file_wrapper.rb

#
# Fluentd
#
#    Licensed under the Apache License, Version 2.0 (the "License");
#    you may not use this file except in compliance with the License.
#    You may obtain a copy of the License at
#
#        http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS,
#    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#    See the License for the specific language governing permissions and
#    limitations under the License.
#

module Fluent
  module FileWrapper
    def self.open(path, mode='r')
      io = WindowsFile.new(path, mode).io
      if block_given?
        v = yield io
        io.close
        v
      else
        io
      end
    end

    def self.stat(path)
      f = WindowsFile.new(path)
      s = f.stat
      f.close
      s
    end
  end

  class WindowsFile
    require 'windows/file'
    require 'windows/handle'

    include File::Constants
    include Windows::File
    include Windows::Handle

    attr_reader :io

    def initialize(path, mode='r')
      @path = path
      @io = File.open(path, mode2flags(mode))
      @file_handle = _get_osfhandle(@io.to_i)
      @io.instance_variable_set(:@file_index, self.ino)
      def @io.ino
        @file_index
      end
    end

    def close
      @io.close
      @file_handle = INVALID_HANDLE_VALUE
    end

    # To keep backward compatibility, we continue to use GetFileInformationByHandle()
    # to get file id.
    # Node that Ruby's File.stat uses GetFileInformationByHandleEx() with FileIdInfo
    # and returned value is different with above one.
    def ino
      by_handle_file_information = '\0'*(4+8+8+8+4+4+4+4+4+4)   #72bytes

      unless GetFileInformationByHandle.call(@file_handle, by_handle_file_information)
        return 0
      end

      by_handle_file_information.unpack("I11Q1")[11] # fileindex
    end

    def stat
      raise Errno::ENOENT if delete_pending
      s = File.stat(@path)
      s.instance_variable_set :@ino, self.ino
      def s.ino; @ino; end
      s
    end

    private

    def mode2flags(mode)
      # Always inject File::Constants::SHARE_DELETE
      # https://github.com/fluent/fluentd/pull/3585#issuecomment-1101502617
      # To enable SHARE_DELETE, BINARY is also required.
      # https://bugs.ruby-lang.org/issues/11218
      # https://github.com/ruby/ruby/blob/d6684f063bc53e3cab025bd39526eca3b480b5e7/win32/win32.c#L6332-L6345
      flags = BINARY | SHARE_DELETE
      case mode.delete("b")
      when "r"
        flags |= RDONLY
      when "r+"
        flags |= RDWR
      when "w"
        flags |= WRONLY | CREAT | TRUNC
      when "w+"
        flags |= RDWR | CREAT | TRUNC
      when "a"
        flags |= WRONLY | CREAT | APPEND
      when "a+"
        flags |= RDWR | CREAT | APPEND
      else
        raise Errno::EINVAL.new("Unsupported mode by Fluent::FileWrapper: #{mode}")
      end
    end

    # DeletePending is a Windows-specific file state that roughly means
    # "this file is queued for deletion, so close any open handlers"
    #
    # This flag can be retrieved via GetFileInformationByHandleEx().
    #
    # https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-getfileinformationbyhandleex
    #
    def delete_pending
      file_standard_info = 0x01
      bufsize = 1024
      buf = '\0' * bufsize

      unless GetFileInformationByHandleEx.call(@file_handle, file_standard_info, buf, bufsize)
        return false
      end

      return buf.unpack("QQICC")[3] != 0
    end
  end
end if Fluent.windows?