semantic_logger =============== Improved logging for Ruby * http://github.com/reidmorrison/semantic_logger ## Note: As of SemanticLogger V2.0 the Rails logging is no longer automatically replaced when including SemanticLogger. Include the [rails_semantic_logger](http://github.com/reidmorrison/rails_semantic_logger) gem to replace the Rails default logger with SemanticLogger ## Overview Semantic Logger takes logging in Ruby to a new level by adding several new capabilities to the commonly used Logging API: Dynamic * Increase the log level at runtime for just one class * For example enable debug level logging for a single class (logging instance) while the program is running to get more detailed logging in production for just that class Tagged Logging * Supply custom data to be added to every log entry within a block of code, including libraries and existing gems * Tagged logging is critical for any high traffic site so that one can narrow down log entries for a single call that is mixed in with log entries from hundreds of other log entries High Performance * Logging is performed in a separate thread so as not to impact performance of running code Customizable * Custom formatting by destination * Easy to "roll your own" destination (Appender). For example to log to Hadoop, Redis, etc.. Payload support * Aside from the regular log message, a hash payload can also be supplied with every log entry * Very powerful when logging to NOSQL destinations that allow queries against any data in the payload Exceptions * Directly log exceptions * Semantic Logger standardizes the logging of exceptions with their backtraces to text destinations and writes the exception elements as a hash to NOSQL destinations Drop-in Replacement * Simple drop-in replacement for the Ruby, or the Rails loggers * Supports current common logging interface * No changes to existing to code to use new logger ( other than replacing the logger ) Thread Safe * Semantic Logger ensures that all logging is fully thread-safe * Supports highly concurrent environments running hundreds of threads * Each appender writes all log entries sequentially in the appender thread so that log entries are written in the correct sequence * Avoids issues that other loggers experience when multiple threads try to write to the same log file at the same time creating partial and overwritten log entries in the log file Thread Aware * Includes the process and thread id information in every log entry * If running JRuby it will also include the name of the thread for every log entry Trace Level * :trace is a new level common in other languages and is commonly used for logging trace level detail. It is intended for logging data at level below :debug. * :trace can be used for logging the actual data sent or received over the network that is rarely needed but is critical when things are not working as expected. * Since :trace can be enabled on a per class basis it can even be turned on in production to resolve what was actually sent to an external vendor Multiple Destinations * Log to multiple destinations at the same time ( File and MongoDB, etc.. ) * Each destination can also have its own log level. For example, only log :info and above to MongoDB, or :warn and above to a second log file Benchmarking * The performance of any block of code can be measured and logged at the same time depending on the active log level Semantic Capabilities * With Semantic Logger it is simple to mix-in additional semantic information with every log entry * The application or class name is automatically included for every log entry under a specific logging instance * Includes the duration of blocks of code * Any hash containing context specific information such as user_id or location information Beyond Tagged Logging * Supply entire hash of custom data to be added to the payload of every log entry within a block of code, including libraries and existing gems NOSQL Destinations * Every log entry is broken down into elements that NOSQL data stores can understand: ```json { "_id" : ObjectId("5034fa48e3f3fea945e83ef2"), "time" : ISODate("2012-08-22T15:27:04.409Z"), "host_name" : "release", "pid" : 16112, "thread_name" : "main", "name" : "UserLocator", "level" : "debug", "message" : "Fetch user information", "duration" : 12, "payload" : { "user" : "Jack", "zip_code" : 12345, "location" : "US" } } ``` Thread Safe * Semantic Logger is completely thread safe and all methods can be called concurrently from any thread * Tagged logging keeps any tagging data on a per-thread basis to ensure that tags from different threads are not inter-mingled ## Introduction Semantic Logger is a Logger that supports logging of meta-data, along with text messages to multiple appenders An appender is a Logging destination such as a File, MongoDB collection, etc.. Multiple Appenders can be active