Rocket: Fairing can't change content type

[messense]

Rocket version: 0.3.5
OS: macOS 10.13.2

As stated in the doc:

The Content-Type header is cached after the first call to this function. As a result, subsequent calls will always return the same value.

so there are no way for fairings to change content type. I need this because some clients don't have Content-Type header set in their requests thus rocket always responds with 404, so I want to ensure all requests has Content-Type header set to application/json but I can't do that using rocket fairings.

Since Request already provides set_method and etc. Can we add more set_xxx methods for example set_content_type, set_accpet for cached headers?

[SergioBenitez]

I'm curious: why would you want to change the Content-Type of the incoming request?

I think the correct fix is to handle this in Request::replace_header() directly. Then you could simply use something like Request::replace_header(ContentType::JSON) to replace the cached value, which is what you may have expected in the first place.

[messense]

I did try replace_header in the first place.

Because some client like Python requests for example don't set default content type if you are passing json data using data= kwargs:

import requests
s = '"some json string"'
requests.post('http://localhost:8000/hello', data=s)

while the data itself is valid json. We want to support it because we can't ask every customer to change their code to add the required header.

[SergioBenitez]

That's...interesting. So you want to change the Content-Type so that the Json data guard succeeds on some handler? If that's your intention, then I'd recommend that instead of changing the Content-Type on incoming requests, you simply write a new data guard that's essentially identical to the existing Json with the exception that it doesn't do the Content-Type check. Then you can use this new data guard in place of Json and get what you're looking for.

In any case, we should improve replace_header.

[messense]

For now I have extracted rocket_contrib::Json to rocket-lenient-json crate.

I think maybe the Json type should not enforce the Content-Type check by default? Since you can enforce that with format = "application/json" in route function, if the Json type still checks Content-Type header then it's wasting CPU time double checking it.

[HellPat]

:-) i stumbled upon this issue while seearching for the same thing.
I wanted to change the content-type.

The Request beeing sent to the application can't be changed and has Content-Type: application/csp-report (see CSP-Report).

The body is JSON.