NServiceBusThe mechanism for header communication is either native headers, if the transport supports that feature, or via a serialized collection of key value pairs. This article covers the various ways of manipulating the message headers.
Reading incoming headers
Headers can be read for an incoming message.
From a behavior
public class IncomingBehavior :
IBehavior<IncomingContext>
{
public void Invoke(IncomingContext context, Action next)
{
var headers = context.PhysicalMessage.Headers;
var nsbVersion = headers[Headers.NServiceBusVersion];
var customHeader = headers["MyCustomHeader"];
next();
}
}
From a mutator
public class MutateIncomingTransportMessages :
IMutateIncomingTransportMessages
{
public void MutateIncoming(TransportMessage transportMessage)
{
var headers = transportMessage.Headers;
var nsbVersion = headers[Headers.NServiceBusVersion];
var customHeader = headers["MyCustomHeader"];
}
}
From a handler
public class ReadHandler :
IHandleMessages<MyMessage>
{
IBus bus;
public ReadHandler(IBus bus)
{
this.bus = bus;
}
public void Handle(MyMessage message)
{
var headers = bus.CurrentMessageContext.Headers;
var nsbVersion = headers[Headers.NServiceBusVersion];
var customHeader = headers["MyCustomHeader"];
}
}
From a saga
public class ReadSaga :
Saga<ReadSagaData>,
IHandleMessages<MyMessage>
{
public void Handle(MyMessage message)
{
var headers = Bus.CurrentMessageContext.Headers;
var nsbVersion = headers[Headers.NServiceBusVersion];
var customHeader = headers["MyCustomHeader"];
}
Writing outgoing headers
Headers can be written for an outgoing message.
From a behavior
public class OutgoingBehavior :
IBehavior<OutgoingContext>
{
public void Invoke(OutgoingContext context, Action next)
{
var headers = context.OutgoingMessage.Headers;
headers["MyCustomHeader"] = "My custom value";
next();
}
}
From a mutator
public class MutateOutgoingTransportMessages :
IMutateOutgoingTransportMessages
{
public void MutateOutgoing(LogicalMessage logicalMessage, TransportMessage transportMessage)
{
var headers = transportMessage.Headers;
headers["MyCustomHeader"] = "My custom value";
}
}
From a handler
public class WriteHandler :
IHandleMessages<MyMessage>
{
IBus bus;
public WriteHandler(IBus bus)
{
this.bus = bus;
}
public void Handle(MyMessage message)
{
var someOtherMessage = new SomeOtherMessage();
bus.SetMessageHeader(
msg: someOtherMessage,
key: "MyCustomHeader",
value: "My custom value");
bus.Send(someOtherMessage);
}
}
From a saga
public class WriteSaga :
Saga<WriteSagaData>,
IHandleMessages<MyMessage>
{
public void Handle(MyMessage message)
{
var someOtherMessage = new SomeOtherMessage();
Bus.SetMessageHeader(
msg: someOtherMessage,
key: "MyCustomHeader",
value: "My custom value");
Bus.Send(someOtherMessage);
}
For all outgoing messages
NServiceBus supports registering headers at configuration time that are then added to all outgoing messages for the endpoint.
var startableBus = Bus.Create(busConfiguration);
startableBus.OutgoingHeaders.Add("AllOutgoing", "ValueAllOutgoing");
using (var bus = startableBus.Start())
{
The global outgoing headers are not thread safe. It is recommended that they be manipulated at startup.
