Earlier swaggest URL parameter validation possible?

[pboguslawski]

Swaggest validates input params when interactor is called.

Is it possible to have URL parameters (from path and/or query) validated by swaggest earlier, to have parameter validated before execution of given middleware that loads resource on the context is called?

[vearutop]

Validation is tightly tied to request decoding, and decoding is dependent on request structure that is represented by usecase input port.

It is technically possible to run validation outside nethttp.Handler in a middleware (perhaps with performance penalty of double validation unless this case is specifically supported), but I hope this is not the actual problem you're solving.

If (as per chi example) you need a shared piece of code that acts on a family of inputs, you can achieve that with usecase middleware.

Please check the following example.

package main

import (
	"context"
	"log"
	"net/http"

	"github.com/swaggest/rest/nethttp"
	"github.com/swaggest/rest/web"
	swgui "github.com/swaggest/swgui/v4emb"
	"github.com/swaggest/usecase"
	"github.com/swaggest/usecase/status"
)

type SomethingExposer interface {
	Something() int
}

type someIn1 struct {
	Foo int `query:"foo" minimum:"10"`
}

func (s someIn1) Something() int {
	return s.Foo
}

type someIn2 struct {
	Bar int `path:"bar" maximum:"20"`
}

func (s someIn2) Something() int {
	return s.Bar
}

func somethingMW(magicNumber int) func(next http.Handler) http.Handler {
	return nethttp.UseCaseMiddlewares(usecase.MiddlewareFunc(func(next usecase.Interactor) usecase.Interactor {
		return usecase.Interact(func(ctx context.Context, input, output interface{}) error {
			if se, ok := input.(SomethingExposer); ok {
				if se.Something() == magicNumber { // Fail on specific condition.
					return status.DataLoss
				}

				// Pass additional info via context (type safety can be improved with input interfaces instead of ctx).
				return next.Interact(context.WithValue(ctx, "extra", 10*se.Something()), input, output)
			}

			return next.Interact(ctx, input, output)
		})
	}))
}

func main() {
	s := web.DefaultService()

	s.Wrap(somethingMW(15))

	// Add use case handler to router.
	s.Get("/one", usecase.NewInteractor(func(ctx context.Context, input someIn1, output *int) error {
		*output = input.Foo

		if extra, ok := ctx.Value("extra").(int); ok {
			*output += extra
		}

		return nil
	}))

	s.Get("/two/{bar}", usecase.NewInteractor(func(ctx context.Context, input someIn2, output *int) error {
		*output = input.Bar

		if extra, ok := ctx.Value("extra").(int); ok {
			*output += extra
		}

		return nil
	}))

	// Swagger UI endpoint at /docs.
	s.Docs("/docs", swgui.New)

	// Start server.
	log.Println("http://localhost:8011/docs")
	if err := http.ListenAndServe("localhost:8011", s); err != nil {
		log.Fatal(err)
	}
}