Handle EOFError raised by Rack

In v2.2.0, Rack started raising an EOFError when given an empty body with a
multipart upload - rack/rack#1572  Previously, Rack had
swallowed this error.

CHANGELOG.md

@@ -8,6 +8,8 @@
 
 * Your contribution here.
 
+* [#2161](https://github.com/ruby-grape/grape/pull/2157): Handle EOFError from Rack when given an empty multipart body - [@bschmeck](https://github.com/bschmeck).
+
 ### 1.5.2 (2021/02/06)
 
 #### Features

lib/grape/request.rb

@@ -15,6 +15,8 @@ def initialize(env, **options)
 
     def params
       @params ||= build_params
+    rescue EOFError
+      raise Grape::Exceptions::InvalidMessageBody, 'multipart/form-data'
     end
 
     def headers

spec/grape/endpoint_spec.rb

@@ -420,6 +420,18 @@ def app
         expect(last_response.status).to eq(201)
         expect(last_response.body).to eq('Bob')
       end
+
+      it 'returns a 400 if given an invalid multipart body' do
+        subject.params do
+          requires :file, type: Rack::Multipart::UploadedFile
+        end
+        subject.post '/upload' do
+          params[:file][:filename]
+        end
+        post '/upload', { file: '' }, 'CONTENT_TYPE' => 'multipart/form-data; boundary=foobar'
+        expect(last_response.status).to eq(400)
+        expect(last_response.body).to include('multipart/form-data')
+      end
     end
 
     it 'responds with a 415 for an unsupported content-type' do