Migration Guide 3.x to 4.0

The 4.0 release includes breaking changes in the API:

• The request handler interfaces are consolidated into one, IRequestHandler
• The notification handler interfaces are consolidated into one, INotificationHandler
• The behavior pipeline interface now has a cancellation token
• The request pre-processor interface now has a cancellation token

The main motivation behind these changes were to remove the ambiguity around handler resolution at runtime. The 3.x releases used a try...catch to find the correct handler implementation. The 4.0 release removes the multiple interfaces, making both configuration and resolution simpler.

To ease the transition, the following find/replace values (using regular expressions) can quickly migrate a codebase from 3.x to 4.0. Run these in order:

Find	Replace
IRequestHandler	RequestHandler
IAsyncRequestHandler	AsyncRequestHandler
ICancellableAsyncRequestHandler	IRequestHandler
INotificationHandler	NotificationHandler
IAsyncNotificationHandler	AsyncNotificationHandler
ICancellableNotificationRequestHandler	INotificationHandler
public async Task<([a-zA-Z0-9_<>]*)> Handle\(([a-zA-Z0-9_<>]*) ([a-zA-Z0-9_<>]*)\)	protected override async Task<$1> HandleCore($2 $3)
public Task<([a-zA-Z0-9_<>]*)> Handle\(([a-zA-Z0-9_<>]*) ([a-zA-Z0-9_<>]*)\)	protected override Task<$1> HandleCore($2 $3)
public async Task Handle\(([a-zA-Z0-9_<>]*) ([a-zA-Z0-9_<>]*)\)	protected override async Task HandleCore($1 $2)
public Task Handle\(([a-zA-Z0-9_<>]*) ([a-zA-Z0-9_<>]*)\)	protected override Task HandleCore($1 $2)
public void Handle\(([a-zA-Z0-9_<>]*) ([a-zA-Z0-9_<>]*)\)	protected override void HandleCore($1 $2)
public ([a-zA-Z0-9_<>]*) Handle\(([a-zA-Z0-9_<>]*) ([a-zA-Z0-9_<>]*)\)	protected override $1 HandleCore($2 $3)

Pipeline and pre-processors will need to be changed manually, adding the new CancellationToken parameter.