class SymmetricEncryption::Reader

Read from encrypted files and other IO streams

Features:

Attributes

pos[R]

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

version[R]

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

Public Class Methods

decrypt(source:, target:, **args) click to toggle source

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

Notes:

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

# File lib/symmetric_encryption/reader.rb, line 95
def self.decrypt(source:, target:, **args)
  Reader.open(source, **args) { |input_file| IO.copy_stream(input_file, target) }
end
empty?(file_name_or_stream) click to toggle source

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

# File lib/symmetric_encryption/reader.rb, line 101
def self.empty?(file_name_or_stream)
  open(file_name_or_stream, &:eof?)
end
header_present?(file_name) click to toggle source

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

# File lib/symmetric_encryption/reader.rb, line 106
def self.header_present?(file_name)
  ::File.open(file_name, "rb") { |file| new(file).header_present? }
end
new(ios, buffer_size: 4096, version: nil) click to toggle source

Decrypt data before reading from the supplied stream

# File lib/symmetric_encryption/reader.rb, line 117
def initialize(ios, buffer_size: 4096, version: nil)
  @ios            = ios
  @buffer_size    = buffer_size
  @version        = version
  @header_present = false
  @closed         = false
  @read_buffer    = "".b

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

  read_header
end
open(file_name_or_stream, buffer_size: 16_384, **args, &block) click to toggle source

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

# 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) click to toggle source

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

Notes:

  • Do not use this method for reading large files.

# File lib/symmetric_encryption/reader.rb, line 78
def self.read(file_name_or_stream, **args)
  Reader.open(file_name_or_stream, **args, &:read)
end

Public Instance Methods

close(close_child_stream = true) click to toggle source

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

# File lib/symmetric_encryption/reader.rb, line 160
def close(close_child_stream = true)
  return if closed?

  @ios.close if close_child_stream
  @closed = true
end
compressed?() click to toggle source

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
# File lib/symmetric_encryption/reader.rb, line 141
def compressed?
  @compressed
end
each(sep_string = "\n")
Alias for: each_line
each_line(sep_string = "\n") { |gets(sep_string) until eof?| ... } click to toggle source

ios.each(sep_string=ā€œnā€) {|line| block } => ios ios.each_line(sep_string=ā€œnā€) {|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.

# File lib/symmetric_encryption/reader.rb, line 240
def each_line(sep_string = "\n")
  yield gets(sep_string) until eof?
  self
end
Also aliased as: each
eof?() click to toggle source

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

# File lib/symmetric_encryption/reader.rb, line 248
def eof?
  @read_buffer.empty? && @ios.eof?
end
flush() click to toggle source

Flush the read stream

Needed by XLS gem
# File lib/symmetric_encryption/reader.rb, line 169
def flush
  @ios.flush
end
gets(sep_string, length = nil) click to toggle source

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.

# File lib/symmetric_encryption/reader.rb, line 219
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?() click to toggle source

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

# File lib/symmetric_encryption/reader.rb, line 112
def header_present?
  @header_present
end
read(length = nil, outbuf = nil) click to toggle source

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

# File lib/symmetric_encryption/reader.rb, line 187
def read(length = nil, outbuf = nil)
  data             = outbuf.nil? ? "" : outbuf.clear
  remaining_length = length

  until remaining_length&.zero? || eof?
    read_block(remaining_length) if @read_buffer.empty?

    if remaining_length && remaining_length < @read_buffer.length
      data << @read_buffer.slice!(0, remaining_length)
    else
      data << @read_buffer
      @read_buffer.clear
    end

    remaining_length = length - data.length if length
  end

  @pos += data.length
  data unless data.empty? && length && length.positive?
end
readline(sep_string = "\n") click to toggle source

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.

# File lib/symmetric_encryption/reader.rb, line 211
def readline(sep_string = "\n")
  gets(sep_string) || raise(EOFError, "End of file reached when trying to read a line")
end
rewind() click to toggle source

Rewind back to the beginning of the file

# File lib/symmetric_encryption/reader.rb, line 256
def rewind
  @read_buffer.clear
  @ios.rewind
  read_header
end
seek(amount, whence = IO::SEEK_SET) click to toggle source

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
# File lib/symmetric_encryption/reader.rb, line 274
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.clear
    end
    rewind
    offset = size + amount
  else
    raise(ArgumentError, "unknown whence:#{whence} supplied to seek()")
  end
  read(offset) if offset.positive?
  0
end
size() click to toggle source

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

Needed by XLS gem
# File lib/symmetric_encryption/reader.rb, line 175
def size
  @ios.size
end

Private Instance Methods

closed?() click to toggle source
# File lib/symmetric_encryption/reader.rb, line 364
def closed?
  @closed || @ios.respond_to?(:closed?) && @ios.closed?
end
decrypt(buf) click to toggle source
# File lib/symmetric_encryption/reader.rb, line 349
def decrypt(buf)
  return if buf.nil? || buf.empty?

  @read_buffer << @stream_cipher.update(buf)
  @read_buffer << @stream_cipher.final if @ios.eof?
end
read_block(length = nil) click to toggle source

Read a block of data and append the decrypted data in the read buffer

# File lib/symmetric_encryption/reader.rb, line 342
def read_block(length = nil)
  buf = @ios.read(length || @buffer_size, @output_buffer ||= "".b)
  decrypt(buf)
end
read_header() click to toggle source

Read the header from the file if present

# File lib/symmetric_encryption/reader.rb, line 309
def read_header
  @pos = 0

  # Read first block and check for the header
  buf = @ios.read(@buffer_size, @output_buffer ||= "".b)

  # Use cipher specified in header, or global cipher if it has no header
  iv, key, cipher_name, cipher = nil
  header                       = Header.new
  if header.parse!(buf)
    @header_present = true
    @compressed     = header.compressed?
    @version        = header.version
    cipher          = header.cipher
    cipher_name     = header.cipher_name || cipher.cipher_name
    key             = header.key
    iv              = header.iv
  else
    @header_present = false
    @compressed     = nil
    cipher          = SymmetricEncryption.cipher(@version)
    cipher_name     = cipher.cipher_name
  end

  @stream_cipher = ::OpenSSL::Cipher.new(cipher_name)
  @stream_cipher.decrypt
  @stream_cipher.key = key || cipher.send(:key)
  @stream_cipher.iv  = iv || cipher.iv

  decrypt(buf)
end