Topics

(using php-amqplib)

In the previous tutorial we improved our logging system. Instead of using a fanout exchange only capable of dummy broadcasting, we used a direct one, and gained a possibility of selectively receiving the logs.

上一节，我们改进了日志系统。取代了fanout交换器仅仅会傻乎乎的广播，我们使用了定向交换器，使得选择性接收消息成为可能。

Although using the direct exchange improved our system, it still has limitations - it can‘t do routing based on multiple criteria.

尽管使用定向交换器改善了我们的系统，但它仍有局限性——不能基于多重条件进行路由。

In our logging system we might want to subscribe to not only logs based on severity, but also based on the source which emitted the log. You might know this concept from the syslog unix tool, which routes logs based on both severity (info/warn/crit...) and facility (auth/cron/kern...).

在日志系统中，我们可能想不仅订阅基于严重等级的内容，而且订阅基于消息发布来源的内容。你可以从syslog unix工具中得知这个概念——基于严重性和设备路由日志。

That would give us a lot of flexibility - we may want to listen to just critical errors coming from ‘cron‘ but also all logs from ‘kern‘.

那会给我们带来很大的灵活性——我们可能想只是收听来自cron的致命错误和来自kern的所有消息。

To implement that in our logging system we need to learn about a more complex topic exchange.

为了在我们的日志系统上实现这种灵活性，我们需要学习一下更为复杂一些的topic交换器。

Topic exchange

Messages sent to a topic exchange can‘t have an arbitrary routing_key - it must be a list of words, delimited by dots. The words can be anything, but usually they specify some features connected to the message. A few valid routing key examples: "stock.usd.nyse", "nyse.vmw", "quick.orange.rabbit". There can be as many words in the routing key as you like, up to the limit of 255 bytes.

发送到topic交换器的消息不能给一个任意的routing_key——它必须是一个由逗号分隔的单词列表。

The binding key must also be in the same form. The logic behind the topic exchange is similar to a direct one - a message sent with a particular routing key will be delivered to all the queues that are bound with a matching binding key. However there are two important special cases for binding keys:

binding key也必须是同样的格式。topic交换器背后的逻辑和定向交换器类似——带有特定routing key的消息会被派送到所有捆绑了与routing key相匹配的binding key的队列。

• * (star) can substitute for exactly one word.
• *（星号）可以代表一个单词
• # (hash) can substitute for zero or more words.
• #（井号）可以代表零个或多个单词

It‘s easiest to explain this in an example:

In this example, we‘re going to send messages which all describe animals. The messages will be sent with a routing key that consists of three words (two dots). The first word in the routing key will describe speed, second a colour and third a species: "<speed>.<colour>.<species>".

这个例子中，我们将发送所有描述动物的消息。发送时，这些消息带有由三个单词（两个点号分隔）组成的routing key.其中起一个单词用来表述速度，第二个用来表示颜色，最后一个用来表示种类："<speed>.<colour>.<species>"

We created three bindings: Q1 is bound with binding key "*.orange.*" and Q2 with "*.*.rabbit" and "lazy.#".

创建三个捆绑：用 "*.orange.*" 来绑定Q1,用 "*.*.rabbit" 和"lazy.#"来绑定Q2.

These bindings can be summarised as:

这几个捆绑可以概括为：

• Q1 is interested in all the orange animals.
• Q1喜欢所有橙色的动物
• Q2 wants to hear everything about rabbits, and everything about lazy animals.
• Q2想知道所有关于兔子和懒惰动物的事情

A message with a routing key set to "quick.orange.rabbit" will be delivered to both queues. Message "lazy.orange.elephant" also will go to both of them. On the other hand "quick.orange.fox" will only go to the first queue, and "lazy.brown.fox" only to the second. "lazy.pink.rabbit" will be delivered to the second queue only once, even though it matches two bindings. "quick.brown.fox" doesn‘t match any binding so it will be discarded.

这两个队列都会接收到routing key设置成"quick.orange.rabbit"的消息。设置成"lazy.orange.elephant"的也一样。

但"quick.orange.fox"仅仅会进入第一个队列，而"lazy.brown.fox"则仅会进入第二个队列。"lazy.pink.rabbit"仅仅会进入到第二个队列一次，虽然它可以匹配到两个困难规则。由于"quick.brown.fox"和谁都匹配不上，所以会被丢弃。

What happens if we break our contract and send a message with one or four words, like "orange" or "quick.orange.male.rabbit"? Well, these messages won‘t match any bindings and will be lost.

要是打破了我们的约束会怎样？比如，发送带有一个或是四个单词的，像"orange"或"quick.orange.male.rabbit"的消息。

好吧！消息会丢失，因为它不匹配任何捆绑规则。

On the other hand "lazy.orange.male.rabbit", even though it has four words, will match the last binding and will be delivered to the second queue.

