
1.1 |
|
409 |
|
|
... |
410 |
|
|
|
411 |
|
|
use AnyEvent::MP; |
412 |
|
|
|
413 |
root |
1.9 |
my $server_node = "127.0.0.1:1299"; |
414 |
elmex |
1.1 |
|
415 |
root |
1.9 |
my $client_port = port; |
416 |
elmex |
1.1 |
|
417 |
root |
1.9 |
snd $server_node, lookup => "chatter", $client_port, "resolved"; |
418 |
elmex |
1.1 |
|
419 |
root |
1.9 |
my $resolved_cv = AnyEvent->condvar; |
420 |
elmex |
1.1 |
my $server_port; |
421 |
|
|
|
422 |
|
|
# setup a receiver callback for the 'resolved' message: |
423 |
root |
1.9 |
rcv $client_port, resolved => sub { |
424 |
|
|
my ($tag, $chatter_port_id) = @_; |
425 |
elmex |
1.1 |
|
426 |
|
|
print "Resolved the server port 'chatter' to $chatter_port_id\n"; |
427 |
|
|
$server_port = $chatter_port_id; |
428 |
|
|
|
429 |
|
|
$resolved_cv->send; |
430 |
|
|
1 |
431 |
root |
1.9 |
}; |
432 |
elmex |
1.1 |
|
433 |
root |
1.9 |
# lets block the client until we have resolved the server port. |
434 |
elmex |
1.1 |
$resolved_cv->recv; |
435 |
|
|
|
436 |
|
|
# now setup another receiver callback for the chat messages: |
437 |
root |
1.9 |
rcv $client_port, message => sub { |
438 |
|
|
my ($tag, $msg) = @_; |
439 |
elmex |
1.1 |
|
440 |
|
|
print "chat> $msg\n"; |
441 |
|
|
0 |
442 |
root |
1.9 |
}; |
443 |
elmex |
1.1 |
|
444 |
root |
1.9 |
# send a 'join' message to the server: |
445 |
elmex |
1.1 |
snd $server_port, join => "$client_port"; |
446 |
|
|
|
447 |
|
|
sub send_message { ... |
448 |
|
|
|
449 |
root |
1.9 |
Now that was a lot of new stuff: |
450 |
elmex |
1.1 |
|
451 |
root |
1.9 |
First we define the C<$server_node>: In order to refer to another node |
452 |
|
|
we need some kind of string to reference it - the node reference. The |
453 |
|
|
I<noderef> is basically a comma separated list of C<address:port> |
454 |
|
|
pairs. We assume in this tutorial that the server runs on C<127.0.0.1> |
455 |
|
|
(localhost) on port 1299, which results in the noderef C<127.0.0.1:1299>. |
456 |
|
|
|
457 |
|
|
Next, in order to receive a reply from the other node or the server we |
458 |
|
|
need to have a I<port> that messages can be sent to. This is what the |
459 |
|
|
C<port> function will do for us, it just creates a new local port and |
460 |
|
|
returns it's I<port ID> that can then be used to receive messages. |
461 |
|
|
|
462 |
|
|
When you look carefully, you will see that the first C<snd> uses the |
463 |
|
|
C<$server_node> (a noderef) as destination port. Well, what I didn't |
464 |
|
|
tell you yet is that each I<node> has a default I<port> to receive |
465 |
|
|
messages. The ID of this port is the same as the noderef. |
466 |
|
|
|
467 |
|
|
This I<default port> provides some special services for us, for example |
468 |
|
|
resolving a registered name to a I<port id> (a-ha! finally!). |
469 |
|
|
|
470 |
|
|
This is exactly what this line does: |
471 |
|
|
|
472 |
|
|
snd $server_node, lookup => "chatter", $client_port, "resolved"; |
473 |
|
|
|
474 |
|
|
This sends a message with first element being C<lookup>, followed by the |
475 |
|
|
(hopefully) registered port name that we want to resolve to a I<port |
476 |
|
|
id>: C<chatter>. And in order for the server node to be able to send us |
477 |
|
|
back the resolved I<port ID> we have to tell it where to send it: The |
478 |
|
|
result message will be sent to C<$client_port> (the I<port id> of the |
479 |
|
|
port we just created), and will have the string C<resolved> as the first |
480 |
|
|
element. |
481 |
|
|
|
482 |
|
|
When the node receives this message, it will look up the name, gobble up |
483 |
|
|
all the extra arguments we passed, append the resolved name, and send the |
