diff options
Diffstat (limited to 'activesupport/lib/active_support/cache.rb')
| -rw-r--r-- | activesupport/lib/active_support/cache.rb | 472 |
1 files changed, 299 insertions, 173 deletions
diff --git a/activesupport/lib/active_support/cache.rb b/activesupport/lib/active_support/cache.rb index 5011014e96..e8518645d9 100644 --- a/activesupport/lib/active_support/cache.rb +++ b/activesupport/lib/active_support/cache.rb @@ -1,29 +1,29 @@ -require 'benchmark' -require 'zlib' -require 'active_support/core_ext/array/extract_options' -require 'active_support/core_ext/array/wrap' -require 'active_support/core_ext/benchmark' -require 'active_support/core_ext/module/attribute_accessors' -require 'active_support/core_ext/numeric/bytes' -require 'active_support/core_ext/numeric/time' -require 'active_support/core_ext/object/to_param' -require 'active_support/core_ext/string/inflections' -require 'active_support/core_ext/string/strip' +# frozen_string_literal: true + +require "zlib" +require "active_support/core_ext/array/extract_options" +require "active_support/core_ext/array/wrap" +require "active_support/core_ext/module/attribute_accessors" +require "active_support/core_ext/numeric/bytes" +require "active_support/core_ext/numeric/time" +require "active_support/core_ext/object/to_param" +require "active_support/core_ext/string/inflections" module ActiveSupport # See ActiveSupport::Cache::Store for documentation. module Cache - autoload :FileStore, 'active_support/cache/file_store' - autoload :MemoryStore, 'active_support/cache/memory_store' - autoload :MemCacheStore, 'active_support/cache/mem_cache_store' - autoload :NullStore, 'active_support/cache/null_store' + autoload :FileStore, "active_support/cache/file_store" + autoload :MemoryStore, "active_support/cache/memory_store" + autoload :MemCacheStore, "active_support/cache/mem_cache_store" + autoload :NullStore, "active_support/cache/null_store" + autoload :RedisCacheStore, "active_support/cache/redis_cache_store" # These options mean something to all cache implementations. Individual cache # implementations may support additional options. UNIVERSAL_OPTIONS = [:namespace, :compress, :compress_threshold, :expires_in, :race_condition_ttl] module Strategy - autoload :LocalCache, 'active_support/cache/strategy/local_cache' + autoload :LocalCache, "active_support/cache/strategy/local_cache" end class << self @@ -73,12 +73,12 @@ module ActiveSupport # each of elements in the array will be turned into parameters/keys and # concatenated into a single key. For example: # - # expand_cache_key([:foo, :bar]) # => "foo/bar" - # expand_cache_key([:foo, :bar], "namespace") # => "namespace/foo/bar" + # ActiveSupport::Cache.expand_cache_key([:foo, :bar]) # => "foo/bar" + # ActiveSupport::Cache.expand_cache_key([:foo, :bar], "namespace") # => "namespace/foo/bar" # # The +key+ argument can also respond to +cache_key+ or +to_param+. def expand_cache_key(key, namespace = nil) - expanded_cache_key = namespace ? "#{namespace}/" : "" + expanded_cache_key = (namespace ? "#{namespace}/" : "").dup if prefix = ENV["RAILS_CACHE_ID"] || ENV["RAILS_APP_VERSION"] expanded_cache_key << "#{prefix}/" @@ -91,16 +91,19 @@ module ActiveSupport private def retrieve_cache_key(key) case - when key.respond_to?(:cache_key) then key.cache_key - when key.is_a?(Array) then key.map { |element| retrieve_cache_key(element) }.to_param - when key.respond_to?(:to_a) then retrieve_cache_key(key.to_a) - else key.to_param + when key.respond_to?(:cache_key_with_version) then key.cache_key_with_version + when key.respond_to?(:cache_key) then key.cache_key + when key.is_a?(Array) then key.map { |element| retrieve_cache_key(element) }.to_param + when key.respond_to?(:to_a) then retrieve_cache_key(key.to_a) + else key.to_param end.to_s end # Obtains the specified cache store class, given the name of the +store+. # Raises an error when the store class cannot be found. def retrieve_store_class(store) + # require_relative cannot be used here because the class might be + # provided by another gem, like redis-activesupport for example. require "active_support/cache/#{store}" rescue LoadError => e raise "Could not find cache store adapter for #{store} (#{e})" @@ -146,32 +149,48 @@ module ActiveSupport # cache.namespace = -> { @last_mod_time } # Set the namespace to a variable # @last_mod_time = Time.now # Invalidate the entire cache by changing namespace # - # Caches can also store values in a compressed format to save space and - # reduce time spent