one of my favorite examples of this is google's protojson package, where
the output of `json.Marshal` is [deliberately
nondeterministic](https://protobuf.dev/reference/go/faq/#unstable-json) to
prevent users from attempting to rely on that property
On Tuesday, April 9, 2024 at 9:10:42 AM UTC-4 Nagaev Boris wrote:
> Hi Juliusz,
>
> I don't know if JSON serialization is deterministic, but I know a couple
> of cases when it is not.
>
> If the type or some type inside it has a custom JSON marshaller (method
> MarshalJSON), then if that function's output is not deterministic, the
> whole JSON for the type is not deterministic. Custom marshaller can do
> whatever it wants, e.g. traverse maps without ordering keys, resulting in
> non-determinism.
>
> Another common pitfall with JSON: nil vs empty slice. E.g. []string{} is
> encoded as "[]", while []string(nil) is encoded as "null", while they both
> mean an empty slice in Go (though NOT considered deep equal according to
> reflect.DeepEqual). The workaround is to add `omitempty` to the JSON tag to
> remove such fields from the encoding. Otherwise you need to make sure that
> empty slices are always nil or always non-nil in the code producing
> structures that are serialized.
>
> Boris
>
> On Tue, Apr 9, 2024 at 9:27 AM Juliusz Chroboczek <j...@irif.fr> wrote:
>
>> Hi,
>>
>> Suppose that I call json.Marshal on two structures that are deep equal,
>> or on the same structure at different times. Are the outputs guaranteed
>> to be bytewise identical?
>>
>> (The reason I'm asking is that I'm sending JSON over HTTP, and I need to
>> know whether it is correct to send a strong ETag with my reply even
>> though I'm generating new JSON every time.)
>>
>> Thanks,
>>
>> -- Juliusz
>>
>>
>>
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>>
>
>
> --
> Best regards,
> Boris Nagaev
>
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