484 |
|
|
resulting list as a message. |
485 |
elmex |
1.1 |
|
486 |
root |
1.9 |
Next we register a receiver for this C<lookup>-request. |
487 |
|
|
|
488 |
|
|
rcv $client_port, resolved => sub { |
489 |
|
|
my ($tag, $chatter_port_id) = @_; |
490 |
|
|
... |
491 |
|
|
1 |
492 |
|
|
}; |
493 |
|
|
|
494 |
|
|
This sets up a receiver on our own port for messages with the first |
495 |
|
|
element being the string C<resolved>. Receivers can match the contents of |
496 |
|
|
the messages before actually executing the specified callback. |
497 |
|
|
|
498 |
|
|
B<Please note> that the every C<rcv> callback has to return either a true |
499 |
|
|
or a false value, indicating whether it is B<successful>/B<done> (true) or |
500 |
|
|
still wants to B<continue> (false) receiving messages. |
501 |
elmex |
1.1 |
|
502 |
root |
1.9 |
In this case we tell the C<$client_port> to look into all the messages |
503 |
|
|
it receives and look for the string C<resolved> in the first element of |
504 |
|
|
the message. If it is found, the given callback will be called with the |
505 |
|
|
message elements as arguments. |
506 |
elmex |
1.1 |
|
507 |
root |
1.9 |
Using a string as the first element of the message is called I<tagging> |
508 |
|
|
the message. It's common practise to code the 'type' of a message into |
509 |
|
|
it's first element, as this allows for simple matching. |
510 |
elmex |
1.1 |
|
511 |
root |
1.9 |
The result message will contain the I<port ID> of the well known port |
512 |
|
|
C<chatter> as second element, which will be stored in C<$chatter_port_id>. |
513 |
elmex |
1.1 |
|
514 |
root |
1.9 |
This port ID will then be stored in C<$server_port>, followed by calling |
515 |
|
|
C<send> on $resolved_cv> so the program will continue. |
516 |
elmex |
1.1 |
|
517 |
root |
1.9 |
The callback then returns a C<1> (a true value), to indicate that it has |
518 |
|
|
done it's job and doesn't want to receive further C<resolved> messages. |
519 |
elmex |
1.1 |
|
520 |
root |
1.9 |
After this the chat message receiver callback is registered with the port: |
521 |
elmex |
1.1 |
|
522 |
root |
1.9 |
rcv $client_port, message => sub { |
523 |
|
|
my ($tag, $msg) = @_; |
524 |
elmex |
1.1 |
|
525 |
|
|
print "chat> $msg\n"; |
526 |
root |
1.9 |
|
527 |
elmex |
1.1 |
0 |
528 |
root |
1.9 |
}; |
529 |
elmex |
1.1 |
|
530 |
root |
1.9 |
We assume that all messages that are broadcast to the clients by the |
531 |
|
|
server contain the string tag C<message> as first element, and the actual |
532 |
|
|
message as second element. The callback returns a false value this time, |
533 |
|
|
to indicate that it is not yet done and wants to receive further messages. |
534 |
|
|
|
535 |
|
|
The last thing to do is to tell the server to send us new chat messages |
536 |
|
|
from other clients. We do so by sending the message C<join> followed by |
537 |
|
|
our own I<port ID>. |
538 |
elmex |
1.1 |
|
539 |
|
|
# send the server a 'join' message: |
540 |
root |
1.9 |
snd $server_port, join => $client_port; |
541 |
elmex |
1.1 |
|
542 |
root |
1.9 |
This way the server knows where to send all the new messages to. |
543 |
elmex |
1.1 |
|
544 |
root |
1.8 |
=head1 The Completed Client |
545 |
elmex |
1.1 |
|
546 |
|
|
This is the complete client script: |
547 |
|
|
|
548 |
|
|
#!perl |
549 |
root |
1.4 |
|
550 |
elmex |
1.1 |
use AnyEvent; |
551 |
|
|
use AnyEvent::Handle; |
552 |
|
|
use AnyEvent::MP; |
553 |
|
|
|
554 |
root |
1.10 |
my $server_node = "127.0.0.1:1299"; |
555 |
elmex |
1.1 |
|
556 |
root |
1.10 |
my $client_port = port; |
557 |
elmex |
1.1 |
|
558 |
root |
1.10 |
