Re: [go-nuts] custom json unmarshaling between object or arrays

[Matt Harden]

https://play.golang.org/p/gWQuthS0D6

On Wed, Dec 28, 2016 at 11:55 PM Sathish VJ  wrote:

> aah, got it. the case []interface{}:  is what I'd not gotten right.
> Thanks for the detailed examples.
>
>
> On Thursday, 29 December 2016 12:57:54 UTC+5:30, Konstantin Khomoutov
> wrote:
>
> On Wed, 28 Dec 2016 21:55:33 -0800 (PST)
>
> Sathish VJ  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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Re: [go-nuts] custom json unmarshaling between object or arrays

[Sathish VJ]

aah, got it. the case []interface{}:  is what I'd not gotten right.  
Thanks for the detailed examples.


On Thursday, 29 December 2016 12:57:54 UTC+5:30, Konstantin Khomoutov wrote:
>
> On Wed, 28 Dec 2016 21:55:33 -0800 (PST) 
> Sathish VJ  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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Re: [go-nuts] custom json unmarshaling between object or arrays

[Konstantin Khomoutov]

On Wed, 28 Dec 2016 21:55:33 -0800 (PST)
Sathish VJ  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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[go-nuts] custom json unmarshaling between object or arrays

[Sathish VJ]

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

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