at the same time. All log entries are written to each appender. Machines can understand the logged data without having to use complex Regular Expressions or other text parsing techniques Semantic Logger, sits on top of existing logger implementations and can also be used as a drop in replacement for existing Ruby loggers. This allows the existing logging to be replaced immediately with the Semantic Logger Appenders, and over time the calls can be replaced with ones that contain the necessary meta-data. Example of current calls: ```ruby logger.info("Queried users table in #{duration} ms, with a result code of #{result}") ``` For a machine to find all queries for table 'users' that took longer than 100 ms, would require using a regular expression just to extract the table name and duration, then apply the necessary logic. It also assumes that the text is not changed and that matches will not be found when another log entry has similar text output. This can be changed over time to: ```ruby logger.info("Queried table", :duration => duration, :result => result, :table => "users", :action => "query") ``` Using the MongoDB appender, we can easily find all queries for table 'users' that took longer than 100 ms: ```javascript db.logs.find({"payload.table":"users", "payload.action":"query", "payload.duration":{$gt:100} }) ``` Since Semantic Logger can call existing Loggers, it does not force end-users to have to adopt a Semantic aware adapter. Although, such adapters create tremendous value in the problem monitoring and determination processes. ## Logging API ### Standard Logging methods The Semantic Logger logging API supports the existing logging interface for the Rails and Ruby Loggers. For example: ```ruby logger.info("Hello World") ``` Or to query whether a specific log level is set ```ruby logger.info? ``` The following logging methods are available ```ruby trace(message, payload=nil, exception=nil, &block) debug(message, payload=nil, exception=nil, &block) info(message, payload=nil, exception=nil, &block) warn(message, payload=nil, exception=nil, &block) error(message, payload=nil, exception=nil, &block) fatal(message, payload=nil, exception=nil, &block) ``` Parameters - message: The text message to log. Mandatory only if no block is supplied - payload: Optional, either a Ruby Exception object or a Hash - exception: Optional, Ruby Exception object. Allows both an exception and a payload to be logged - block: The optional block is executed only if the corresponding log level is active. Can be used to prevent unnecessary calculations of debug data in production. Examples: ```ruby logger.debug("Calling Supplier") logger.debug("Calling Supplier", :request => 'update', :user => 'Jack') logger.debug { "A total of #{result.inject(0) {|sum, i| i+sum }} were processed" } ``` ## Exceptions The Semantic Logger adds an optional parameter to the existing log methods so that a corresponding Exception can be logged in a standard way ```ruby begin # ... Code that can raise an exception rescue Exception => exception logger.error("Oops external call failed", exception) # Re-raise or handle the exception raise exception end ``` ### Payload The Semantic Logger adds an extra parameter to the existing log methods so that additional payload can be logged, such as a Hash or a Ruby Exception object. ```ruby logger.info("Oops external call failed", :result => :failed, :reason_code => -10) ``` The additional payload is machine readable so that we don't have to write complex regular expressions so that a program can analyze log output. With the MongoDB appender the payload is written directly to MongoDB as part of the document and is therefore fully searchable ### Benchmarking Another common logging requirement is to measure the time it takes to execute a block of code based on the log level. For example: ```ruby Rails.logger.benchmark_info "Calling external interface" do # Code to call external service ... end ``` The following output will be written to file: 2012-08-30 15:37:29.474 I [48308:ScriptThreadProcess: script/rails] (5.2ms) Rails -- Calling external interface If an exception is raised during the block the exception is logged at the same log level as the benchmark along with the duration and message. The exception will flow through to the caller unchanged The following benchmarking methods are available ```ruby benchmark_trace(message, params=nil, &block) benchmark_debug(message, params=nil, &block) benchmark_info(message, params=nil, &block) benchmark_warn(message, params=nil, &block) benchmark_error(message, params=nil, &block) benchmark_fatal(message, params=nil, &block) ``` Parameters - message: The mandatory text message to log. - params: ``` :log_exception Control whether or how an exception thrown in the block is reported by Semantic Logger. Values: :full Log the exception