snd $server_node, lookup => "chatter", $client_port, "resolved"; |
559 |
elmex |
1.1 |
|
560 |
root |
1.10 |
my $resolved_cv = AnyEvent->condvar; |
561 |
elmex |
1.1 |
my $server_port; |
562 |
|
|
|
563 |
|
|
# setup a receiver callback for the 'resolved' message: |
564 |
root |
1.10 |
rcv $client_port, resolved => sub { |
565 |
|
|
my ($tag, $chatter_port_id) = @_; |
566 |
elmex |
1.1 |
|
567 |
|
|
print "Resolved the server port 'chatter' to $chatter_port_id\n"; |
568 |
|
|
$server_port = $chatter_port_id; |
569 |
|
|
|
570 |
|
|
$resolved_cv->send; |
571 |
|
|
1 |
572 |
root |
1.10 |
}; |
573 |
elmex |
1.1 |
|
574 |
root |
1.10 |
# lets block the client until we have resolved the server port. |
575 |
elmex |
1.1 |
$resolved_cv->recv; |
576 |
|
|
|
577 |
|
|
# now setup another receiver callback for the chat messages: |
578 |
root |
1.10 |
rcv $client_port, message => sub { |
579 |
|
|
my ($tag, $msg) = @_; |
580 |
elmex |
1.1 |
|
581 |
|
|
print "chat> $msg\n"; |
582 |
|
|
0 |
583 |
root |
1.10 |
}; |
584 |
elmex |
1.1 |
|
585 |
root |
1.10 |
# send a 'join' message to the server: |
586 |
elmex |
1.1 |
snd $server_port, join => "$client_port"; |
587 |
|
|
|
588 |
|
|
sub send_message { |
589 |
|
|
my ($msg) = @_; |
590 |
|
|
|
591 |
|
|
snd $server_port, message => $msg; |
592 |
|
|
} |
593 |
|
|
|
594 |
|
|
# make an AnyEvent condition variable for the 'quit' condition |
595 |
|
|
# (when we want to exit the client). |
596 |
|
|
my $quit_cv = AnyEvent->condvar; |
597 |
|
|
|
598 |
|
|
my $stdin_hdl = AnyEvent::Handle->new ( |
599 |
root |
1.10 |
fh => *STDIN, |
600 |
|
|
on_error => sub { $quit_cv->send }, |
601 |
|
|
on_read => sub { |
602 |
elmex |
1.1 |
my ($hdl) = @_; |
603 |
|
|
|
604 |
|
|
$hdl->push_read (line => sub { |
605 |
|
|
my ($hdl, $line) = @_; |
606 |
|
|
|
607 |
|
|
if ($line =~ /^\/quit/) { # /quit will end the client |
608 |
|
|
$quit_cv->send; |
609 |
|
|
} else { |
610 |
|
|
send_message ($line); |
611 |
|
|
} |
612 |
|
|
}); |
613 |
|
|
} |
614 |
|
|
); |
615 |
|
|
|
616 |
|
|
$quit_cv->recv; |
617 |
|
|
|
618 |
root |
1.8 |
=head1 The Server |
619 |
elmex |
1.1 |
|
620 |
root |
1.10 |
Ok, we finally come to the server. |
621 |
|
|
|
622 |
|
|
The server of course also needs to set up a port, and in addition needs to |
623 |
|
|
I<register> it, so the clients can find it. |
624 |
elmex |
1.1 |
|
625 |
root |
1.10 |
Again, let's jump directly into the code: |
626 |
elmex |
1.1 |
|
627 |
|
|
#!perl |
628 |
root |
1.4 |
|
629 |
elmex |
1.1 |
use AnyEvent; |
630 |
|
|
use AnyEvent::MP; |
631 |
|
|
|
632 |
root |
1.10 |
become_public "127.0.0.1:1299"; |
633 |
elmex |
1.1 |
|
634 |
root |
1.10 |
my $chatter_port = port; |
635 |
|
|
|
636 |
|
|
reg $chatter_port, "chatter"; |
637 |
elmex |
1.1 |
|
638 |
|
|
my %client_ports; |
639 |
|
|
|
640 |
root |
1.10 |
rcv $chatter_port, |
641 |
|
|
join => sub { |
642 |
|
|
my ($tag, $client_port) = @_; |
643 |
elmex |
1.1 |
|
644 |
root |
1.10 |
print "got new client port: $client_port\n"; |
645 |
|
|
$client_ports{$client_port} = 1; |
646 |
elmex |
1.5 |
|
647 |
root |
1.10 |
0 |
648 |
|
|
}, |
649 |
|
|
message => sub { |
650 |
|
|
my ($tag, $msg) = @_; |
651 |
elmex |
1.1 |
|
652 |
root |
1.10 |
print "message> $msg\n"; |
653 |
elmex |
1.1 |
|
654 |
root |
1.10 |
snd $_, message => $msg |
655 |
|
|
for keys %client_ports; |
656 |
elmex |
1.5 |
|
657 |
root |
1.10 |
0 |
658 |
root |
1.11 |
}; |
659 |
elmex |
1.1 |
|
660 |
|
|
AnyEvent->condvar->recv; |
661 |
|
|
|
662 |
root |
1.10 |
That is all. Looks much simpler than the client, doesn't it? |
663 |
|
|
|
664 |
|
|
Let's quickly look over it, as C<rcv> has already been discussed in the |
