Validation

Kashvi's validation engine lives in pkg/validate. It has zero external dependencies and supports 28 rules via struct tags.

Struct Tags

Add a validate tag to any field:

gogo

type RegisterInput struct {
    Name            string  `json:"name"             validate:"required,min=2,max=100"`
    Email           string  `json:"email"            validate:"required,email"`
    Age             int     `json:"age"              validate:"required,min=18,max=120"`
    Role            string  `json:"role"             validate:"in=admin,user,editor"`
    Password        string  `json:"password"         validate:"required,min=8"`
    PasswordConfirm string  `json:"password_confirm" validate:"confirmed=password"`
    Website         *string `json:"website"          validate:"nullable,url"`
}

All Validation Rules

Rule	Example Tag	Description
`required`	`validate:"required"`	Field must be non-zero
`email`	`validate:"email"`	Valid email address
`min`	`validate:"min=3"`	String min length / numeric min value
`max`	`validate:"max=100"`	String max length / numeric max value
`between`	`validate:"between=1,10"`	Numeric between two values (inclusive)
`in`	`validate:"in=a,b,c"`	Value must be one of the listed options
`not_in`	`validate:"not_in=bad,worse"`	Value must NOT be in the list
`confirmed`	`validate:"confirmed=password"`	Must match another field's value
`url`	`validate:"url"`	Valid HTTP/HTTPS URL
`alpha`	`validate:"alpha"`	Letters only
`alpha_num`	`validate:"alpha_num"`	Letters and numbers only
`alpha_dash`	`validate:"alpha_dash"`	Letters, numbers, -, _
`numeric`	`validate:"numeric"`	Any number (int or float)
`integer`	`validate:"integer"`	Must be an integer
`boolean`	`validate:"boolean"`	true or false
`ip`	`validate:"ip"`	Valid IPv4 or IPv6 address
`uuid`	`validate:"uuid"`	Valid UUID
`date`	`validate:"date"`	Valid date in YYYY-MM-DD format
`date_format`	`validate:"date_format=2006-01-02"`	Custom Go time layout
`starts_with`	`validate:"starts_with=https"`	String prefix check
`ends_with`	`validate:"ends_with=.go"`	String suffix check
`contains`	`validate:"contains=@"`	Substring check
`regex`	`validate:"regex=^[A-Z]+"`	Custom regex pattern
`json`	`validate:"json"`	Valid JSON string
`len`	`validate:"len=6"`	Exact string length
`same`	`validate:"same=other_field"`	Alias for confirmed
`different`	`validate:"different=old_password"`	Must differ from field
`nullable`	`validate:"nullable,email"`	Skip other rules if field is empty/nil

Using Validation Directly

In a handler with `BindJSON`

gogo

func (ctrl *UserController) Register(c *appctx.Context) {
    var input RegisterInput
    if !c.BindJSON(&input) {
        return // 422 already sent
    }
    // input is valid here
}

Manual validation

gogo

import "github.com/shashiranjanraj/kashvi/pkg/validate"

errs := validate.Struct(&input)
if validate.HasErrors(errs) {
    // errs = map[string]string{"email": "The email field must be a valid email address."}
}

Error Messages

Errors are returned as map[string]string where the key is the JSON field name:

gogo

{
  "status": 422,
  "message": "Validation failed",
  "errors": {
    "email": "The email field must be a valid email address.",
    "password": "The password field must be at least 8 characters.",
    "password_confirm": "The password_confirm field must match password."
  }
}

Nullable Fields

Use nullable to skip all other rules when the field is empty/nil:

gogo

type UpdateInput struct {
    // These are all optional — only validated if provided
    Bio     *string `json:"bio"     validate:"nullable,max=500"`
    Website *string `json:"website" validate:"nullable,url"`
    Age     *int    `json:"age"     validate:"nullable,min=18"`
}

Combining Rules

Rules are comma-separated and evaluated in order. All failures are collected (not short-circuit):

gogo

validate:"required,min=8,max=64,alpha_num"

Validation

Struct Tags

All Validation Rules

Using Validation Directly

In a handler with BindJSON

Manual validation

Error Messages

Nullable Fields

Combining Rules

In a handler with `BindJSON`