译-PHP rabbitMQ Tutorial-4

Routing（路由）

(using php-amqplib)

In the previous tutorial we built a simple logging system. We were able to broadcast log messages to many receivers.

上次，我们构建了一个简单的日志系统来广播消息到多个接收者。

In this tutorial we're going to add a feature to it - we're going to make it possible to subscribe only to a subset of the messages. For example, we will be able to direct only critical error messages to the log file (to save disk space), while still being able to print all of the log messages on the console.

这次我们要添加一个特性上去??使它可以仅仅收听部分消息。例如，我们可以仅指示存储致命错误消息到日志文件（存储到硬盘），然而仍然可以在控制台打印所有消息。

Bindings（捆绑）

In previous examples we were already creating bindings. You may recall code like:

上个例子，我们已经创建了捆绑。你可能想起来了，如下：

$channel->queue_bind($queue_name, 'logs');

A binding is a relationship between an exchange and a queue. This can be simply read as: the queue is interested in messages from this exchange.

交换器和队列之间的关系称之为捆绑。可以简单理解为：这个队列对这个特定的交换器的消息感兴趣。

Bindings can take an extra routing_key parameter. To avoid the confusion with a $channel::basic_publish parameter we're going to call it a binding key. This is how we could create a binding with a key:

捆绑可以设置一个额外的routing_key参数。为了避免和$channel:basic_publish的参数混淆，我们就叫它捆绑键（banding key）。这就是我们如何用key来创建一个捆绑。

$binding_key = 'black';$channel->queue_bind($queue_name, $exchange_name, $binding_key);

The meaning of a binding key depends on the exchange type. The fanout exchanges, which we used previously, simply ignored its value.

binding key的意义在于交换器类型。之前用的fanout类型的交换器会简单忽略这个值。

Direct exchange（定向交换器）

Our logging system from the previous tutorial broadcasts all messages to all consumers. We want to extend that to allow filtering messages based on their severity. For example we may want the script which is writing log messages to the disk to only receive critical errors, and not waste disk space on warning or info log messages.

之前的日志系统广播所有消息到所有的消费者。我们想扩展它??允许基于严重程度来过滤消息。例如，我们可能想让日志持久化的脚本仅仅持久化致命错误，就不会在警告和信息(info)消息上浪费硬盘空间。

We were using a fanout exchange, which doesn't give us much flexibility - it's only capable of mindless broadcasting.

我们用的fanout交换器没给我们带来多少灵活性??它仅仅是无头蒙的广播。

We will use a direct exchange instead. The routing algorithm behind a direct exchange is simple - a message goes to the queues whose binding key exactly matches the routing key of the message.

我们将用定向交换器来代替fanout交换器。定向交换器背后的算法很简单??消息会推送到：消息routing key和队列binding key完全匹配的的队列中。

To illustrate that, consider the following setup:

为了阐述清楚，思考一下下面的结构：

In this setup, we can see the direct exchange X with two queues bound to it. The first queue is bound with binding key orange, and the second has two bindings, one with binding key blackand the other one with green.

在这个结构上，我们可以看到交换器X上捆绑了两个队列。第一个队列用binding key 橘子 捆绑，第二个有两个绑定，

头一个用的是binding key 黑色，另外一个是用的是绿色.

In such a setup a message published to the exchange with a routing key orange will be routed to queue Q1. Messages with a routing key of black or green will go to Q2. All other messages will be discarded.

这个结构中，派送到交换器的带有routing key 橘子的消息会被路由到队列Q1. 带有黑色和绿色routing key的消息会进入到Q2. 所有这之外消息都会被丢弃。

Multiple bindings（多重捆绑）

It is perfectly legal to bind multiple queues with the same binding key. In our example we could add a binding between X and Q1 with binding key black. In that case, the direct exchange will behave like fanout and will broadcast the message to all the matching queues. A message with routing key black will be delivered to both Q1 and Q2.

