http: add errback to Request constructor

--HG--
extra : convert_revision : svn%3Ab85faa78-f9eb-468e-a121-7cced6da292c%401018

scrapy/trunk/docs/ref/request-response.rst

@@ -25,7 +25,7 @@ functionality not required in the base classes. See
 Request objects
 ===============
 
-.. class:: Request(url, callback=None, method='GET', body=None, headers=None, cookies=None, meta=None, encoding='utf-8', dont_filter=None)
+.. class:: Request(url, callback=None, method='GET', body=None, headers=None, cookies=None, meta=None, encoding='utf-8', dont_filter=False, errback=None)
 
     A :class:`Request` object represents an HTTP request, which is usually
     generated in the Spider and executed by the Downloader, and thus generating
@@ -75,6 +75,11 @@ Request objects
     be filtered by the scheduler. This is used when you want to perform an
     identical request multiple times, for whatever reason
 
+    ``errback`` is a function that will be called if any exception was raised while
+    processing the request, it takes a `Twisted Failure`_ instance as first parameter.
+
+.. _Twisted Failure: http://twistedmatrix.com/documents/8.2.0/api/twisted.python.failure.Failure.html
+
 Request Attributes
 ------------------
 
@@ -147,7 +152,7 @@ Copying Requests and callbacks
 When you copy a request using the :meth:`Request.copy` or
 :meth:`Request.replace` methods the callback of the request is not copied by
 default. This is because of legacy reasons along with limitations in the
-underlying network library, which doesn't allow sharing `Twisted deferreds`.
+underlying network library, which doesn't allow sharing `Twisted deferreds`_.
 
 .. _Twisted deferreds: http://twistedmatrix.com/projects/core/documentation/howto/defer.html
 

scrapy/trunk/scrapy/http/request/__init__.py

@@ -18,7 +18,8 @@ from scrapy.utils.defer import chain_deferred
 class Request(object):
 
     def __init__(self, url, callback=None, method='GET', headers=None, body=None, 
-                 cookies=None, meta=None, encoding='utf-8', dont_filter=False):
+                 cookies=None, meta=None, encoding='utf-8', dont_filter=False,
+                 errback=None):
 
         self._encoding = encoding  # this one has to be set first
         self.method = method.upper()
@@ -26,7 +27,7 @@ class Request(object):
         self.set_body(body)
 
         if callable(callback):
-            callback = defer.Deferred().addCallback(callback)
+            callback = defer.Deferred().addCallbacks(callback, errback)
         self.deferred = callback or defer.Deferred()
 
         self.cookies = cookies or {}