Always set CONTENT_TYPE for non-GET requests (#223)

...even when no parameters are provided (or the provided parameters are `nil`)

The long story:

- #132 changed the behavior for HTTP DELETE requests to behave like GET: put the parameters in the query string, and don't set the Content-Type. This change was merged in d016695
- This broke `rack-test` for certain people, which was highlighted in #200. Arguably, the change incorporated in d016695 was too brutal.
- #212 tried to sort it out, by not setting Content-Type if params are nil, and also reverting the change to put DELETE parameters in the query string. The first part of this (params being nil) caused issues for certain people.

So this PR now tries to once and for all sort this out by:

- Always setting `env['CONTENT_TYPE']`, even when params are `nil`.
- Adding more tests for how `CONTENT_TYPE` and `CONTENT_LENGTH` should behave; some of this does not come from us, but from Rack upstream.
- Settles with the discussion in #220: if you are using `DELETE` and must use query params, put them manually in there like this: `delete '/foo?bar=baz'`. Arguably not very clean, but better than changing back and forth. `params` are overloaded in rack 0.x and will be so in 1.0 also. I am thinking that we should go with the excellent suggestion provided by @malacalypse in #200 to use dedicated `body` and `params` parameters in the long run (and probably use keyword parameters instead, but that's definitely a 2.x feature since it breaks all existing usage.) For now, I think we'll live with the ugliness.

I encourage everyone to give this a try before we merge, to ensure we don't have to revert once more.

lib/rack/test.rb

@@ -233,14 +233,16 @@ def env_for(uri, env)
             uri.query = [uri.query, build_nested_query(params)].compact.reject { |v| v == '' }.join('&')
           end
         elsif !env.key?(:input)
-          env['CONTENT_TYPE'] ||= 'application/x-www-form-urlencoded' unless params.nil?
+          env['CONTENT_TYPE'] ||= 'application/x-www-form-urlencoded'
 
           if params.is_a?(Hash)
             if data = build_multipart(params)
               env[:input] = data
               env['CONTENT_LENGTH'] ||= data.length.to_s
               env['CONTENT_TYPE'] = "multipart/form-data; boundary=#{MULTIPART_BOUNDARY}"
             else
+              # NB: We do not need to set CONTENT_LENGTH here;
+              # Rack::ContentLength will determine it automatically.
               env[:input] = params_to_string(params)
             end
           else

spec/rack/test_spec.rb

@@ -457,11 +457,11 @@ def close
     end
   end
 
-  shared_examples_for 'any #verb methods' do
+  shared_examples_for 'any #verb methods' do |verb|
     it 'requests the URL using VERB' do
       public_send(verb, '/')
 
-      check expect(last_request.env['REQUEST_METHOD']).to eq(verb.upcase)
+      check expect(last_request.env['REQUEST_METHOD']).to eq(verb.to_s.upcase)
       expect(last_response).to be_ok
     end
 
@@ -470,9 +470,28 @@ def close
       expect(last_request.env['HTTP_USER_AGENT']).to eq('Rack::Test')
     end
 
-    it 'does not set CONTENT_TYPE if params are explicitly set to nil' do
-      public_send(verb, '/', nil)
-      expect(last_request.env['CONTENT_TYPE']).to be_nil
+    context 'when params are not provided', unless: verb == :get do
+      it 'sets CONTENT_TYPE to application/x-www-form-urlencoded' do
+        public_send(verb, '/')
+        expect(last_request.env['CONTENT_TYPE']).to eq 'application/x-www-form-urlencoded'
+      end
+
+      it 'sets CONTENT_LENGTH to zero' do
+        public_send(verb, '/')
+        expect(last_request.env['CONTENT_LENGTH']).to eq '0'
+      end
+    end
+
+    context 'when params are explicitly set to nil', unless: verb == :get do
+      it 'sets CONTENT_TYPE to application/x-www-form-urlencoded' do
+        public_send(verb, '/', nil)
+        expect(last_request.env['CONTENT_TYPE']).to eq 'application/x-www-form-urlencoded'
+      end
+
+      it 'sets CONTENT_LENGTH to 0' do
+        public_send(verb, '/')
+        expect(last_request.env['CONTENT_LENGTH']).to eq '0'
+      end
     end
 
