View Source ring_logger
This is an in-memory ring buffer backend for the Elixir Logger with convenience methods for accessing the logs from the IEx prompt.
Use cases:
- Get log messages in real-time over remote IEx sessions
- Grep and tail through log messages without setting up anything else
- Keep logs in limited resource environments
- Capture recent log events for error reports
As a bonus, ring_logger
is nice to your IEx prompt. If you attach to the log
and are receiving messages as they're sent, they won't stomp what you're typing.
Configuration
Add ring_logger
to your projects dependencies in your mix.exs
:
def deps do
[{:ring_logger, "~> 0.6"}]
end
Then configure the logger in your config/config.exs
:
use Mix.Config
# Add the RingLogger backend. This removes the default :console backend.
config :logger, backends: [RingLogger]
# Periodically save logs to a file, and load logs on GenServer start from this file
config :logger, RingLogger, persist_path: "./myapp.log", persist_seconds: 300
# Save messages to one circular buffer that holds 1024 entries.
config :logger, RingLogger, max_size: 1024
# Separate out `:error` and `:warning` messages to their own circular buffer.
# All other log messages are stored in the default circular buffer.
config :logger, RingLogger, buffers: %{
errors: %{
levels: [:error, :warning],
max_size: 1024
}
}
# Specify circular buffers for all log levels. The default circular buffer won't
# be used in this example configuration.
config :logger, RingLogger, buffers: %{
low_priority: %{
levels: [:warning, :notice, :info, :debug],
max_size: 1024
},
high_priority: %{
levels: [:emergency, :alert, :critical, :error],
max_size: 1024
}
}
# You can also configure `RingLogger.Client` options to be used
# with every client by default
config :logger, RingLogger,
application_levels: %{my_app: :error},
colors: [debug: :yellow],
level: :debug
Or you can start the backend manually by running the following:
Logger.add_backend(RingLogger)
Logger.configure_backend(RingLogger, max_size: 1024)
IEx session usage
See the example project for a hands-on walk-through of using the logger. Read on for the highlights.
For the purpose of the example, when you're in IEx, log messages shouldn't be printed to the console by default. They'll be coming from the console logger, so turn them off:
iex> Logger.remove_backend(:console)
:ok
To see log messages as they come in with RingLogger, call RingLogger.attach()
and then to make the log messages stop, call RingLogger.detach()
. The attach
method takes options if you want to limit the log level, change the formatting,
etc.
Here's an example:
iex> Logger.add_backend(RingLogger)
{:ok, #PID<0.199.0>}
iex> RingLogger.attach
:ok
iex> require Logger
iex> Logger.info("hello")
:ok
14:04:52.516 [info] hello
If you prefer polling for log messages rather than having them print when they
show up. If you're still attached, then detach
and next
:
iex> RingLogger.detach
:ok
iex> Logger.info("Hello logger, how are you?")
:ok
iex> Logger.info("It's a nice day. Wouldn't you say?")
:ok
iex> RingLogger.next
14:04:52.516 [info] hello
14:11:54.397 [info] Hello logger, how are you?
14:12:09.180 [info] It's a nice day. Wouldn't you say?
:ok
iex> RingLogger.next
:ok
If you only want to see the most recent entries, run tail
:
iex> RingLogger.tail
14:04:52.516 [info] hello
14:11:54.397 [info] Hello logger, how are you?
14:12:09.180 [info] It's a nice day. Wouldn't you say?
:ok
You can also grep
:
iex> RingLogger.grep(~r/[Nn]eedle/)
16:55:41.614 [info] Needle in a haystack
RingLogger TUI
RingLogger provides a simple text UI that lets you access log viewing features in a friendly way.
iex> RingLogger.viewer()
Type h
and then enter for help.
Module and Application Level Filtering
If you want to filter a module or modules at a particular level you pass a map
where the key is the module name and value in the level into the
:module_levels
option to RingLogger.attach/1
.
For example:
iex> RingLogger.attach(module_levels: %{MyModule => :info})
This will ignore all the :debug
messages from MyModule
.
Also, it allows for filtering the whole project on a higher level, but a particular module, or a subset of modules, to log at a lower level like so:
iex> RingLogger.attach(module_levels: %{MyModule => :debug}, level: :warn)
In the example above log messages at the :debug
level will be logged, but
every other module will be logging at the :warn
level. You can also turn off a
module's logging completely by specifying :none
.
Additionally, you can specify the same options at the application level to
disable logging for all its modules using the :application_levels
option
with OTP application names as the key:
iex> RingLogger.attach(application_levels: %{my_app: :info})
module_levels
takes precedence in the case of including both module and
application level filtering:
iex> RingLogger.attach(application_levels: %{my_app: :info}, module_levels: %{MyApp.Important => :debug})
In the above example, all modules of :my_app
with have a level of :info
except
for MyApp.Important
, which will have a level of :debug
.
As a note if the Elixir Logger
level is set too low you will miss some log
messages.
Saving the log
By design, RingLogger
doesn't save logs. It can be convenient to share the
current log buffer for later analysis:
iex> RingLogger.save("/tmp/log.txt")
:ok
Log messages are formatted the same way as the RingLogger
functions that
output to the console.
Formatting
If you want to use a specific string format with the built in Elixir
Logger.Formatter, you can pass that as the :format
option to
RingLogger.attach/1
.
If you want to use a custom formatter function, you can pass it through the
:format
option to RingLogger.attach/1
instead.
For example, to print the file and line number of each log message, you could define a function as follows:
defmodule CustomFormatter do
def format(_level, message, _timestamp, metadata) do
"#{message} #{metadata[:file]}:#{metadata[:line]}\n"
rescue
_ -> message
end
end
and attach to the RingLogger with:
iex> RingLogger.attach(format: {CustomFormatter, :format}, metadata: [:file, :line])
:ok
iex> require Logger
Logger
iex> Logger.info("Important message!")
:ok
Important message! iex:4
Within an application, the iex:4
would be the source file path and line number.
See Logger custom formatting for more information.
Programmatic usage
It can be useful to get a snapshot of the log when an unexpected event occurs.
The commandline functions demonstrated above are available, but you can also get
the raw log entries by calling RingLogger.get/0
:
iex> RingLogger.get
[
debug: {Logger, "8", {{2018, 2, 5}, {17, 44, 7, 675}},
[
pid: #PID<0.139.0>,
application: :example,
module: Example,
function: "log/1",
file: "ring_logger/example/lib/example.ex",
line: 11
]},
debug: {Logger, "9", {{2018, 2, 5}, {17, 44, 8, 676}},
[
pid: #PID<0.139.0>,
application: :example,
module: Example,
function: "log/1",
file: "ring_logger/example/lib/example.ex",
line: 11
]},
debug: {Logger, "10", {{2018, 2, 5}, {17, 44, 9, 677}},
[
pid: #PID<0.139.0>,
application: :example,
module: Example,
function: "log/1",
file: "ring_logger/example/lib/example.ex",
line: 11
]}
]