def fetch(self, request, callback=None, **kwargs):
"""Executes a request, asynchronously returning an `HTTPResponse`.
The request may be either a string URL or an `HTTPRequest` object.
If it is a string, we construct an `HTTPRequest` using any additional
kwargs: ``HTTPRequest(request, **kwargs)``
This method returns a `.Future` whose result is an
`HTTPResponse`. The ``Future`` wil raise an `HTTPError` if
the request returned a non-200 response code.
If a ``callback`` is given, it will be invoked with the `HTTPResponse`.
In the callback interface, `HTTPError` is not automatically raised.
Instead, you must check the response's ``error`` attribute or
call its `~HTTPResponse.rethrow` method.
"""
if not isinstance(request, HTTPRequest):
request = HTTPRequest(url=request, **kwargs)
# We may modify this (to add Host, Accept-Encoding, etc),
# so make sure we don't modify the caller's object. This is also
# where normal dicts get converted to HTTPHeaders objects.
request.headers = httputil.HTTPHeaders(request.headers)
request = _RequestProxy(request, self.defaults)
future = TracebackFuture()
if callback is not None:
callback = stack_context.wrap(callback)
def handle_future(future):
exc = future.exception()
if isinstance(exc, HTTPError) and exc.response is not None:
response = exc.response
elif exc is not None:
response = HTTPResponse(
request, 599, error=exc,
request_time=time.time() - request.start_time)
else:
response = future.result()
self.io_loop.add_callback(callback, response)
future.add_done_callback(handle_future)
def handle_response(response):
if response.error:
future.set_exception(response.error)
else:
future.set_result(response)
self.fetch_impl(request, handle_response)
return future
