Class: SymmetricEncryption::Reader

Inherits:
Object
  • Object
show all
Defined in:
lib/symmetric_encryption/reader.rb

Overview

Read from encrypted files and other IO streams

Features:

  • Decryption on the fly whilst reading files

  • Large file support by only buffering small amounts of data in memory

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(ios, buffer_size: 4096, version: nil) ⇒ Reader

Decrypt data before reading from the supplied stream

Raises:

  • (ArgumentError) 


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# File 'lib/symmetric_encryption/reader.rb', line 129

def initialize(ios, buffer_size: 4096, version: nil)
  @ios            = ios
  @buffer_size    = buffer_size
  @version        = version
  @header_present = false
  @closed         = false

  raise(ArgumentError, 'Buffer size cannot be smaller than 128') unless @buffer_size >= 128

  read_header
end

Instance Attribute Details

#pos ⇒ Object (readonly)

Return the number of bytes read so far from the input stream



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# File 'lib/symmetric_encryption/reader.rb', line 271

def pos
  @pos
end

#version ⇒ Object (readonly)

Returns the Cipher encryption version used to encrypt this file Returns nil when the header was not present in the stream and no :version

option was supplied

Note: When no header is present, the version is set to the one supplied

in the options



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# File 'lib/symmetric_encryption/reader.rb', line 162

def version
  @version
end

Class Method Details

.decrypt(source:, target:, block_size: 65_535, **args) ⇒ Object

Decrypt an entire file.

Returns [Integer] the number of unencrypted bytes written to the target file.

Params:

source: [String|IO]
  Source file_name or IOStream

target: [String|IO]
  Target file_name or IOStream

block_size: [Integer]
  Number of bytes to read into memory for each read.
  For very large files using a larger block size is faster.
  Default: 65535

Notes:

  • The file contents are streamed so that the entire file is not loaded into memory.



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# File 'lib/symmetric_encryption/reader.rb', line 100

def self.decrypt(source:, target:, block_size: 65_535, **args)
  target_ios    = target.is_a?(String) ? ::File.open(target, 'wb') : target
  bytes_written = 0
  self.open(source, **args) do |input_ios|
    bytes_written += target_ios.write(input_ios.read(block_size)) until input_ios.eof?
  end
  bytes_written
ensure
  target_ios.close if target_ios&.respond_to?(:closed?) && !target_ios.closed?
end

.empty?(file_name_or_stream) ⇒ Boolean

Returns [true|false] whether the file or stream contains any data excluding the header should it have one

Returns:

  • (Boolean) 


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# File 'lib/symmetric_encryption/reader.rb', line 113

def self.empty?(file_name_or_stream)
  open(file_name_or_stream, &:eof?)
end

.header_present?(file_name) ⇒ Boolean

Returns [true|false] whether the file contains the encryption header

Returns:

  • (Boolean) 


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# File 'lib/symmetric_encryption/reader.rb', line 118

def self.header_present?(file_name)
  ::File.open(file_name, 'rb') { |file| new(file).header_present? }
end

.open(file_name_or_stream, buffer_size: 16_384, **args, &block) ⇒ Object

Open a file for reading, or use the supplied IO Stream

Parameters:

file_name_or_stream:
  The file_name to open if a string, otherwise the stream to use
  The file or stream will be closed on completion, use .initialize to
  avoid having the stream closed automatically

buffer_size:
  Amount of data to read at a time.
  Minimum Value 128
  Default: 16384

Note: Decryption occurs before decompression

# Example: Read and decrypt a line at a time from a file SymmetricEncryption::Reader.open(‘test_file’) do |file|

file.each_line {|line| p line }

end

# Example: Read and decrypt entire file in memory # Not recommended for large files SymmetricEncryption::Reader.open(‘test_file’) {|f| f.read }

