[BUG] User specified value 0 is ignored when default is not zero

[klajok]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

Following code prints the default integer value 10 of field Level, despite the fact that specified level was "0".

type Example struct {
	Level int `schema:"level,default:10"`
}

func main() {
	var example Example
	input := map[string][]string{"level": {"0"}}

	schema.NewDecoder().Decode(&example, input)

	// instead of 0 program prints 10
	fmt.Println(example.Level)
}

Expected Behavior

Decoder should not ignore user specified integer value even if it is equal to 0. Program should print 0.

Steps To Reproduce

Run the above program.

Anything else?

This bug affects fields of type int, uint32, float64,... and so on.

[jaitaiwan]

Mismatched types. Should be map[string]string{} not map[string][]string{}

[klajok]

I think the type shown in the example snippet is correct. It matches the type url.Values. Additionally the proposed type map[string]string causes compilation error.

But... today I have finally spotted big blue note at the very bottom of README:

Because primitive types like int, float, bool, unint and their variants have their default (or zero) values set by Golang, it is not possible to distinguish them from a provided value when decoding/encoding form values. In this case, the value provided by the default option tag will be always applied. (...) In such cases, it is highly recommended to use pointers to allow schema to distinguish between when a form field has no provided value and when a form has a value equal to the corresponding default set by Golang for a particular type.

I'm not sure about encoding, but in case decoding we have all values in the form of map of string list. We can easily distinguish between [""], ["0"] and no entry in the values map.

As a workaround we use following code (adapted to the reported "example") - it works but looks ugly:

value := input["level"] 
// inspect **last** value of the potentially polluted HTTP param (to be consistent
// with behavior of other library which parses HTTP parameters)
if len(value) > 0 && value[len(value)-1] == "0" {
  example.Level = 0
}

This proves that it is possible to "distinguish them [default (or zero) values] from a provided value".