LoggingExtras is designs around allowing you to build arbitrarily complicated
systems for "log plumbing". That is to say basically routing logged information to different places.
It is built around the idea of simple parts which are composed together,
to allow for powerful and flexible definition of your logging system.
Without you having to define any custom loggers by subtyping AbstractLogger.
When we talk about composability we mean to say that the composition of any set of Loggers is itself a Logger.
LoggingExtras is a composable logging system.
Loggers can be broken down into 4 types:
- Sinks: Sinks are the final end point of a log messages journey. They write it to file, or display it on the console, or set off a red flashing light in the laboratory. A Sink should never decide what to accept, only what to do with it.
- Filters: Filters wrap around other loggers and decide whether or not to pass on a message. They can further be broken down by when that decision occurs (See
ActiveFilteredLoggervsEarlyFilteredLogger). - Transformers: Transformers modify the content of log messages, before passing them on. This includes the metadata like severity level. Unlike Filters they can't block a log message, but they could drop its level down to say
Debugso that normally noone would see it. - Demux: There is only one possible Demux Logger. and it is central to log routing. It acts as a hub that receives 1 log message, and then sends copies of it to all its child loggers. Like in the diagram above, it can be composed with Filters to control what goes where.
This is a basically full taxonomy of all compositional loggers. This package implements the full set. So you shouldn't need to build your own routing components, just configure the ones included in this package.
It is worth understanding the idea of logging purity. The loggers defined in this package are all pure. The Filters, only filter, the Sinks only sink, the transformers only Transform.
We can contrast this to the the ConsoleLogger (the standard logger in the REPL).
The ConsoleLogger is an impure sink.
As well as displaying logs to the user (as a Sink);
it uses the log content, in the form of the max_log kwarg to decide if a log should be displayed (Active Filtering);
and it has a min_enabled_level setting, that controls if it will accept a message at all
(Early Filtering, in particular see MinLevelLogger).
If it was to be defined in a compositional way,
we would write something along the lines of:
ConsoleLogger(stream, min_level) =
MinLevelLogger(
ActiveFilteredLogger(max_log_filter,
PureSinkConsoleLogger(stream)
),
min_level
)Load the package with using LoggingExtras.
For convenience, this also re-exports the Logging standard library.
For full details, see the Julia documentation on Logging
To use a logger in a given scope do
with_logger(logger) do
#things
endTo make a logger the global logger, use
global_logger(logger)To get the current logger (which can vary per task) use
logger = current_logger()To get the current global logger (which does not vary per task), use
logger = global_logger()This package introduces 8 new loggers.
The TeeLogger, the TransformerLogger, 3 types of filtered logger, the FileLogger,
the DatetimeRotatingFileLogger and the FormatLogger.
All of them, except FormatLogger, just wrap existing loggers.
- The
TeeLoggersends the logs to multiple different loggers. - The 3 filter loggers are used to control if a message is written or not
- The
MinLevelLoggeronly allows messages to pass that are above a given level of severity - The
EarlyFilteredLoggerlets you write filter rules based on thelevel,module,groupandidof the log message - The
ActiveFilteredLoggerlets you filter based on the full content
- The
- The
TransformerLoggerapplies a function to modify log messages before passing them on. - The
FileLoggeris a simple logger sink that writes to file. - The
DatetimeRotatingFileLoggeris a logger sink that writes to file, rotating logs based upon a user-providedDateFormat. - The
FormatLoggeris a logger sink that simply formats the message and writes to the logger stream.
By combining TeeLogger with filter loggers you can arbitrarily route log messages, wherever you want.
The TeeLogger sends the log messages to multiple places.
It takes a list of loggers.
You often want to pass the current_logger() or global_logger()
as one of those inputs so it keeps going to that one as well.
It is up to those loggers to determine if they will accept it.
Which they do using their methods for shouldlog and min_enabled_level.
Or you can do, by wrapping them in a filtered logger as discussed below.
The ActiveFilteredLogger exists to give more control over which messages should be logged.
It warps any logger, and before sending messages to the logger to log,
checks them against a filter function.
The filter function takes the full set of parameters of the message.
(See it's docstring with ?ActiveFilteredLogger for more details.)
