ePay JSON to struct validator

With actual JSON validation included!

go get github.com/epay-technology/json-validator-go

This JSON validator operates differently from popular struct validators like gookit/validate and go-playground/validator. It validates JSON directly against a target data structure, rather than after unmarshalling.

The validator distinguishes between a missing key and a given value with a data type's default zero value. This redefines the semantics of the required validation rule and introduces the new rule present. In traditional struct validators, required means "not the data type's default zero value" but in this JSON validator, it means "the key exists in JSON and the value is not null."

This allows requiring a field from a client while permitting the data type's default zero value.

Advantages over Traditional Struct Validators

Better Handling of Invalid Value Types

Traditional struct validators struggle to handle cases where the JSON value type doesn't match the struct field type. For instance, if a struct requires an integer but receives a string in the JSON, the default Go JSON unmarshaler would return a generic error, making it hard for struct validators to inform the client about the mismatch. Consequently, these validators often return a generic error code 400 with a vague message like "invalid payload," leaving clients unsure how to correct their code.

In contrast, the JsonValidator enables APIs to return more informative error responses. By validating the JSON directly, it allows for precise error messages, such as returning a 422 status code with a validation error stating "The field must be an integer." This clarity empowers clients to align their code with API specifications more effectively.

Introduction of the "Present" Rule

Another significant benefit is the introduction of the "present" rule, which is not feasible with traditional struct validators. This rule mandates that a field must be present within the JSON, ensuring that clients send values for all required fields rather than relying on the default zero values of Go struct data types.

This capability enables APIs to differentiate between a client not sending any value and a client intentionally sending the default zero value. Consequently, it allows for scenarios where numeric fields can accept values like 0 while enforcing the requirement for clients to provide explicit values.

Usage

type MyRequest struct {
Id string `json:"id" validation:"required|string|uuid"` // Id must be present with non-null uuid string
User *User `json:"user" validation:"required|object"`   // User must be present with non-null object value
}

type User struct {
Name *string `json:"name" validation:"present|nullable|lenMax:255"` // Name must be present, but can be null or a string with a maximum length of 255 chars
}

func main() {
jsonBytes := (...)

myRequest, err := JsonValidator.Validate[MyRequest](jsonBytes)
}

Rules

Name	Description
nullable/nilable	Explicitly allows the field to be nullable. (Disables other validation rules when value is null)
required	The field key must be both present in the JSON and have a non-null value.
requiredWith:{x}	The field key must be both present in the JSON and have a non-null value if sibling field {x} is present.
requiredWithout:{x}	The field key must be both present in the JSON and have a non-null value if sibling field {x} is not present.
requiredWithAny:{x},{z},...	The field key must be both present in the JSON and have a non-null value if any of the sibling fields {x},{z},... is present.
requiredWithoutAny:{x},{z},...	The field key must be both present in the JSON and have a non-null value if any of the sibling fields {x},{z},... is not present.
requiredWithAll:{x},{z},...	The field key must be both present in the JSON and have a non-null value if all of the sibling fields {x},{z},... is present.
requiredWithoutAll:{x},{z},...	The field key must be both present in the JSON and have a non-null value if all of the sibling fields {x},{z},... is not present.
requireOneInGroup:{groupName}	Exactly one field with the {groupName} must be present and have a non-null value
missingIf:{x},{y}	The field must not be present if {x} is present and has value {y}.
missingUnless:{x},{y}	The field must not be present unless {x} is present and has value {y}.
missingWith:{x}	The field must not be present if {x} is present.
missingWithout:{x}	The field must not be present if {x} is not present.
missingWithAny:{x},{z},...	The field must not be present if any of fields {x},{z},... is present.
missingWithoutAny:{x},{z},...	The field must not be present if any of fields {x},{z},... is not present.
missingWithAll:{x},{z},...	The field must not be present if all of fields {x},{z},... is present.
missingWithoutAll:{x},{z},...	The field must not be present if all of fields {x},{z},... is not present.
present	The field key must be present in the JSON.
len:{n}	Checks value is countable and length is exactly {n} (string, array, object)
lenMax:{n}	Checks value is countable and length is at most {n} (string, array, object)
lenMin:{n}	Checks value is countable and length is at least {n} (string, array, object)
lenBetween:{n},{m}	Checks value is countable and length is between {n} and {m} inclusively (string, array, object)
array	Checks value is an array/slice
object	Checks value is an object/map/struct
string	Checks value is a string
int/integer	Checks value is an integer
float	Checks value is a float
bool/boolean	Checks value is a boolean
date	Checks value is a YYYY-MM-DD formatted string
in:{a},{b},...	Checks that the value is within the the list {a},{b},... If the list has a trailing , or if a ,, is present, an empty string will be considered valid.
uuid	Checks that the value is a valid non-zero UUID string.
zeroableUuid	Checks that the value is any valid UUID string.
regex:{x}	Checks that the value is a string that is matched by the {x} regex definition
between:{x},{z}	Checks that the value is a number between {x} and {z} inclusively
min:{x}	Checks that the value is a number greater than or equal to {x}
max:{x}	Checks that the value is a number less than or equal to {x}
url:{?options}	Checks that the value is a non-empty URL string. An optional list of options can be given to allow certain formats. Options: [localhost]
ip	Checks that the value is a non-empty IP string
email	Checks that the value is a non-empty email string
json	Checks that the value is a valid json string
alpha3Currency	Checks that the value is a valid alpha-3 currency code