refactor: let handlers check if they are applicable

Instead of testing the preconditions for each handler in the dispatcher
the dispatcher hands a request to one handler after the other until one of
them responds.

This is similar to the Chain of Responsibility patter but we iterate over the
'handler_chain' array instead of a linked list.

To change the order of handlers or add other handlers change the array in the
handler_chain function.

3 files changed, 38 insertions, 11 deletions

diff --git a/lib/nickserver/dispatcher.rb b/lib/nickserver/dispatcher.rb
index b818b98..833a2ad 100644
--- a/lib/nickserver/dispatcher.rb
+++ b/lib/nickserver/dispatcher.rb
@@ -1,3 +1,18 @@
+#
+# Dispatcher
+#
+# Dispatch a request so it get's handled by the correct handler.
+#
+# The dispatcher hands a request to one handler after the other until one of
+# them responds.
+#
+# This is similar to the Chain of Responsibility patter but we iterate over the
+# 'handler_chain' array instead of a linked list.
+#
+# To change the order of handlers or add other handlers change the array in the
+# handler_chain function.
+#
+
 require 'nickserver/request'
 require 'nickserver/request_handlers/email_handler'
 require 'nickserver/request_handlers/fingerprint_handler'
@@ -18,22 +33,22 @@ module Nickserver
     protected
 
     def handle(request)
-      handler = handler_for_request request
-      handler.call request
+      handler_chain.each do |handler|
+        response = handler.call request
+        return response if response
+      end
     rescue RuntimeError => exc
       puts "Error: #{exc}"
       puts exc.backtrace
       ErrorResponse.new(exc.to_s)
     end
 
-    def handler_for_request(request)
-      if request.email
-        RequestHandlers::EmailHandler.new
-      elsif request.fingerprint
-        RequestHandlers::FingerprintHandler.new
-      else
+    def handler_chain
+      [
+        RequestHandlers::EmailHandler.new,
+        RequestHandlers::FingerprintHandler.new,
         Proc.new { Nickserver::Response.new(404, "Not Found\n") }
-      end
+      ]
     end
 
     def send_response(status = 200, content = '')
diff --git a/lib/nickserver/request_handlers/email_handler.rb b/lib/nickserver/request_handlers/email_handler.rb
index 3f7515d..b163b27 100644
--- a/lib/nickserver/request_handlers/email_handler.rb
+++ b/lib/nickserver/request_handlers/email_handler.rb
@@ -8,6 +8,13 @@ module Nickserver
     class EmailHandler
 
       def call(request)
+        return unless request.email
+        handle_request(request)
+      end
+
+      protected
+
+      def handle_request(request)
         email = EmailAddress.new(request.email)
         if email.invalid?
           ErrorResponse.new("Not a valid address")
@@ -16,8 +23,6 @@ module Nickserver
         end
       end
 
-      protected
-
       def send_key(email, request)
         if local_address?(email, request)
           source = Nickserver::CouchDB::Source.new
diff --git a/lib/nickserver/request_handlers/fingerprint_handler.rb b/lib/nickserver/request_handlers/fingerprint_handler.rb
index 3202c41..3c04fcd 100644
--- a/lib/nickserver/request_handlers/fingerprint_handler.rb
+++ b/lib/nickserver/request_handlers/fingerprint_handler.rb
@@ -6,6 +6,13 @@ module Nickserver
     class FingerprintHandler
 
       def call(request)
+        return unless request.fingerprint
+        handle_request(request)
+      end
+
+      protected
+
+      def handle_request(request)
         fingerprint = request.fingerprint
         if fingerprint.length == 40 && !fingerprint[/\H/]
           source = Nickserver::Hkp::Source.new