sending data. Since there is overhead, values must be - # large enough to warrant compression. To turn on compression either pass - # <tt>compress: true</tt> in the initializer or as an option to +fetch+ - # or +write+. To specify the threshold at which to compress values, set the - # <tt>:compress_threshold</tt> option. The default threshold is 16K. + # Cached data larger than 1kB are compressed by default. To turn off + # compression, pass <tt>compress: false</tt> to the initializer or to + # individual +fetch+ or +write+ method calls. The 1kB compression + # threshold is configurable with the <tt>:compress_threshold</tt> option, + # specified in bytes. class Store - cattr_accessor :logger, :instance_writer => true + cattr_accessor :logger, instance_writer: true attr_reader :silence, :options alias :silence? :silence - # Create a new cache. The options will be passed to any write method calls + class << self + private + def retrieve_pool_options(options) + {}.tap do |pool_options| + pool_options[:size] = options.delete(:pool_size) if options[:pool_size] + pool_options[:timeout] = options.delete(:pool_timeout) if options[:pool_timeout] + end + end + + def ensure_connection_pool_added! + require "connection_pool" + rescue LoadError => e + $stderr.puts "You don't have connection_pool installed in your application. Please add it to your Gemfile and run bundle install" + raise e + end + end + + # Creates a new cache. The options will be passed to any write method calls # except for <tt>:namespace</tt> which can be used to set the global # namespace for the cache. def initialize(options = nil) @options = options ? options.dup : {} end - # Silence the logger. + # Silences the logger. def silence! @silence = true self end - # Silence the logger within a block. + # Silences the logger within a block. def mute previous_silence, @silence = defined?(@silence) && @silence, true yield @@ -198,13 +217,27 @@ module ActiveSupport # cache.fetch('city') # => "Duckburgh" # # You may also specify additional options via the +options+ argument. - # Setting <tt>force: true</tt> will force a cache miss: + # Setting <tt>force: true</tt> forces a cache "miss," meaning we treat + # the cache value as missing even if it's present. Passing a block is + # required when +force+ is true so this always results in a cache write. # # cache.write('today', 'Monday') - # cache.fetch('today', force: true) # => nil + # cache.fetch('today', force: true) { 'Tuesday' } # => 'Tuesday' + # cache.fetch('today', force: true) # => ArgumentError # - # Setting <tt>:compress</tt> will store a large cache entry set by the call - # in a compressed format. + # The +:force+ option is useful when you're calling some other method to + # ask whether you should force a cache write. Otherwise, it's clearer to + # just call <tt>Cache#write</tt>. + # + # Setting <tt>skip_nil: true</tt> will not cache nil result: + # + # cache.fetch('foo') { nil } + # cache.fetch('bar', skip_nil: true) { nil } + # cache.exist?('foo') # => true + # cache.exist?('bar') # => false + # + # + # Setting <tt>compress: false</tt> disables compression of the cache entry. # # Setting <tt>:expires_in</tt> will set an expiration time on the cache. # All caches support auto-expiring content after a specified number of @@ -215,6 +248,10 @@ module ActiveSupport # cache = ActiveSupport::Cache::MemoryStore.new(expires_in: 5.minutes) # cache.write(key, value, expires_in: 1.minute) # Set a lower value for one entry # + # Setting <tt>:version</tt> verifies the cache stored under <tt>name</tt> + # is of the same version. nil is returned on mismatches despite contents. + # This feature is used to support recyclable cache keys. + # # Setting <tt>:race_condition_ttl</tt> is very useful in situations where # a cache entry is used very frequently and is under heavy load. If a # cache expires and due to heavy load several different processes will try @@ -243,22 +280,23 @@ module ActiveSupport # sleep 60 # # Thread.new do - # val_1 = cache.fetch('foo', race_condition_ttl: 10) do + # val_1 = cache.fetch('foo', race_condition_ttl: 10.seconds) do # sleep 1 # 'new value 1' # end # end # # Thread.new do - # val_2 = cache.fetch('foo', race_condition_ttl: 10) do + # val_2 = cache.fetch('foo', race_condition_ttl: 10.seconds) do # 'new value 2' # end # end # - # # val_1 => "new value 1" - # # val_2 => "original value" - # # sleep 10 # First thread extend the life of cache by another 10 seconds - # # cache.fetch('foo') => "new value 