Class: CZTop::Z85::Padded

Inherits:
CZTop::Z85 show all
Defined in:
lib/cztop/z85/padded.rb

Overview

Note:

Warning: Z85 doesn’t have a standardized padding procedure. So other implementations won’t automatically recognize and chop off the padding. Only use this if you really need padding, like when you can’t guarantee the input for #encode is always a multiple of 4 bytes.

Z85 with simple padding. This allows you to #encode input of any length.

Padding Scheme

If the data to be encoded is empty (0 bytes), it is encoded to the empty string, just like in Z85.

Otherwise, a small padding sequence of 1 to 4 (identical) bytes is appended to the binary data. Its last byte denotes the number of padding bytes. This padding is done even if the length of the binary input is a multiple of 4 bytes. This is similar to PKCS#7 padding.

+----------------------------------------+------------+
|                 binary data            |   padding  |
|           any number of bytes          |  1-4 bytes |
+----------------------------------------+------------+

The resulting blob is encoded using #encode.

When decoding, #decode does the inverse. After decoding, it checks the last byte to determine the number of bytes of padding used, and chops those off.

See Also:

Instance Attribute Summary

Attributes included from HasFFIDelegate

#ffi_delegate

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from CZTop::Z85

#initialize

Methods included from HasFFIDelegate::ClassMethods

#ffi_delegate, #from_ffi_delegate

Methods included from HasFFIDelegate

#attach_ffi_delegate, #from_ffi_delegate, raise_zmq_err, #to_ptr

Constructor Details

This class inherits a constructor from CZTop::Z85

Class Method Details

.decode(input) ⇒ String

Same as #decode, but without the need to create an instance first.

Parameters:

  • input (String) —

    Z85 encoded data (including padding, or empty string)

Returns:

  • (String) —

    original data as binary string

Raises:

  • (SystemCallError) —

    if this fails



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# File 'lib/cztop/z85/padded.rb', line 56

def decode(input)
  default.decode(input)
end

.encode(input) ⇒ String

Same as #encode, but without the need to create an instance first.

Parameters:

  • input (String) —

    possibly binary input data

Returns:

  • (String) —

    Z85 encoded data as ASCII string, including encoded length and padding

Raises:

  • (SystemCallError) —

    if this fails



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# File 'lib/cztop/z85/padded.rb', line 44

def encode(input)
  default.encode(input)
end

Instance Method Details

#decode(input) ⇒ String

Decodes from Z85 with padding.

Parameters:

  • input (String) —

    Z85 encoded data (including padding, or empty string)

Returns:

  • (String) —

    original data as binary string

Raises:

  • (SystemCallError) —

    if this fails



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# File 'lib/cztop/z85/padded.rb', line 96

def decode(input)
  return super if input.empty?

  decoded = super

  # last byte contains number of padding bytes
  padding_bytes = decoded.byteslice(-1).ord

  decoded.byteslice(0...-padding_bytes)
end

#encode(input) ⇒ String

Encododes to Z85, with padding if needed.

Parameters:

  • input (String) —

    possibly binary input data

Returns:

  • (String) —

    Z85 encoded data as ASCII string, including padding

Raises:

  • (SystemCallError) —

    if this fails



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# File 'lib/cztop/z85/padded.rb', line 75

def encode(input)
  return super if input.empty?

  padding_bytes = 4 - (input.bytesize % 4)

  # if 0, make it 4. we MUST append padding.
  padding_bytes = 4 if padding_bytes.zero?

  # generate and append padding
  padding = [padding_bytes].pack('C') * padding_bytes

  super("#{input}#{padding}")
end