LoggingFormats.jl

This package is an aggregation of various useful format functions to use with the FormatLogger from the LoggingExtras package.

Currently, the following functors are available:

• JSON: output log events as JSON
• LogFmt: output log events formatted as logfmt
• Truncated: truncation of log messages

JSON: Output log events as JSON

LoggingFormats.JSON() is a function which formats the log message and the log metadata as JSON. Example:

julia> using LoggingFormats, LoggingExtras

julia> with_logger(FormatLogger(LoggingFormats.JSON(), stderr)) do
           @info "hello, world"
           @error "something is wrong"
       end
{"level":"info","msg":"hello, world","module":"Main","file":"REPL[10]","line":2,"group":"REPL[10]","id":"Main_6972c828","kwargs":{}}
{"level":"error","msg":"something is wrong","module":"Main","file":"REPL[10]","line":3,"group":"REPL[10]","id":"Main_2289c7f9","kwargs":{}}

One can also pass recursive=true to recursively serialize the kwargs as JSON:

julia> using LoggingFormats, LoggingExtras

julia> with_logger(FormatLogger(LoggingFormats.JSON(; recursive=true), stderr)) do
                  @info "hello, world" key=Dict("hello" => true)
       end
{"level":"info","msg":"hello, world","module":"Main","file":"REPL[18]","line":2,"group":"REPL[18]","id":"Main_ffce16b5","kwargs":{"key":{"hello":true}}}

If it encounters something which does not have a defined StructTypes.StructType to use for serializing to JSON (or otherwise errors when serializing to JSON), it will fallback to converting the objects to strings, like the default recursive=false option does. Handles exceptions specially, by printing errors and stacktraces using Base.showerror.

julia> f() = try
                throw(ArgumentError("Bad input"))
            catch e
                @error "Input error" exception=(e, catch_backtrace())
            end

julia> with_logger(f, FormatLogger(LoggingFormats.JSON(; recursive=true), stderr))
{"level":"error","msg":"Input error","module":"Main","file":"REPL[2]","line":4,"group":"REPL[2]","id":"Main_a226875f","kwargs":{"exception":"ERROR: ArgumentError: Bad input\nStacktrace:\n [1] f()\n   @ Main ./REPL[2]:2\n [2] with_logstate(f::Function, logstate::Any)\n   @ Base.CoreLogging ./logging.jl:511\n [3] with_logger(f::Function, logger::FormatLogger)\n   @ Base.CoreLogging ./logging.jl:623\n [4] top-level scope\n   @ REPL[3]:1\n"}}

LogFmt: Format log events as logfmt

LoggingFormats.LogFmt() is a function which formats the log message in the logfmt format. Example:

julia> using LoggingFormats, LoggingExtras

julia> with_logger(FormatLogger(LoggingFormats.LogFmt(), stderr)) do
           @info "hello, world"
           @error "something is wrong"
       end
level=info msg="hello, world" module=Main file="REPL[2]" line=2 group="REPL[2]" id=Main_6972c827
level=error msg="something is wrong" module=Main file="REPL[2]" line=3 group="REPL[2]" id=Main_2289c7f8

Similarly to the JSON logger, LogFmt handles exceptions specially, by printing errors and stacktraces using Base.showerror.

One can also restrict the "standard" keys used in the log message, for example:

julia> using LoggingFormats, LoggingExtras

julia> with_logger(FormatLogger(LoggingFormats.LogFmt((:level, :message, :file)), stderr)) do
           @info "hello, world" extra="bye"
           @error "something is wrong"
       end
level=info msg="hello, world" file="REPL[5]" extra="bye"
level=error msg="something is wrong" file="REPL[5]"

Note here that the module, group, id do not appear, since they weren't specified, but the "custom" key extra still appears. The full set of standard keys is (:level, :msg, :module, :file, :line, :group, :id), which are all used by default, in that order.

Truncated: Truncate long variables and messages

LoggingFormats.Truncated(max_var_len=5_000) is a function which formats data in similar manner as ConsoleLogger, but with truncation of string representation when it exceeds max_var_len. This format truncates the length of message itself, and truncates string representation of individual variables, but does not truncate the size of whole printed text.

See the examples:

julia> using LoggingFormats, LoggingExtras

julia> with_logger(FormatLogger(LoggingFormats.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 message a very lo…
│   short_var = aaaaa
│   long_var = aaaaaaaaaaaa…
└ @ Main REPL[46]:5