On Wed, 28 Dec 2016 21:55:33 -0800 (PST)
Sathish VJ <sathis...@gmail.com> wrote:
> I'm trying to do custom json unmarshaling when there could be an
> error.
>
> In case there is an error, it will have json like: { "error": "err
> msg"} Else, it could be anything.
>
> If it is another json object, then I'm having no issues. But if the
> incoming data is an array, then it fails. How do I take care of this
> case?
>
> source: https://play.golang.org/p/xyiDWZh9Rt
One way around this is to rely on Go's encoding/json doing the Right
Thing™ when unmarshaling into a value of type interface{}.
This way, you'll get an appropriately-typed value as a result, and
could do type switching on it [1].
The downside of this approach is that if your "non-error case" JSON
streams are compilcated, and you'd like to actually parse them into
objects of your custom (struct) types, this approach would require
re-parsing the source JSON stream for a non-error case.
You can get around this problem by resorting to low-level parsing of
the JSON stream and switching the processing logic as soon as you
detect you were sent a JSON object (which might contain the
field "error" signalizing an error). Unfortunately, the JSON decoder
seems to not support "peeking" at the next token or "pushing back" the
just read token so you'll need to resort to a somewhat contrived
solution such as [2], which I'd use only if your "non-error case" data
streams are large enough to warrant such dancing.
You could also condider exploring 3rd-party JSON decoders such as [3] or
[4] which might contain enough controls to facilitate such fine-grained
parsing you need.
1. https://play.golang.org/p/VVm6pxN8rh
2. https://play.golang.org/p/6wntcKxKBR
3. https://github.com/ugorji/go
4. https://github.com/clbanning/mxj
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