1" + # cache.fetch('foo') # => "original value" + # sleep 10 # First thread extended the life of cache by another 10 seconds + # cache.fetch('foo') # => "new value 1" + # val_1 # => "new value 1" + # val_2 # => "original value" # # Other options will be handled by the specific cache store implementation. # Internally, #fetch calls #read_entry, and calls #write_entry on a cache @@ -278,39 +316,52 @@ module ActiveSupport options = merged_options(options) key = normalize_key(name, options) + entry = nil instrument(:read, name, options) do |payload| cached_entry = read_entry(key, options) unless options[:force] - payload[:super_operation] = :fetch if payload entry = handle_expired_entry(cached_entry, key, options) + entry = nil if entry && entry.mismatched?(normalize_version(name, options)) + payload[:super_operation] = :fetch if payload + payload[:hit] = !!entry if payload + end - if entry - payload[:hit] = true if payload - get_entry_value(entry, name, options) - else - payload[:hit] = false if payload - save_block_result_to_cache(name, options) { |_name| yield _name } - end + if entry + get_entry_value(entry, name, options) + else + save_block_result_to_cache(name, options) { |_name| yield _name } end + elsif options && options[:force] + raise ArgumentError, "Missing block: Calling `Cache#fetch` with `force: true` requires a block." else read(name, options) end end - # Fetches data from the cache, using the given key. If there is data in + # Reads data from the cache, using the given key. If there is data in # the cache with the given key, then that data is returned. Otherwise, # +nil+ is returned. # + # Note, if data was written with the <tt>:expires_in</tt> or + # <tt>:version</tt> options, both of these conditions are applied before + # the data is returned. + # # Options are passed to the underlying cache implementation. def read(name, options = nil) options = merged_options(options) - key = normalize_key(name, options) + key = normalize_key(name, options) + version = normalize_version(name, options) + instrument(:read, name, options) do |payload| entry = read_entry(key, options) + if entry if entry.expired? delete_entry(key, options) payload[:hit] = false if payload nil + elsif entry.mismatched?(version) + payload[:hit] = false if payload + nil else payload[:hit] = true if payload entry.value @@ -322,7 +373,7 @@ module ActiveSupport end end - # Read multiple values at once from the cache. Options can be passed + # Reads multiple values at once from the cache. Options can be passed # in the last argument. # # Some cache implementation may optimize this method. @@ -332,20 +383,23 @@ module ActiveSupport options = names.extract_options! options = merged_options(options) - instrument_multi(:read, names, options) do |payload| - results = {} - names.each do |name| - key = normalize_key(name, options) - entry = read_entry(key, options) - if entry - if entry.expired? - delete_entry(key, options) - else - results[name] = entry.value - end - end + instrument :read_multi, names, options do |payload| + read_multi_entries(names, options).tap do |results| + payload[:hits] = results.keys end - results + end + end + + # Cache Storage API to write multiple values at once. + def write_multi(hash, options = nil) + options = merged_options(options) + + instrument :write_multi, hash, options do |payload| + entries = hash.each_with_object({}) do |(name, value), memo| + memo[normalize_key(name, options)] = Entry.new(value, options.merge(version: normalize_version(name, options))) + end + + write_multi_entries entries, options end end @@ -353,8 +407,9 @@ module ActiveSupport # the cache with the given keys, then that data is returned. Otherwise, # the supplied block is called for each key for which there was no data, # and the result will be written to the cache and returned. - # - # Options are passed to the underlying cache implementation. + # Therefore, you need to pass a block that returns the data to be written + # to the cache. If you do not want to write the cache when the cache is + # not found, use #read_multi. # # Returns a hash with the data for each of the names. For example: # @@ -365,16 +420,35 @@ module ActiveSupport # # => { "bim" => "bam", # # "unknown_key" => "Fallback value for key: unknown_key" } # + # Options are passed to the underlying cache implementation. For example: + # + # cache.fetch_multi("fizz", expires_in: 5.seconds) do |key| + # "buzz" + # end + # # => {"fizz"=>"buzz"} + # cache.read("fizz") + # # => "buzz" + # sleep(6) + # cache.read("fizz") + # # => nil