smullins7 / context_logging

context_logging

This project is a demonstration of using the Python logging framework to inject request context specific information into every log message, without passing that information into every log message function call.

example

If your log format looked like this:

FORMAT = "%(asctime)s|%(levelname)s|%(REMOTE_ADDR)s|%(CUSTOMER_NAME)s|%(message)s"

The logging framework would not know what to do with REMOTE_ADDR and CUSTOMER_NAME.

Use the following filter in your logging config to inject these values into the log message:

import logging
from logmdc import filter
filter = ContextFilter(keys=['REMOTE_ADDR', 'CUSTOMER_NAME'])
logger = logging.getLogger()
logger.addFilter(filter)

Now all you have to do is have code to set those values within a running process:

from logmdc.storage import mapped_context
mapped_context.put('CUSTOMER_NAME', 'foobar')
mapped_context.put('REMOTE_ADDR', '127.0.0.1')

Of course, this isn't all that useful by itself. If you're using this within a web application/service, you can automatically pull information from HTTP headers in this web.py example:

from logmdc.webheaders import HeaderRequestFilter
header_filter = HeaderRequestFilter([
    "REMOTE_ADDR",
    "CUSTOMER_NAME",
])

urls = ('/', 'IndexController')
app = web.application(urls, globals())
app.add_processor(web.loadhook(header_filter))
app.run()

With this, any request to this web.py app will look for the headers REMOTE_ADDR and CUSTOMER_NAME and set their values in local storage for the logging filter to inject those values in the log message.

Note that customer HTTP client request headers get prefixed with HTTP_ in web.py, as such the HeaderRequestFilter by default will strip that prefix out to prevent a mismatch between the value set by the client and header name used by the logging filter.

details

The core logic involves usage of the following:

• logging.filters
• logging.config.dictConfig

This project contains a dummy application to showcase the usage of the context logging. The code for logging is under src/logmdc.