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Class: LDPBuffer

Parent class: streambuf

Description:
This class is for reading the contents of a Swift Large Data Product. To use it, you first must connect a stream of LDP packets to the input pipe returned by the pipe() method. Then you probably want to create an istream wrapped around the LDPBuffer. At this point you can read from the istream just as you would a file containing the decoded contents of the LDP. A typical use would be to wrap the istream in a Reader object so you can decode binary data.

A streambuf has a limited way of signaling errors. All it can do is report EOF. However, many complicated things can go wrong with a stream of LDP packets. Therefore this class uses the following strategy. Whenever anything goes wrong it signals EOF. You may then call one of the moreData(), newProduct(), missingPages(), or missingBytes() status methods to figure out what is going on. In some cases you might want to continue reading data after the LDPBuffer reports EOF. Then you simply reset the istream status using its clear() method.

The apid(), product(), page(), and size() methods and their "prev_" counterparts can be used to get information about the current (or previous) packet being read.

This class does not currently support "seeking". In other words each byte must be read sequentially.

Data Fields

public static const int first_page

public static const int unknown

private PacketPipe* _pipe

private LDPPacket* p

private int position

private int _npages

private int _prev_npages

private double _prev_time

private int _prev_apid

private int _prev_product

private int _prev_page

private int _prev_size

private int hit_eof_in_last_block_read

Constructors / Destructor

public LDPBuffer()
Constructor.

public ~LDPBuffer()

Methods

public virtual PacketPipe& pipe()

public virtual int prev_apid()

public virtual int prev_product()

public virtual int prev_page()

public virtual int prev_size()

public virtual double prev_time()

public virtual int apid()

public virtual int product()

public virtual int page()

public virtual int size()

public virtual double time()

public virtual int moreData()
Returns 0 if we have read all the packets from the stream
Returns 1 otherwise

public virtual int newProduct()
Returns 1 if the current and previous packets were in different products
Returns 0 if the current and previous packets were in the same product
Returns 1 if the current packet is the first ever read or if no packets have been read.
Returns 1 if at the end of the data stream

public virtual int missingPages()
Returns the number of pages missing between the packet currently being read and the previous packet. If called at EOF, this will tell whether a gap was encountered and how large it was (in packets). Returns 0 if no packets have been read yet or if a product ended, but we didn't know how many pages it should contain.

public virtual int missingBytes()
Returns the result of missingPages() multiplied by the number of bytes per page. It looks at the packets on either side of the gap (if any) to determine the page size. Returns LDPBuffer::unknown if the page size can't be determined. This method assumes packets have uniform size, except for the last non-redundant packet. If this is not true, this method could return incorrect results.

public virtual int underflow()
This method is required to implement a streambuf subclass. It gets called whenever someone tries to read past the end of the current packet. It resets the internal buffer to the next packet, and returns the first byte in that packet as an int. It returns EOF if there are any problems.

public virtual int uflow()
This is just like the "underflow" method, except that it increments the buffer pointer by one to account for the character it returns.

private int nextPacket()
Private method for pulling the next packet out of the pipe. Returns 1 if there is anything funny going on between the two packets, like a gap or a product number or APID change, or if a NULL packet was pulled out of the pipe. Returns 0 if everything is fine.

Operators

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Data Fields
public	static const int	first_page
public	static const int	unknown
private	PacketPipe*	_pipe
private	LDPPacket*	p
private	int	position
private	int	_npages
private	int	_prev_npages
private	double	_prev_time
private	int	_prev_apid
private	int	_prev_product
private	int	_prev_page
private	int	_prev_size
private	int	hit_eof_in_last_block_read

Constructors / Destructor
public	LDPBuffer() Constructor.
public	~LDPBuffer()

Methods
public	virtual	PacketPipe&	pipe()
public	virtual	int	prev_apid()
public	virtual	int	prev_product()
public	virtual	int	prev_page()
public	virtual	int	prev_size()
public	virtual	double	prev_time()
public	virtual	int	apid()
public	virtual	int	product()
public	virtual	int	page()
public	virtual	int	size()
public	virtual	double	time()
public	virtual	int	moreData() Returns 0 if we have read all the packets from the stream Returns 1 otherwise
public	virtual	int	newProduct() Returns 1 if the current and previous packets were in different products Returns 0 if the current and previous packets were in the same product Returns 1 if the current packet is the first ever read or if no packets have been read. Returns 1 if at the end of the data stream
public	virtual	int	missingPages() Returns the number of pages missing between the packet currently being read and the previous packet. If called at EOF, this will tell whether a gap was encountered and how large it was (in packets). Returns 0 if no packets have been read yet or if a product ended, but we didn't know how many pages it should contain.
public	virtual	int	missingBytes() Returns the result of missingPages() multiplied by the number of bytes per page. It looks at the packets on either side of the gap (if any) to determine the page size. Returns LDPBuffer::unknown if the page size can't be determined. This method assumes packets have uniform size, except for the last non-redundant packet. If this is not true, this method could return incorrect results.
public	virtual	int	underflow() This method is required to implement a streambuf subclass. It gets called whenever someone tries to read past the end of the current packet. It resets the internal buffer to the next packet, and returns the first byte in that packet as an int. It returns EOF if there are any problems.
public	virtual	int	uflow() This is just like the "underflow" method, except that it increments the buffer pointer by one to account for the character it returns.
private		int	nextPacket() Private method for pulling the next packet out of the pipe. Returns 1 if there is anything funny going on between the two packets, like a gap or a product number or APID change, or if a NULL packet was pulled out of the pipe. Returns 0 if everything is fine.