def fetch_multi(*names) + raise ArgumentError, "Missing block: `Cache#fetch_multi` requires a block." unless block_given? + options = names.extract_options! options = merged_options(options) - results = read_multi(*names, options) - names.each_with_object({}) do |name, memo| - memo[name] = results.fetch(name) do - value = yield name - write(name, value, options) - value + instrument :read_multi, names, options do |payload| + read_multi_entries(names, options).tap do |results| + payload[:hits] = results.keys + payload[:super_operation] = :fetch_multi + + writes = {} + + (names - results.keys).each do |name| + results[name] = writes[name] = yield(name) + end + + write_multi writes, options end end end @@ -386,7 +460,7 @@ module ActiveSupport options = merged_options(options) instrument(:write, name, options) do - entry = Entry.new(value, options) + entry = Entry.new(value, options.merge(version: normalize_version(name, options))) write_entry(normalize_key(name, options), entry, options) end end @@ -410,11 +484,11 @@ module ActiveSupport instrument(:exist?, name) do entry = read_entry(normalize_key(name, options), options) - (entry && !entry.expired?) || false + (entry && !entry.expired? && !entry.mismatched?(normalize_version(name, options))) || false end end - # Delete all entries with keys matching the pattern. + # Deletes all entries with keys matching the pattern. # # Options are passed to the underlying cache implementation. # @@ -423,7 +497,7 @@ module ActiveSupport raise NotImplementedError.new("#{self.class.name} does not support delete_matched") end - # Increment an integer value in the cache. + # Increments an integer value in the cache. # # Options are passed to the underlying cache implementation. # @@ -432,7 +506,7 @@ module ActiveSupport raise NotImplementedError.new("#{self.class.name} does not support increment") end - # Decrement an integer value in the cache. + # Decrements an integer value in the cache. # # Options are passed to the underlying cache implementation. # @@ -441,7 +515,7 @@ module ActiveSupport raise NotImplementedError.new("#{self.class.name} does not support decrement") end - # Cleanup the cache by removing expired entries. + # Cleanups the cache by removing expired entries. # # Options are passed to the underlying cache implementation. # @@ -450,7 +524,7 @@ module ActiveSupport raise NotImplementedError.new("#{self.class.name} does not support cleanup") end - # Clear the entire cache. Be careful with this method since it could + # Clears the entire cache. Be careful with this method since it could # affect other processes if shared cache is being used. # # The options hash is passed to the underlying cache implementation. @@ -460,16 +534,16 @@ module ActiveSupport raise NotImplementedError.new("#{self.class.name} does not support clear") end - protected - # Add the namespace defined in the options to a pattern designed to + private + # Adds the namespace defined in the options to a pattern designed to # match keys. Implementations that support delete_matched should call # this method to translate a pattern that matches names into one that # matches namespaced keys. - def key_matcher(pattern, options) + def key_matcher(pattern, options) # :doc: prefix = options[:namespace].is_a?(Proc) ? options[:namespace].call : options[:namespace] if prefix source = pattern.source - if source.start_with?('^') + if source.start_with?("^") source = source[1, source.length] else source = ".*#{source[0, source.length]}" @@ -480,89 +554,135 @@ module ActiveSupport end end - # Read an entry from the cache implementation. Subclasses must implement + # Reads an entry from the cache implementation. Subclasses must implement # this method. - def read_entry(key, options) # :nodoc: + def read_entry(key, options) raise NotImplementedError.new end - # Write an entry to the cache implementation. Subclasses must implement + # Writes an entry to the cache implementation. Subclasses must implement # this method. - def write_entry(key, entry, options) # :nodoc: + def write_entry(key, entry, options) raise NotImplementedError.new end - # Delete an entry from the cache implementation. Subclasses must + # Reads multiple entries from the cache implementation. Subclasses MAY # implement this method. - def delete_entry(key, options) # :nodoc: + def read_multi_entries(names, options) + results = {} + names.each do |name| + key = normalize_key(name, options) + version = normalize_version(name, options) + entry = read_entry(key, options) + + if entry + if entry.expired? + delete_entry(key, options) + elsif entry.mismatched?