We want to filter to only log strings staring with "Yo Dawg!".
julia> function yodawg_filter(log_args)
startswith(log_args.message, "Yo Dawg!")
end
yodawg_filter (generic function with 1 method)
julia> filtered_logger = ActiveFilteredLogger(yodawg_filter, global_logger());
julia> with_logger(filtered_logger) do
@info "Boring message"
@warn "Yo Dawg! it is bad"
@info "Another boring message"
@info "Yo Dawg! it is all good"
end
┌ Warning: Yo Dawg! it is bad
└ @ Main REPL[28]:3
[ Info: Yo Dawg! it is all goodThe EarlyFilteredLogger is similar to the ActiveFilteredLogger,
but it runs earlier in the logging pipeline.
In particular it runs before the message is computed.
It can be useful to filter things early if creating the log message is expensive.
E.g. if it includes summary statistics of the error.
The filter function for early filter logging only has access to the
level, _module, id and group fields of the log message.
The most notable use of it is to filter based on modules,
see the HTTP example below.
Another example is using them to stop messages every being repeated within a given time period.
using Dates, LoggingExtras
julia> function make_throttled_logger(period)
history = Dict{Symbol, DateTime}()
# We are going to use a closure
EarlyFilteredLogger(global_logger()) do log
if !haskey(history, log.id) || (period < now() - history[log.id])
# then we will log it, and update record of when we did
history[log.id] = now()
return true
else
return false
end
end
end
make_throttled_logger (generic function with 1 method)
julia> throttled_logger = make_throttled_logger(Second(3));
julia> with_logger(throttled_logger) do
for ii in 1:10
sleep(1)
@info "It happened" ii
end
end
┌ Info: It happened
└ ii = 1
┌ Info: It happened
└ ii = 4
┌ Info: It happened
└ ii = 7
┌ Info: It happened
└ ii = 10This is basically a special case of the early filtered logger, that just checks if the level of the message is above the level specified when it was created.
julia> using LoggingExtras
julia> error_only_logger = MinLevelLogger(current_logger(), Logging.Error);
julia> with_logger(error_only_logger) do
@info("You won't see this")
@warn("won't see this either")
@error("You will only see this")
end
┌ Error: You will only see this
└ @ Main REPL[18]:4The transformer logger allows for the modification of log messages.
This modification includes such things as its log level, and content,
and all the other arguments passed to handle_message.
When constructing a TransformerLogger you pass in a transformation function,
and a logger to be wrapped.
The transformation function takes a named tuple containing all the log message fields,
and should return a new modified named tuple.
A simple example of its use is truncating messages.
julia> using LoggingExtras
julia> truncating_logger = TransformerLogger(global_logger()) do log
if length(log.message) > 128
short_message = log.message[1:min(end, 125)] * "..."
return merge(log, (;message=short_message))
else
return log
end
end;
julia> with_logger(truncating_logger) do
@info "the truncating logger only truncates long messages"
@info "Like this one that is this is a long and rambling message, it just keeps going and going and going, and it seems like it will never end."
@info "Not like this one, that is is short"
end
[ Info: the truncating logger only truncates long messages
[ Info: Like this one that is this is a long and rambling message, it just keeps going and going and going, and it seems like it wil...
[ Info: Not like this one, that is is shortIt can also be used to do things such as change the log level of messages from a particular module (see the example below).
Or to set common properties for all log messages within the with_logger block,
for example to set them all to the same group.
The FileLogger does logging to file.
It is just a convenience wrapper around the base julia SimpleLogger,
to make it easier to pass in a filename, rather than a stream.
It is really simple.
- It takes a filename,
- a kwarg to check if should
always_flush(default:true). - a kwarg to
appendrather than overwrite (defaultfalse. i.e. overwrite by default) The resulting file format is similar to that which is shown in the REPL. (Not identical, but similar)
We are going to log info and above to one file, and warnings and above to another.
