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Add a public API for broadcasting logs:
- ## Context While working on rails#44695, I realised that Broadcasting was still a private API, although it’s commonly used. Rafael mentioned that making it public would require some refactor because of the original implementation which was hard to understand and maintain. ### Changing how broadcasting works: Broadcasting in a nutshell worked by “transforming” an existing logger into a broadcasted one. The logger would then be responsible to log and format its own messages as well as passing the message along to other logger it broadcasts to. The problem with this approach was the following: - Heavy use of metaprogramming. - Accessing the loggers in the broadcast wasn’t possible. Removing a logger from the broadcast either. - More importantly, modifying the main logger (the one that broadcasts logs to the others) wasn’t possible and the main source of misunderstanding. ```ruby logger = Logger.new(STDOUT) stderr_logger = Logger.new(STDER)) logger.extend(AS::Logger.broadcast(stderr_logger)) logger.level = DEBUG # This modifies the level on all other loggers logger.formatter = … # Modified the formatter on all other loggers ``` To keep the contract unchanged on what Rails.logger returns, the new BroadcastLogger class implement duck typing with all methods that has the vanilla Ruby Logger class. It's a simple and boring PORO that keeps an array of all the loggers that are part of the broadcast and iterate over whenever a log is sent. Now, users can access all loggers inside the broadcast and modify them on the fly. They can also remove any logger from the broadcast at any time. ```ruby # Before stdout_logger = Logger.new(STDOUT) stderr_logger = Logger.new(STDER) file_logger = Logger.new(“development.log”) stdout_logger.extend(AS::Logger.broadcast(stderr_logger)) stdout_logger.extend(AS::Logger.broadcast(file_logger)) # After broadcast = BroadcastLogger.new(stdout_logger, stderr_logger, file_logger) ``` I also think that now, it should be more clear for users that the broadcast sole job is to pass everything to the whole loggers in the broadcast. So there should be no surprise that all loggers in the broadcast get their level modified when they call `broadcast.level = DEBUG` . It’s also easier to wrap your head around more complex setup such as broadcasting logs to another broadcast: `broadcast.broadcast_to(stdout_logger, other_broadcast)`
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# frozen_string_literal: true | ||
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module ActiveSupport | ||
# = Active Support Broadcast Logger | ||
# | ||
# The Broadcast logger is a logger used to write messages to multiple IO. It is commonly used | ||
# in development to display messages on STDOUT and also write them to a file (development.log). | ||
# With the Broadcast logger, you can broadcast your logs to a unlimited number of sinks. | ||
# | ||
# The BroadcastLogger acts as a standard logger and all methods you are used to are available. | ||
# However, all the methods on this logger will propagate and be delegated to the other loggers | ||
# that are part of the broadcast. | ||
# | ||
# Broadcasting your logs. | ||
# | ||
# stdout_logger = Logger.new(STDOUT) | ||
# file_logger = Logger.new("development.log") | ||
# broadcast = BroadcastLogger.new(stdout_logger, file_logger) | ||
# | ||
# broadcast.info("Hello world!") # Writes the log to STDOUT and the development.log file. | ||
# | ||
# Add a logger to the broadcast. | ||
# | ||
# stdout_logger = Logger.new(STDOUT) | ||
# broadcast = BroadcastLogger.new(stdout_logger) | ||
# file_logger = Logger.new("development.log") | ||
# broadcast.broadcast_to(file_logger) | ||
# | ||
# broadcast.info("Hello world!") # Writes the log to STDOUT and the development.log file. | ||
# | ||
# Modifying the log level for all broadcasted loggers. | ||
# | ||
# stdout_logger = Logger.new(STDOUT) | ||
# file_logger = Logger.new("development.log") | ||
# broadcast = BroadcastLogger.new(stdout_logger, file_logger) | ||
# | ||
# broadcast.level = Logger::FATAL # Modify the log level for the whole broadcast. | ||
# | ||
# Stop broadcasting log to a sink. | ||
# | ||
# stdout_logger = Logger.new(STDOUT) | ||
# file_logger = Logger.new("development.log") | ||
# broadcast = BroadcastLogger.new(stdout_logger, file_logger) | ||
# broadcast.info("Hello world!") # Writes the log to STDOUT and the development.log file. | ||
# | ||
# broadcast.stop_broadcasting_to(file_logger) | ||
# broadcast.info("Hello world!") # Writes the log *only* to STDOUT. | ||
# | ||
# At least one sink has to be part of the broadcast. Otherwise, your logs will not | ||
# be written anywhere. For instance: | ||
# | ||
# broadcast = BroadcastLogger.new | ||
# broadcast.info("Hello world") # The log message will appear nowhere. | ||
class BroadcastLogger | ||
include ActiveSupport::LoggerSilence | ||
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# Returns all the logger that are part of this broadcast. | ||
attr_reader :broadcasts | ||
attr_reader :formatter | ||
attr_accessor :progname | ||
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def initialize(*loggers) | ||
@broadcasts = [] | ||
@progname = "Broadcast" | ||