(version) + # Skip mismatched versions + else + results[name] = entry.value + end + end + end + results + end + + # Writes multiple entries to the cache implementation. Subclasses MAY + # implement this method. + def write_multi_entries(hash, options) + hash.each do |key, entry| + write_entry key, entry, options + end + end + + # Deletes an entry from the cache implementation. Subclasses must + # implement this method. + def delete_entry(key, options) raise NotImplementedError.new end - private - # Merge the default options with ones specific to a method call. - def merged_options(call_options) # :nodoc: + # Merges the default options with ones specific to a method call. + def merged_options(call_options) if call_options - options.merge(call_options) + if options.empty? + call_options + else + options.merge(call_options) + end else - options.dup + options end end - # Expand key to be a consistent string value. Invoke +cache_key+ if + # Expands and namespaces the cache key. May be overridden by + # cache stores to do additional normalization. + def normalize_key(key, options = nil) + namespace_key expanded_key(key), options + end + + # Prefix the key with a namespace string: + # + # namespace_key 'foo', namespace: 'cache' + # # => 'cache:foo' + # + # With a namespace block: + # + # namespace_key 'foo', namespace: -> { 'cache' } + # # => 'cache:foo' + def namespace_key(key, options = nil) + options = merged_options(options) + namespace = options[:namespace] + + if namespace.respond_to?(:call) + namespace = namespace.call + end + + if namespace + "#{namespace}:#{key}" + else + key + end + end + + # Expands key to be a consistent string value. Invokes +cache_key+ if # object responds to +cache_key+. Otherwise, +to_param+ method will be # called. If the key is a Hash, then keys will be sorted alphabetically. - def expanded_key(key) # :nodoc: + def expanded_key(key) return key.cache_key.to_s if key.respond_to?(:cache_key) case key when Array if key.size > 1 - key = key.collect{|element| expanded_key(element)} + key = key.collect { |element| expanded_key(element) } else - key = key.first + key = expanded_key(key.first) end when Hash - key = key.sort_by { |k,_| k.to_s }.collect{|k,v| "#{k}=#{v}"} + key = key.sort_by { |k, _| k.to_s }.collect { |k, v| "#{k}=#{v}" } end key.to_param end - # Prefix a key with the namespace. Namespace and key will be delimited - # with a colon. - def normalize_key(key, options) - key = expanded_key(key) - namespace = options[:namespace] if options - prefix = namespace.is_a?(Proc) ? namespace.call : namespace - key = "#{prefix}:#{key}" if prefix - key + def normalize_version(key, options = nil) + (options && options[:version].try(:to_param)) || expanded_version(key) end - def namespaced_key(*args) - ActiveSupport::Deprecation.warn(<<-MESSAGE.strip_heredoc) - `namespaced_key` is deprecated and will be removed from Rails 5.1. - Please use `normalize_key` which will return a fully resolved key. - MESSAGE - normalize_key(*args) + def expanded_version(key) + case + when key.respond_to?(:cache_version) then key.cache_version.to_param + when key.is_a?(Array) then key.map { |element| expanded_version(element) }.compact.to_param + when key.respond_to?(:to_a) then expanded_version(key.to_a) + end end def instrument(operation, key, options = nil) log { "Cache #{operation}: #{normalize_key(key, options)}#{options.blank? ? "" : " (#{options.inspect})"}" } - payload = { :key => key } - payload.merge!(options) if options.is_a?(Hash) - ActiveSupport::Notifications.instrument("cache_#{operation}.active_support", payload){ yield(payload) } - end - - def instrument_multi(operation, keys, options = nil) - log do - formatted_keys = keys.map { |k| "- #{k}" }.join("\n") - "Caches multi #{operation}:\n#{formatted_keys}#{options.blank? ? "" : " (#{options.inspect})"}" - end - - payload = { key: keys } + payload = { key: key } payload.merge!(options) if options.is_a?