feat: useBody takes content-type header into account

[tobiasdiez]

Improves the body parsing methods in the following ways:

• readBody: only parse body as JSON if content-type indicates it is JSON
• improve internal and public typing information
• add tests, especially for empty string handling (refs readBody returns a empty string when no body request is sent #197)

Depends on unjs/destr#10.

[tobiasdiez]

I think it would also make sense that readBody actually throws an error if the content type says its json but there are parse errors. Currently, this is hidden and devs don't get the chance to react to this (e.g. return an error). Any idea how to make this happen? A boolean object to destr that disables the validation checks?

[pi0]

@tobiasdiez Would you please open a new PR that adds { validateJSON: true } support JSON validation to useBody?

[tobiasdiez]

I can do this, but what should be the semantics of validateJSON?

[pi0]

Maybe as you mentioned in this PR, validate both headers and also we can throw an error on failed parsing with readBody(event, { validateJSON: true }) ?

(We can add an option for destr { strict: true } here that throws error instead of silent fallback)

[tobiasdiez]

Okay, first step is at unjs/destr#11.