//--------------------------------------------------------------------------
// For variable content messages, the message length cannot be known until
// the entire message has been written to a byte buffer. Therefore, the
// message header cannot be written to a byte buffer until the entire
// message has been written and the length is known.
//
// The procedure to write a message to a byte buffer is to skip over the
// buffer segment where the header is located, write the message payload
// to the buffer, set the header message length based on the now known
// payload length, and write the header to the buffer.
//
// These are called explicitly by inheriting messages at the
// beginning and end of their copyToFrom's to manage the headers.
// For "get" operations, headerCopyToFrom "gets" the header and
// headerReCopyToFrom does nothing. For "put" operations,
// headerCopyToFrom stores the buffer pointer and advances past where the
// header will be written and headerReCopyToFrom "puts" the header at the
// stored position. Both functions are passed a byte buffer pointer to
// where the copy is to take place. Both are also passed a MessageContent
// pointer to where they can get and mMessageType
// which they transfer into and out of the headers.
//--------------------------------------------------------------------------
public void headerCopyToFrom(Ris.ByteBuffer aBuffer, BaseMsg aParent)
{
//---------------------------------------------------------------------
// Instances of this class are members of parent message classes.
// A call to this function should be the first line of code in a
// containing parent message class's copyToFrom. It performs pre-copyToFrom
// operations. It's purpose is to copy headers to/from byte buffers. The
// corresponding function headerReCopyToFrom should be called as the last
// line of code in the containing message class' copyToFrom. Lines of code
// in between should copy individual data elements into/out of the buffer.
//---------------------------------------------------------------------
// for a "copy to" put
//
// If this is a "copy to" put operation then the header copy will actually
// be done by the headerReCopyToFrom, after the rest of the message has been
// copied into the buffer. This is because some of the fields in the header
// cannot be set until after the rest of the message has been put into the
// buffer. (You don't know the length of the message until you put all of
// the data into it, you also can't compute a checksum). This call stores
// the original buffer position that is passed to it when it is called for
// later use by the headerReCopyToFrom. The original buffer position points
// to where the header should be copied. This call then forward advances
// the buffer to point past the header. Forward advancing the buffer
// position to point just after where the header should be is the same as
// doing a pretend copy of the header. After this pretend copy of the
// header, the buffer position points to where the data should be put into
// the buffer.
//
// Store the original buffer position for later use by the
// headerReCopyToFrom and advance the buffer position forward
// to point past the header.
if (aBuffer.isCopyTo())
{
// Store the buffer parameters for later use by the
// headerReCopyToFrom
mInitialPosition = aBuffer.getPosition();
mInitialLength = aBuffer.getLength();
// Advance the buffer position to point past the header.
aBuffer.forward(Header.cLength);
}
//---------------------------------------------------------------------
// for a "copy from" get
//
// If this is a "copy from" get operation then copy the header from the
// buffer into the header member. Also set the message content type from
// the variable datum id
else
{
// Copy the buffer content into the header object.
copyToFrom(aBuffer);
// Set the message content type.
aParent.mMessageType = mMessageIdentifier;
}
}
public void headerReCopyToFrom(Ris.ByteBuffer aBuffer, BaseMsg aParent)
{
// If this is a put operation then this actually copies the header into
// the buffer.
// This sets some header length parameters and copies the header into the
// buffer position that was stored when headerCopyToFrom was called.
if (aBuffer.isCopyTo())
{
// Store the buffer parameters for later use by the
// headerReCopyToFrom
int tFinalPosition = aBuffer.getPosition();
int tFinalLength = aBuffer.getLength();
// Get message parameters from parent
mMessageIdentifier = aParent.mMessageType;
mMessageLength = aBuffer.getLength();
// Restore buffer parameters
// to the initial position
aBuffer.setPosition(mInitialPosition);
aBuffer.setLength(mInitialPosition);
// Copy the adjusted header into the buffer'
// at the original position
copyToFrom(aBuffer);
// Restore buffer parameters
// to the final position
aBuffer.setPosition(tFinalPosition);
aBuffer.setLength(tFinalPosition);
}
else
{
}
}