class, message, and backtrace :partial Log the exception class and messag The backtrace will not be logged :off Any unhandled exception from the block will not be logged :min_duration Only log if the block takes longer than this duration in ms Default: 0.0 :payload Optional, Hash payload :exception Optional, Ruby Exception object to log along with the duration of the supplied block ``` ### Logging levels The following logging levels are available through Semantic Logger :trace, :debug, :info, :warn, :error, :fatal The log levels are listed above in the order of precedence with the most detail to the least. For example :debug would include :info, :warn, :error, :fatal levels but not :trace And :fatal would only log :fatal error messages and nothing else :unknown has been mapped to :fatal for Rails and Ruby Logger :trace is a new level that is often used for tracing low level calls such as the data sent or received to external web services. It is also commonly used in the development environment for low level trace logging of methods calls etc. If only the rails logger is being used, then :trace level calls will be logged as debug calls only if the log level is set to trace ### Changing the Class name for Log Entries When Semantic Logger is included in a Rails project it automatically replaces the loggers for Rails, ActiveRecord::Base, ActionController::Base, and ActiveResource::Base with wrappers that set their Class name. For example in semantic_logger/railtie.rb: ```ruby ActiveRecord::Base.logger = SemanticLogger[ActiveRecord] ``` By replacing their loggers we now get the class name in the text logging output: 2012-08-30 15:24:13.439 D [47900:main] ActiveRecord -- SQL (12.0ms) SELECT `schema_migrations`.`version` FROM `schema_migrations` It is recommended to include a class specific logger for all major classes that will be logging using the SemanticLogger::Loggable mix-in. For Example: ```ruby class ExternalSupplier # Lazy load logger class variable on first use include SemanticLogger::Loggable def call_supplier(amount, name) logger.debug "Calculating with amount", { :amount => amount, :name => name } # Measure and log on completion how long the call took to the external supplier logger.benchmark_info "Calling external interface" do # Code to call the external supplier ... end end end ``` This will result in the log output identifying the log entry as from the ExternalSupplier class 2012-08-30 15:37:29.474 I [48308:ScriptThreadProcess: script/rails] (5.2ms) ExternalSupplier -- Calling external interface ### Changing the log level for a single class at runtime Since the logger is class specific, its log level can be changed dynamically at runtime. For example, to temporarily set the log level to :trace to diagnose an issue: ```ruby require 'semantic_logger' SemanticLogger.default_level = :info SemanticLogger.add_appender('example.log') class ExternalSupplier # Lazy load logger class variable on first use include SemanticLogger::Loggable def call_supplier(amount, name) logger.trace "Calculating with amount", { :amount => amount, :name => name } # Measure and log on completion how long the call took to the external supplier logger.benchmark_info "Calling external interface" do # Code to call the external supplier ... end end end # Create and use the class supplier = ExternalSupplier.new supplier.call_supplier(100, 'Jack') # Now change the log level to :trace ExternalSupplier.logger.level = :trace # Call the supplier, this time including trace level messages supplier.call_supplier(100, 'Jack') # Change the log level back to the default level ExternalSupplier.logger.level = SemanticLogger.default_level ``` Below is the output from the above example showing the :trace log level message that was written during the second call to the ExternalSupplier: ``` 2013-11-07 16:19:26.496 I [35674:main] (0.0ms) ExternalSupplier -- Calling external interface 2013-11-07 16:19:26.683 T [35674:main] ExternalSupplier -- Calculating with amount -- {:amount=>100, :name=>"Jack"} 2013-11-07 16:19:26.683 I [35674:main] (0.0ms) ExternalSupplier -- Calling external interface ``` ### Tagged Logging Semantic Logger allows any Ruby or Rails program to also include tagged logging. This means that any logging performed within a block, including any called libraries or gems to include the specified tag with every log entry. Using Tagged logging is critical in any highly concurrent environment so that one can quickly find all related log entries across all levels of code, and even across threads ```ruby logger.tagged(tracking_number) do logger.debug("Hello World") # ... end ``` ### Beyond Tagged Logging Blocks of code can be tagged with not only values, but can be tagged with entire hashes of data. The additional hash of data will be merged into the payload of every log entry For example every corresponding log