Class: MessageFormatter  - X-Ref

Formats log messages using variable substitutions for requests, responses,
and other transactional data.

The following variable substitutions are supported:

- {request}:        Full HTTP request message
- {response}:       Full HTTP response message
- {ts}:             ISO 8601 date in GMT
- {date_iso_8601}   ISO 8601 date in GMT
- {date_common_log} Apache common log date using the configured timezone.
- {host}:           Host of the request
- {method}:         Method of the request
- {uri}:            URI of the request
- {version}:        Protocol version
- {target}:         Request target of the request (path + query + fragment)
- {hostname}:       Hostname of the machine that sent the request
- {code}:           Status code of the response (if available)
- {phrase}:         Reason phrase of the response  (if available)
- {error}:          Any error messages (if available)
- {req_header_*}:   Replace `*` with the lowercased name of a request header to add to the message
- {res_header_*}:   Replace `*` with the lowercased name of a response header to add to the message
- {req_headers}:    Request headers
- {res_headers}:    Response headers
- {req_body}:       Request body
- {res_body}:       Response body