# Example: Reading a limited number of bytes at a time from the file SymmetricEncryption::Reader.open(‘test_file’) do |file|

file.read(1)
file.read(5)
file.read

end

# Example: Read and decrypt 5 bytes at a time until the end of file is reached SymmetricEncryption::Reader.open(‘test_file’) do |file|

while !file.eof? do
  file.read(5)
end

end

# Example: Read, Unencrypt and decompress data in a file SymmetricEncryption::Reader.open(‘encrypted_compressed.zip’, compress: true) do |file|

file.each_line {|line| p line }

end

# Example: Reading from a CSV file

require ‘csv’ begin

csv = CSV.new(SymmetricEncryption::Reader.open('csv_encrypted'))
csv.each {|row| p row}

ensure

csv.close if csv

end



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# File 'lib/symmetric_encryption/reader.rb', line 62

def self.open(file_name_or_stream, buffer_size: 16_384, **args, &block)
  ios = file_name_or_stream.is_a?(String) ? ::File.open(file_name_or_stream, 'rb') : file_name_or_stream

  begin
    file = new(ios, buffer_size: buffer_size, **args)
    file = Zlib::GzipReader.new(file) if !file.eof? && file.compressed?
    block ? block.call(file) : file
  ensure
    file.close if block && file && (file.respond_to?(:closed?) && !file.closed?)
  end
end

.read(file_name_or_stream, **args) ⇒ Object

Read the entire contents of a file or stream into memory.

Notes:

  • Do not use this method for reading large files.



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# File 'lib/symmetric_encryption/reader.rb', line 78

def self.read(file_name_or_stream, **args)
  self.open(file_name_or_stream, **args, &:read)
end

Instance Method Details

#close(close_child_stream = true) ⇒ Object

Close the IO Stream

Note: Also closes the passed in io stream or file

It is recommended to call Symmetric::EncryptedStream.open or Symmetric::EncryptedStream.io rather than creating an instance of Symmetric::EncryptedStream directly to ensure that the encrypted stream is closed before the stream itself is closed



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# File 'lib/symmetric_encryption/reader.rb', line 171

def close(close_child_stream = true)
  return if closed?
  @ios.close if close_child_stream
  @closed = true
end

#compressed? ⇒ Boolean

Returns whether the stream being read is compressed

Should be called before any reads are performed to determine if the file or stream is compressed.

Returns true when the header is present in the stream and it is compressed Returns false when the header is present in the stream and it is not compressed Returns nil when the header is not present in the stream

Note: The file will not be decompressed automatically when compressed.

To decompress the data automatically call SymmetricEncryption.open

Returns:

  • (Boolean) 


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# File 'lib/symmetric_encryption/reader.rb', line 152

def compressed?
  @compressed
end

#each_line(sep_string = "\n") ⇒ Object Also known as: each

ios.each(sep_string=“n”) {|line| block } => ios ios.each_line(sep_string=“n”) {|line| block } => ios Executes the block for every line in ios, where lines are separated by sep_string. ios must be opened for reading or an IOError will be raised.



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# File 'lib/symmetric_encryption/reader.rb', line 258

def each_line(sep_string = "\n")
  yield gets(sep_string) until eof?
  self
end

#eof? ⇒ Boolean

Returns whether the end of file has been reached for this stream

Returns:

  • (Boolean) 


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# File 'lib/symmetric_encryption/reader.rb', line 266

def eof?
  @read_buffer.empty? && @ios.eof?
end

#flush ⇒ Object

Flush the read stream

Needed by XLS gem



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# File 'lib/symmetric_encryption/reader.rb', line 179

def flush
  @ios.flush
end

#gets(sep_string, length = nil) ⇒ Object

Reads a single decrypted line from the file up to and including the optional sep_string. A sep_string of nil reads the entire contents of the file Returns nil on eof The stream must be opened for reading or an IOError will be raised.



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# File 'lib/symmetric_encryption/reader.rb', line 239

def gets(sep_string, length = nil)
  return read(length) if sep_string.nil?

