Doesn't it make sense that this is an error? You're telling it to decode a string into an integer but then don't provide a valid integer in the string.

@erikdubbelboer
usualy, we received data from web frontend.
for example,
the html code like this:

<select name="demo">
    <option value="">please select</option>
    <option value="1">option1</option>
    <option value="2">option2</option>
</select>

some time, them submit json data like this:

{ 
    "demo": ""
}

or them submit form data like this demo=""
ignore form data at the moment.
let we take a look json data. it is an empty string in the json data.

the go code:

type Data struct {

    Demo int `json:",string"`

}

zero value of string is "". so, in my opinion, received a zero value of string convert to json. must not get a error.

@hhniao if your values are supposed to be numbers then it should obviously be <option value="0">please select</option>. Forms also don't submit JSON so there is some part of your code which takes the values of the form and turns it into JSON. This part is where you would normally make sure the JSON values are of the correct type.

because we cant change code of frontend .
we just try to re-write backend using golang from php.

I don't think you not being able to fix your frontend means that the Go JSON parser should make exceptions for invalid JSON.

no, no, no.
for JSON. it is valid.
{
"demo": ""
}
{
"demo": "0"
}

and i think json:",string". it is must able to parse a valid string. any string. empty string also it is a string, valid string. is it?

It's a valid string yes but not a valid number. What if it's "a" which is also a valid string, should it accept that as well? What should the value be then? 0, or 10 or ...?
I think it should produce an error with all strings that are not numbers, like it is now.

hmm, you are right. thought php can be parse empty string. but it is not standard or valid. for strict of standard, we must write "0" instead "".
thanks.

may i should close this issue?

I think that it should parse empty string as a default parameter (like nil)
If we got an empty string it means that it's default (default for string is "").
If we got a default string it means that we want to use default value for int, isn't it?

so?! Update i coming?! Working with not my api and cant improve it... plix add! or change json:"field,string,omitempty" to json:"field,omitempty,string" if field is empty just leave (,string tag didnt launched)...

@asiman161 then what if in Go I have a string but in my JSON I get 0 (not a string). Should it then also result in an empty string seeing as 0 is the default for numbers?

@bsbak I don't think the Go team will fix this as it's not a bug.
If you're working with a broken JSON API you should either ask them to fix their API, you should use json.RawMessage or you implement your own type that can be both a number and an empty string: https://play.golang.org/p/nWl2toE2RAE

The error message is there for a reason. Empty strings do not mean 0. There are various ways you can fix this already mentioned above.

• Fix the frontend.
• Change the type to string, and then handle "" to 0 later in the code.
• Use a custom Unmarshaler.

Probably others that I can't think of now.

Closing as this is WAI.

/cc @mvdan if I missed something.