validation

Documentation

Overview

Package validation defines the validation contract.

There is no reflection and there are no struct tags: every request type implements Validate and returns the errors per field. It is more verbose than `binding:"required"`, and deliberately so -- the message is written by whoever knows the domain, and the CLI generates the method skeleton along with the struct.

Index

• func Email(e Errors, field, value string)
• func MaxLen(e Errors, field, value string, n int)
• func MinLen(e Errors, field, value string, n int)
• func NotZero[T comparable](e Errors, field string, value T)
• func Required(e Errors, field, value string)
• type Errors
  • func (e Errors) Add(field, msg string)
  • func (e Errors) Any() bool
  • func (e Errors) Error() string
  • func (e Errors) First() string
• type Validatable

Functions

func Email

func Email(e Errors, field, value string)

Email checks the shape only. Deliverability is proven by sending mail, never by a regular expression.

Whitespace is rejected rather than trimmed: an address with a space in it is almost always a paste accident, and silently trimming input hides the mistake from the person who made it.

func MaxLen

func MaxLen(e Errors, field, value string, n int)

MaxLen counts runes, not bytes.

func MinLen

func MinLen(e Errors, field, value string, n int)

MinLen counts runes, not bytes: a limit measured in bytes rejects valid input in any language that needs more than one byte per character.

func NotZero

func NotZero[T comparable](e Errors, field string, value T)

NotZero reports a value that was never filled in.

It is Required for everything that is not text. Required takes a string and the generator used to hand it a literal "" for an int, a date or an amount -- so every required field of those types failed validation with "is required" no matter what was sent, and the generated create endpoint could not be used at all. Found by audit.

A time.Time is asked rather than compared: a parsed "0001-01-01T00:00:00Z" carries a location the zero value does not, so == says they differ when they do not.

Bool has no meaningful zero to reject -- false is an answer, not an absence -- and the specification refuses `required` on a bool for that reason.

func Required

func Required(e Errors, field, value string)

Required rejects an empty or blank value.

Types

type Errors

type Errors map[string][]string

Errors maps a field to its messages. It serializes straight into the HTMX partial that re-renders the form with inline errors.

func (Errors) Add

func (e Errors) Add(field, msg string)

Add appends a message to a field. It is a no-op on a nil map, so a caller that forgot to initialize the map does not panic in the middle of a request.

func (Errors) Any

func (e Errors) Any() bool

Any reports whether validation failed.

func (Errors) Error

func (e Errors) Error() string

Error renders the errors with fields in a stable order, so that logs and golden files do not change between runs.

func (Errors) First

func (e Errors) First() string

First returns one message, for a view that shows a single line.

A form that lists every error next to its field uses the map directly. One that shows a banner needs one sentence, and picking it at the call site means every template does it slightly differently.

The field order is not stable -- a map has none -- so this is for the case where any of them answers the question "what is wrong". When which field failed matters, read the map.

type Validatable

type Validatable interface {
	Validate() Errors
}

Validatable is implemented by every request type.