Package org.bouncycastle.openpgp

Class PGPCompressedDataGenerator

java.lang.Object
org.bouncycastle.openpgp.PGPCompressedDataGenerator
All Implemented Interfaces:
CompressionAlgorithmTags
public class PGPCompressedDataGenerator extends Object implements CompressionAlgorithmTags
Generator for producing compressed data packets.

A PGPCompressedDataGenerator is used by invoking one of the open functions to create an OutputStream that raw data can be supplied to for compression:

  • If the data needs to written out in blocks, use open(OutputStream, byte[]) to create a packet consisting of a series of compressed data objects (partials).

A PGPCompressedDataGenerator is usually used to wrap the OutputStream obtained from a PGPEncryptedDataGenerator (i.e. to compress data prior to encrypting it).

Raw data is not typically written directly to the OutputStream obtained from a PGPCompressedDataGenerator. The OutputStream is usually wrapped by a PGPLiteralDataGenerator, which encodes the raw data prior to compression.

Once data for compression has been written to the constructed OutputStream, writing of the object stream is completed by closing the OutputStream obtained from the #open() method, or equivalently invoking close() on this generator.

  • Constructor Details

    • PGPCompressedDataGenerator

      public PGPCompressedDataGenerator(int algorithm)
      Construct a new compressed data generator.
      Parameters:
      algorithm - the identifier of the compression algorithm to use.

    • PGPCompressedDataGenerator

      public PGPCompressedDataGenerator(int algorithm, int compression)
      Construct a new compressed data generator.
      Parameters:
      algorithm - the identifier of the compression algorithm to use.
      compression - the Deflater compression level to use.

  • Method Details

    • open

      public OutputStream open(OutputStream out) throws IOException
      Return an OutputStream which will save the data being written to the compressed object.

      The stream created can be closed off by either calling close() on the stream or close() on the generator. Closing the returned stream does not close off the OutputStream parameter out.

      Parameters:
      out - underlying OutputStream to be used.
      Returns:
      OutputStream
      Throws:
      IOException
      IllegalStateException

    • open

      public OutputStream open(OutputStream out, byte[] buffer) throws IOException, PGPException
      Return an OutputStream which will compress the data as it is written to it. The stream will be written out in chunks (partials) according to the size of the passed in buffer.

      The stream created can be closed off by either calling close() on the stream or close() on the generator. Closing the returned stream does not close off the OutputStream parameter out.

      Note: if the buffer is not a power of 2 in length only the largest power of 2 bytes worth of the buffer will be used.

      Note: using this may break compatibility with RFC 1991 compliant tools. Only recent OpenPGP implementations are capable of accepting these streams.

      Parameters:
      out - the stream to write compressed packets to.
      buffer - a buffer to use to buffer and write partial packets. The returned stream takes ownership of the buffer and will use it to buffer plaintext data for compression.
      Returns:
      the output stream to write data to.
      Throws:
      IOException - if an error occurs writing stream header information to the provider output stream.
      PGPException
      IllegalStateException - if this generator already has an open OutputStream.

    • close

      public void close() throws IOException
      Close the compressed object - this is equivalent to calling close on the stream returned by the open() method.
      Throws:
      IOException