julia> using LoggingExtras;
julia> demux_logger = TeeLogger(
MinLevelLogger(FileLogger("info.log"), Logging.Info),
MinLevelLogger(FileLogger("warn.log"), Logging.Warn),
);
julia> with_logger(demux_logger) do
@warn("It is bad")
@info("normal stuff")
@error("THE WORSE THING")
@debug("it is chill")
end
shell> cat warn.log
┌ Warning: It is bad
└ @ Main REPL[34]:2
┌ Error: THE WORSE THING
└ @ Main REPL[34]:4
shell> cat info.log
┌ Warning: It is bad
└ @ Main REPL[34]:2
┌ Info: normal stuff
└ @ Main REPL[34]:3
┌ Error: THE WORSE THING
└ @ Main REPL[34]:4Use this sink to rotate your logs based upon a given DateFormat, automatically closing one file and opening another
when the DateFormat would change the filename. Note that if you wish to have static portions of your filename, you must
escape them so they are not interpreted by the DateFormat code. Example:
julia> using LoggingExtras
julia> rotating_logger = DatetimeRotatingFileLogger(pwd(), raw"\a\c\c\e\s\s-YYYY-mm-dd-HH-MM.\l\o\g");
julia> with_logger(rotating_logger) do
@info("This goes in one file")
sleep(61) # Sleep until next minute
@info("This goes in another file")
end
julia> filter(f -> endswith(f, ".log"), readdir(pwd()))
2-element Array{String,1}:
"access-2020-07-13-13-24.log"
"access-2020-07-13-13-25.log"The user implicitly controls when the files will be rolled over based on the DateFormat given.
To post-process the newly rotated file pass rotation_callback::Function as a keyword argument.
See the docstring with (?DatetimeRotatingFileLogger in the REPL) for more details.
To control the logging output it is possible to pass a formatter function as the first argument
in the constructor. See FormatLogger for the requirements on the formatter function.
The FormatLogger is a sink that formats the message and prints to a wrapped IO.
Formatting is done by providing a function f(io::IO, log_args::NamedTuple).
julia> using LoggingExtras
julia> logger = FormatLogger() do io, args
println(io, args._module, " | ", "[", args.level, "] ", args.message)
end;
julia> with_logger(logger) do
@info "This is an informational message."
@warn "This is a warning, should take a look."
end
Main | [Info] This is an informational message.
Main | [Warn] This is a warning, should take a look.using LoggingExtras
function sensible_message_filter(log)
length(log.message) < 1028
end
global_logger(ActiveFilteredLogger(sensible_message_filter, global_logger()))using LoggingExtras
using HTTP
function not_HTTP_message_filter(log)
# HTTP.jl utilizes internal modules so call parentmodule(...)
log.module !== HTTP && parentmodule(log._module) !== HTTP
end
global_logger(EarlyFilteredLogger(not_HTTP_message_filter, global_logger()))using LoggingExtras
using HTTP
transformer_logger(global_logger()) do log
# HTTP.jl utilizes internal modules so call parentmodule(...)
if (log._module === HTTP || parentmodule(log._module) === HTTP) && log.level === Logging.Debug
# Merge can be used to construct a new NamedTuple
# which effectively is the overwriting of fields of a NamedTuple
return merge(log, (; level=Logging.Info))
else
return log
end
end
global_logger(transformer_logger)using LoggingExtras, Dates
const date_format = "yyyy-mm-dd HH:MM:SS"
timestamp_logger(logger) = TransformerLogger(logger) do log
merge(log, (; message = "$(Dates.format(now(), date_format)) $(log.message)"))
end
ConsoleLogger(stdout, Logging.Debug) |> timestamp_logger |> global_loggerThis will produce output similar to:
[ Info: 2019-09-20 17:43:54 /es/update 200
┌ Debug: 2019-09-20 18:03:25 Recompiling stale cache file /.julia/compiled/v1.2/TranslationsController.ji for TranslationsController [top-level]
└ @ Base loading.jl:1240
┌ Error: 2019-09-20 17:43:54 ErrorException("SearchLight validation error(s) for Translations.Translation")
└ @ TranslationsController ~/Dropbox/Projects/LiteCMS/app/resources/translations/TranslationsController.jl:69The FormatLogger is quite general and can be used e.g. to truncate long variables.
There is LoggingExtras.make_log_truncated(max_var_len=5_000) function which formats data in similar manner as ConsoleLogger, but with truncation of string representation when it exceeds max_var_len.
julia> using LoggingExtras
julia> with_logger(FormatLogger(LoggingExtras.make_log_truncated(30))) do
short_var = "a"^5
long_var = "a"^50
@info "a short message" short_var long_var
@info "a very long message"^20 short_var long_var
end
┌ Info: a short message
│ short_var = aaaaa
│ long_var = aaaaaaaaaaaa…
└ @ Main REPL[46]:4
┌ Info: a very long messagea very lon…
│ short_var = aaaaa
│ long_var = aaaaaaaaaaaa…
└ @ Main REPL[46]:5