     it 'yields the response to a given block' do
@@ -506,10 +525,43 @@ def close
   end
 
   describe '#get' do
-    it_should_behave_like 'any #verb methods'
+    it_should_behave_like 'any #verb methods', :get
+
+    context 'when params are not provided' do
+      # This is not actually explicitly stated in the relevant RFCs;
+      # https://tools.ietf.org/html/rfc7231#section-3.1.1.5
+      # ...but e.g. curl do not set it for GET requests.
+      it 'does not set CONTENT_TYPE' do
+        get '/'
+        expect(last_request.env.key?('CONTENT_TYPE')).to eq false
+      end
+
+      # Quoting from https://tools.ietf.org/html/rfc7230#section-3.3.2:
+      #
+      #   A user agent SHOULD NOT send a Content-Length header field when
+      #   the request message does not contain a payload body and the
+      #   method semantics do not anticipate such a body.
+      #
+      # _However_, something causes CONTENT_LENGTH to always be present.
+      # Even when we don't set it ourselves. It could be
+      # Rack::ContentLength that is playing tricks with us:
+      # https://github.com/rack/rack/blob/master/lib/rack/content_length.rb
+      it 'sets CONTENT_LENGTH to zero' do
+        get '/'
+        expect(last_request.env['CONTENT_LENGTH']).to eq '0'
+      end
+    end
 
-    def verb
-      'get'
+    context 'when params are explicitly set to nil' do
+      it 'sets CONTENT_TYPE to application/x-www-form-urlencoded' do
+        get '/', nil
+        expect(last_request.env.key?('CONTENT_TYPE')).to eq false
+      end
+
+      it 'sets CONTENT_LENGTH to zero' do
+        get '/', nil
+        expect(last_request.env['CONTENT_LENGTH']).to eq '0'
+      end
     end
 
     it 'uses the provided params hash' do
@@ -539,19 +591,11 @@ def verb
   end
 
   describe '#head' do
-    it_should_behave_like 'any #verb methods'
-
-    def verb
-      'head'
-    end
+    it_should_behave_like 'any #verb methods', :head
   end
 
   describe '#post' do
-    it_should_behave_like 'any #verb methods'
-
-    def verb
-      'post'
-    end
+    it_should_behave_like 'any #verb methods', :post
 
     it 'uses the provided params hash' do
       post '/', foo: 'bar'
@@ -568,6 +612,13 @@ def verb
       expect(last_request.env['CONTENT_TYPE']).to eq('application/x-www-form-urlencoded')
     end
 
+    # NB: This is never set in _our code_, but is added automatically
+    # (presumably by Rack::ContentLength)
+    it 'sets the CONTENT_LENGTH' do
+      post '/', foo: 'bar'
+      expect(last_request.env['CONTENT_LENGTH']).to eq('7')
+    end
+
     it 'accepts a body' do
       post '/', 'Lobsterlicious!'
       expect(last_request.body.read).to eq('Lobsterlicious!')
@@ -582,11 +633,7 @@ def verb
   end
 
   describe '#put' do
-    it_should_behave_like 'any #verb methods'
-
-    def verb
-      'put'
-    end
+    it_should_behave_like 'any #verb methods', :put
 
     it 'accepts a body' do
       put '/', 'Lobsterlicious!'
@@ -595,11 +642,7 @@ def verb
   end
 
   describe '#patch' do
-    it_should_behave_like 'any #verb methods'
-
-    def verb
-      'patch'
-    end
+    it_should_behave_like 'any #verb methods', :patch
 
     it 'accepts a body' do
       patch '/', 'Lobsterlicious!'
@@ -608,11 +651,7 @@ def verb
   end
 
   describe '#delete' do
-    it_should_behave_like 'any #verb methods'
-
-    def verb
-      'delete'
-    end
+    it_should_behave_like 'any #verb methods', :delete
 
     it 'uses the provided params hash' do
       delete '/', foo: 'bar'
@@ -636,11 +675,7 @@ def verb
   end
 
   describe '#options' do
-    it_should_behave_like 'any #verb methods'
-
-    def verb
-      'options'
-    end
+    it_should_behave_like 'any #verb methods', :options
   end
 
   describe '#custom_request' do