Strange type assertion error

[Jeff Rooney]

Hi there, I ran into a strange type assertion error today and was hoping someone could help point me in the right direction. I have a uint32 that I am storing in a net/context but when I try and access it, I am getting the following error:

panic: interface conversion: interface is float64, not uint32

Here is how I store it in the context:

ctx = context.WithValue(ctx, "auth.uid", token.Claims["sub"])

If I dump the context I see:

WithValue("auth.uid", 1)

Then when I access the value from the context I assert uint32 and receive the error.

uid := ctx.Value("auth.uid).(uint32)

I'm sure I am missing something obvious, but i have been spinning on this for a bit now. Thanks for any pointers

Jeff

[Dan Kortschak]

Presumably token.Claims["sub"] is a float64. How was it created?

[Jeff Rooney]

That is was I was thinking, but it is set via:

        token.Claims["sub"] = uint32(user.Id)

where user.Id is defined as a uint32 as well.

Jeff Rooney
jtro...@nexdlevel.com

[Caleb Spare]

Can you show a complete, runnable example?

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[Jeff Rooney]

I'll see if I can put together a runnable example, but it will take some reworking. I'm using github.com/dgrijalva/jwt-go to parse a json web token that has "sub": 1 The claims are stored as map[string]interface{} and when I try and convert the "sub" value to uint32 I receive an error that the interface is a float64 and I am unable to type assert it.

Jeff Rooney
jtro...@nexdlevel.com

[Dan Kortschak]

On Tue, 2016-01-26 at 19:51 -0600, Jeff Rooney wrote:
> I'll see if I can put together a runnable example, but it will take
> some reworking. I'm using github.com/dgrijalva/jwt-go to parse a json
> web token that has "sub": 1 The claims are stored as
> map[string]interface{} and when I try and convert the "sub" value to
> uint32 I receive an error that the interface is a float64 and I am
> unable to type assert it.
>

The most likely thing is that encoding/json is decoding the JSON number
as float64 (as documented).

You should be able to just `ctx = context.WithValue(ctx, "auth.uid",
uint32(token.Claims["sub"].(float64)))` to get the behaviour you want.

[Jeff Rooney]

Thank you very much, I was so focused as on why I wasnt able to to assert using .(uint32) that I missed that encoding/json parses numbers as float64.

Thanks again!