com.sun.spot.util
Class CrcOutputStream

java.lang.Object
  java.io.OutputStream
      com.sun.spot.util.CrcOutputStream

public class CrcOutputStream
extends OutputStream

CrcOutputStream provides CRC checking and flow control for two Java programs communicating with two input and output stream pairs. To use this class, open a CrcOutputStream around the InputStream and OutputStream at each end. Then use the accessor getInputStream() to obtain an InputStream and do further io using the CrcOutputStream and the InputStream obtained from getInputStream(). Data is sent over the output stream in blocks whose size can be specified in CrcOutputStream constructor. A smaller block is sent whenever a flush is done on the CrcOutputStream. If data corruption occurs, IOExceptions will be thrown on both the sending and receiving threads. Subsequent read and writes will still be valid. The streams are not thread-safe in the presence of multiple simultaneous accessors; each stream should be accessed from one thread.

Constructor Summary

CrcOutputStream(OutputStream outputStream, InputStream inputStream)
Open an output stream that will add CRC checking and flow control to the outgoing data stream.

CrcOutputStream(OutputStream outputStream, InputStream inputStream, int blockSize)
Open an output stream that will add CRC checking and flow control to the outgoing data stream.

Method Summary

void	close() Closes this output stream and releases any system resources associated with this stream.
void	flush() Flushes this output stream and forces any buffered output bytes to be written out.
InputStream	getInputStream()
boolean	probe() Returns true if there's a CrcOutputStream at the far end, and someone there is waiting on a read.
void	write(byte[] b, int off, int len) Writes len bytes from the specified byte array starting at offset off to this output stream.
void	write(int b) Writes the specified byte to this output stream.

Methods inherited from class java.io.OutputStream

write

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

CrcOutputStream

public CrcOutputStream(OutputStream outputStream,
                       InputStream inputStream)

Open an output stream that will add CRC checking and flow control to the outgoing data stream.

Parameters:

outputStream - the underlying output stream on which to write data.

inputStream - to receive data from the remote CRCOutputStream, and acknowledgements and CRC hashes from the remote CRC InputStream.

CrcOutputStream

public CrcOutputStream(OutputStream outputStream,
                       InputStream inputStream,
                       int blockSize)

Open an output stream that will add CRC checking and flow control to the outgoing data stream.

Parameters:

outputStream - the underlying output stream on which to write data.

inputStream - to receive data from the remote CRCOutputStream, and acknowledgements and CRC hashes from the remote CRC InputStream.

blockSize - the maximum number of bytes of data to be written before waiting for a CRC confirmation from the remote device. Also, the remote device will never buffer more than (2 * blockSize) bytes of data awaiting reading from the containing CRC InputStream.

Method Detail

getInputStream

public InputStream getInputStream()

Returns:

a CRC InputStream. This supplies data received from the remote device's CrcOutputStream whose integrity has been checked using a CRC hash. No more than (2 * blockSize) bytes of data will be buffered locally.

write

public void write(int b)
           throws IOException

Description copied from class: OutputStream

Writes the specified byte to this output stream. The general contract for write is that one byte is written to the output stream. The byte to be written is the eight low-order bits of the argument b. The 24 high-order bits of b are ignored.

Subclasses of OutputStream must provide an implementation for this method.

Specified by:

write in class OutputStream

Parameters:

b - the byte.

Throws:

IOException - if an I/O error occurs. In particular, an IOException may be thrown if the output stream has been closed.

See Also:

OutputStream.write(int)

write

public void write(byte[] b,
                  int off,
                  int len)
           throws IOException

Description copied from class: OutputStream

Writes len bytes from the specified byte array starting at offset off to this output stream. The general contract for write(b, off, len) is that some of the bytes in the array b are written to the output stream in order; element b[off] is the first byte written and b[off+len-1] is the last byte written by this operation.

The write method of OutputStream calls the write method of one argument on each of the bytes to be written out. Subclasses are encouraged to override this method and provide a more efficient implementation.

If b is null, a NullPointerException is thrown.

If off is negative, or len is negative, or off+len is greater than the length of the array b, then an IndexOutOfBoundsException is thrown.

Overrides:

write in class OutputStream

Parameters:

b - the data.

off - the start offset in the data.

len - the number of bytes to write.

Throws:

IOException - if an I/O error occurs. In particular, an IOException is thrown if the output stream is closed.

See Also:

OutputStream.write(byte[], int, int)

flush

public void flush()
           throws IOException

Description copied from class: OutputStream

Flushes this output stream and forces any buffered output bytes to be written out. The general contract of flush is that calling it is an indication that, if any bytes previously written have been buffered by the implementation of the output stream, such bytes should immediately be written to their intended destination.

The flush method of OutputStream does nothing.

Overrides:

flush in class OutputStream

Throws:

IOException - if an I/O error occurs.

See Also:

OutputStream.flush()

close

public void close()
           throws IOException

Description copied from class: OutputStream

Closes this output stream and releases any system resources associated with this stream. The general contract of close is that it closes the output stream. A closed stream cannot perform output operations and cannot be reopened.

The close method of OutputStream does nothing.

Overrides:

close in class OutputStream

Throws:

IOException - if an I/O error occurs.

See Also:

OutputStream.close()

probe

public boolean probe()
              throws IOException

Returns true if there's a CrcOutputStream at the far end, and someone there is waiting on a read. This method can only be called when no-one is waiting on a local read, and will hang if this condition is not met.

Returns:

true if there's a reader at the far end

Throws:

IOException