reg_middlewares.md

Registration Middlewares

Similar to familiar middlewares that are used in request handling pipeline, the library introduces the "Registration Middleware" concept.

type RegMiddleware func(op huma.Operation, next func(huma.Operation))

Registration Middlewares are stored in each APIGen instance and are chained and called upon registration of each operation with the APIGen instance.

They are used only during the registration process and don't slow down request handling.

This powerful concept allows you to control the registration process flexibly:

• Modify operation properties before registration
• Prevent registration of some operations
• Register operation multiple times with different properties
• Produce side effects during registration (e.g. maintain own permission registry)

Add a Registration Middleware

To create a new APIGen instance with given Registration Middlewares attached:

myRegMiddleware := func(op huma.Operation, next func(huma.Operation)) {
    // do something with the operation
    next(op)
}

myApi := api.AddRegMiddleware(myRegMiddleware)

Simple operation modifications

For most of the cases when you need to modify an operation and produce some side effects, you can use Operation Handlers (see library provided ones) and add them as Registration Middlewares.

Actually, when you do the following:

myApi := api.AddOpHandler(op_handlers.AddTags("tag1", "tag2"))

It's the same as:

myRegMiddleware := func(op huma.Operation, next func(huma.Operation)) {
    op_handlers.AddTags("tag1", "tag2")(&op)
    next(op)
}

Advanced: bubbling registration middlewares

If you want to see the changes made by all registration middlewares in the chain (in derived APIGen instances) before an operation will be actually registered in Huma, here is the way:

bubblingRegMiddleware := func(op huma.Operation, next func(huma.Operation)) {
    // do something with the operation
    next(op)
}
api = api.AddBubblingRegMiddleware(bubblingRegMiddleware)
derived = api.AddOpHandler(op_handlers.AddTags("tag1"))

In this example bubblingRegMiddleware will receive an operation registered with derived back being able to observe added tags.

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