The HTTP server log function. The log function is optional and if specified will be called after attempting to send a response. This should be a function, a symbol naming a function, or nil. The function is called with four required arguments: the server, request, the generate response, and the sent response. The function is also passed keyword arguments, and should allow other keys for future compatibility. The keywords arguments are:

:content-bytes-written

The number of bytes of content written. If an error occurs and is detected by the server then this may be less than the response body size.

:response-write-complete-p

A flag which is true if the complete response was written. If an error occurs and is detected by the server then this will be false.

:response-write-milliseconds

The number of milliseconds that elapsed while transmitting the response. This does not include the time to read and generate the response.

:internal-errors

A list of error strings. When the server encounters errors processing a request it places them in this list and these may be useful for debugging and diagnostics.