665 |
|
|
client part of this tutorial above. |
666 |
elmex |
1.2 |
|
667 |
|
|
First this: |
668 |
|
|
|
669 |
root |
1.10 |
become_public "127.0.0.1:1299"; |
670 |
elmex |
1.1 |
|
671 |
root |
1.10 |
This will tell our I<node> to become a I<public> node, which means that it |
672 |
|
|
can be contacted via TCP. The first argument should be the I<noderef> the |
673 |
|
|
server wants to be reachable at. In this case it's the TCP port 1299 on |
674 |
|
|
C<127.0.0.1>. |
675 |
|
|
|
676 |
|
|
Next we set up two receivers, one for the C<join> messages and another one |
677 |
|
|
for the actual messages of type C<messsage>. This is done with a single |
678 |
|
|
call to C<rcv>, which allows multiple C<< match => $callback >> pairs. |
679 |
|
|
|
680 |
|
|
In the C<join> callback we receive the client port, which is simply |
681 |
|
|
remembered in the C<%client_ports> hash. In the C<message> callback we |
682 |
|
|
just iterate through all known C<%client_ports> and relay the message to |
683 |
|
|
them. |
684 |
elmex |
1.1 |
|
685 |
root |
1.10 |
That concludes the server. |
686 |
elmex |
1.2 |
|
687 |
root |
1.8 |
=head1 The Remaining Problems |
688 |
elmex |
1.1 |
|
689 |
root |
1.10 |
The implementation as shown still has some bugs. For instance: How does |
690 |
|
|
the server know that the client isn't there anymore, so it can clean up |
691 |
|
|
the C<%client_ports> hash? Also, the chat messages have no originator, so |
692 |
|
|
we don't know who actually sent the message (which would be quite useful |
693 |
elmex |
1.1 |
for human-to-human interaction: to know who the other one is :). |
694 |
|
|
|
695 |
root |
1.10 |
But aside from these issues I hope this tutorial showed you the basics of |
696 |
elmex |
1.1 |
L<AnyEvent::MP> and explained some common idioms. |
697 |
|
|
|
698 |
elmex |
1.7 |
How to solve the reliability and C<%client_ports> cleanup problem will |
699 |
|
|
be explained later in this tutorial (TODO). |
700 |
|
|
|
701 |
root |
1.8 |
=head1 Inside The Protocol |
702 |
elmex |
1.7 |
|
703 |
|
|
Now, for the interested parties, let me explain some details about the protocol |
704 |
|
|
that L<AnyEvent::MP> nodes use to communicate to each other. If you are not |
705 |
|
|
interested you can skip this section. |
706 |
|
|
|
707 |
root |
1.14 |
Usually TCP is used for communication. Each I<node>, if configured to be |
708 |
|
|
a I<public> node with the C<initialise_node> function will listen on the |
709 |
|
|
configured TCP port (default is 4040). |
710 |
elmex |
1.7 |
|
711 |
root |
1.10 |
If then one I<node> wants to send a message to another I<node> it will |
712 |
|
|
connect to the host and port given in the I<port ID>. |
713 |
elmex |
1.7 |
|
714 |
root |
1.10 |
Then some handshaking occurs to check whether both I<nodes> know the |
715 |
|
|
I<shared secret>. Optionally, TLS can be enabled (about how to do this |
716 |
|
|
exactly please consult the L<AnyEvent::MP> man page, just a hint: It |
717 |
|
|
should be enough to put the private key and (self signed) certificate in |
718 |
|
|
the C<~/.aemp-secret> file of all nodes). |
719 |
|
|
|
720 |
|
|
After the handshake, messages will be exchanged using a serialiser |
721 |
|
|
(usually L<JSON> is used for this, but it is also possible to use other |
722 |
|
|
serialization formats such as L<Storable>). |
723 |
elmex |
1.7 |
|
724 |
elmex |
1.1 |
=head1 SEE ALSO |
725 |
|
|
|
726 |
|
|
L<AnyEvent> |
727 |
|
|
|
728 |
|
|
L<AnyEvent::Handle> |
729 |
|
|
|
730 |
|
|
L<AnyEvent::MP> |
731 |
|
|
|
732 |
|
|
=head1 AUTHOR |
733 |
|
|
|
734 |
|
|
Robin Redeker <elmex@ta-sa.org> |
735 |
root |
1.4 |
|