NServiceBus Customization Part 1: IWantCustomInitialization

In this first part we're going to explore how to take control of NServiceBus during the initialization phase.  By implementing the IWantCustomInitialization interface, you take full control away from NSB Roles.  What is a Role?  A Role tells an Endpoint how to participate on the bus.  Typical Roles are the Server, Client, and Publisher Roles.  These are defined by a class in your project, typically named EndpointConfig.  A Role will define certain aspects of behavior, like whether or not it can receive messages(AsA_Client).

Most of the time you don't end up ever overriding the default behavior of the Roles.  When you do, you'll implement the IWantCustomInitialization interface and have full control over NServiceBus.  You will use the static NServiceBus.Configure class to get things going.  Let's take a look at all the options(as of 2.5, 3.0 follows):

• .With()/.WithWeb() - these first methods give you the ability to control assembly scanning.  When NSB fires up, it will scan the bin directory by default.  This gives you control over what gets scanned.  You can provide a list of Assemblies, a list of Types, or a path.  You'll want to use the WithWeb() version if you are using NSB with ASP.NET.  
• NServiceBus.AllAssemblies -  This class allows you to provide a list of assemblies not to load.  An example of this would be "AllAssemblies.Except( "Assembly1" ).And("Assembly2")".  
• .Synchronization() - tells NSB that message processing with occur in a synchronization domain.  This is useful for rich client applications where you need to marshal from a background thread back to the UI.
• .DefaultBuilder() or .MyContainerOfChoiceBuilder() - this next set of methods controls the container.  You can take the default container(AutoFac as of 2.5) or specify your own.  You'll need to include the builder implementation for your container as well as specify an instance of your container.  
• .UnicastBus() - use unicast messaging
• DoNotAutoSubscribe() - do not auto subscribe to a Publisher's messages
• ForwardReceivedMessagesTo( String ) - forward all messages to another endpoint.  This is helpful if you want to do some auditing.
• LoadMessageHandlers() - tells the bus to scan and load message handlers.  There are a couple interesting variants on this method:
• LoadMessageHandlers<TFirst> - tells the bus to load the handlers but load the assembly where TFirst resides before the rest
• LoadMessageHandlers<T>( First<T> ) - load the handlers and specifies that the handlers in the given order should go first.  To use the First class to specify ordering, it has 2 methods, "Then" and "AndThen".  A typical usages would be "First<IHandler1>.Then<IHandler2>().AndThen<IHandler3>()"
• PropagateReturnAddressOnSend( Boolean ) - receivers of the messages sent by this endpoint will see the address of the incoming messages
• .XmlSerializer() or .BinarySerializer() - specify the serialization technique you'd like to use.
• .CustomConfigurationSource( IConfigurationSource source ) - if you would rather not use the standard app.config file or its sections for Administrative configuration, you are welcome to use your own. Simply implement the IConfigurationSource interface and you are on your way.
• .MsmqTransport() - tells NSB to use MSMQ as the underlying communication mechanism.  This may be swapped out in favor of other transports.  Along with this setting, you can configure a few things underneath it:
• .DoNotCreateQueues() - don't try to create queues if they don't exist
• .IsolationLevel( IsolationLevel ) - the isolation level of the transaction that MSMQ uses.  You may consider tweaking this for performance reasons or otherwise.
• .IsTransactional( Boolean ) - for web scenarios, you may not want to use a transaction when pushing a message to the queue
• .PurgeOnStartup( Boolean ) - determine whether or not to purge queues when NSB starts up.
• .TransactionTimeout( Timespan ) - the time to wait for a transaction
• .MsmqSubscriptionStorage() or DBSubscriptionStorage() - tells NSB where to persist subscriptions.  If you are using Profiles, this is set in the Profile of choice(Lite, Integration, or Production).  If using MSMQ, the queue to use is in the config file.  If  using NHibernate, you can default to the config file for NH properties or supply an IDictionary to the overload.
• .DBSubscriptionStorageWithSQLLiteAndAutomaticSchemaGeneration() - pretty sure we all have this one down.
• .Sagas() - tells NSB to look for Sagas in the assemblies provided to NSB in the beginning of the process.
• .NHibernateSagaPersister() - this will use NH for Saga persistence.  Unless supplied to the overload, NSB will use the config file for the NH properties.  You can give this method an IDictionary of properties as this point.  
• NHibernateSagaPersisterWithSQLLiteAndAutomaticSchemaGeneration() - pretty self explanatory I think.
• .RijdaelEncryptionService() - if you are encrypting messages, this will load the keys from the config.
• .Log4Net() - there are a few overloads here for you to tweak Log4Net.  You have access to the Appender, AppenderSkeleton, and you and specify your own configuration.
• .RunCustomAction( Action ) - this is a place where you can run anything you want really.  Typically I've seen this used to tweak the container very early in the boot strapping process.

New 3.0 Options

     Some of the options have moved around to new classes, but the semantics remain the same.  Below are some of the new options available to address new features.

• .MessageForwardingInCaseOfFault() - tells the bus to forward messages when there is a fault
• .FtpTransport() - FTP transport options
• .ImpersonateSender(Boolean) - whether we should impersonate the sender or not
• .InMemoryFaultManagement() - sets up the in memory fault manager.  Faults are lost when the process shuts down.
• .NHibernateFaultManager() - sets up the NH fault manager.  Faults are saved to a database with the exception that caused them.
• .NHibernateUnitOfWork() - sets the UOW manager to use the internal NSB NH manager.  You can supply your own if you are also using NH in your code.

As we've found out, you have full control over how NSB is configured right from the start.  Next time we'll a close look at the Roles we talked about earlier in the article.