rescue and track exceptions in handler chain

2 files changed, 48 insertions, 3 deletions

diff --git a/lib/nickserver/handler_chain.rb b/lib/nickserver/handler_chain.rb
index a0eba4d..afc24a5 100644
--- a/lib/nickserver/handler_chain.rb
+++ b/lib/nickserver/handler_chain.rb
@@ -5,8 +5,11 @@
 # will call the handlers with the given args until one of them returns a result
 # that is truethy (i.e. not false or nil).
 #
-# Extracted from the dispatcher so we can also handle exceptions here in the
-# future.
+# You can specify exception classes to rescue with
+#   handler_chain.continue_on ErrorClass1, ErrorClass2
+# These exceptions will be rescued and tracked. The chain will proceed even if
+# one handler raised the given exception. Afterwards you can inspect them with
+#   handler_chain.rescued_exceptions
 #
 
 module Nickserver
@@ -14,13 +17,32 @@ module Nickserver
 
     def initialize(*handlers)
       @handlers = handlers
+      @exceptions_to_rescue = []
+      @rescued_exceptions = []
+    end
+
+    def continue_on(*exceptions)
+      self.exceptions_to_rescue += exceptions
     end
 
     def handle(*args)
       result = nil
-      _handled_by = @handlers.find{|h| result = h.call(*args)}
+      _handled_by = @handlers.find{|h| result = try_handler(h, *args)}
       result
     end
 
+    attr_reader :rescued_exceptions
+
+    protected
+
+    attr_writer :rescued_exceptions
+    attr_accessor :exceptions_to_rescue
+
+    def try_handler(handler, *args)
+      result = handler.call(*args)
+    rescue *exceptions_to_rescue
+      self.rescued_exceptions << $!
+      result = false
+    end
   end
 end
diff --git a/test/unit/handler_chain_test.rb b/test/unit/handler_chain_test.rb
index 067f11e..fae0418 100644
--- a/test/unit/handler_chain_test.rb
+++ b/test/unit/handler_chain_test.rb
@@ -23,6 +23,26 @@ class HandlerChainTest < Minitest::Test
     assert_equal :result, chain.handle
   end
 
+  def test_raise_exception
+    chain handler_raising, handler_with_result
+    assert_raises RuntimeError do
+      chain.handle
+    end
+  end
+
+  def test_continue_on_exception
+    chain handler_raising, handler_with_result
+    chain.continue_on(RuntimeError)
+    assert_equal :result, chain.handle
+    assert_equal [RuntimeError], chain.rescued_exceptions.map(&:class)
+  end
+
+  def test_continue_on_exception_with_nil
+    chain handler_raising, handler_with_nil
+    chain.continue_on(RuntimeError)
+    assert_nil chain.handle
+    assert_equal [RuntimeError], chain.rescued_exceptions.map(&:class)
+  end
 
   protected
 
@@ -42,4 +62,7 @@ class HandlerChainTest < Minitest::Test
     Proc.new { :result }
   end
 
+  def handler_raising(exception = RuntimeError)
+    Proc.new { raise exception }
+  end
 end