class Archive::Zip::Codec::TraditionalEncryption::Decrypt
Archive::Zip::Codec::TraditionalEncryption::Decrypt is a readable, IO-like object which decrypts data data it reads from a delegate IO object using the traditional encryption algorithm as documented in the ZIP specification. A close method is also provided which can optionally close the delegate object.
Instances of this class should only be accessed via the Archive::Zip::Codec::TraditionalEncryption#decompressor method.
Public Class Methods
Creates a new instance of this class using io as a data source. io must be readable and provide a read method as an IO instance would or errors will be raised when performing read operations. password should be the encryption key. mtime must be the last modified time of the entry to be encrypted/decrypted.
This class has extremely limited seek capabilities. It is possible to seek
with an offset of 0
and a whence of IO::SEEK_CUR
.
As a result, the pos and tell methods also work as
expected.
Due to certain optimizations within IO::Like#seek and if there is data in the read buffer, the seek method can be used to seek forward from the current stream position up to the end of the buffer. Unless it is known definitively how much data is in the buffer, it is best to avoid relying on this behavior.
If io also responds to rewind, then the rewind
method of this class can be used to reset the whole stream back to the
beginning. Using seek of this class to seek directly to offset
0
using IO::SEEK_SET
for whence will also work in
this case.
Any other seeking attempts, will raise Errno::EINVAL exceptions.
The fill_size attribute is set to 0
by default under
the assumption that io is already buffered.
# File lib/archive/zip/codec/traditional_encryption.rb, line 276 def initialize(io, password, mtime) # Keep track of the total number of bytes read. # Set this here so that the call to #initialize_keys caused by the call # to super below does not cause errors in #unbuffered_read due to this # attribute being uninitialized. @total_bytes_out = 0 super(io, password, mtime) # Assume that the delegate IO object is already buffered. self.fill_size = 0 end
Creates a new instance of this class with the given argument using new and then passes the instance to the given block. The close method is guaranteed to be called after the block completes.
Equivalent to new if no block is given.
# File lib/archive/zip/codec/traditional_encryption.rb, line 240 def self.open(io, password, mtime) decrypt_io = new(io, password, mtime) return decrypt_io unless block_given? begin yield(decrypt_io) ensure decrypt_io.close unless decrypt_io.closed? end end
Public Instance Methods
Closes this object so that further write operations will fail. If
close_delegate is true
, the delegate object used as a
data source will also be closed using its close method.
# File lib/archive/zip/codec/traditional_encryption.rb, line 292 def close(close_delegate = true) super() io.close if close_delegate end
Private Instance Methods
Extend the inherited #initialize_keys method to further initialize the keys by encrypting and writing a 12 byte header to the delegate IO object.
# File lib/archive/zip/codec/traditional_encryption.rb, line 302 def initialize_keys super # Load the 12 byte header taking care to ensure that all bytes are read. bytes_needed = 12 while bytes_needed > 0 do begin bytes_read = unbuffered_read(bytes_needed) bytes_needed -= bytes_read.size rescue Errno::EAGAIN, Errno::EINTR sleep(1) end end # Reset the total bytes read in order to disregard the header. @total_bytes_out = 0 nil end
Reads, decrypts, and returns at most length bytes from the delegate IO object.
Raises EOFError if there is no data to read.
# File lib/archive/zip/codec/traditional_encryption.rb, line 326 def unbuffered_read(length) buffer = io.read(length) raise EOFError, 'end of file reached' if buffer.nil? @total_bytes_out += buffer.length 0.upto(buffer.length - 1) do |i| buffer[i] = (buffer[i].ord ^ decrypt_byte).chr update_keys(buffer[i].chr) end buffer end
Allows resetting this object and the delegate object back to the beginning of the stream or reporting the current position in the stream.
Raises Errno::EINVAL unless offset is 0
and
whence is either IO::SEEK_SET or IO::SEEK_CUR. Raises
Errno::EINVAL if whence is IO::SEEK_SEK and the delegate object
does not respond to the rewind method.
# File lib/archive/zip/codec/traditional_encryption.rb, line 345 def unbuffered_seek(offset, whence = IO::SEEK_SET) unless offset == 0 && ((whence == IO::SEEK_SET && @io.respond_to?(:rewind)) || whence == IO::SEEK_CUR) then raise Errno::EINVAL end case whence when IO::SEEK_SET io.rewind initialize_keys @total_bytes_out = 0 when IO::SEEK_CUR @total_bytes_out end end