timbre/README.md

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Current [semantic](http://semver.org/) version:
```clojure
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[com.taoensso/timbre "1.4.0"]
```
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# Timbre, a (sane) Clojure logging & profiling library
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Logging with Java can be maddeningly, unnecessarily hard. Particularly if all you want is something *simple that works out-the-box*. [tools.logging](https://github.com/clojure/tools.logging) helps, but it doesn't save you from the mess of logger dependencies and configuration hell.
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Timbre is an attempt to make **simple logging simple** and more **complex logging reasonable**. No XML!
## What's In The Box?
* Small, uncomplicated **all-Clojure** library.
* **Super-simple map-based config**: no arcane XML or properties files!
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* **Decent performance** (low overhead).
* Flexible **fn-centric appender model** with **middleware**.
* Sensible built-in appenders including simple **email appender**.
* Tunable **flood control** and **asynchronous** logging support.
* Robust **namespace filtering**.
* Dead-simple, logging-level-aware **logging profiler**.
## Getting Started
### Leiningen
Depend on Timbre in your `project.clj`:
```clojure
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[com.taoensso/timbre "1.4.0"]
```
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and `use` the library:
```clojure
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(ns my-app (:use [taoensso.timbre :as timbre :only (trace debug info warn error fatal spy)]))
```
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### Logging
By default, Timbre gives you basic print output to `*out*`/`*err*` at a `debug` logging level:
```clojure
(info "This will print")
=> nil
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%> 2012-May-28 17:26:11:444 +0700 localhost INFO [my-app] - This will print
(spy :info (* 5 4 3 2 1))
=> 120
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%> 2012-May-28 17:26:14:138 +0700 localhost INFO [my-app] - (* 5 4 3 2 1) 120
(trace "This won't print due to insufficient logging level")
=> nil
```
There's little overhead for checking logging levels:
```clojure
(time (trace (Thread/sleep 5000)))
%> "Elapsed time: 0.054 msecs"
(time (when true))
%> "Elapsed time: 0.051 msecs"
```
First-argument exceptions generate a stack trace:
```clojure
(info (Exception. "Oh noes") "arg1" "arg2")
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%> 2012-May-28 17:35:16:132 +0700 localhost INFO [my-app] - arg1 arg2
java.lang.Exception: Oh noes
NO_SOURCE_FILE:1 my-app/eval6409
Compiler.java:6511 clojure.lang.Compiler.eval
<...>
```
### Configuration
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Configuring Timbre couldn't be simpler. Let's check out (some of) the defaults:
```clojure
@timbre/config
=>
{:current-level :debug
:ns-whitelist []
:ns-blacklist []
:middleware [] ; As of 1.4.0, see source code
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:timestamp-pattern "yyyy-MMM-dd HH:mm:ss ZZ"
:timestamp-locale nil
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:appenders
{:standard-out { <...> }
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:spit { <...> }
<...> }
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:shared-appender-config {}}
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```
Easily adjust the current logging level:
```clojure
(timbre/set-level! :warn)
```
And the default timestamp formatting for log messages:
```clojure
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(timbre/set-config! [:timestamp-pattern] "yyyy-MMM-dd HH:mm:ss ZZ")
(timbre/set-config! [:timestamp-locale] (java.util.Locale/GERMAN))
```
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Filter logging output by namespaces:
```clojure
(timbre/set-config! [:ns-whitelist] ["some.library.core" "my-app.*"])
```
### Email Appender
To enable the standard [Postal](https://github.com/drewr/postal)-based email appender, add the Postal dependency to your `project.clj`:
```clojure
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[com.draines/postal "1.9.1"]
```
And add the appender to your `ns` declaration:
```clojure
(:require [taoensso.timbre.appenders (postal :as postal-appender)])
```
Then adjust your Timbre config:
```clojure
(timbre/set-config! [:appenders :postal] postal-appender/postal-appender)
(timbre/set-config! [:shared-appender-config :postal]
^{:host "mail.isp.net" :user "jsmith" :pass "sekrat!!1"}
{:from "me@draines.com" :to "foo@example.com"})
```
Rate-limit to one email per message per minute:
```clojure
(timbre/set-config! [:appenders :postal :max-message-per-msecs] 60000)
```
And make sure emails are sent asynchronously:
```clojure
(timbre/set-config! [:appenders :postal :async?] true)
```
### Custom Appenders
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Writing a custom appender is dead-easy:
```clojure
(timbre/set-config!