但是 "lazy.orange.male.rabbit"这种routing key，尽管它有四个单词，但是还是会进入到第二个队列（为喵呢？你来说说）

Topic exchange

Topic exchange is powerful and can behave like other exchanges.

Topic 交换器很强大，它可以模拟其他交换器的行为

When a queue is bound with "#" (hash) binding key - it will receive all the messages, regardless of the routing key - like in fanout exchange.

当一个队列捆绑一个#的binding key——它会像fanout交换器一样，忽略掉routing key，接收所有的消息.（还记得#代表什喵么？）

When special characters "*" (star) and "#" (hash) aren‘t used in bindings, the topic exchange will behave just like a direct one.

在捆绑中如果没有使用特殊字符星号和井号，topic交换器的行为就跟定向交换器一样。

Putting it all together（合体！！！烦死了是吧？哈，还有一次！）

We‘re going to use a topic exchange in our logging system. We‘ll start off with a working assumption that the routing keys of logs will have two words: "<facility>.<severity>".

在我们的日志系统中使用topic交换器。我们假设日志的routing keyes有"<facility>.<severity>"组成。

The code is almost the same as in the previous tutorial.

代码和之前的几乎一妈生的。

The code for emit_log_topic.php:

emit_log_topic.php代码：

<?php

require_once __DIR__ . ‘/vendor/autoload.php‘;
use PhpAmqpLib\Connection\AMQPConnection;
use PhpAmqpLib\Message\AMQPMessage;

$connection = new AMQPConnection(‘localhost‘, 5672, ‘guest‘, ‘guest‘);
$channel = $connection->channel();

$channel->exchange_declare(‘topic_logs‘, ‘topic‘, false, false, false);

$routing_key = $argv[1];
if(empty($routing_key)) $routing_key = "anonymous.info";
$data = implode(‘ ‘, array_slice($argv, 2));
if(empty($data)) $data = "Hello World!";

$msg = new AMQPMessage($data);

$channel->basic_publish($msg, ‘topic_logs‘, $routing_key);

echo " [x] Sent ",$routing_key,‘:‘,$data," \n";

$channel->close();
$connection->close();

?>

The code for receive_logs_topic.php:

<?php

require_once __DIR__ . ‘/vendor/autoload.php‘;
use PhpAmqpLib\Connection\AMQPConnection;

$connection = new AMQPConnection(‘localhost‘, 5672, ‘guest‘, ‘guest‘);
$channel = $connection->channel();

$channel->exchange_declare(‘topic_logs‘, ‘topic‘, false, false, false);

list($queue_name, ,) = $channel->queue_declare("", false, false, true, false);

$binding_keys = array_slice($argv, 1);
if( empty($binding_keys )) {
    file_put_contents(‘php://stderr‘, "Usage: $argv[0] [binding_key]\n");
    exit(1);
}

foreach($binding_keys as $binding_key) {
    $channel->queue_bind($queue_name, ‘topic_logs‘, $binding_key);
}

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();

?>

To receive all the logs:

接收所有日志：

$ php receive_logs_topic.php "#"

To receive all logs from the facility "kern":

接收所有来自kern的日志：

$ phpreceive_logs_topic.php "kern.*"

Or if you want to hear only about "critical" logs:

或是你想仅仅接收”致命“日志

$ php receive_logs_topic.php "*.critical"

You can create multiple bindings:

你也可以多重绑定

$ php receive_logs_topic.php "kern.*" "*.critical"

And to emit a log with a routing key "kern.critical" type:

发布一个带有"kern.critical"routing key的日志就输入：

$ php emit_log_topic.php "kern.critical" "A critical kernel error"

Have fun playing with these programs. Note that the code doesn‘t make any assumption about the routing or binding keys, you may want to play with more than two routing key parameters.

玩的开心哈！注意上面的代码没有做路由或捆绑的例子，有可能想体验两个以上的routing key参数。

Some teasers:

• Will "*" binding catch a message sent with an empty routing key?
• 星号会匹配带有空routing key的消息吗？
• Will "#.*" catch a message with a string ".." as a key? Will it catch a message with a single word key?
• "#.*"会匹配".."的消息吗？ 它是匹配到一个单一的单词吗？
• How different is "a.*.#" from "a.#"?
• "a.*.#"和"a.#"有啥不同？

(Full source code for emit_log_topic.php and receive_logs_topic.php)

emit_log_topic.php和receive_logs_topic.php源码。

Next, find out how to do a round trip message as a remote procedure call in tutorial 6

下次，我们讲如何像远程过程调用一样完成信息往返。

译-PHP rabbitMQ Tutorial-5,布布扣,bubuko.com

译-PHP rabbitMQ Tutorial-5