Add api_format function accessible from inside_route

fetch_formatter will look api.format first
Use fetch {} instead of [] ||
Update spec
Add HTTP_VERSION in Grape::Http::Headers
Update README

README.md

@@ -3066,15 +3066,15 @@ end
 * `GET /hello.xls` with an `Accept: application/xml` header has an unrecognized extension, but the `Accept` header corresponds to a recognized format, so it will respond with XML.
 * `GET /hello.xls` with an `Accept: text/plain` header has an unrecognized extension *and* an unrecognized `Accept` header, so it will respond with JSON (the default format).
 
-You can override this process explicitly by specifying `env['api.format']` in the API itself.
+You can override this process explicitly by calling `api_format` in the API itself.
 For example, the following API will let you upload arbitrary files and return their contents as an attachment with the correct MIME type.
 
 ```ruby
 class Twitter::API < Grape::API
   post 'attachment' do
     filename = params[:file][:filename]
     content_type MIME::Types.type_for(filename)[0].to_s
-    env['api.format'] = :binary # there's no formatter for :binary, data will be returned "as is"
+    api_format :binary # there's no formatter for :binary, data will be returned "as is"
     header 'Content-Disposition', "attachment; filename*=UTF-8''#{CGI.escape(filename)}"
     params[:file][:tempfile].read
   end

lib/grape/dsl/inside_route.rb

@@ -452,7 +452,11 @@ def entity_representation_for(entity_class, object, options)
       end
 
       def http_version
-        env['HTTP_VERSION'] || env[Rack::SERVER_PROTOCOL]
+        env.fetch(Grape::Http::Headers::HTTP_VERSION) { env[Rack::SERVER_PROTOCOL] }
+      end
+
+      def api_format(format)
+        env[Grape::Env::API_FORMAT] = format
       end
 
       def context

lib/grape/http/headers.rb

@@ -6,6 +6,7 @@ module Headers
       HTTP_ACCEPT_VERSION = 'HTTP_ACCEPT_VERSION'
       HTTP_ACCEPT = 'HTTP_ACCEPT'
       HTTP_TRANSFER_ENCODING = 'HTTP_TRANSFER_ENCODING'
+      HTTP_VERSION = 'HTTP_VERSION'
 
       ALLOW = 'Allow'
       LOCATION = 'Location'

lib/grape/middleware/formatter.rb

@@ -53,7 +53,7 @@ def build_formatted_response(status, headers, bodies)
       end
 
       def fetch_formatter(headers, options)
-        api_format = mime_types[headers[Rack::CONTENT_TYPE]] || env[Grape::Env::API_FORMAT]
+        api_format = env.fetch(Grape::Env::API_FORMAT) { mime_types[headers[Rack::CONTENT_TYPE]] }
         Grape::Formatter.formatter_for(api_format, options[:formatters])
       end
 

spec/grape/api_spec.rb

@@ -4092,9 +4092,9 @@ def my_method
         expect(last_response.body).to eq({ meaning_of_life: 42 }.to_json)
       end
 
-      it 'can be overwritten with an explicit content type' do
+      it 'can be overwritten with an explicit api_format' do
         subject.get '/meaning_of_life_with_content_type' do
-          content_type 'text/plain'
+          api_format 'text/plain'
           { meaning_of_life: 42 }.to_s
         end
         get '/meaning_of_life_with_content_type'