Exiv2::MemIo Class Reference

Provides binary IO on blocks of memory by implementing the BasicIo interface. A copy-on-write implementation ensures that the data passed in is only copied when necessary, i.e., as soon as data is written to the MemIo. The original data is only used for reading. If writes are performed, the changed data can be retrieved using the read methods (since the data used in construction is never modified). More...

#include <basicio.hpp>

Inheritance diagram for Exiv2::MemIo:

Public Member Functions
Creators
	MemIo ()
	Default constructor that results in an empty object.
	MemIo (const byte *data, size_t size)
	Constructor that accepts a block of memory. A copy-on-write algorithm allows read operations directly from the original data and will create a copy of the buffer on the first write operation.
	~MemIo () override
	Destructor. Releases all managed memory.
Manipulators
int	open () override
	Memory IO is always open for reading and writing. This method therefore only resets the IO position to the start.
int	close () override
	Does nothing on MemIo objects.
size_t	write (const byte *data, size_t wcount) override
	Write data to the memory block. If needed, the size of the internal memory block is expanded. The IO position is advanced by the number of bytes written.
size_t	write (BasicIo &src) override
	Write data that is read from another BasicIo instance to the memory block. If needed, the size of the internal memory block is expanded. The IO position is advanced by the number of bytes written.
int	putb (byte data) override
	Write one byte to the memory block. The IO position is advanced by one byte.
DataBuf	read (size_t rcount) override
	Read data from the memory block. Reading starts at the current IO position and the position is advanced by the number of bytes read.
size_t	read (byte *buf, size_t rcount) override
	Read data from the memory block. Reading starts at the current IO position and the position is advanced by the number of bytes read.
int	getb () override
	Read one byte from the memory block. The IO position is advanced by one byte.
void	transfer (BasicIo &src) override
	Clear the memory block and then transfer data from the src BasicIo object into a new block of memory.
int	seek (int64_t offset, Position pos) override
	Move the current IO position.
byte *	mmap (bool=false) override
	Allow direct access to the underlying data buffer. The buffer is not protected against write access in any way, the argument is ignored.
int	munmap () override
	Remove a mapping established with mmap(). If the mapped area is writeable, this ensures that changes are written back.
Public Member Functions inherited from Exiv2::BasicIo
virtual	~BasicIo ()=default
	Destructor.
void	readOrThrow (byte *buf, size_t rcount, ErrorCode err=ErrorCode::kerCorruptedMetadata)
	Safe version of read() that checks for errors and throws an exception if the read was unsuccessful.
void	seekOrThrow (int64_t offset, Position pos, ErrorCode err)
	Safe version of seek() that checks for errors and throws an exception if the seek was unsuccessful.

Accessors
size_t	tell () const override
	Get the current IO position.
size_t	size () const override
	Get the current memory buffer size in bytes.
bool	isopen () const override
	Always returns true.
int	error () const override
	Always returns 0.
bool	eof () const override
	Returns true if the IO position has reached the end, otherwise false.
const std::string &	path () const noexcept override
	Returns a dummy path, indicating that memory access is used.
void	populateFakeData () override
	Mark all the bNone blocks to bKnow. This avoids allocating memory for parts of the file that contain image-date (non-metadata/pixel data)
	MemIo (const MemIo &)=delete
	Copy constructor.
MemIo &	operator= (const MemIo &)=delete
	Assignment operator.

Additional Inherited Members
Public Types inherited from Exiv2::BasicIo
enum	Position { beg , cur , end }
	Seek starting positions.
using	UniquePtr = std::unique_ptr< BasicIo >
	BasicIo auto_ptr type.
Public Attributes inherited from Exiv2::BasicIo
byte *	bigBlock_ {}
	this is allocated and populated by mmap()

Detailed Description

Provides binary IO on blocks of memory by implementing the BasicIo interface. A copy-on-write implementation ensures that the data passed in is only copied when necessary, i.e., as soon as data is written to the MemIo. The original data is only used for reading. If writes are performed, the changed data can be retrieved using the read methods (since the data used in construction is never modified).

Note

If read only usage of this class is common, it might be worth creating a specialized readonly class or changing this one to have a readonly mode.

Constructor & Destructor Documentation

MemIo()

Exiv2::MemIo::MemIo	(	const byte *	data,
		size_t	size
	)

Constructor that accepts a block of memory. A copy-on-write algorithm allows read operations directly from the original data and will create a copy of the buffer on the first write operation.

Parameters

data	Pointer to data. Data must be at least size bytes long
size	Number of bytes to copy.

Member Function Documentation

close()

int Exiv2::MemIo::close ( )

overridevirtual

Does nothing on MemIo objects.

Returns

0

Implements Exiv2::BasicIo.

eof()

bool Exiv2::MemIo::eof ( ) const

overridevirtual

Returns true if the IO position has reached the end, otherwise false.

Implements Exiv2::BasicIo.

error()

int Exiv2::MemIo::error ( ) const

overridevirtual

Always returns 0.

Implements Exiv2::BasicIo.

getb()

int Exiv2::MemIo::getb ( )

overridevirtual

Read one byte from the memory block. The IO position is advanced by one byte.

