前言
为什么要使用消息确认？
某些场景中需要确保每条消息都要被成功处理，消息确认分为两种：
- 一种是生产者发送消息到Broker时，Broker给生产者发送消息确认回执，告诉生产者消息已被成功发送到Broker。
- 另外一种是消费者接收到Broker发送的消息时，消费者给Broker发送确认回执，用于通知消息已被成功消费。
第一种：生产者端消息确认
生产者向Broker发送消息，Broker接收到消息后给生产者发送确认回执。主要有两种方式：Tx机制模式和Confirm模式
Tx机制模式：
Tx机制可以叫事务机制，RabbitMQ中有三个Tx机制的方法：TxSelect(),TxCommit(),TxRollback()。
channel.TxSelect()将当前channel设置成transaction模式开启事务，channel.TxCommit()提交事务，channel.TxRollback()回滚事务使用Tx机制，首先使用channel.TxSelect()开启事务，然后发布消息给Broker服务器，如果执行channel.TxCommit()成功了表示消息被Broker接收了。当channel.TxCommit()提交时失败，可以捕获异常然后channel.TxRollback()回滚事务。
channel.TxSelect();
try {
for (int i = 0; i < 10; i++)
{
string msg = $"第{i + 1}条消息";
//5.发布消息
channel.BasicPublish("", "simple", null, Encoding.UTF8.GetBytes(msg));
Console.WriteLine($"已发送消息：{msg}");
}
channel.TxCommit();
}
catch
{
channel.TxRollback();
}View Code
Confirm模式：
Confirm主要方法：ConfirmSelect() , WaitForCnofirms()和WaitForCnofirmOrDie()。
channel.ConfirmSelect()表示开启Confirm模式。channel.WaitForConfirms()等待所有消息确认，如果所有的消息都被服务端成功接收返回true，只要有一条没有被成功接收就返回false。channel.WaitForConfirmsOrDie()与channel.WaitForConfirms()相似，也是等待消息确认，区别在于该方法没有返回值，只要有任意一条消息没被成功接收，会抛出一个OperationInterrupedException类型异常；
//
// 摘要:
// Wait until all published messages have been confirmed.
//
// 参数:
// timeout:
// How long to wait (at most) before returning whether or not any nacks were returned.
//
// timedOut:
// True if the method returned because the timeout elapsed, not because all messages
// were ack'd or at least one nack'd.
//
// 返回结果:
// True if no nacks were received within the timeout, otherwise false.
//
// 言论：
// Waits until all messages published since the last call have been either ack'd
// or nack'd by the broker. Returns whether all the messages were ack'd (and none
// were nack'd). Note, throws an exception when called on a non-Confirm channel.
[AmqpMethodDoNotImplementAttribute(null)]
bool WaitForConfirms(TimeSpan timeout, out bool timedOut);
//
// 摘要:
// Wait until all published messages have been confirmed.
//
// 参数:
// timeout:
// How long to wait (at most) before returning whether or not any nacks were returned.
//
// 返回结果:
// True if no nacks were received within the timeout, otherwise false.
//
// 言论：
// Waits until all messages published since the last call have been either ack'd
// or nack'd by the broker. Returns whether all the messages were ack'd (and none
// were nack'd). Note, throws an exception when called on a non-Confirm channel.
[AmqpMethodDoNotImplementAttribute(null)]
bool WaitForConfirms(TimeSpan timeout);
//
// 摘要:
// Wait until all published messages have been confirmed.
//
// 言论：
// Waits until all messages published since the last call have been either ack'd
// or nack'd by the broker. Returns whether all the messages were ack'd (and none
// were nack'd). Note, throws an exception when called on a non-Confirm channel.
[AmqpMethodDoNotImplementAttribute(null)]
bool WaitForConfirms();
//
// 摘要:
// Wait until all published messages have been confirmed.
//
// 言论：
// Waits until all messages published since the last call have been ack'd by the
// broker. If a nack is received, throws an OperationInterrupedException exception
// immediately.
[AmqpMethodDoNotImplementAttribute(null)]
void WaitForConfirmsOrDie();
//
// 摘要:
// Wait until all published messages have been confirmed.
//
// 言论：
// Waits until all messages published since the last call have been ack'd by the
// broker. If a nack is received or the timeout elapses, throws an OperationInterrupedException
// exception immediately.
[AmqpMethodDoNotImplementAttribute(null)]
void WaitForConfirmsOrDie(TimeSpan timeout);Confirm API
//开启事务
//channel.TxSelect();
channel.ConfirmSelect();
try {
for (int i = 0; i < 10; i++)
{
string msg = $"第{i + 1}条消息";
//5.发布消息
channel.BasicPublish("", "simple", null, Encoding.UTF8.GetBytes(msg));
Console.WriteLine($"已发送消息：{msg}");
}
//channel.TxCommit();
channel.WaitForConfirmsOrDie();
Console.WriteLine("发送完成");
}
catch(Exception ex)
{
//channel.TxRollback();
Console.WriteLine(ex.Message);
}View Code
第二种：消费者端消息确认
Broker发送到消费者时，提供了两种消息确认方式：自动确认和显示确认。
自动确认：
当Broker向消费者发送消息后，不等消息处理结束，立即自动返回一个确认回执。使用：设置消费方法的参数autoAck为true。当Broker接收到确认回执时会删除消息，如果消费者在接收到消息并返回了确认回执后，然后消息还没处理消费者挂了，这条消息就找不回了。
channel.BasicConsume("simple", true, consumer);
显示确认：
自动确认会出现消息丢失，如果让消息处理完再返回确认回执那么久不存在消息丢失问题了，这就是显示确认的思路。使用：先设置消费方法的参数autoAck为false，再使用channel.BasicAck()或channel.BasicReject()方法确认、拒绝消息。
//确认消息：deliveryTag参数是分发的标记，multiple表示是否确认多条
channel.BasicAck(deliveryTag: ea.DeliveryTag, multiple: false);
//拒绝消息：deliveryTag参数也是分发的标记，requeue表示消息被拒绝后是否重新入队
channel.BasicReject(deliveryTag: ea.DeliveryTag, requeue: false);
当使用显示确认时，如果消费者处理完消息不发送回执，那么消息不会被删除，消息的状态一直是Unacked，这条消息也不会再发送给其他消费者。如果一个消费者在处理消息时尚未发送确认回执的情况下挂了，那么消息会被重新放入队列（状态从Unacked变成Ready），有其他消费者存在时，消息会发送给其他消费者。
consumer.Received += (model, e) =>
{
byte[] message = e.Body.ToArray();
//返回消息确认（true/false，自动/手动确认）,没确认就不会消费掉消息
if (Encoding.UTF8.GetString(message).Contains("1"))
{
Console.WriteLine("接收消息:" + Encoding.UTF8.GetString(message));
channel.BasicAck(e.DeliveryTag, false);
}
else
{
Console.WriteLine("拒绝消息:" + Encoding.UTF8.GetString(message));
//拒绝消息 false：拒绝后丢弃 true：拒绝后重新入队
channel.BasicReject(e.DeliveryTag, false);
}
};
//消费者开启监听
channel.BasicConsume("simple", false, consumer);View Code
