forms/validate.go

package forms

import (
	"net/http"
	"reflect"
)

/* ValidateForm parses a POST form into a pre-defined struct */
func ValidateForm(r *http.Request, p any) (formErr error) {
	/* asserts */
	switch {
	case r == nil:
		/* error on nil requestst */
		return ENilRequest
	case r.Method != http.MethodPost:
		/* only support with POST methods */
		return EInvalidMethod
	case p == nil:
		/* error on nil form */
		return ENilForm
	}
	/* assert on form being a pointer */
	fv := reflect.ValueOf(p)
	if fv.Kind() != reflect.Pointer || fv.IsNil() {
		return EInvalidForm
	}
	/* assert on form being a pointer to a struct */
	fv = fv.Elem()
	if fv.Kind() != reflect.Struct {
		return EInvalidForm
	}
	/* parse form in the request */
	if err := r.ParseForm(); err != nil {
		/* TODO: handle multipart forms / file uploads */
		return err
	}
	/* walk target form fields */
	for idx := 0; idx < fv.NumField(); idx++ {
		f := fv.Field(idx)
		/* ignore non-pointer form fields or nil fields */
		if f.Kind() != reflect.Pointer || f.IsNil() {
			continue
		}
		/* ignore fields of type different from *FormField */
		ff, ok := f.Interface().(*FormField)
		if !ok || ff == nil {
			continue
		}
		ff.Error = nil
		/* store value in *FormField */
		defaultValue := ff.Value
		if v, ok := r.PostForm[ff.Name]; ok {
			ff.Value = v[0]
		} else {
			ff.Value = ""
		}
		/* assert on required fields */
		if ff.Required && ff.Value == "" {
			ff.Error = append(ff.Error, ERequiredField)
			formErr = EFormHasErrors
			continue
		}
		/* do not run validators on empty values */
		if ff.Value == "" {
			continue
		}
		/* run field validators if any */
		for _, fieldValidator := range ff.Validators {
			if fieldValidator == nil {
				continue
			}
			if err := fieldValidator(ff, r.Context()); err != nil {
				ff.Error = append(ff.Error, err)
				formErr = EFormHasErrors
				break
			}
		}
		/* restore default value if necessary */
		if ff.Sticky {
			ff.Value = defaultValue
		}
	}
	return
}