Add support for domain alias lookup. Fixes codemancers#202

Config now accepts a new directive: alias
Multiple aliases can be separated by a comma
Special characters are:
        *: Will match one subpath
        **: Will match any subpaths

lib/invoker/dns_cache.rb

@@ -7,17 +7,41 @@ def initialize(config)
       @dns_mutex = Mutex.new
       Invoker.config.processes.each do |process|
         if process.port
-          dns_data[process.label] = { 'port' => process.port }
+          dns_data[process.label] = { 'port' => process.port, 'alias' => make_regex(process.alias) }
         end
       end
     end
 
     def [](process_name)
-      @dns_mutex.synchronize { dns_data[process_name] }
+      @dns_mutex.synchronize { dns_data[process_name] || alias_lookup(process_name) }
     end
 
     def add(name, port, ip = nil)
       @dns_mutex.synchronize { dns_data[name] = { 'port' => port, 'ip' => ip } }
     end
+
+    def alias_lookup(process_name)
+      dns_data.each do |label, opts|
+        if re = opts['alias']
+          return opts if re =~ process_name
+        end
+      end
+      nil
+    end
+
+    def make_regex(aliases)
+      return unless aliases
+      aliases = aliases.split(/\s*,\s*/)
+
+      aliases.map! do |path|
+        path.gsub!('.', '\.')
+        path.gsub!(/\*+/) do |match|
+          match == '*' ? '[^.]+' : '.*'
+        end
+        %r/\A#{path}\z/
+      end
+
+      Regexp.union aliases
+    end
   end
 end

spec/invoker/power/url_rewriter_spec.rb

@@ -124,6 +124,53 @@ def rewriter.dns_check(*args)
         match = rewriter.select_backend_config('baz.foo.dev')
         expect(match.port).to eql(1)
       end
+
+      it 'does not match baz.dev' do
+        match = rewriter.select_backend_config('baz.dev')
+        expect(match.port).to be_nil
+      end
+
+      context 'with an alias' do
+        it 'matches baz.foo.dev to the alias' do
+          @processes[1][:alias] = '*.foo'
+          Invoker.dns_cache = Invoker::DNSCache.new(nil)
+
+          match = rewriter.select_backend_config('baz.foo.dev')
+          expect(match.port).to eql(2)
+        end
+
+        it 'matches baz.dev to the alias' do
+          @processes[1][:alias] = '*'
+          Invoker.dns_cache = Invoker::DNSCache.new(nil)
+
+          match = rewriter.select_backend_config('baz.dev')
+          expect(match.port).to eql(2)
+        end
+
+        it 'matches non wildcard alias' do
+          @processes[1][:alias] = 'baz'
+          Invoker.dns_cache = Invoker::DNSCache.new(nil)
+
+          match = rewriter.select_backend_config('baz.dev')
+          expect(match.port).to eql(2)
+        end
+
+        it 'does not match baz.foo.blah.dev' do
+          @processes[1][:alias] = '*.foo'
+          Invoker.dns_cache = Invoker::DNSCache.new(nil)
+
+          match = rewriter.select_backend_config('baz.foo.blah.dev')
+          expect(match.port).to be_nil
+        end
+
+        it 'matches **' do
+          @processes[1][:alias] = '**.foo'
+          Invoker.dns_cache = Invoker::DNSCache.new(nil)
+
+          match = rewriter.select_backend_config('a.b.c.foo.dev')
+          expect(match.port).to eql(2)
+        end
+      end
     end
   end
 end