[:appenders :my-appender]
{:doc "Hello-world appender"
:min-level :debug
:enabled? true
:async? false
:max-message-per-msecs nil ; No rate limiting
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:fn (fn [{:keys [ap-config level prefix message more] :as args}]
(when-not (:my-production-mode? ap-config)
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(apply println prefix "Hello world!" message more)))
```
And because appender fns are just regular Clojure fns, you have *unlimited power*: write to your database, send a message over the network, check some other state (e.g. environment config) before making a choice, etc.
See the `timbre/config` docstring for more information on appenders.
## Profiling
The usual recommendation for Clojure profiling is: use a good **JVM profiler** like [YourKit](http://www.yourkit.com/), [JProfiler](http://www.ej-technologies.com/products/jprofiler/overview.html), or [VisualVM](http://docs.oracle.com/javase/6/docs/technotes/guides/visualvm/index.html).
And these certainly do the job. But as with many Java tools, they can be a little hairy and often heavy-handed - especially when applied to Clojure. Timbre includes an alternative.
Let's add it to our app's `ns` declaration:
```clojure
(:use [taoensso.timbre.profiling :as profiling :only (p profile)])
```
Wrap forms that you'd like to profile with the `p` macro and give them a name:
```clojure
(defn my-fn
[]
(let [nums (vec (range 1000))]
(+ (p :fast-sleep (Thread/sleep 1) 10)
(p :slow-sleep (Thread/sleep 2) 32)
(p :add (reduce + nums))
(p :sub (reduce - nums))
(p :mult (reduce * nums))
(p :div (reduce / nums)))))
(my-fn)
=> 42
```
The `profile` macro can now be used to log times for any wrapped forms:
```clojure
(profile :info :Arithmetic (dotimes [n 100] (my-fn)))
=> "Done!"
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%> 2012-Jul-03 20:46:17 +0700 localhost INFO [my-app] - Profiling my-app/Arithmetic
Name Calls Min Max MAD Mean Total% Total
my-app/slow-sleep 100 2ms 2ms 31μs 2ms 57 231ms
my-app/fast-sleep 100 1ms 1ms 27μs 1ms 29 118ms
my-app/add 100 44μs 2ms 46μs 100μs 2 10ms
my-app/sub 100 42μs 564μs 26μs 72μs 2 7ms
my-app/div 100 54μs 191μs 17μs 71μs 2 7ms
my-app/mult 100 31μs 165μs 11μs 44μs 1 4ms
Unaccounted 6 26ms
Total 100 405ms
```
It's important to note that Timbre profiling is fully **logging-level aware**: if the level is insufficient, you *won't pay for profiling*. Likewise, normal namespace filtering applies. (Performance characteristics for both checks are inherited from Timbre itself).
And since `p` and `profile` **always return their body's result** regardless of whether profiling actually happens or not, it becomes feasible to use profiling more often as part of your normal workflow: just *leave profiling code in production as you do for logging code*.
A simple **sampling profiler** is also available: `taoensso.timbre.profiling/sampling-profile`.
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## Timbre Supports the ClojureWerkz and CDS Project Goals
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ClojureWerkz is a growing collection of open-source, batteries-included [Clojure libraries](http://clojurewerkz.org/) that emphasise modern targets, great documentation, and thorough testing.
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CDS (Clojure Documentation Site) is a contributor-friendly community project aimed at producing top-notch [Clojure tutorials](http://clojure-doc.org/) and documentation.
## Contact & Contribution
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Reach me (Peter Taoussanis) at [taoensso.com](https://www.taoensso.com) for questions/comments/suggestions/whatever. I'm very open to ideas if you have any! I'm also on Twitter: [@ptaoussanis](https://twitter.com/#!/ptaoussanis).
## License
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Copyright &copy; 2012 Peter Taoussanis. Distributed under the [Eclipse Public License](http://www.eclipse.org/legal/epl-v10.html), the same as Clojure.