hooks.md

Hooks

Hooks are a way to extend the functionality of the core library. Hooks enable to inject some custom behavior before and after client operations.

User can register before and after hooks by calling AddHook method on resource providers such as InMemoryStorageProvider. When adding a hook, user targets one or more client operations to which the hook should be applied and a function that should be executed before or after the operation. This function receives a context which contains information about the currently executed operation.

var provider = new InMemoryStorageProvider();

// Register hook

// Before all storage operations:

provider.AddHook(hook => hook.Before(context => { ... }));

// Before creating any container in any storage account:

provider.AddHook(hook => hook.ForBlobService().ForContainerOperations().BeforeCreate(context => { ... }));

// Before creating specific container in any storage account:

provider.AddHook(hook => hook
  .ForBlobService()
  .ForContainerOperations(containerName: "container")
  .BeforeCreate(context => { ... }));

// After creating any container or uploading any blob within a specific storage account:

provider.AddHook(hook => hook
  .ForBlobService(storageAccountName: "account")
  .ForContainerOperations()
  .After(context => { ... }), containerOperations: ContainerOperations.Create, blobOperations: BlobOperations.Upload);

Contexts

The contexts passed to the hook functions are organized into an inheritance hierarchy. For example, after hook for blob upload receives BlobUploadAfterHookContext type which inherits from the BlobAfterHookContext -> BlobServiceAfterHookContext -> StorageAfterHookContext hierarchy.

This enabled the hook functions to access specific information about the currently executed operation even if the hook targets a more general group of operations (e.g. all storage operations). This can be done e.g via pattern matching:

provider.AddHook(hook => hook.Before(hookFunc));

static Task hookFunc(StorageAfterHookContext context)
{
  if(context is BlobUploadAfterHookContext blobUpload)
  {
    ...
  }
  else
  {
    ...
  }
}