class Log
inherits Reference
¶
The Log class provides a logging utility that you can use to output messages.
The messages, or Log::Entry have associated levels, such as Info or Error
that indicate their importance. See Log::Severity.
To log a message trace, debug, info, notice, warn, error, and fatal methods
can be used. They expect a block that will evaluate to the message of the entry.
require "log"
Log.info { "Program started" }
Data can be associated with a log entry via the Log::Emitter yielded in the logging methods.
Log.info &.emit("User logged in", user_id: 42)
If you want to log an exception, you can indicate it in the exception: named argument.
Log.warn(exception: e) { "Oh no!" }
Log.warn exception: e, &.emit("Oh no!", user_id: 42)
The block is only evaluated if the current message is to be emitted to some Log::Backend.
To add structured information to the message you can use the Log::Context.
When creating log messages they belong to a source. If the top-level Log is used
as in the above examples its source is the empty string.
The source can be used to identify the module or part of the application that is logging. You can configure for each source a different level to filter the messages.
A recommended pattern is to declare a Log constant in the namespace of your shard or module as follows:
module DB
Log = ::Log.for("db") # => Log for db source
def do_something
Log.info { "this is logged in db source" }
end
end
DB::Log.info { "this is also logged in db source" }
Log.for("db").info { "this is also logged in db source" }
Log.info { "this is logged in top-level source" }
That way, any Log.info call within the DB module will use the db source. And not the top-level ::Log.info.
Sources can be nested. Continuing the last example, to declare a Log constant db.pool source you can do as follows:
class DB::Pool
Log = DB::Log.for("pool") # => Log for db.pool source
end
A Log will emit the messages to the Log::Backends attached to it as long as
the configured severity filter level permits it.
Logs can also be created from a type directly. For the type DB::Pool the source db.pool will be used.
For generic types as Foo::Bar(Baz) the source foo.bar will be used (i.e. without generic arguments).
module DB
Log = ::Log.for(self) # => Log for db source
end
Default logging configuration¶
By default entries from all sources with Info and above severity will
be logged to STDOUT using the Log::IOBackend.
If you need to change the default level, backend or sources call Log.setup upon startup.
Log.setup(:debug) # Log debug and above for all sources to STDOUT
Log.setup("myapp.*, http.*", :notice) # Log notice and above for myapp.* and http.* sources only, and log nothing for any other source.
backend_with_formatter = Log::IOBackend.new(formatter: custom_formatter)
Log.setup(:debug, backend_with_formatter) # Log debug and above for all sources to using a custom backend
Configure logging explicitly in the code¶
Use Log.setup methods to indicate which sources should go to which backends.
You can indicate actual sources or patterns.
- the empty string matches only the top-level source
*matches all the sourcesfoo.bar.*matchesfoo.barand every nested sourcefoo.barmatchesfoo.bar, but not its nested sources- Any comma separated combination of the above
The following configuration will setup for all sources to emit
warnings (or higher) to STDOUT, allow any of the db.* and
nested source to emit debug (or higher), and to also emit for all
sources errors (or higher) to an elasticsearch backend.
Log.setup do |c|
backend = Log::IOBackend.new
c.bind "*", :warn, backend
c.bind "db.*", :debug, backend
c.bind "*", :error, ElasticSearchBackend.new("http://localhost:9200")
end
Configure logging from environment variables¶
Include the following line to allow configuration from environment variables.
Log.setup_from_env
The environment variable LOG_LEVEL is used to indicate which severity level to emit.
By default entries from all sources with Info and above severity will
be logged to STDOUT using the Log::IOBackend.
To change the level and sources change the environment variable value:
$ LOG_LEVEL=DEBUG ./bin/app
You can tweak the default values (used when LOG_LEVEL variable is not defined):
Log.setup_from_env(default_level: :error)
Class methods¶
.capture(source : String = "*", level : Severity = Log::Severity::Trace, *, builder = Log
¶
(source : String = "*", level : Severity = Log::Severity::Trace, *, builder = Log
Returns and yields an EntriesChecker that allows checking specific log entries
were emitted.
This capture will even work if there are currently no backends configured, effectively adding a temporary backend.
require "spec"
require "log"
require "log/spec"
Log.setup(:none)
def greet(name)
Log.info { "Greeting #{name}" }
end
it "greets" do
Log.capture do |logs|
greet("Harry")
greet("Hermione")
greet("Ron")
logs.check(:info, /greeting harry/i)
logs.next(:info, /greeting hermione/i)
end
end
By default logs of all sources and severities will be captured.
Use level to only capture of the given severity or above.
Use source to narrow which source are captured. Values that represent single pattern like http.* are allowed.
The EntriesChecker will hold a list of emitted entries.
EntriesChecker#check will find the next entry which matches the level and message.
EntriesChecker#next will validate that the following entry in the list matches the given level and message.
EntriesChecker#clear will clear the emitted and captured entries.
With these methods it is possible to express expected traces in either a strict or loose way, while checking ordering.
EntriesChecker#entry returns the last matched Entry. Useful to check additional entry properties other than the message.
EntriesChecker#empty validates there are no pending entries to match.
Using the yielded EntriesChecker allows clearing the entries between statements.
Invocations can be nested in order to capture each source in their own EntriesChecker.
.capture(level : Log::Severity = Log::Severity::Trace, *, builder : Log::Builder = Log
¶
(level : Log::Severity = Log::Severity::Trace, *, builder : Log::Builder = Log
Returns and yields an EntriesChecker that allows checking specific log entries
were emitted.
