Fix nested form body parsing happening for all content types

lib/hanami/router.rb

@@ -1040,18 +1040,36 @@ def _params(env, params)
       params ||= {}
       env[PARAMS] ||= {}
 
-      if !env.key?(ROUTER_PARSED_BODY) && (input = env[::Rack::RACK_INPUT]) and input.rewind
-        env[PARAMS].merge!(::Rack::Utils.parse_nested_query(input.read))
-        input.rewind
-      end
-
+      _merge_form_urlencoded_body!(env)
       env[PARAMS].merge!(::Rack::Utils.parse_nested_query(env[::Rack::QUERY_STRING]))
       env[PARAMS].merge!(params)
       env[PARAMS] = Params.deep_symbolize(env[PARAMS])
 
       env
     end
 
+    # @since x.x.x
+    # @api private
+    def _merge_form_urlencoded_body!(env)
+      return if env.key?(ROUTER_PARSED_BODY)
+      return unless _form_urlencoded?(env)
+      return unless (input = env[::Rack::RACK_INPUT])
+
+      input.rewind
+      env[PARAMS].merge!(::Rack::Utils.parse_nested_query(input.read))
+      input.rewind # leave the stream readable for downstream consumers
+    end
+
+    # @since x.x.x
+    # @api private
+    def _form_urlencoded?(env)
+      content_type = env[CONTENT_TYPE]
+      return false unless content_type
+
+      content_type == FORM_URLENCODED_MEDIA_TYPE ||
+        content_type.start_with?("#{FORM_URLENCODED_MEDIA_TYPE};")
+    end
+
     # @since 2.0.0
     # @api private
     def _not_allowed_fixed(env)

lib/hanami/router/constants.rb

@@ -5,5 +5,13 @@ class Router
     # @api private
     # @since 2.0.0
     ROUTER_PARSED_BODY = "router.parsed_body"
+
+    # @api private
+    # @since x.x.x
+    CONTENT_TYPE = "CONTENT_TYPE"
+
+    # @api private
+    # @since x.x.x
+    FORM_URLENCODED_MEDIA_TYPE = "application/x-www-form-urlencoded"
   end
 end

spec/integration/hanami/router/params_spec.rb

@@ -118,6 +118,28 @@
     end
   end
 
+  context "JSON payload without body parser" do
+    # See: https://github.com/hanami/router/issues/237
+    it "doesn't merge a JSON body into params" do
+      input = JSON.generate("foo" => "bar")
+      env = Rack::MockRequest.env_for("/submit?from=ui", method: "POST", params: input)
+      env["CONTENT_TYPE"] = "application/json"
+      subject.call(env)
+
+      expect(env["router.params"]).to eq(from: "ui")
+    end
+  end
+
+  context "multipart payload without body parser" do
+    # See: https://github.com/hanami/router/issues/296
+    it "doesn't merge a multipart body into params" do
+      env, _contents = multipart_fixture("foo.xml")
+      subject.call(env)
+
+      expect(env["router.params"]).to eq({})
+    end
+  end
+
   context "priority" do
     it "gives first level priority to path variables" do
       expected = "23"