go-validator

Struct validator for Go based on reflection. It builds a mapper of a struct from its json tags or protobuf fields, checks required fields, collects per-field errors and converts them into a JSON-friendly map or gRPC BadRequest error details.

Module github.com/ralvarezdev/go-validator (Go 1.24.0). Docs: https://pkg.go.dev/github.com/ralvarezdev/go-validator.

Installation

go get github.com/ralvarezdev/go-validator

Depends on go-reflect, go-strings (both by the same author) and google.golang.org/genproto/googleapis/rpc.

Concepts

• Mapper (mapper) — reflection-based description of a struct. A field is required unless its JSON tag is missing or contains omitempty. NewJSONGenerator(logger) and NewProtobufGenerator(logger) implement Generator (NewMapper, NewMapperWithNoError).
• Validations (mapper/validation) — StructValidations and FieldValidations hold the errors collected for an instance, including nested structs.
• Validator (mapper/validator) — DefaultValidator checks that required fields are initialised. NewDefaultService(rawParser, endParser, validator, birthdateOptions, passwordOptions, logger) returns the Service.
• Parsers (mapper/parser) — a RawParser flattens validations and an EndParser renders them. Implementations in parser/json and parser/grpc (ErrorDetails.GetBadRequest()).
• Field validators — Email, Username, Birthdate, Password on Service, configured with BirthdateOptions{MinimumAge, MaximumAge} and PasswordOptions{MinimumLength, MinimumSpecialCount, MinimumNumbersCount, MinimumCapsCount}. Error values live in field/.
• Running — Service.Validate(mapper, auxiliaryValidatorFns...) and Service.CreateValidateFn(mapper, cache, auxiliaryValidatorFns...).

Usage

type CreateUser struct {
	Username string `json:"username"`
	Email    string `json:"email"`
	Nickname string `json:"nickname,omitempty"` // optional
}

generator := govalidatormapper.NewJSONGenerator(nil)
m, err := generator.NewMapper(CreateUser{})

Pass the mapper to a validator.Service (see mapper/validator/service.go). No end-to-end example is included in the repository.

Project structure

field/        error values for birthdate, mail, password, username
mapper/       Mapper, JSON and protobuf generators
  parser/     parser interfaces; json/ and grpc/ implementations
  validation/ StructValidations and FieldValidations
  validator/  Validator, Service and DefaultService

The repository has no tests; .golangci.yml is provided for linting.

License

GNU General Public License v3.0.