[Proposal] Add context code for validation errors.

[brycereitano]

I propose that we add some extra metadata to the various validation helpers. With the addition to customizing the error responses. (#1321) This would aide in further customizing the error response.

It would include adding an extra key to the various validation helpers. For example,

// InvalidParamTypeError is the error produced when the type of a parameter does not match the type
// defined in the design.
func InvalidParamTypeError(name string, val interface{}, expected string) error {
	msg := fmt.Sprintf("invalid value %#v for parameter %#v, must be a %s", val, name, expected)
	return ErrInvalidRequest(msg, "validation_code", "invalid_param_type, "param", name, "value", val, "expected", expected)
}

It would be preferable to include variables or constants (whether editing these should be allowed) for easier consumption of this change.

const (
	InvalidParamTypeErrorCode     = "invalid_param_type"
	MissingParamErrorCode         = "missing_param"
	InvalidAttributeTypeErrorCode = "invalid_attribute_type"
	MissingAttributeErrorCode     = "missing_attribute"
	MissingHeaderErrorCode        = "missing_header"
	InvalidEnumValueErrorCode     = "invalid_enum_value"
	InvalidFormatErrorCode        = "invalid_format"
	InvalidPatternErrorCode       = "invalid_pattern"
	InvalidRangeErrorCode         = "invalid_range"
	InvalidLengthErrorCode        = "invalid_length"
)

[raphael]

Not sure I follow, the responses already have a code - the error class code. Can you expand a little bit on what you are trying to achieve?

[brycereitano]

This isn't mission critical, but the idea is to provide codes for every error in the response.

{
    "code": "unprocessable_entity",
    "details": {
         "username": [
            {
                "Code": "invalid_format",
                "Message": "username must match the regexp \"^[A-Za-z0-9'_-]+(?:[.][A-Za-z0-9]+)*$\" but got value \"!aaaa\""
            },
            {
                "Code": "invalid_length",
                "Message": "length of username must be greater than or equal to 6 but got value \"!aaaa\" (len=5)"
            }
        ]
    },
    "id": "Fa8iKyff",
    "message": "Invalid user input.",
    "status": 422
}

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.