Goval

Goval is a tool for generate validation functions for Go structs.

Goval uses struct tags to generate validation functions for the struct fields.

Note: This tool is in the early stages of development and may contain bugs. Also, not all types are supported yet.

Install

Install the CLI tool

go install github.com/negasus/goval/cmd/goval@latest

And add the package to your project

go get github.com/negasus/goval

Usage

Add tags to struct fields and run goval command from current directory.

type Request struct {
    Name string `goval:"min=3;max=10"`
    Age  int    `goval:"min=18"`
}

goval --type Request

I recommend use go:generate directive.

//go:generate goval --type Request

go generate ./...

Goval will generate a file goval_request.go with validation functions for the struct.

CLI flags

• -t or --type - type name, you can use multiple types -t One -t Two, required
• -o or --output - output file name (default: goval_{snake_cased_type}.go)
• -d or --debug - debug mode, verbose output, default false
• -n or --tag - struct tag name, default goval

Rules

Rules are defined in the struct tags with the goval key. You can redefine the tag name by the --tag CLI flag.

You can use multiple rules separated by ;.

Rule	Description	Support Types
min	minimum value or length	int, float64, string, any slices
max	maximum value or length	int, float64, string, any slices
in	list of valid values	int, string, []int, []string

For in rule you can define a list of valid values separated by ,.

Also, you can use syntax in={variable_name} to use a variable as the list of valid values.

var validKeys = []string{"foo", "bar"}

type Request struct {
	Foo string `goval:"in=foo,bar"`
	Key string `goval:"in={validKeys}"`
}

Custom validation function

You can use a custom validation function.

type Request struct {
    Name string `goval:"@customValidate"`
}

func (r *Request) customValidate() goval.Errors {
    errors := goval.Errors{}

    e := goval.NewError(goval.ErrorTypeInvalid).
        AddValue("field", "Custom")

    errors.Add("Custom", e)

    return errors
}

Custom validation function must return goval.Errors and have no arguments.

You can use alias @ for call Valiadate() function for embedded structs.

//go:generate goval --type Request --type Meta

type Meta struct {
	ID int `goval:"min=1"`
}

type Request struct {
	Meta `goval:"@"`
	Name string `goval:"min=3;max=10"`
}

Error messages

Type Error implements Stringer interface and has two methods to generate error messages.

• String() - returns a string representation of the error with default language.
• StringLang(ln string) - returns a string representation of the error with the specified language.

Now the tool supports only English and Russian languages.

The default language is English.

You can redefine the default language by call SetDefaultLang("ru").

Custom error messages

You can use a custom error message for the field.

var customMessageID = 1

func main() {
    goval.AddCustomMessage(customMessageID, "en", "My Message {value}")
}

type Request struct {
    Name string `goval:"@customValidate"`
}

func (r *Request) customValidate() goval.Errors {
    errors := goval.Errors{}

    e := goval.NewCustomError(customMessageID).AddValue("value", c.Index)

    errors.Add("Name", e)

    return errors
}

Custom Message ID must be unique and greater than 0.