/**
* Try to read a specified number of bytes.
*
* @param amountToRead is the number of bytes we need
* @param collectData is true if we need to actually look at the data. If false, we know we're
* skipping this entry, and all we need to do is to count until we get to the right spot.
* @return a byte buffer positioned at the head of the desired portion, or null if we reached eof.
*/
private ByteBuffer readData(int amountToRead, boolean collectData)
throws ChecksumException, EOFException, FileNotFoundException, DatabaseException {
int alreadyRead = 0;
ByteBuffer completeBuffer = null;
saveBuffer.clear();
while ((alreadyRead < amountToRead) && !eof) {
int bytesNeeded = amountToRead - alreadyRead;
if (window.hasRemaining()) {
/* There's data in the window, process it. */
if (collectData) {
/*
* Save data in a buffer for processing.
*/
if ((alreadyRead > 0) || (window.remaining() < bytesNeeded)) {
/* We need to piece an entry together. */
copyToSaveBuffer(bytesNeeded);
alreadyRead = threadSafeBufferPosition(saveBuffer);
completeBuffer = saveBuffer;
} else {
/* A complete entry is available in this buffer. */
completeBuffer = window.getBuffer();
alreadyRead = amountToRead;
}
} else {
/*
* We're not processing the data, so need to save it. just
* move buffer positions.
*/
int positionIncrement =
(window.remaining() > bytesNeeded) ? bytesNeeded : window.remaining();
alreadyRead += positionIncrement;
window.incrementBufferPosition(positionIncrement);
completeBuffer = window.getBuffer();
}
} else {
/*
* Look for more data.
*/
if (window.fillNext(singleFile, bytesNeeded)) {
/* This call to fillNext slid the window to a new file. */
nextEntryOffset = 0;
}
}
}
/* Flip the save buffer just in case we've been accumulating in it. */
threadSafeBufferFlip(saveBuffer);
return completeBuffer;
}