entry could include a hash containing a user_id, name, region, zip_code, tracking_number, etc... ```ruby logger.with_payload(:user => 'Jack', :zip_code => 12345) do logger.debug("Hello World") # ... end ``` ### Named threads SemanticLogger logs the name or id of the thread in every log message. On Ruby MRI the thread name is by default the thread's object_id, For example: 70184354571980 ``` 2013-11-07 16:25:14.279627 I [35841:70184354571980] (0.0ms) ExternalSupplier -- Calling external interface ``` To set a custom name for any thread so that it shows up in the logger: ```ruby Thread.current.name = "User calculation thread 32" ``` Sample output: ``` 2013-11-07 16:26:02.744139 I [35841:User calculation thread 32] (0.0ms) ExternalSupplier -- Calling external interface ``` #### NOTE: Make sure that the assigned thread name is unique otherwise it will be difficult to distinguish between concurrently running threads if they have the same name. For example, use the current thread object_id to ensure uniqueness: ```ruby Thread.current.name = "Worker Thread:#{Thread.current.object_id}" ``` ## Standalone SemanticLogger When using SemanticLogger inside of Rails all we need to do is include the rails_semantic_logger gem and the default Rails logger will be replaced with Semantic Logger. In a stand-alone or non-rails environment we can easily log to a file called 'development.log' as follows: ```ruby require 'semantic_logger' SemanticLogger.add_appender('development.log') logger = SemanticLogger['Example'] logger.info "Hello World" ``` By default it will only log :info and above, to log everything to the log file: ```ruby require 'semantic_logger' SemanticLogger.default_level = :trace SemanticLogger.add_appender('development.log') logger = SemanticLogger['Example'] logger.info "Hello World" logger.trace "Low level trace information" ``` By supplying multiple appenders Semantic Logger can write to multiple destinations at the same time. For example, log to a file and the screen: ```ruby require 'semantic_logger' SemanticLogger.default_level = :trace SemanticLogger.add_appender('development.log') SemanticLogger.add_appender(STDOUT) logger = SemanticLogger['Example'] logger.info "Hello World" logger.trace "Low level trace information" ``` To reduce the log level of logging to STDOUT to just :info and above, add the log_level such as :info as the second parameter when adding the appender: ```ruby require 'semantic_logger' SemanticLogger.default_level = :trace SemanticLogger.add_appender('development.log') SemanticLogger.add_appender(STDOUT, :info) logger = SemanticLogger['Example'] logger.info "Hello World" logger.trace "Low level trace information" ``` To log :debug and above to a log file, :error and above to $stderr, and :info and above to MongoDB: ```ruby require 'semantic_logger' require 'mongo' SemanticLogger.default_level = :debug SemanticLogger.add_appender('development.log') SemanticLogger.add_appender($stderr, :error) mongo_appender = SemanticLogger::Appender::MongoDB.new( :db => Mongodb::Connection.new['production_logging'], :collection_size => 25.gigabytes ) SemanticLogger.add_appender(mongo_appender, :info) logger = SemanticLogger['Example'] logger.info "Hello World" logger.trace "Low level trace information" logger.error "Oops an error occurred" logger.info("Login time", :user => 'Mary', :duration => 230, :ip_address=>'192.168.0.1') ``` When starting out with Semantic Logger it can be useful to gain all the benefits of Semantic Logger and still continue to log to an existing logger: ```ruby require 'logger' require 'semantic_logger' # Built-in Ruby logger log = Logger.new(STDOUT) log.level = Logger::DEBUG SemanticLogger.default_level = :debug SemanticLogger.add_appender(log) logger = SemanticLogger['Example'] logger.info "Hello World" logger.debug("Login time", :user => 'Joe', :duration => 100, :ip_address=>'127.0.0.1') ``` It is recommended that every class or module have it's own logging instance. This can be achieved by including SemanticLogger::Loggable: ```ruby require 'semantic_logger' SemanticLogger.default_level = :trace SemanticLogger.add_appender('development.log') class ExternalSupplier # Makes available a class and instance level logger # ExternalSupplier.logger and ExternalSupplier#logger include SemanticLogger::Loggable # logger class method example def self.hostname=(hostname) logger.debug "Setting hostname to #{hostname}" @@hostname = hostname end # logger instance method example def call_supplier(amount, name) logger.debug "Calculating with amount", { :amount => amount, :name => name } # Measure and log on completion how long the call took to the external supplier logger.benchmark_info "Calling external interface" do # Code to call the external supplier ... end end end ``` ### Logging to Syslog Log to a local Syslog: ```ruby require 'semantic_logger' SemanticLogger.default_level = :trace SemanticLogger.add_appender(SemanticLogger::Appender::Syslog.new) ``` Log to a local file and to a remote Syslog server such as syslog-ng over TCP: ```ruby require 'semantic_logger' SemanticLogger.default_level = :trace SemanticLogger.add_appender('development.log') SemanticLogger.add_appender(SemanticLogger::Appender::Syslog.new(:server => 'tcp://myloghost:514')) ``` ## Configuration The Semantic Logger follows the principle where multiple appenders can be active at the same time. For example, this allows one to log to MongoDB and the Rails log file at the same time. ### Rails Configuration To automatically replace the Rails logger with Semantic Logger use the gem [rails_semantic_logger](http://github.com/reidmorrison/rails_semantic_logger) ## Log Struct Internally all log messages are passed around in a Log Struct. In order to write your own custom formatter or log appender it is necessary to understand the fields: ```ruby Log = Struct.new(:level, :thread_name, :name, :message, :payload, :time, :duration, :tags, :level_index) ``` level [Symbol] * Log level of the supplied log call * :trace, :debug, :info, :warn, :error, :fatal thread_name [String] * Name or id of the thread in which the logging call was called name [String] * Class name supplied to the logging instance message [String] * Text message to be logged payload [Hash|Exception] * Optional Hash or Ruby Exception object to be logged time [Time] * The time at which the log entry was created duration [Float] * The time taken in milli-seconds to complete a benchmark call tags [Array] * Any tags active on the thread when the log call was made level_index [Integer] * Internal use only. Index of the log level ### Mixing Logging Levels It is sometimes useful to log a subset of the log messages to a separate file or appender. For example, log :error and :fatal level messages to a special error file. Below is a stand-alone example that better shows this behavior: ```ruby require 'semantic_logger' # Set default log level for new logger instances SemanticLogger.default_level = :info # Log all warning messages and above to warnings.log SemanticLogger.add_appender('log/warnings.log', :warn) # Log all trace messages and above to trace.log SemanticLogger.add_appender('log/trace.log', :trace) logger = SemanticLogger['MyClass'] logger.level = :trace logger.trace "This is a trace message" logger.info "This is an info message" logger.warn "This is a warning message" ``` The output is as follows: ```bash ==> trace.log <== 2013-08-02 14:15:56.733532 T [35669:70176909690580] MyClass -- This is a trace message 2013-08-02 14:15:56.734273 I [35669:70176909690580] MyClass -- This is an info message 2013-08-02 14:15:56.735273 W [35669:70176909690580] MyClass -- This is a warning message ==> warnings.log <== 2013-08-02 14:15:56.735273 W [35669:70176909690580] MyClass -- This is a warning message ``` ### Custom Formatters The formatting for each appender can be replaced with custom code. To replace the existing formatter supply a block of code when creating the appender. Example: Formatter that just returns the Log Struct ```ruby require 'semantic_logger' SemanticLogger.default_level = :trace SemanticLogger.add_appender(STDOUT) do |log| # This formatter just returns the log struct as a string log.inspect end logger = SemanticLogger['Hello'] logger.info "Hello World" ``` Output: # Example: Replace the default log file formatter ```ruby require 'semantic_logger' SemanticLogger.default_level = :trace SemanticLogger.add_appender('development.log') do |log| tags = log.tags.collect { |tag| "[#{tag}]" }.join(" ") + " " if log.tags && (log.tags.size > 0) message = log.message.to_s message << " -- " << log.payload.inspect if log.payload message << " -- " << "#{log.exception.class}: #{log.exception.message}\n#{(log.exception.backtrace || []).join("\n")}" if log.exception duration_str = log.duration ? "(#{'%.1f' % log.duration}ms) " : '' "#{SemanticLogger::Appender::Base.formatted_time(log.time)} #{log.level.to_s[0..0].upcase} [#{$$}:#{log.thread_name}] #{tags}#{duration_str}#{log.name} -- #{message}" end ``` Example: Replace the default MongoDB formatter ```ruby # Log to MongoDB and supply a custom document formatter mongodb_appender = SemanticLogger::Appender::MongoDB.new( :db => Cache::Work.db, :collection_size => 25.gigabytes ) do |log| # Return a document (Hash) of the data to be saved to MongoDB document = { :time => log.time, :host_name => SemanticLogger::Appender::MongoDB.host_name, :pid => $PID, :thread_name => log.thread_name, :name => log.name, :level => log.level, :level_index => log.level_index, } document[:application] = 'MyApplication' document[:message] = SemanticLogger::Appender::MongoDB.strip_colorizing(log.message) if log.message document[:duration] = log.duration if log.duration document[:tags] = log.tags