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# frozen_string_literal: true # = PStore -- Transactional File Storage for Ruby Objects # # pstore.rb - # originally by matz # documentation by Kev Jackson and James Edward Gray II # improved by Hongli Lai # # See PStore for documentation. require "digest" # \PStore implements a file based persistence mechanism based on a Hash. # User code can store hierarchies of Ruby objects (values) # into the data store by name (keys). # An object hierarchy may be just a single object. # User code may later read values back from the data store # or even update data, as needed. # # The transactional behavior ensures that any changes succeed or fail together. # This can be used to ensure that the data store is not left in a transitory state, # where some values were updated but others were not. # # Behind the scenes, Ruby objects are stored to the data store file with Marshal. # That carries the usual limitations. Proc objects cannot be marshalled, # for example. # # There are three important concepts here (details at the links): # # - {Store}[rdoc-ref:PStore@The+Store]: a store is an instance of \PStore. # - {Entries}[rdoc-ref:PStore@Entries]: the store is hash-like; # each entry is the key for a stored object. # - {Transactions}[rdoc-ref:PStore@Transactions]: each transaction is a collection # of prospective changes to the store; # a transaction is defined in the block given with a call # to PStore#transaction. # # == About the Examples # # Examples on this page need a store that has known properties. # They can get a new (and populated) store by calling thus: # # example_store do |store| # # Example code using store goes here. # end # # All we really need to know about +example_store+ # is that it yields a fresh store with a known population of entries; # its implementation: # # require 'pstore' # require 'tempfile' # # Yield a pristine store for use in examples. # def example_store # # Create the store in a temporary file. # Tempfile.create do |file| # store = PStore.new(file) # # Populate the store. # store.transaction do # store[:foo] = 0 # store[:bar] = 1 # store[:baz] = 2 # end # yield store # end # end # # == The Store # # The contents of the store are maintained in a file whose path is specified # when the store is created (see PStore.new). # The objects are stored and retrieved using # module Marshal, which means that certain objects cannot be added to the store; # see {Marshal::dump}[rdoc-ref:Marshal.dump]. # # == Entries # # A store may have any number of entries. # Each entry has a key and a value, just as in a hash: # # - Key: as in a hash, the key can be (almost) any object; # see {Hash Keys}[rdoc-ref:Hash@Hash+Keys]. # You may find it convenient to keep it simple by using only # symbols or strings as keys. # - Value: the value may be any object that can be marshalled by \Marshal # (see {Marshal::dump}[rdoc-ref:Marshal.dump]) # and in fact may be a collection # (e.g., an array, a hash, a set, a range, etc). # That collection may in turn contain nested objects, # including collections, to any depth; # those objects must also be \Marshal-able. # See {Hierarchical Values}[rdoc-ref:PStore@Hierarchical+Values]. # # == Transactions # # === The Transaction Block # # The block given with a call to method #transaction# # contains a _transaction_, # which consists of calls to \PStore methods that # read from or write to the store # (that is, all \PStore methods except #transaction itself, # #path, and Pstore.new): # # example_store do |store| # store.transaction do # store.keys # => [:foo, :bar, :baz] # store[:bat] = 3 # store.keys # => [:foo, :bar, :baz, :bat] # end # end # # Execution of the transaction is deferred until the block exits, # and is executed _atomically_ (all-or-nothing): # either all transaction calls are executed, or none are. # This maintains the integrity of the store. # # Other code in the block (including even calls to #path and PStore.new) # is executed immediately, not deferred. # # The transaction block: # # - May not contain a nested call to #transaction. # - Is the only context where methods that read from or write to # the store are allowed. # # As seen above, changes in a transaction are made automatically # when the block exits. # The block may be exited early by calling method #commit or #abort. # # - Method #commit triggers the update to the store and exits the block: # # example_store do |store| # store.transaction do # store.keys # => [:foo, :bar, :baz] # store[:bat] = 3 # store.commit # fail 'Cannot get here' # end # store.transaction do # # Update was completed. # store.keys # => [:foo, :bar, :baz, :bat] # end # end # # - Method #abort discards