基本知识

路由的作用是在交换机的基础上将消息的分发继续细分，实现让消息的接受者只订阅消息的一部分内容

在交换机章节，我们使用了 QueueBindAsync 绑定了队列和交换机，这个函数还可以指定 routingKey 来指定路由

路由键的含义取决于交换机类型。我们之前使用的“分发”交换类型则根本不考虑其值。

直连交换机

直连交换器背后的路由算法很简单——消息会发送到绑定键与消息路由键完全匹配的队列

带有标签“orange”的消息进入第一个队列，带有标签“black”和“green”的消息会进入第二个队列，其他消息会被丢弃

多个队列绑定相同的路由键也是可以的，这样就会变成一种分发模式

消息发布

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using RabbitMQ.Client;
using System.Text;

var factory = new ConnectionFactory { HostName = "localhost" };
using var connection = await factory.CreateConnectionAsync();
using var channel = await connection.CreateChannelAsync();

await channel.ExchangeDeclareAsync(exchange: "direct_logs", type: ExchangeType.Direct);

var severity = (args.Length > 0) ? args[0] : "info";
var message = (args.Length > 1) ? string.Join(" ", args.Skip(1).ToArray()) : "Hello World!";
var body = Encoding.UTF8.GetBytes(message);
await channel.BasicPublishAsync(exchange: "direct_logs", routingKey: severity, body: body);
Console.WriteLine($" [x] Sent '{severity}':'{message}'");

Console.WriteLine(" Press [enter] to exit.");
Console.ReadLine();

消息接收

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using RabbitMQ.Client;
using RabbitMQ.Client.Events;
using System.Text;

if (args.Length < 1)
{
    Console.Error.WriteLine("Usage: {0} [info] [warning] [error]",
                            Environment.GetCommandLineArgs()[0]);
    Console.WriteLine(" Press [enter] to exit.");
    Console.ReadLine();
    Environment.ExitCode = 1;
    return;
}

var factory = new ConnectionFactory { HostName = "localhost" };

using var connection = await factory.CreateConnectionAsync();
using var channel = await connection.CreateChannelAsync();

await channel.ExchangeDeclareAsync(exchange: "direct_logs", type: ExchangeType.Direct);

// declare a server-named queue
var queueDeclareResult = await channel.QueueDeclareAsync();
string queueName = queueDeclareResult.QueueName;

foreach (string? severity in args)
{
    // 绑定交换机并指定路由键
    await channel.QueueBindAsync(queue: queueName, exchange: "direct_logs", routingKey: severity);
}

Console.WriteLine(" [*] Waiting for messages.");

var consumer = new AsyncEventingBasicConsumer(channel);
consumer.ReceivedAsync += (model, ea) =>
{
    var body = ea.Body.ToArray();
    var message = Encoding.UTF8.GetString(body);
    var routingKey = ea.RoutingKey;
    Console.WriteLine($" [x] Received '{routingKey}':'{message}'");
    return Task.CompletedTask;
};

await channel.BasicConsumeAsync(queueName, autoAck: true, consumer: consumer);

Console.WriteLine(" Press [enter] to exit.");
Console.ReadLine();