Add routing constraints

lib/rack_reverse_proxy/rule.rb

@@ -48,7 +48,7 @@ def matches(path, *args)
         spec,
         url,
         path,
-        options[:accept_headers],
+        options,
         has_custom_url,
         *args
       )
@@ -124,14 +124,15 @@ class Matches
       # rubocop:disable Metrics/ParameterLists
 
       # FIXME: eliminate :url, :accept_headers, :has_custom_url
-      def initialize(spec, url, path, accept_headers, has_custom_url, headers, rackreq, *_)
+      def initialize(spec, url, path, options, has_custom_url, headers, rackreq, *_)
         @spec = spec
         @url = url
         @path = path
         @has_custom_url = has_custom_url
         @rackreq = rackreq
 
-        @headers = headers if accept_headers
+        @headers = headers if options[:accept_headers]
+        @constraint = options[:constraint]
         @spec_arity = spec.method(spec_match_method_name).arity
       end
 
@@ -164,15 +165,15 @@ def transform(response, request_uri)
 
       private
 
-      attr_reader :spec, :url, :path, :headers, :rackreq, :spec_arity, :has_custom_url
+      attr_reader :spec, :url, :path, :headers, :rackreq, :spec_arity, :has_custom_url, :constraint
 
       def found
         @_found ||= find_matches
       end
 
       def find_matches
         Array(
-          spec.send(spec_match_method_name, *spec_params)
+          spec.send(spec_match_method_name, *spec_params) && apply_constraints!
         )
       end
 
@@ -201,6 +202,14 @@ def spec_match_method_name
         return :match if spec.respond_to?(:match)
         :call
       end
+
+      def apply_constraints!
+        if constraint.blank?
+          return true
+        end
+
+        constraint.call(rackreq)
+      end
     end
   end
 end

spec/rack/reverse_proxy_spec.rb

@@ -440,6 +440,26 @@ def app
       end
     end
 
+    describe "with a matching constraint" do
+      def app
+        Rack::ReverseProxy.new(dummy_app) do
+          reverse_proxy "/test", "http://example1.com/", constraint: ->() { true }
+          reverse_proxy "/test2", "http://example2.com/", constraint: ->() { false }
+        end
+      end
+
+      it "is considered when the route matches" do
+        stub_request(:get, "http://example1.com/test").to_return(:body => "Proxied App")
+        get "/test"
+        expect(last_response.body).to eq("Proxied App")
+      end
+
+      it "forwards requests to the calling app when path matches but constraint returns false" do
+        get "/test2"
+        expect(last_response.body).to eq("Dummy App")
+      end
+    end 
+
     describe "with force ssl turned on" do
       def app
         Rack::ReverseProxy.new(dummy_app) do