feat: add audio validation

[dapzthelegend]

Fixes Or Enhances

Adds built-in audio validation tag support via a new isAudio validator.

isAudio implementation

// isAudio is the validation function for validating if the current field's value contains the path to a valid audio file
func isAudio(fl FieldLevel) bool {
	mime, ok := detectFileMIMEType(fl.Field())
	if !ok {
		return false
	}

	return strings.HasPrefix(mime, "audio/")
}

Example Usage

package main

import (
	"fmt"

	"github.com/go-playground/validator/v10"
)

type Upload struct {
	AudioPath string `validate:"required,audio"`
}

func main() {
	validate := validator.New()

	u := Upload{AudioPath: "testdata/music.mp3"}
	if err := validate.Struct(u); err != nil {
		fmt.Println("validation failed:", err)
		return
	}

	fmt.Println("validation passed")
}

Make sure that you've checked the boxes below before you submit PR:

• Tests exist or have been written that cover this particular change.

@go-playground/validator-maintainers

[dapzthelegend]

@the-fanan

[the-fanan]

Looks good to me. Let's ship this please!

[zemzale]

One small thing that could be changed, but other than that don't see an issue with this. Is 90% the same thing as isImage.

There is an idea maybe that we can just have a generic mimetype or smth validator, but that is besides this PR.

[zemzale]

Everything down to here is exactly the same code as isImage so maybe we can extract that logic so we don't have to rewrite it twice.

[dapzthelegend]

We could create a isMimeType validator, that matches based on type and/or subtyle

would be resuable in the code base to avoid repetition and would also allow more flexibility for when using the library

Something like:

validate.Var("photo.png", "mimetype=image/png")  //type and subtype validation
validate.Var("photo.png", "mimetype=image/*")    //type validation only

[zemzale]

That is something that came to my mind also, but didn't bring it up, since I am not against a specific audio path.

[dapzthelegend]

Rebased this branch on #1539