Returns

The byte read from the memory block if successful;
EOF if failure;

Implements Exiv2::BasicIo.

isopen()

bool Exiv2::MemIo::isopen ( ) const

overridevirtual

Always returns true.

Implements Exiv2::BasicIo.

mmap()

byte * Exiv2::MemIo::mmap ( bool  = false )

overridevirtual

Allow direct access to the underlying data buffer. The buffer is not protected against write access in any way, the argument is ignored.

Note

The application must ensure that the memory pointed to by the returned pointer remains valid and allocated as long as the MemIo object exists.

Implements Exiv2::BasicIo.

munmap()

int Exiv2::MemIo::munmap ( )

overridevirtual

Remove a mapping established with mmap(). If the mapped area is writeable, this ensures that changes are written back.

Returns

0 if successful;
Nonzero if failure;

Implements Exiv2::BasicIo.

open()

int Exiv2::MemIo::open ( )

overridevirtual

Memory IO is always open for reading and writing. This method therefore only resets the IO position to the start.

Returns

0

Implements Exiv2::BasicIo.

path()

const std::string & Exiv2::MemIo::path ( ) const

overridevirtualnoexcept

Returns a dummy path, indicating that memory access is used.

Implements Exiv2::BasicIo.

populateFakeData()

void Exiv2::MemIo::populateFakeData ( )

overridevirtual

Mark all the bNone blocks to bKnow. This avoids allocating memory for parts of the file that contain image-date (non-metadata/pixel data)

Note

This method should be only called after the concerned data (metadata) are all downloaded from the remote file to memory.

Implements Exiv2::BasicIo.

putb()

int Exiv2::MemIo::putb ( byte  data )

overridevirtual

Write one byte to the memory block. The IO position is advanced by one byte.

Parameters

data	The single byte to be written.

Returns

The value of the byte written if successful;
EOF if failure;

Implements Exiv2::BasicIo.

read() [1/2]

size_t Exiv2::MemIo::read ( byte *  buf, size_t  rcount  )

overridevirtual

Read data from the memory block. Reading starts at the current IO position and the position is advanced by the number of bytes read.

Parameters

buf	Pointer to a block of memory into which the read data is stored. The memory block must be at least rcount bytes long.
rcount	Maximum number of bytes to read. Fewer bytes may be read if rcount bytes are not available.

Returns

Number of bytes read from the memory block successfully;
0 if failure;

Implements Exiv2::BasicIo.

read() [2/2]

DataBuf Exiv2::MemIo::read ( size_t  rcount )

overridevirtual

Read data from the memory block. Reading starts at the current IO position and the position is advanced by the number of bytes read.

Parameters

rcount

Maximum number of bytes to read. Fewer bytes may be read if rcount bytes are not available.

Returns

DataBuf instance containing the bytes read. Use the DataBuf::size_ member to find the number of bytes read. DataBuf::size_ will be 0 on failure.

Implements Exiv2::BasicIo.

seek()

int Exiv2::MemIo::seek ( int64_t  offset, Position  pos  )

overridevirtual

Move the current IO position.

Parameters

offset	Number of bytes to move the position relative to the starting position specified by pos
pos	Position from which the seek should start

Returns

0 if successful;
Nonzero if failure;

Implements Exiv2::BasicIo.

size()

size_t Exiv2::MemIo::size ( ) const

overridevirtual

Get the current memory buffer size in bytes.

Returns

Size of the in memory data in bytes;
-1 if failure;

Implements Exiv2::BasicIo.

tell()

size_t Exiv2::MemIo::tell ( ) const

overridevirtual

Get the current IO position.

Returns

Offset from the start of the memory block

Implements Exiv2::BasicIo.

transfer()

void Exiv2::MemIo::transfer ( BasicIo &  src )

overridevirtual

Clear the memory block and then transfer data from the src BasicIo object into a new block of memory.

This method is optimized to simply swap memory block if the source object is another MemIo instance. The source BasicIo instance is invalidated by this operation and should not be used after this method returns. This method exists primarily to be used with the BasicIo::temporary() method.

Parameters

src	Reference to another BasicIo instance. The entire contents of src are transferred to this object. The src object is invalidated by the method.

Exceptions

Error

In case of failure

Implements Exiv2::BasicIo.

write() [1/2]

size_t Exiv2::MemIo::write ( BasicIo &  src )

overridevirtual

Write data that is read from another BasicIo instance to the memory block. If needed, the size of the internal memory block is expanded. The IO position is advanced by the number of bytes written.

Parameters

src	Reference to another BasicIo instance. Reading start at the source's current IO position

Returns

Number of bytes written to the memory block successfully;
0 if failure;

Implements Exiv2::BasicIo.

write() [2/2]

size_t Exiv2::MemIo::write ( const byte *  data, size_t  wcount  )

overridevirtual

Write data to the memory block. If needed, the size of the internal memory block is expanded. The IO position is advanced by the number of bytes written.

Parameters

data	Pointer to data. Data must be at least wcount bytes long
wcount	Number of bytes to be written.

Returns

Number of bytes written to the memory block successfully;
0 if failure;

Implements Exiv2::BasicIo.

---

The documentation for this class was generated from the following file:

• basicio.hpp