Hard to return preformatted json with application/json content-type

[iabdulin]

For example, we have the following endpoint, returning preformatted json (I return json right from the database)

get 'all_json' do
   {key: 123}.to_json
end

Here's what will be returned:
"{\"key\":123}" with application/json content-type
Grape applies additional .to_json call.

Now let's try to fix this problem, taking into assumption that I already have a prebuilt JSON in my endpoint.

Options:

1. Adding env['api.format'] = :binary or :txt — {"key":123} but empty content-type

2. Adding content_type 'application/json' or header 'Content-Type', 'application/json' to :txt or :binary format — "{\"key\":123}"

The only way I was able to solve this is by overwriting :json formatter with:

formatter :json, ->(object, env) {
      if object.is_a?(String)
        object
      else
        return object.to_json if object.respond_to?(:to_json)
        Grape::Json.dump(object)
      end
    }

Maybe there's another way?

[dblock]

I think in your case a custom formatter for JSON is the right answer.

You don't have pre-built JSON, you have a string. Grape can't guess that it's JSON. And the JSON formatter will translate a string into ... JSON.

[iabdulin]

My issue is that even if I explicitly set a :txt or :binary formatter, it still applies :json formatter when I set
content_type 'application/json'
or
header 'Content-Type', 'application/json'.

Setting a content_type or header should not overwrite formatter.

This:

env['api.format'] = :binary # or :txt
content_type 'application/json' # or header 'Content-Type', 'application/json'
{key: 123}.to_json

outputs
"{\"key\":123}"

[dblock]

You're sending JSON, not binary. So you should just be replacing the default JSON formatter with yours with formatter :json,-> as you did above. Does that not work?

[iabdulin]

It works, I just think that there should be a way to specify 'application/json' header without grape applying :json formatter.
I couldn't find a way to send this header.

env['api.format'] = :txt — sends empty content-type
adding content_type 'application/json' or header 'Content-Type', 'application/json' invokes :json formatter

[iabdulin]

Even if I do this:

env['api.format'] = :txt
content_type 'application/json'
body {key: 123}.to_json

grape still applies :json formatter

[dblock]

This should work as is, and we have specs for this. I think something else is going on.

Turn it onto a spec or a small repro of some kind? Maybe add an example to https://github.com/ruby-grape/grape-on-rack?

[waynerobinson]

I'm having exactly the same issue.

If this is used:

env['api.format'] = :binary # or :txt
content_type 'application/json' # or header 'Content-Type', 'application/json'
{key: 123}.to_json

Then it still calls the JSON formatter. If the content_type method is left off, it doesn't.

[waynerobinson]

Here is an example using grape-on-rack:

https://github.com/waynerobinson/grape-on-rack

Please take a look at the extra methods added to Acme::Ping.

The only one that doesn't call the JSON formatter is the one where the content type is set to text/plain.

[dblock]

This does look like a bug, and shouldn't have been closed. Let's fix it in #2171.