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broadcast_to(*loggers) | ||
end | ||
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# Add logger(s) to the broadcast. | ||
# | ||
# broadcast_logger = ActiveSupport::BroadcastLogger.new | ||
# broadcast_logger.broadcast_to(Logger.new(STDOUT), Logger.new(STDERR)) | ||
def broadcast_to(*loggers) | ||
@broadcasts.concat(loggers) | ||
end | ||
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# Remove a logger from the broadcast. When a logger is removed, messages sent to | ||
# the broadcast will no longer be written to its sink. | ||
# | ||
# sink = Logger.new(STDOUT) | ||
# broadcast_logger = ActiveSupport::BroadcastLogger.new | ||
# | ||
# broadcast_logger.stop_broadcasting_to(sink) | ||
def stop_broadcasting_to(logger) | ||
@broadcasts.delete(logger) | ||
end | ||
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def level | ||
@broadcasts.map(&:level).min | ||
end | ||
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def <<(message) | ||
dispatch { |logger| logger.<<(message) } | ||
end | ||
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def add(*args, &block) | ||
dispatch { |logger| logger.add(*args, &block) } | ||
end | ||
alias_method :log, :add | ||
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def debug(*args, &block) | ||
dispatch { |logger| logger.debug(*args, &block) } | ||
end | ||
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def info(*args, &block) | ||
dispatch { |logger| logger.info(*args, &block) } | ||
end | ||
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def warn(*args, &block) | ||
dispatch { |logger| logger.warn(*args, &block) } | ||
end | ||
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def error(*args, &block) | ||
dispatch { |logger| logger.error(*args, &block) } | ||
end | ||
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def fatal(*args, &block) | ||
dispatch { |logger| logger.fatal(*args, &block) } | ||
end | ||
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def unknown(*args, &block) | ||
dispatch { |logger| logger.unknown(*args, &block) } | ||
end | ||
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def formatter=(formatter) | ||
dispatch { |logger| logger.formatter = formatter } | ||
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@formatter = formatter | ||
end | ||
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def level=(level) | ||
dispatch { |logger| logger.level = level } | ||
end | ||
alias_method :sev_threshold=, :level= | ||
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def local_level=(level) | ||
dispatch do |logger| | ||
logger.local_level = level if logger.respond_to?(:local_level=) | ||
end | ||
end | ||
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def close | ||
dispatch { |logger| logger.close } | ||
end | ||
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# +True+ if the log level allows entries with severity Logger::DEBUG to be written | ||
# to at least one broadcast. +False+ otherwise. | ||
def debug? | ||
@broadcasts.any? { |logger| logger.debug? } | ||
end | ||
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# Sets the log level to Logger::DEBUG for the whole broadcast. | ||
def debug! | ||
dispatch { |logger| logger.debug! } | ||
end | ||
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# +True+ if the log level allows entries with severity Logger::INFO to be written | ||
# to at least one broadcast. +False+ otherwise. | ||
def info? | ||
@broadcasts.any? { |logger| logger.info? } | ||
end | ||
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# Sets the log level to Logger::INFO for the whole broadcast. | ||
def info! | ||
dispatch { |logger| logger.info! } | ||
end | ||
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# +True+ if the log level allows entries with severity Logger::WARN to be written | ||
# to at least one broadcast. +False+ otherwise. | ||
def warn? | ||
@broadcasts.any? { |logger| logger.warn? } | ||
end | ||
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# Sets the log level to Logger::WARN for the whole broadcast. | ||
def warn! | ||
dispatch { |logger| logger.warn! } | ||
end | ||
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# +True+ if the log level allows entries with severity Logger::ERROR to be written | ||
# to at least one broadcast. +False+ otherwise. | ||
def error? | ||
@broadcasts.any? { |logger| logger.error? } | ||
end | ||
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# Sets the log level to Logger::ERROR for the whole broadcast. | ||
def error! | ||
dispatch { |logger| logger.error! } | ||
end | ||
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# +True+ if the log level allows entries with severity Logger::FATAL to be written | ||
# to at least one broadcast. +False+ otherwise. | ||
def fatal? | ||
@broadcasts.any? { |logger| logger.fatal? } | ||
end | ||
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# Sets the log level to Logger::FATAL for the whole broadcast. | ||
def fatal! | ||
dispatch { |logger| logger.fatal! } | ||
end | ||
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private | ||
def dispatch(&block) | ||
@broadcasts.each { |logger| block.call(logger) } | ||
end | ||
end | ||
end |
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