用相同的binding key捆绑多个队列毛问题没有。我们的例子中，我们可以用黑色来建立X和Q1之间的捆绑。这种情况下，定向交换器的行为就回像fanout交换器一样，广播消息到所有匹配的队列。Q1和Q2都会收到带有routing key黑色的消息。

Emitting logs（日志发布）

We'll use this model for our logging system. Instead of fanout we'll send messages to a direct exchange. We will supply the log severity as a routing key. That way the receiving script will be able to select the severity it wants to receive. Let's focus on emitting logs first.

我们将应用这种模式到我们的日志系统。与fanout交换器不同的是我们发送消息到指定的交换器。用日志严重等级来作为

routing key。 那样的话接收脚本就可以根据严重等级来选择想要接收的消息。我们先来把发布日志搞定。

As always, we need to create an exchange first:

老样子，先要创建一个交换器：

$channel->exchange_declare('direct_logs', 'direct', false, false, false);

And we're ready to send a message:

准备发射！！！??消息 - -#

$channel->exchange_declare('direct_logs', 'direct', false, false, false);$channel->basic_publish($msg, 'direct_logs', $severity);

To simplify things we will assume that 'severity' can be one of 'info', 'warning', 'error'.

简单起见，我们假定严重等级可以是info,warning,error中的一个。

Subscribing（订阅）

Receiving messages will work just like in the previous tutorial, with one exception - we're going to create a new binding for each severity we're interested in.

接收消息就跟之前一样，但有一点不同??我们得为每一个感兴趣的严重等级创建一个捆绑。

foreach($severities as $severity) {    $channel->queue_bind($queue_name, 'direct_logs', $severity);}

Putting it all together（合体！！！还来？？哈哈）

The code for emit_log_direct.php class:

emit_log_direct.php类代码：

channel();$channel->exchange_declare('direct_logs', 'direct', false, false, false);$severity = $argv[1];if(empty($severity)) $severity = "info";$data = implode(' ', array_slice($argv, 2));if(empty($data)) $data = "Hello World!";$msg = new AMQPMessage($data);$channel->basic_publish($msg, 'direct_logs', $severity);echo " [x] Sent ",$severity,':',$data," \n";$channel->close();$connection->close();?>

The code for receive_logs_direct.php:

receive_logs_direct.php代码：

channel();$channel->exchange_declare('direct_logs', 'direct', false, false, false);list($queue_name, ,) = $channel->queue_declare("", false, false, true, false);$severities = array_slice($argv, 1);if(empty($severities )) {    file_put_contents('php://stderr', "Usage: $argv[0] [info] [warning] [error]\n");    exit(1);}foreach($severities as $severity) {    $channel->queue_bind($queue_name, 'direct_logs', $severity);}echo ' [*] Waiting for logs. To exit press CTRL+C', "\n";$callback = function($msg){  echo ' [x] ',$msg->delivery_info['routing_key'], ':', $msg->body, "\n";};$channel->basic_consume($queue_name, '', false, true, false, false, $callback);while(count($channel->callbacks)) {    $channel->wait();}$channel->close();$connection->close();?>

If you want to save only 'warning' and 'error' (and not 'info') log messages to a file, just open a console and type:

如果你想仅存储warning和error的消息到日志文件，就打开控制台输入：

$ php receive_logs_direct.php warning error > logs_from_rabbit.log

If you'd like to see all the log messages on your screen, open a new terminal and do:

要想在屏幕上查看所有的消息，打开一个新窗口输入：

$ php receive_logs_direct.php info warning error [*] Waiting for logs. To exit press CTRL+C

And, for example, to emit an error log message just type:

对了，例如，要发布错误消息就输入：

$ php emit_log_direct.php error "Run. Run. Or it will explode." [x] Sent 'error':'Run. Run. Or it will explode.'

(Full source code for (emit_log_direct.php source) and (receive_logs_direct.php source))

emit_log_direct.php和receive_logs_direct.php的源码

Move on to tutorial 5 to find out how to listen for messages based on a pattern.

下回呢我们讲讲如何基于模式来收听消息。