The Message Context is an object that accompanies the actual message. In earlier versions of RawRabbit, the Message Context was mandatory and had to implement the interface IMessageContext. Since 2.0, this is an optional feature.
It depends on the application. If messages are published on behalf of an authenticated user, it might contain claims or tokens that can be used to verify access rights. If the message is published as part of a scheduled job, it could contain a job id, initiator and more. As a rule of thumb, it makes sense to add properties there that describes the domain or context.
Message Context is enabled for outgoing messages by registering it as a plugin
new RawRabbitOptions
{
Plugins = p => p
.UseMessageContext(ctx => new CustomContext
{
MachineName = Environment.MachineName,
Sent = DateTime.Now
})
}If no factory method is provided, the message context is just new’ed up.
The outgoing message context can be overridden when the message is published. Note that the plugin must be registered for that to work.
await publisher.PublishAsync(new BasicMessage(), ctx => ctx
.UseMessageContext(new AnotherContext {
SomeProp = "SomeValue"
}));The Subscribe and Response operations each have dedicated enrichers that adds new methods to the bus client for consuming a message with message context
await c.SubscribeAsync<BasicMessage, MessageContext>(async (message, context) =>
{
//code goes here
});If desired, the message context passed into the message handler can be replaced by any property found in the pipe.
await client.SubscribeAsync<BasicMessage, BasicDeliverEventArgs>(async (msg, args) =>
{
if (args.Redelivered) // example usage of delivery args.
{
return new Nack();
}
// code goes here
return new Ack();
}, ctx => ctx.UseMessageContext(c => c.GetDeliveryEventArgs()));In the example above, the subscriber method gets access to the entire BasicDeliveryEventArgs, giving access to headers, body and other metadata.
RawRabbit can be configured to forward received message contexts in publishes that happens within the message handler.
await firstClient.SubscribeAsync<FirstMessage, CustomContext>((async msg, context) =>
{
// the context here...
await subscriber.PublishAsync(new SecondMessage());
});
await secondClient.SubscribeAsync<SecondMessage, CustomContext>((async msg, context) =>
{
// ...is the same as here.
});The feature can be enabled by registering it as a plugin. As of the current version, both UseMessageContext<TMessageContext> and UseContextForwarding needs to be registered for this to work.
new RawRabbitOptions
{
Plugins = p => p
.UseMessageContext<TodoContext>()
.UseContextForwarding()
}