validation

validation

Validate structs (tags), maps, or single fields with built-in rules and custom rules.

Install

go get github.com/fatkulnurk/foundation/validation@v0.3.0

Struct tags

type User struct {
    Name  string `json:"name" validate:"required,minlen=2,maxlen=50"`
    Email string `json:"email" validate:"required,email"`
    Age   int    `json:"age" validate:"nummin=18,nummax=120"`
}

errs := validation.ValidateStruct(user)
if errs.HasErrors() {
    fmt.Println(errs.Error())
    for _, e := range errs.ForField("email") {
        fmt.Println(e.Message)
    }
}

Error field names prefer the json tag when present.

Map and single field

errs := validation.ValidateMap(data, map[string][]validation.Rule{
    "email": {validation.Custom(func(field string, value any) *validation.Error {
        // ...
        return nil
    })},
})

err := validation.Validate("email", "bad", "required,email")

Tag rules

Canonical names and aliases:

Tag	Alias	Meaning
required		Non-empty
strminlen=N	minlen=N	Min string length
strmaxlen=N	maxlen=N	Max string length
nummin=N	min=N	Min number
nummax=N	max=N	Max number
email		Contains @ (simple check)
phone		Phone format
username		Username rules
password		Password complexity
url		URL format
date		YYYY-MM-DD
alphanumeric		Letters + digits
uuid		UUID
json		Valid JSON string
hexcolor		Hex color
creditcard		Luhn check
postalcode		Postal code
base64		Base64
ip / ipv4 / ipv6		IP addresses

Unknown tags are ignored (no panic).

Custom rules

rule := validation.Custom(func(field string, value any) *validation.Error {
    s, _ := value.(string)
    if s != "ok" {
        return &validation.Error{Field: field, Message: "must be ok"}
    }
    return nil
})

See also

• Root README
• Examples: example/