  # Read more data until we get the sep_string
  while (index = @read_buffer.index(sep_string)).nil? && !@ios.eof?
    break if length && @read_buffer.length >= length
    read_block
  end
  index ||= -1
  data  = @read_buffer.slice!(0..index)
  @pos  += data.length
  return nil if data.empty? && eof?
  data
end

#header_present? ⇒ Boolean

After opening a file Returns [true|false] whether the file being read has an encryption header

Returns:

  • (Boolean) 


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# File 'lib/symmetric_encryption/reader.rb', line 124

def header_present?
  @header_present
end

#read(length = nil) ⇒ Object

Read from the stream and return the decrypted data See IOS#read

Reads at most length bytes from the I/O stream, or to the end of file if length is omitted or is nil. length must be a non-negative integer or nil.

At end of file, it returns nil if no more data is available, or the last remaining bytes



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# File 'lib/symmetric_encryption/reader.rb', line 197

def read(length = nil)
  data = nil
  if length
    return '' if length.zero?
    return nil if eof?
    # Read length bytes
    read_block while (@read_buffer.length < length) && !@ios.eof?
    if @read_buffer.empty?
      data = nil
    elsif @read_buffer.length > length
      data = @read_buffer.slice!(0..length - 1)
    else
      data         = @read_buffer
      @read_buffer = ''
    end
  else
    # Capture anything already in the buffer
    data         = @read_buffer
    @read_buffer = ''

    unless @ios.eof?
      # Read entire file
      buf = @ios.read || ''
      data << @stream_cipher.update(buf) if buf && !buf.empty?
      data << @stream_cipher.final
    end
  end
  @pos += data.length
  data
end

#readline(sep_string = "\n") ⇒ Object

Reads a single decrypted line from the file up to and including the optional sep_string. Raises EOFError on eof The stream must be opened for reading or an IOError will be raised.



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# File 'lib/symmetric_encryption/reader.rb', line 231

def readline(sep_string = "\n")
  gets(sep_string) || raise(EOFError, 'End of file reached when trying to read a line')
end

#rewind ⇒ Object

Rewind back to the beginning of the file



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# File 'lib/symmetric_encryption/reader.rb', line 274

def rewind
  @read_buffer = ''
  @ios.rewind
  read_header
end

#seek(amount, whence = IO::SEEK_SET) ⇒ Object

Seeks to a given offset (Integer) in the stream according to the value of whence:

IO::SEEK_CUR  | Seeks to _amount_ plus current position
--------------+----------------------------------------------------
IO::SEEK_END  | Seeks to _amount_ plus end of stream (you probably
              | want a negative value for _amount_)
--------------+----------------------------------------------------
IO::SEEK_SET  | Seeks to the absolute location given by _amount_

WARNING: IO::SEEK_SET will jump to the beginning of the file and

then re-read upto the point specified

WARNING: IO::SEEK_END will read the entire file and then again

upto the point specified



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# File 'lib/symmetric_encryption/reader.rb', line 292

def seek(amount, whence = IO::SEEK_SET)
  offset = 0
  case whence
  when IO::SEEK_SET
    offset = amount
    rewind
  when IO::SEEK_CUR
    if amount >= 0
      offset = amount
    else
      offset = @pos + amount
      rewind
    end
  when IO::SEEK_END
    rewind
    # Read and decrypt entire file a block at a time to get its total
    # unencrypted size
    size = 0
    until eof
      read_block
      size         += @read_buffer.size
      @read_buffer = ''
    end
    rewind
    offset = size + amount
  else
    raise(ArgumentError, "unknown whence:#{whence} supplied to seek()")
  end
  read(offset) if offset.positive?
  0
end

#size ⇒ Object

Return the size of the file rounded up to the nearest encryption block size

Needed by XLS gem



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# File 'lib/symmetric_encryption/reader.rb', line 185

def size
  @ios.size
end