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cache.rb
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cache.rb
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require 'logger'
require 'sprockets/digest_utils'
module Sprockets
# Public: Wrapper interface to backend cache stores. Ensures a consistent API
# even when the backend uses get/set or read/write.
#
# Public cache interface
#
# Always assign the backend store instance to Environment#cache=.
#
# environment.cache = Sprockets::Cache::MemoryStore.new(1000)
#
# Environment#cache will always return a wrapped Cache interface. See the
# methods marked public on this class.
#
#
# Backend cache interface
#
# The Backend cache store must implement two methods.
#
# get(key)
#
# key - An opaque String with a length less than 250 characters.
#
# Returns an JSON serializable object.
#
# set(key, value)
#
# Will only be called once per key. Setting a key "foo" with value "bar",
# then later key "foo" with value "baz" is an undefined behavior.
#
# key - An opaque String with a length less than 250 characters.
# value - A JSON serializable object.
#
# Returns argument value.
#
class Cache
# Builtin cache stores.
autoload :FileStore, 'sprockets/cache/file_store'
autoload :MemoryStore, 'sprockets/cache/memory_store'
autoload :NullStore, 'sprockets/cache/null_store'
# Internal: Cache key version for this class. Rarely should have to change
# unless the cache format radically changes. Will be bump on major version
# releases though.
VERSION = '3.0'
def self.default_logger
logger = Logger.new($stderr)
logger.level = Logger::FATAL
logger
end
# Internal: Wrap a backend cache store.
#
# Always assign a backend cache store instance to Environment#cache= and
# use Environment#cache to retreive a wrapped interface.
#
# cache - A compatible backend cache store instance.
def initialize(cache = nil, logger = self.class.default_logger)
@cache_wrapper = get_cache_wrapper(cache)
@fetch_cache = Cache::MemoryStore.new
@logger = logger
end
# Public: Prefer API to retrieve and set values in the cache store.
#
# key - JSON serializable key
# block -
# Must return a consistent JSON serializable object for the given key.
#
# Examples
#
# cache.fetch("foo") { "bar" }
#
# Returns a JSON serializable object.
def fetch(key)
start = Time.now.to_f
expanded_key = expand_key(key)
value = @fetch_cache.get(expanded_key)
if value.nil?
value = @cache_wrapper.get(expanded_key)
if value.nil?
value = yield
@cache_wrapper.set(expanded_key, value)
@logger.debug do
ms = "(#{((Time.now.to_f - start) * 1000).to_i}ms)"
"Sprockets Cache miss #{peek_key(key)} #{ms}"
end
end
@fetch_cache.set(expanded_key, value)
end
value
end
# Public: Low level API to retrieve item directly from the backend cache
# store.
#
# This API may be used publicly, but may have undefined behavior
# depending on the backend store being used. Prefer the
# Cache#fetch API over using this.
#
# key - JSON serializable key
# local - Check local cache first (default: false)
#
# Returns a JSON serializable object or nil if there was a cache miss.
def get(key, local = false)
expanded_key = expand_key(key)
if local && value = @fetch_cache.get(expanded_key)
return value
end
value = @cache_wrapper.get(expanded_key)
@fetch_cache.set(expanded_key, value) if local
value
end
# Public: Low level API to set item directly to the backend cache store.
#
# This API may be used publicly, but may have undefined behavior
# depending on the backend store being used. Prefer the
# Cache#fetch API over using this.
#
# key - JSON serializable key
# value - A consistent JSON serializable object for the given key. Setting
# a different value for the given key has undefined behavior.
# local - Set on local cache (default: false)
#
# Returns the value argument.
def set(key, value, local = false)
expanded_key = expand_key(key)
@fetch_cache.set(expanded_key, value) if local
@cache_wrapper.set(expanded_key, value)
end
# Public: Pretty inspect
#
# Returns String.
def inspect
"#<#{self.class} local=#{@fetch_cache.inspect} store=#{@cache_wrapper.cache.inspect}>"
end
private
# Internal: Expand object cache key into a short String key.
#
# The String should be under 250 characters so its compatible with
# Memcache.
#
# key - JSON serializable key
#
# Returns a String with a length less than 250 characters.
def expand_key(key)
digest_key = DigestUtils.pack_urlsafe_base64digest(DigestUtils.digest(key))
namespace = digest_key[0, 2]
"sprockets/v#{VERSION}/#{namespace}/#{digest_key}"
end
PEEK_SIZE = 100
# Internal: Show first 100 characters of cache key for logging purposes.
#
# Returns a String with a length less than 100 characters.
def peek_key(key)
case key
when Integer
key.to_s
when String
key[0, PEEK_SIZE].inspect
when Array
str = []
key.each { |k| str << peek_key(k) }
str.join(':')[0, PEEK_SIZE]
else
peek_key(DigestUtils.pack_urlsafe_base64digest(DigestUtils.digest(key)))
end
end
def get_cache_wrapper(cache)
if cache.is_a?(Cache)
cache
# `Cache#get(key)` for Memcache
elsif cache.respond_to?(:get)
GetWrapper.new(cache)
# `Cache#[key]` so `Hash` can be used
elsif cache.respond_to?(:[])
HashWrapper.new(cache)
# `Cache#read(key)` for `ActiveSupport::Cache` support
elsif cache.respond_to?(:read)
ReadWriteWrapper.new(cache)
else
cache = Sprockets::Cache::NullStore.new
GetWrapper.new(cache)
end
end
class Wrapper < Struct.new(:cache)
end
class GetWrapper < Wrapper
def get(key)
cache.get(key)
end
def set(key, value)
cache.set(key, value)
end
end
class HashWrapper < Wrapper
def get(key)
cache[key]
end
def set(key, value)
cache[key] = value
end
end
class ReadWriteWrapper < Wrapper
def get(key)
cache.read(key)
end
def set(key, value)
cache.write(key, value)
end
end
end
end