Logging

A device server may send log messages to clients about events happening in the server. aiokatcp provides the DeviceServer.LogHandler class to connect Python loggers to this logging mechanism.

To use this mechanism, one should create a handler, then attach it to an existing Python logger. The simplest case is to attach it to the root logger, like so:

handler = DeviceServer.LogHandler(server)
logging.getLogger().addHandler(handler)

The handler will forward messages from the logging system to each of the clients, according to the log level set with the ?log-level request. However, the handler will only get to see the messages if the level of the logger itself allows the message. Python has log levels for both loggers and handlers, and messages are only processed if the priority of the log message is high enough for both. There are a few options to deal with this:

1. Set the logger level to logging.NOTSET, and instead set a logging level on each non-aiokatcp handler to control the overall logging level. In this scenario, ?log-level has no effect on logging outside of what katcp clients see.

2. Override DeviceServer.request_log_level() in your subclass and use the requested level to change the level of the root logger. In this case, ?log-level affects all logging in the application.

Logger adapters

A Connection contains a logger attribute which is a logging.LoggerAdapter. It provides an extra address attribute to log records. Similarly, RequestContext contains a Logger which adds address and req attributes.

By themselves, this has no effect on logging. However, you could provide a custom formatter for your log handlers that will display this information when provided.