the update to the store and exits the block: # # example_store do |store| # store.transaction do # store.keys # => [:foo, :bar, :baz] # store[:bat] = 3 # store.abort # fail 'Cannot get here' # end # store.transaction do # # Update was not completed. # store.keys # => [:foo, :bar, :baz] # end # end # # === Read-Only Transactions # # By default, a transaction allows both reading from and writing to # the store: # # store.transaction do # # Read-write transaction. # # Any code except a call to #transaction is allowed here. # end # # If argument +read_only+ is passed as +true+, # only reading is allowed: # # store.transaction(true) do # # Read-only transaction: # # Calls to #transaction, #[]=, and #delete are not allowed here. # end # # == Hierarchical Values # # The value for an entry may be a simple object (as seen above). # It may also be a hierarchy of objects nested to any depth: # # deep_store = PStore.new('deep.store') # deep_store.transaction do # array_of_hashes = [{}, {}, {}] # deep_store[:array_of_hashes] = array_of_hashes # deep_store[:array_of_hashes] # => [{}, {}, {}] # hash_of_arrays = {foo: [], bar: [], baz: []} # deep_store[:hash_of_arrays] = hash_of_arrays # deep_store[:hash_of_arrays] # => {:foo=>[], :bar=>[], :baz=>[]} # deep_store[:hash_of_arrays][:foo].push(:bat) # deep_store[:hash_of_arrays] # => {:foo=>[:bat], :bar=>[], :baz=>[]} # end # # And recall that you can use # {dig methods}[rdoc-ref:dig_methods.rdoc] # in a returned hierarchy of objects. # # == Working with the Store # # === Creating a Store # # Use method PStore.new to create a store. # The new store creates or opens its containing file: # # store = PStore.new('t.store') # # === Modifying the Store # # Use method #[]= to update or create an entry: # # example_store do |store| # store.transaction do # store[:foo] = 1 # Update. # store[:bam] = 1 # Create. # end # end # # Use method #delete to remove an entry: # # example_store do |store| # store.transaction do # store.delete(:foo) # store[:foo] # => nil # end # end # # === Retrieving Values # # Use method #fetch (allows default) or #[] (defaults to +nil+) # to retrieve an entry: # # example_store do |store| # store.transaction do # store[:foo] # => 0 # store[:nope] # => nil # store.fetch(:baz) # => 2 # store.fetch(:nope, nil) # => nil # store.fetch(:nope) # Raises exception. # end # end # # === Querying the Store # # Use method #key? to determine whether a given key exists: # # example_store do |store| # store.transaction do # store.key?(:foo) # => true # end # end # # Use method #keys to retrieve keys: # # example_store do |store| # store.transaction do # store.keys # => [:foo, :bar, :baz] # end # end # # Use method #path to retrieve the path to the store's underlying file; # this method may be called from outside a transaction block: # # store = PStore.new('t.store') # store.path # => "t.store" # # == Transaction Safety # # For transaction safety, see: # # - Optional argument +thread_safe+ at method PStore.new. # - Attribute #ultra_safe. # # Needless to say, if you're storing valuable data with \PStore, then you should # backup the \PStore file from time to time. # # == An Example Store # # require "pstore" # # # A mock wiki object. # class WikiPage # # attr_reader :page_name # # def initialize(page_name, author, contents) # @page_name = page_name # @revisions = Array.new # add_revision(author, contents) # end # # def add_revision(author, contents) # @revisions << {created: Time.now, # author: author, # contents: contents} # end # # def wiki_page_references # [@page_name] + @revisions.last[:contents].scan(/\b(?:[A-Z]+[a-z]+){2,}/) # end # # end # # # Create a new wiki page. # home_page = WikiPage.new("HomePage", "James Edward Gray II", # "A page about the JoysOfDocumentation..." ) # # wiki = PStore.new("wiki_pages.pstore") # # Update page data and the index together, or not at all. # wiki.transaction do # # Store page. # wiki[home_page.page_name] = home_page # # Create page index. # wiki[:wiki_index] ||= Array.new # # Update wiki index. # wiki[:wiki_index].push(*home_page.wiki_page_references) # end # # # Read wiki data, setting argument read_only to true. # wiki.transaction(true) do # wiki.keys.each do |key| # puts key # puts wiki[key] # end # end # class PStore VERSION = "0.1.2" RDWR_ACCESS = {mode: IO::RDWR | IO::CREAT | IO::BINARY, encoding: Encoding::ASCII_8BIT}.freeze RD_ACCESS = {mode: IO::RDONLY | IO::BINARY, encoding: Encoding::ASCII_8BIT}.freeze WR_ACCESS = {mode: IO::WRONLY | IO::CREAT | IO::TRUNC | IO::BINARY, encoding: Encoding::ASCII_8BIT}.freeze # The error type thrown by all PStore methods. class Error < StandardError end # Whether \PStore should do its best to prevent file