(Hash) - ActiveSupport::Notifications.instrument("cache_#{operation}_multi.active_support", payload) { yield(payload) } + ActiveSupport::Notifications.instrument("cache_#{operation}.active_support", payload) { yield(payload) } end def log @@ -577,7 +697,7 @@ module ActiveSupport # When an entry has a positive :race_condition_ttl defined, put the stale entry back into the cache # for a brief period while the entry is being recalculated. entry.expires_at = Time.now + race_ttl - write_entry(key, entry, :expires_in => race_ttl * 2) + write_entry(key, entry, expires_in: race_ttl * 2) else delete_entry(key, options) end @@ -587,49 +707,52 @@ module ActiveSupport end def get_entry_value(entry, name, options) - instrument(:fetch_hit, name, options) { |payload| } + instrument(:fetch_hit, name, options) { } entry.value end def save_block_result_to_cache(name, options) - result = instrument(:generate, name, options) do |payload| + result = instrument(:generate, name, options) do yield(name) end - write(name, result, options) + write(name, result, options) unless result.nil? && options[:skip_nil] result end end - # This class is used to represent cache entries. Cache entries have a value and an optional - # expiration time. The expiration time is used to support the :race_condition_ttl option - # on the cache. + # This class is used to represent cache entries. Cache entries have a value, an optional + # expiration time, and an optional version. The expiration time is used to support the :race_condition_ttl option + # on the cache. The version is used to support the :version option on the cache for rejecting + # mismatches. # # Since cache entries in most instances will be serialized, the internals of this class are highly optimized # using short instance variable names that are lazily defined. class Entry # :nodoc: - DEFAULT_COMPRESS_LIMIT = 16.kilobytes - - # Create a new cache entry for the specified value. Options supported are - # +:compress+, +:compress_threshold+, and +:expires_in+. - def initialize(value, options = {}) - if should_compress?(value, options) - @value = compress(value) - @compressed = true - else - @value = value - end + attr_reader :version + + DEFAULT_COMPRESS_LIMIT = 1.kilobyte + # Creates a new cache entry for the specified value. Options supported are + # +:compress+, +:compress_threshold+, +:version+ and +:expires_in+. + def initialize(value, compress: true, compress_threshold: DEFAULT_COMPRESS_LIMIT, version: nil, expires_in: nil, **) + @value = value + @version = version @created_at = Time.now.to_f - @expires_in = options[:expires_in] - @expires_in = @expires_in.to_f if @expires_in + @expires_in = expires_in && expires_in.to_f + + compress!(compress_threshold) if compress end def value compressed? ? uncompress(@value) : @value end - # Check if the entry is expired. The +expires_in+ parameter can override + def mismatched?(version) + @version && version && @version != version + end + + # Checks if the entry is expired. The +expires_in+ parameter can override # the value set when the entry was created. def expired? @expires_in && @created_at + @expires_in <= Time.now.to_f @@ -650,21 +773,17 @@ module ActiveSupport # Returns the size of the cached value. This could be less than # <tt>value.size</tt> if the data is compressed. def size - if defined?(@s) - @s + case value + when NilClass + 0 + when String + @value.bytesize else - case value - when NilClass - 0 - when String - @value.bytesize - else - @s = Marshal.dump(@value).bytesize - end + @s ||= Marshal.dump(@value).bytesize end end - # Duplicate the value in a class. This is used by cache implementations that don't natively + # Duplicates the value in a class. This is used by cache implementations that don't natively # serialize entries to protect against accidental cache modifications. def dup_value! if @value && !compressed? && !(@value.is_a?(Numeric) || @value == true || @value == false) @@ -677,23 +796,30 @@ module ActiveSupport end private - def should_compress?(value, options) - if value && options[:compress] - compress_threshold = options[:compress_threshold] || DEFAULT_COMPRESS_LIMIT - serialized_value_size = (value.is_a?(String) ? value : Marshal.dump(value)).bytesize - - return true if serialized_value_size >= compress_threshold + def compress!(compress_threshold) + case @value + when nil, true, false, Numeric + uncompressed_size = 0 + when String + uncompressed_size = @value.bytesize + else + serialized = Marshal.dump(@value) + uncompressed_size = serialized.bytesize end - false - end + if uncompressed_size >= compress_threshold + serialized ||= Marshal.dump(@value) + compressed = Zlib::Deflate.deflate(serialized) - def compressed? - defined?(@compressed) ? @compressed : false + if compressed.bytesize < uncompressed_size + @value = compressed + @compressed = true + end + end end - def compress(value) - Zlib::Deflate.deflate(Marshal.dump(value)) + def compressed? + defined?(@compressed) end def uncompress(value) |