if log.tags && (log.tags.size > 0) document[:payload] = log.payload if log.payload document[:exception] = { :name => log.exception.class.name, :message => log.exception.message, :stack_trace => log.exception.backtrace } if log.exception document end SemanticLogger.add_appender(mongodb_appender) ``` ## Performance The traditional logging implementations write their log information to file in the same thread of execution as the program itself. This means that for every log entry the program has to wait for the data to be written. With Semantic Logger it uses a dedicated thread for logging so that writing to the log file or other appenders does not hold up program execution. Also, since the logging is in this separate thread there is no impact to program execution if we decided to add another appender. For example, log to both a file and a MongoDB collection. ## Log Rotation Since the log file is not re-opened with every call, when the log file needs to be rotated, use a copy-truncate operation over deleting the file. ## Why Semantic logging? Just as there is the initiative to add Semantic information to data on the web so that computers can directly understand the content without having to resort to complex regular expressions or machine learning techniques, it is important to be able to do the same with log files or data. Semantic Logger allows every log entry to have not only a message, but a payload that can be written to a file or a NOSQL destination. Once the logging data is in the NOSQL data store it can be queried quickly and efficiently. Some SQL data stores also allow complex data types that could be used for storing and querying the logging data ## Architecture & Performance In order to ensure that logging does not hinder the performance of the application all log entries are written to thread-safe Queue. A separate thread is responsible for writing the log entries to each of the appenders. In this way formatting and disk or network write delays will not affect the performance of the application. Also adding more than one appender does not affect the runtime performance of the application. The logging thread is automatically started on initialization. When the program terminates it will call flush on each of the appenders. Calling SemanticLogger::Logger#flush will wait until all outstanding log messages have been written and flushed to their respective appenders before returning. ## Write your own Appender To write your own appender it should meet the following requirements: * Inherit from SemanticLogger::Base * In the initializer connect to the resource being logged to * Implement #log(log) which needs to write to the relevant resource * Implement #flush if the resource can be flushed * Write a test for the new appender The #log method takes the log struct as a parameter which is described above. Basic outline for an Appender: ```ruby require 'semantic_logger' class SimpleAppender < SemanticLogger::Appender::Base def initialize(level=nil, &block) # Set the log level and formatter if supplied super(level, &block) end # Display the log struct and the text formatted output def log(log) p log puts formatter.call(log) end # Optional def flush puts "Flush :)" end end ``` Sample program calling the above appender: ```ruby SemanticLogger.default_level = :trace # Log to file dev.log SemanticLogger.add_appender('dev.log') # Also log the above sample appender SemanticLogger.add_appender(SimpleAppender.new) logger = SemanticLogger['Hello'] logger.info "Hello World" ``` Look at the [existing appenders](https://github.com/reidmorrison/semantic_logger/tree/master/lib/semantic_logger/appender) for good examples To have your appender included in the standard list of appenders follow the fork instructions below. Very Important: New appenders will not be accepted without complete working tests. See the [MongoDB Appender Test](https://github.com/reidmorrison/semantic_logger/blob/master/test/appender_mongodb_test.rb) for an example. ## Dependencies - Ruby MRI 1.8.7, 1.9.3 (or above) Or, JRuby 1.6.3 (or above) - Optional: To log to MongoDB, Mongo Ruby Driver 1.5.2 or above ## Install gem install semantic_logger To log to MongoDB, it also needs the Ruby Mongo Driver gem install mongo ## Future - Add support for a configuration file that can set log level by class name - Configuration file to support adding appenders - Based on end-user demand add appenders for: Syslog, hadoop, redis, etc.. Meta ---- * Code: `git clone git://github.com/reidmorrison/semantic_logger.git` * Home: * Bugs: * Gems: This project uses [Semantic Versioning](http://semver.org/). Author ------- Reid Morrison :: reidmo@gmail.com :: @reidmorrison Contributors ------------ Marc Bellingrath :: marrrc.b@gmail.com License ------- Copyright 2012, 2013 Reid Morrison Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.