corruptions, # even when an unlikely error (such as memory-error or filesystem error) occurs: # # - +true+: changes are posted by creating a temporary file, # writing the updated data to it, then renaming the file to the given #path. # File integrity is maintained. # Note: has effect only if the filesystem has atomic file rename # (as do POSIX platforms Linux, MacOS, FreeBSD and others). # # - +false+ (the default): changes are posted by rewinding the open file # and writing the updated data. # File integrity is maintained if the filesystem raises # no unexpected I/O error; # if such an error occurs during a write to the store, # the file may become corrupted. # attr_accessor :ultra_safe # Returns a new \PStore object. # # Argument +file+ is the path to the file in which objects are to be stored; # if the file exists, it should be one that was written by \PStore. # # path = 't.store' # store = PStore.new(path) # # A \PStore object is # {reentrant}[https://en.wikipedia.org/wiki/Reentrancy_(computing)]. # If argument +thread_safe+ is given as +true+, # the object is also thread-safe (at the cost of a small performance penalty): # # store = PStore.new(path, true) # def initialize(file, thread_safe = false) dir = File::dirname(file) unless File::directory? dir raise PStore::Error, format("directory %s does not exist", dir) end if File::exist? file and not File::readable? file raise PStore::Error, format("file %s not readable", file) end @filename = file @abort = false @ultra_safe = false @thread_safe = thread_safe @lock = Thread::Mutex.new end # Raises PStore::Error if the calling code is not in a PStore#transaction. def in_transaction raise PStore::Error, "not in transaction" unless @lock.locked? end # # Raises PStore::Error if the calling code is not in a PStore#transaction or # if the code is in a read-only PStore#transaction. # def in_transaction_wr in_transaction raise PStore::Error, "in read-only transaction" if @rdonly end private :in_transaction, :in_transaction_wr # Returns the value for the given +key+ if the key exists. # +nil+ otherwise; # if not +nil+, the returned value is an object or a hierarchy of objects: # # example_store do |store| # store.transaction do # store[:foo] # => 0 # store[:nope] # => nil # end # end # # Returns +nil+ if there is no such key. # # See also {Hierarchical Values}[rdoc-ref:PStore@Hierarchical+Values]. # # Raises an exception if called outside a transaction block. def [](key) in_transaction @table[key] end # Like #[], except that it accepts a default value for the store. # If the +key+ does not exist: # # - Raises an exception if +default+ is +PStore::Error+. # - Returns the value of +default+ otherwise: # # example_store do |store| # store.transaction do # store.fetch(:nope, nil) # => nil # store.fetch(:nope) # Raises an exception. # end # end # # Raises an exception if called outside a transaction block. def fetch(key, default=PStore::Error) in_transaction unless @table.key? key if default == PStore::Error raise PStore::Error, format("undefined key `%s'", key) else return default end end @table[key] end # Creates or replaces the value for the given +key+: # # example_store do |store| # temp.transaction do # temp[:bat] = 3 # end # end # # See also {Hierarchical Values}[rdoc-ref:PStore@Hierarchical+Values]. # # Raises an exception if called outside a transaction block. def []=(key, value) in_transaction_wr @table[key] = value end # Removes and returns the value at +key+ if it exists: # # example_store do |store| # store.transaction do # store[:bat] = 3 # store.delete(:bat) # end # end # # Returns +nil+ if there is no such key. # # Raises an exception if called outside a transaction block. def delete(key) in_transaction_wr @table.delete key end # Returns an array of the existing keys: # # example_store do |store| # store.transaction do # store.keys # => [:foo, :bar, :baz] # end # end # # Raises an exception if called outside a transaction block. # # PStore#roots is an alias for PStore#keys. def keys in_transaction @table.keys end alias roots keys # Returns +true+ if +key+ exists, +false+ otherwise: # # example_store do |store| # store.transaction do # store.key?(:foo) # => true # end # end # # Raises an exception if called outside a transaction block. # # PStore#root? is an alias for PStore#key?. def key?