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require "dbm"
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require "json"
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require "timeout"
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#
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# `CacheStoreDatabase` acts as an interface to a persistent storage mechanism
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# residing in the `HOMEBREW_CACHE`
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#
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class CacheStoreDatabase
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# Yields the cache store database.
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# Closes the database after use if it has been loaded.
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#
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# @param [Symbol] type
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# @yield [CacheStoreDatabase] self
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def self.use(type)
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database = CacheStoreDatabase.new(type)
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return_value = yield(database)
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database.close_if_open!
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return_value
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end
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# Sets a value in the underlying database (and creates it if necessary).
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def set(key, value)
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db[key] = value
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end
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# Gets a value from the underlying database (if it already exists).
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def get(key)
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return unless created?
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db[key]
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end
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# Gets a value from the underlying database (if it already exists).
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def delete(key)
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return unless created?
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db.delete(key)
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end
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# Closes the underlying database (if it created and open).
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def close_if_open!
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@db&.close
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end
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# Returns `true` if the cache file has been created for the given `@type`
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#
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# @return [Boolean]
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def created?
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cache_path.exist?
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end
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private
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# The mode of any created files will be 0664 (that is, readable and writable
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# by the owner and the group, and readable by everyone else). Files created
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# will also be modified by the process' umask value at the time of creation:
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# https://docs.oracle.com/cd/E17276_01/html/api_reference/C/envopen.html
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DATABASE_MODE = 0664
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# Spend 5 seconds trying to read the DBM file. If it takes longer than this it
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# has likely hung or segfaulted.
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DBM_TEST_READ_TIMEOUT = 5
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# Lazily loaded database in read/write mode. If this method is called, a
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# database file with be created in the `HOMEBREW_CACHE` with name
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# corresponding to the `@type` instance variable
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#
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# @return [DBM] db
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def db
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# DBM::WRCREAT: Creates the database if it does not already exist
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@db ||= begin
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HOMEBREW_CACHE.mkpath
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if created?
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dbm_test_read_cmd = SystemCommand.new(
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ENV["HOMEBREW_RUBY_PATH"],
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args: [
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"-rdbm",
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"-e",
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"DBM.open('#{dbm_file_path}', #{DATABASE_MODE}, DBM::READER).size",
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],
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print_stderr: false,
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must_succeed: true,
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)
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dbm_test_read_success = begin
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Timeout.timeout(DBM_TEST_READ_TIMEOUT) do
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dbm_test_read_cmd.run!
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true
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end
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rescue ErrorDuringExecution, Timeout::Error
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odebug "Failed to read #{dbm_file_path}!"
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begin
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Process.kill(:KILL, dbm_test_read_cmd.pid)
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rescue Errno::ESRCH
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# Process has already terminated.
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nil
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end
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false
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end
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Utils::Analytics.report_event("dbm_test_read", dbm_test_read_success.to_s)
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cache_path.delete unless dbm_test_read_success
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end
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DBM.open(dbm_file_path, DATABASE_MODE, DBM::WRCREAT)
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end
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end
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# Creates a CacheStoreDatabase
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#
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# @param [Symbol] type
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# @return [nil]
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def initialize(type)
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@type = type
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end
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# `DBM` appends `.db` file extension to the path provided, which is why it's
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# not included
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#
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# @return [String]
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def dbm_file_path
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"#{HOMEBREW_CACHE}/#{@type}"
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end
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# The path where the database resides in the `HOMEBREW_CACHE` for the given
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# `@type`
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#
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# @return [String]
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def cache_path
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Pathname("#{dbm_file_path}.db")
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end
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end
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#
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# `CacheStore` provides methods to mutate and fetch data from a persistent
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# storage mechanism
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#
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class CacheStore
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# @param [CacheStoreDatabase] database
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# @return [nil]
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def initialize(database)
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@database = database
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end
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# Inserts new values or updates existing cached values to persistent storage
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# mechanism
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#
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# @abstract
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def update!(*)
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raise NotImplementedError
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end
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# Fetches cached values in persistent storage according to the type of data
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# stored
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#
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# @abstract
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def fetch_type(*)
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raise NotImplementedError
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end
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# Deletes data from the cache based on a condition defined in a concrete class
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#
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# @abstract
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def flush_cache!
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raise NotImplementedError
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end
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protected
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# @return [CacheStoreDatabase]
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attr_reader :database
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# DBM stores ruby objects as a ruby `String`. Hence, when fetching the data,
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# to convert the ruby string back into a ruby `Hash`, the string is converted
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# into a JSON compatible string in `ruby_hash_to_json_string`, where it may
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# later be parsed by `JSON.parse` in the `json_string_to_ruby_hash` method
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#
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# @param [Hash] ruby `Hash` to be converted to `JSON` string
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# @return [String]
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def ruby_hash_to_json_string(hash)
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hash.to_json
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end
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# @param [String] `JSON` string to be converted to ruby `Hash`
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# @return [Hash]
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def json_string_to_ruby_hash(string)
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JSON.parse(string)
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end
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end
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