This capture will even work if there are currently no backends configured, effectively adding a temporary backend.
require "spec"
require "log"
require "log/spec"
Log.setup(:none)
def greet(name)
Log.info { "Greeting #{name}" }
end
it "greets" do
Log.capture do |logs|
greet("Harry")
greet("Hermione")
greet("Ron")
logs.check(:info, /greeting harry/i)
logs.next(:info, /greeting hermione/i)
end
end
By default logs of all sources and severities will be captured.
Use level to only capture of the given severity or above.
Use source to narrow which source are captured. Values that represent single pattern like http.* are allowed.
The EntriesChecker will hold a list of emitted entries.
EntriesChecker#check will find the next entry which matches the level and message.
EntriesChecker#next will validate that the following entry in the list matches the given level and message.
EntriesChecker#clear will clear the emitted and captured entries.
With these methods it is possible to express expected traces in either a strict or loose way, while checking ordering.
EntriesChecker#entry returns the last matched Entry. Useful to check additional entry properties other than the message.
EntriesChecker#empty validates there are no pending entries to match.
Using the yielded EntriesChecker allows clearing the entries between statements.
Invocations can be nested in order to capture each source in their own EntriesChecker.
.progname=(progname)
¶
(progname)
The program name used for log entries
Defaults to the executable name
.setup(*, builder : Log::Builder = Log
¶
(*, builder : Log::Builder = Log
Setups logging bindings discarding all previous configurations.
.setup(sources : String = "*", level : Log::Severity = Log::Severity::Info, backend : Log::Backend = IOBackend.new, *, builder : Log::Builder = Log.builder)
¶
(sources : String = "*", level : Log::Severity = Log::Severity::Info, backend : Log::Backend = IOBackend.new, *, builder : Log::Builder = Log.builder)
Setups logging for sources using the specified level, backend.
.setup(level : Log::Severity = Log::Severity::Info, backend : Log::Backend = IOBackend.new, *, builder : Log::Builder = Log.builder)
¶
(level : Log::Severity = Log::Severity::Info, backend : Log::Backend = IOBackend.new, *, builder : Log::Builder = Log.builder)
Setups logging for all sources using the specified level, backend.
.setup_from_env(*, builder : Log::Builder = Log.builder, default_level : Log::Severity = Log::Severity::Info, default_sources = "*", log_level_env = "LOG_LEVEL", backend = Log::IOBackend.new)
¶
(*, builder : Log::Builder = Log.builder, default_level : Log::Severity = Log::Severity::Info, default_sources = "*", log_level_env = "LOG_LEVEL", backend = Log::IOBackend.new)
Setups logging based on LOG_LEVEL environment variable.
.with_context
¶
Method to save and restore the current logging context.
Log.context.set a: 1
Log.info { %(message with {"a" => 1} context) }
Log.with_context do
Log.context.set b: 2
Log.info { %(message with {"a" => 1, "b" => 2} context) }
end
Log.info { %(message with {"a" => 1} context) }
.for(type : Class, level : Severity? = nil) : Log
¶
(type : Class, level : Severity? = nil) : Log
Creates a Log for the given type.
A type Foo::Bar(Baz) corresponds to the source foo.bar.
If level is given, it will override the configuration.
.for(source : String, level : Severity? = nil) : Log
¶
(source : String, level : Severity? = nil) : Log
Creates a Log for the given source.
If level is given, it will override the configuration.
Methods¶
#context=(value : Log::Metadata | Log::Context)
¶
(value : Log::Metadata | Log::Context)
Sets the current fiber logging context.
#debug(*, exception : Exception? = nil
¶
(*, exception : Exception? = nil
Logs a message if the logger's current severity is lower or equal to 1.
#error(*, exception : Exception? = nil
¶
(*, exception : Exception? = nil
Logs a message if the logger's current severity is lower or equal to 5.
#fatal(*, exception : Exception? = nil
¶
(*, exception : Exception? = nil
Logs a message if the logger's current severity is lower or equal to 6.
#for(child_source : String, level : Severity? = nil) : Log
¶
(child_source : String, level : Severity? = nil) : Log
Creates a Log for the given nested source.
If level is given, it will override the configuration.
#for(type : Class, level : Severity? = nil) : Log
¶
(type : Class, level : Severity? = nil) : Log
Creates a Log for the given type.
A type Foo::Bar(Baz) corresponds to the source foo.bar.
If level is given, it will override the configuration.
#info(*, exception : Exception? = nil
¶
(*, exception : Exception? = nil
Logs a message if the logger's current severity is lower or equal to 2.
#notice(*, exception : Exception? = nil
¶
(*, exception : Exception? = nil
Logs a message if the logger's current severity is lower or equal to 3.
#trace(*, exception : Exception? = nil
¶
(*, exception : Exception? = nil
Logs a message if the logger's current severity is lower or equal to 0.
#warn(*, exception : Exception? = nil
¶
(*, exception : Exception? = nil
Logs a message if the logger's current severity is lower or equal to 4.
#with_context
¶
Method to save and restore the current logging context.
Log.context.set a: 1
Log.info { %(message with {"a" => 1} context) }
Log.with_context do
Log.context.set b: 2
Log.info { %(message with {"a" => 1, "b" => 2} context) }
end
Log.info { %(message with {"a" => 1} context) }
Macros¶
define_formatter(name, pattern)
¶
(name, pattern)
Generate subclasses of Log::StaticFormatter from a string with interpolations
Example:
Log.define_formatter MyFormat, "- #{severity}: #{message}"
Log::StaticFormatter for the available methods that can
be called within the interpolations.