add error handling to deferred execution

README.md

@@ -27,16 +27,20 @@ def call(env)
 end
 ```
 
-Nothing to configure, just drop it in to your Rack middleware stack and
-use Thin as your server:
+Only one thing to configure, the error handler if something explodes during the deferred
+callback (since you no longer have your Rack handlers at that point):
 
 ``` ruby
 # for Rails:
 
-config.middleware.insert_before(::Rack::Lock, ::Rack::EMStream)
+config.middleware.insert_before(::Rack::Lock, ::Rack::EMStream) do |exception, environment|
+  # do something when there's a deferred error
+end
 
 # for Rack::Builder and derivatives:
 
-use Rack::EMStream
+use Rack::EMStream do |exception, environment|
+  # do something when there's a deferred error
+end
 ```
 

lib/rack-emstream.rb

@@ -4,8 +4,8 @@ module Rack
   class EMStream
     include EventMachine::Deferrable
 
-    def initialize(app)
-      @app = app
+    def initialize(app, &block)
+      @app, @block = app, block
     end
 
     def each(&b)
@@ -22,7 +22,20 @@ module Rack
       EM.next_tick {
         env['async.callback'].call [ result[0], result[1], self ]
 
-        result[2].each { |data| EM.next_tick { @callback.call(data) } }
+        begin
+          result[2].each { |data|
+            EM.next_tick {
+              begin
+                @callback.call(data)
+              rescue => e
+                @callback.call(@block.call(e, env)) if @block
+              end
+            }
+          }
+        rescue => e
+          @callback.call(@block.call(e, env)) if @block
+        end
+
         EM.next_tick { succeed }
       }
 

lib/rack-emstream/version.rb

@@ -1,5 +1,5 @@
 module Rack
   class EMStream
-    VERSION = "0.1.0"
+    VERSION = "0.1.1"
   end
 end