validation

validation

Struct validation using tags, with errors compatible with the errors package.

What it does

• ValidateStruct[T]: Validates a struct using go-playground/validator and struct tags.
• Errors: On failure returns *errors.CustomError (400) with field-level details (BadInputField), using json tag names in error responses.
• Tag name: The validator uses the json tag for field names (e.g. json:"email" → "email" in the error).
• RegisterValidation: Lets you register custom validator functions for your own tags.

Installation

go get github.com/teathedev/pkg/validation

Requires: github.com/teathedev/pkg/errors, github.com/go-playground/validator/v10.

Usage

import (
	"github.com/teathedev/pkg/errors"
	"github.com/teathedev/pkg/validation"
	validator "github.com/go-playground/validator/v10"
)

type CreateUserRequest struct {
	Email    string `json:"email"    validate:"required,email"`
	Password string `json:"password" validate:"required,min=8"`
	Role     string `json:"role"     validate:"oneof=admin user"`
}

func createUser(body *CreateUserRequest) *errors.CustomError {
	if err := validation.ValidateStruct(body); err != nil {
		return err // *errors.CustomError, status 400, with BadInputField list
	}
	// proceed with body
	return nil
}

// Register a custom validation tag
func init() {
	_ = validation.RegisterValidation("startsWithA", func(fl validator.FieldLevel) bool {
		s, ok := fl.Field().Interface().(string)
		if !ok {
			return false
		}
		return strings.HasPrefix(s, "A")
	})
}

API

Function	Description
ValidateStruct[T any](data *T) *errors.CustomError	Validates data; nil on success. On failure returns 400-style CustomError with validation field details; field names come from json tags.
RegisterValidation(tag string, fn func(fl validator.FieldLevel) bool, callEvenIfNull ...bool)	Registers a custom validation under tag. Delegates to validator.RegisterValidation; callEvenIfNull is passed through to control validation-on-nil.

Validator

Uses go-playground/validator. Use standard tags such as required, email, min, max, oneof, etc.