import { RotatingFileHandler } from "https://deno.land/std@0.208.0/log/handlers.ts";
This handler extends the functionality of the FileHandler
by
"rotating" the log file when it reaches a certain size. maxBytes
specifies
the maximum size in bytes that the log file can grow to before rolling over
to a new one. If the size of the new log message plus the current log file
size exceeds maxBytes
then a roll-over is triggered. When a roll-over
occurs, before the log message is written, the log file is renamed and
appended with .1
. If a .1
version already existed, it would have been
renamed .2
first and so on. The maximum number of log files to keep is
specified by maxBackupCount
. After the renames are complete the log message
is written to the original, now blank, file.
Example: Given log.txt
, log.txt.1
, log.txt.2
and log.txt.3
, a
maxBackupCount
of 3 and a new log message which would cause log.txt
to
exceed maxBytes
, then log.txt.2
would be renamed to log.txt.3
(thereby
discarding the original contents of log.txt.3
since 3 is the maximum number
of backups to keep), log.txt.1
would be renamed to log.txt.2
, log.txt
would be renamed to log.txt.1
and finally log.txt
would be created from
scratch where the new log message would be written.
This handler uses a buffer for writing log messages to file. Logs can be
manually flushed with fileHandler.flush()
. Log messages with a log level
greater than ERROR are immediately flushed. Logs are also flushed on process
completion.
Additional notes on mode
as described above:
'a'
Default mode. As above, this will pick up where the logs left off in rotation, or create a new log file if it doesn't exist.'w'
in addition to starting with a cleanfilename
, this mode will also cause any existing backups (up tomaxBackupCount
) to be deleted on setup giving a fully clean slate.'x'
requires that neitherfilename
, nor any backups (up tomaxBackupCount
), exist before setup.
This handler requires both --allow-read
and --allow-write
permissions on
the log files.