mirror of
https://github.com/sprockets/sprockets.mixins.correlation.git
synced 2024-11-23 19:29:55 +00:00
117 lines
4.6 KiB
Python
117 lines
4.6 KiB
Python
import asyncio
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import uuid
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from tornado import log
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class HandlerMixin(object):
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"""
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Mix this in over a ``RequestHandler`` for a correlating header.
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:keyword str correlation_header: the name of the header to use
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for correlation. If this keyword is omitted, then the header
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is named ``Correlation-ID``.
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This mix-in ensures that responses include a header that correlates
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requests and responses. If there header is set on the incoming
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request, then it will be copied to the outgoing response. Otherwise,
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a new UUIDv4 will be generated and inserted. The value can be
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examined or modified via the ``correlation_id`` property.
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The MRO needs to contain something that resembles a standard
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:class:`tornado.web.RequestHandler`. Specifically, we need the
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following things to be available:
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- :meth:`~tornado.web.RequestHandler.prepare` needs to be called
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appropriately
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- :meth:`~tornado.web.RequestHandler.set_header` needs to exist in
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the MRO and it needs to overwrite the header value
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- :meth:`~tornado.web.RequestHandler.set_default_headers` should be
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called to establish the default header values
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- ``self.request`` is a object that has a ``headers`` property that
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contains the request headers as a ``dict``.
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"""
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def __init__(self, *args, **kwargs):
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# correlation_id is used from within set_default_headers
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# which is called from within super().__init__() so we need
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# to make sure that it is set *BEFORE* we call super.
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self.__header_name = kwargs.pop(
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'correlation_header', 'Correlation-ID')
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self.__correlation_id = str(uuid.uuid4())
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super(HandlerMixin, self).__init__(*args, **kwargs)
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async def prepare(self):
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# Here we want to copy an incoming Correlation-ID header if
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# one exists. We also want to set it in the outgoing response
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# which the property setter does for us.
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maybe_coro = super(HandlerMixin, self).prepare()
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if asyncio.iscoroutine(maybe_coro):
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await maybe_coro
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correlation_id = self.get_request_header(self.__header_name, None)
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if correlation_id is not None:
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self.correlation_id = correlation_id
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def set_default_headers(self):
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# This is called during initialization as well as *AFTER*
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# calling clear() when an error occurs so we need to make
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# sure that our header is set again...
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super(HandlerMixin, self).set_default_headers()
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self.set_header(self.__header_name, self.correlation_id)
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@property
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def correlation_id(self):
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"""Correlation header value."""
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return self.__correlation_id
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@correlation_id.setter
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def correlation_id(self, value):
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self.__correlation_id = value
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self.set_header(self.__header_name, self.__correlation_id)
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def get_request_header(self, name, default):
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"""
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Retrieve the value of a request header.
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:param str name: the name of the header to retrieve
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:param default: the value to return if the header is not set
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This method abstracts the act of retrieving a header value out
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from the implementation. This makes it possible to implement
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a *RequestHandler* that is something other than a
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:class:`tornado.web.RequestHandler` by simply implementing this
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method and ``set_header`` over the underlying implementation,
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for example, say AMQP message properties.
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"""
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return self.request.headers.get(name, default)
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def correlation_id_logger(handler):
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""" Custom Tornado access log writer that appends correlation-id.
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This function can be used to append the coorelation-id to the
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Tornado access logs. To use, simply set the value of the
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log_function kwarg of the Tornado Application constructor to this
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function.
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*Example*
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web.Application([], log_function=correlation_id_logger)
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:param tornado.web.RequestHandler handler: the request handler that
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is processing the client request.
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"""
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if handler.get_status() < 400:
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log_method = log.access_log.info
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elif handler.get_status() < 500:
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log_method = log.access_log.warning
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else:
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log_method = log.access_log.error
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request_time = 1000.0 * handler.request.request_time()
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correlation_id = getattr(handler, "correlation_id", None)
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if correlation_id is None:
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correlation_id = handler.request.headers.get('Correlation-ID', None)
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log_method("%d %s %.2fms {CID %s}", handler.get_status(),
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handler._request_summary(), request_time, correlation_id)
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