Class: Gem::AtomicFileWriter

Relationships & Source Files
Inherits:	Object
Defined in:	lib/rubygems/util/atomic_file_writer.rb

Class Method Summary

.open(file_name)

Write to a file atomically.
.probe_permissions_in(dir) Internal use only

Class Method Details

.open(file_name)

Write to a file atomically. Useful for situations where you don’t want other processes or threads to see half-written files.

[ GitHub ]

# File 'lib/rubygems/util/atomic_file_writer.rb', line 14


def self.open(file_name)
  temp_dir = File.dirname(file_name)
  require "tempfile" unless defined?(Tempfile)

  Tempfile.create(".#{File.basename(file_name)}", temp_dir) do |temp_file|
    temp_file.binmode
    return_value = yield temp_file
    temp_file.close

    original_permissions = if File.exist?(file_name)
      File.stat(file_name)
    else
      # If not possible, probe which are the default permissions in the
      # destination directory.
      probe_permissions_in(File.dirname(file_name))
    end

    # Set correct permissions on new file
    if original_permissions
      begin
        File.chown(original_permissions.uid, original_permissions.gid, temp_file.path)
        File.chmod(original_permissions.mode, temp_file.path)
      rescue Errno::EPERM, Errno::EACCES
        # Changing file ownership failed, moving on.
      end
    end

    # Overwrite original file with temp file
    File.rename(temp_file.path, file_name)
    return_value
  end
end

.probe_permissions_in(dir)

This method is for internal use only.

[ GitHub ]

# File 'lib/rubygems/util/atomic_file_writer.rb', line 47


def self.probe_permissions_in(dir) # :nodoc:
  basename = [
    ".permissions_check",
    Thread.current.object_id,
    Process.pid,
    rand(1_000_000),
  ].join(".")

  file_name = File.join(dir, basename)
  File.open(file_name, "w") {}
  File.stat(file_name)
rescue Errno::ENOENT
  nil
ensure
  begin
    File.unlink(file_name) if File.exist?(file_name)
  rescue SystemCallError
  end
end