(key) in_transaction @table.key? key end alias root? key? # Returns the string file path used to create the store: # # store.path # => "flat.store" # def path @filename end # Exits the current transaction block, committing any changes # specified in the transaction block. # See {Committing or Aborting}[rdoc-ref:PStore@Committing+or+Aborting]. # # Raises an exception if called outside a transaction block. def commit in_transaction @abort = false throw :pstore_abort_transaction end # Exits the current transaction block, discarding any changes # specified in the transaction block. # See {Committing or Aborting}[rdoc-ref:PStore@Committing+or+Aborting]. # # Raises an exception if called outside a transaction block. def abort in_transaction @abort = true throw :pstore_abort_transaction end # Opens a transaction block for the store. # See {Transactions}[rdoc-ref:PStore@Transactions]. # # With argument +read_only+ as +false+, the block may both read from # and write to the store. # # With argument +read_only+ as +true+, the block may not include calls # to #transaction, #[]=, or #delete. # # Raises an exception if called within a transaction block. def transaction(read_only = false) # :yields: pstore value = nil if !@thread_safe raise PStore::Error, "nested transaction" unless @lock.try_lock else begin @lock.lock rescue ThreadError raise PStore::Error, "nested transaction" end end begin @rdonly = read_only @abort = false file = open_and_lock_file(@filename, read_only) if file begin @table, checksum, original_data_size = load_data(file, read_only) catch(:pstore_abort_transaction) do value = yield(self) end if !@abort && !read_only save_data(checksum, original_data_size, file) end ensure file.close end else # This can only occur if read_only == true. @table = {} catch(:pstore_abort_transaction) do value = yield(self) end end ensure @lock.unlock end value end private # Constant for relieving Ruby's garbage collector. CHECKSUM_ALGO = %w[SHA512 SHA384 SHA256 SHA1 RMD160 MD5].each do |algo| begin break Digest(algo) rescue LoadError end end EMPTY_STRING = "" EMPTY_MARSHAL_DATA = Marshal.dump({}) EMPTY_MARSHAL_CHECKSUM = CHECKSUM_ALGO.digest(EMPTY_MARSHAL_DATA) # # Open the specified filename (either in read-only mode or in # read-write mode) and lock it for reading or writing. # # The opened File object will be returned. If _read_only_ is true, # and the file does not exist, then nil will be returned. # # All exceptions are propagated. # def open_and_lock_file(filename, read_only) if read_only begin file = File.new(filename, **RD_ACCESS) begin file.flock(File::LOCK_SH) return file rescue file.close raise end rescue Errno::ENOENT return nil end else file = File.new(filename, **RDWR_ACCESS) file.flock(File::LOCK_EX) return file end end # Load the given PStore file. # If +read_only+ is true, the unmarshalled Hash will be returned. # If +read_only+ is false, a 3-tuple will be returned: the unmarshalled # Hash, a checksum of the data, and the size of the data. def load_data(file, read_only) if read_only begin table = load(file) raise Error, "PStore file seems to be corrupted." unless table.is_a?(Hash) rescue EOFError # This seems to be a newly-created file. table = {} end table else data = file.read if data.empty? # This seems to be a newly-created file. table = {} checksum = empty_marshal_checksum size = empty_marshal_data.bytesize else table = load(data) checksum = CHECKSUM_ALGO.digest(data) size = data.bytesize raise Error, "PStore file seems to be corrupted." unless table.is_a?(Hash) end data.replace(EMPTY_STRING) [table, checksum, size] end end def on_windows? is_windows = RUBY_PLATFORM =~ /mswin|mingw|bccwin|wince/ self.class.__send__(:define_method, :on_windows?) do is_windows end is_windows end def save_data(original_checksum, original_file_size, file) new_data = dump(@table) if new_data.bytesize != original_file_size || CHECKSUM_ALGO.digest(new_data) != original_checksum if @ultra_safe && !on_windows? # Windows doesn't support atomic file renames. save_data_with_atomic_file_rename_strategy(new_data, file) else save_data_with_fast_strategy(new_data, file) end end new_data.replace(EMPTY_STRING) end def save_data_with_atomic_file_rename_strategy(data, file) temp_filename = "#{@filename}.tmp.#{Process.pid}.#{rand 1000000}" temp_file = File.new(temp_filename, **WR_ACCESS) begin temp_file.flock(File::LOCK_EX) temp_file.write(data) temp_file.flush File.rename(temp_filename, @filename) rescue File.unlink(temp_file) rescue nil raise ensure temp_file.close end end def save_data_with_fast_strategy(data, file) file.rewind file.write(data) file.truncate(data.bytesize) end # This method is just a wrapped around Marshal.dump # to allow subclass overriding used in YAML::Store. def dump(table) # :nodoc: Marshal::dump(table) end # This method is just a wrapped around Marshal.load. # to allow subclass overriding used in YAML::Store. def load(content) # :nodoc: Marshal::load(content) end def empty_marshal_data EMPTY_MARSHAL_DATA end def empty_marshal_checksum EMPTY_MARSHAL_CHECKSUM end end
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