Kea 2.5.9
isc::util::OutputBuffer Class Reference

The OutputBuffer class is a buffer abstraction for manipulating mutable data. More...

#include <buffer.h>

Public Member Functions

 OutputBuffer (const OutputBuffer &other)
 Copy constructor.
 
 OutputBuffer (size_t len)
 Constructor.
 
 ~OutputBuffer ()=default
 Destructor.
 
void clear ()
 Clear buffer content.
 
size_t getCapacity () const
 Return the current capacity of the buffer.
 
const uint8_t * getData () const
 Return a pointer to the head of the data stored in the buffer.
 
const void * getDataAsVoidPtr () const
 Return data as a pointer to void.
 
size_t getLength () const
 Return the length of data written in the buffer.
 
const std::vector< uint8_t > & getVector () const
 Return the buffer.
 
OutputBufferoperator= (const OutputBuffer &other)
 Assignment operator.
 
uint8_t operator[] (size_t position) const
 Return the value of the buffer at the specified position.
 
void skip (size_t len)
 Insert a specified length of gap at the end of the buffer.
 
void trim (size_t len)
 Trim the specified length of data from the end of the buffer.
 
void writeData (const void *data, size_t len)
 Copy an arbitrary length of data into the buffer.
 
void writeUint16 (uint16_t data)
 Write an unsigned 16-bit integer in host byte order into the buffer in network byte order.
 
void writeUint16At (uint16_t data, size_t position)
 Write an unsigned 16-bit integer in host byte order at the specified position of the buffer in network byte order.
 
void writeUint32 (uint32_t data)
 Write an unsigned 32-bit integer in host byte order into the buffer in network byte order.
 
void writeUint64 (uint64_t data)
 Write an unsigned 64-bit integer in host byte order into the buffer in network byte order.
 
void writeUint8 (uint8_t data)
 Write an unsigned 8-bit integer into the buffer.
 
void writeUint8At (uint8_t data, size_t position)
 Write an unsigned 8-bit integer into the buffer.
 

Detailed Description

The OutputBuffer class is a buffer abstraction for manipulating mutable data.

The main purpose of this class is to provide a safe workplace for constructing wire-format data to be sent out to a network. Here, safe means that it automatically allocates necessary memory and avoid buffer overrun.

Like for the InputBuffer class, applications normally use this class only in a limited situation. One common usage of this class for an application would be something like this:

OutputBuffer buffer(4096); // give a sufficiently large initial size
// Pass the buffer to a DNS message object to construct a wire-format DNS message.
struct sockaddr to_address;
sendto(s, buffer.getDataAsVoidPtr(), buffer.getLength(), 0, &to_address, sizeof(to_address));
The OutputBuffer class is a buffer abstraction for manipulating mutable data.
Definition: buffer.h:343

where the getData() (in fact getDataAsVoidPtr()) method gives a reference to the internal memory region stored in the buffer object. This is a suboptimal design in that it exposes an encapsulated "handle" of an object to its user. Unfortunately, there is no easy way to avoid this without involving expensive data copy if we want to use this object with a legacy API such as a BSD socket interface. And, indeed, this is one major purpose for this object. Applications should use this method only under such a special circumstance. It should also be noted that the memory region returned by getData() may be invalidated after a subsequent write operation.

An OutputBuffer class object automatically extends its memory region when data is written beyond the end of the current buffer. However, it will involve performance overhead such as reallocating more memory and copying data. It is therefore recommended to construct the buffer object with a sufficiently large initial size. The getCapacity() method provides the current maximum size of data (including the portion already written) that can be written into the buffer without causing memory reallocation.

Methods for writing data into the buffer generally work like an output stream: it begins with the head of the buffer, and once some length of data is written into the buffer, the next write operation will take place from the end of the buffer. Other methods to emulate "random access" are also provided (e.g., writeUint16At()). The normal write operations are normally exception-free as this class automatically extends the buffer when necessary. However, in extreme cases such as an attempt of writing multi-GB data, a separate exception (e.g., std::bad_alloc) may be thrown by the system. This also applies to the constructor with a very large initial size.

Note to developers: it may make more sense to introduce an abstract base class for the OutputBuffer and define the simple implementation as a concrete derived class. That way we can provide flexibility for future extension such as more efficient buffer implementation or allowing users to have their own customized version without modifying the source code. We in fact considered that option, but at the moment chose the simpler approach with a single concrete class, because it may make the implementation unnecessarily complicated while we were still not certain if we really want that flexibility. We may revisit the class design as we see more applications of the class. The same considerations apply to the InputBuffer and MessageRenderer classes.

Definition at line 343 of file buffer.h.

Constructor & Destructor Documentation

◆ OutputBuffer() [1/2]

isc::util::OutputBuffer::OutputBuffer ( size_t  len)
inlineexplicit

Constructor.

Parameters
lenThe initial allocated length of the buffer in bytes.

Definition at line 348 of file buffer.h.

◆ OutputBuffer() [2/2]

isc::util::OutputBuffer::OutputBuffer ( const OutputBuffer other)
inline

Copy constructor.

Parameters
otherSource object from which to make a copy.

Definition at line 357 of file buffer.h.

◆ ~OutputBuffer()

isc::util::OutputBuffer::~OutputBuffer ( )
default

Destructor.

Member Function Documentation

◆ clear()

◆ getCapacity()

size_t isc::util::OutputBuffer::getCapacity ( ) const
inline

Return the current capacity of the buffer.

Definition at line 384 of file buffer.h.

Referenced by isc::dhcp::Option6Auth::pack(), and isc::dhcp::Option6Auth::packHashInput().

◆ getData()

◆ getDataAsVoidPtr()

const void * isc::util::OutputBuffer::getDataAsVoidPtr ( ) const
inline

Return data as a pointer to void.

Definition at line 404 of file buffer.h.

References getData().

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◆ getLength()

◆ getVector()

const std::vector< uint8_t > & isc::util::OutputBuffer::getVector ( ) const
inline

Return the buffer.

Note
The main use is to avoid a copy.

Definition at line 433 of file buffer.h.

Referenced by isc::dhcp::Dhcpv6Srv::createNameChangeRequests(), and isc::dhcp::Pkt4o6::pack().

◆ operator=()

OutputBuffer & isc::util::OutputBuffer::operator= ( const OutputBuffer other)
inline

Assignment operator.

Parameters
otherObject to copy into "this".

Definition at line 370 of file buffer.h.

◆ operator[]()

uint8_t isc::util::OutputBuffer::operator[] ( size_t  position) const
inline

Return the value of the buffer at the specified position.

pos must specify the valid position of the buffer; otherwise an exception class of isc::OutOfRange will be thrown.

Parameters
positionThe position in the buffer to be returned.

Definition at line 420 of file buffer.h.

References isc_throw.

◆ skip()

void isc::util::OutputBuffer::skip ( size_t  len)
inline

Insert a specified length of gap at the end of the buffer.

The caller should not assume any particular value to be inserted. This method is provided as a shortcut to make a hole in the buffer that is to be filled in later, e.g, by writeUint16At().

Parameters
lenThe length of the gap to be inserted in bytes.

Definition at line 445 of file buffer.h.

◆ trim()

void isc::util::OutputBuffer::trim ( size_t  len)
inline

Trim the specified length of data from the end of the buffer.

The specified length must not exceed the current data size of the buffer; otherwise an exception of class isc::OutOfRange will be thrown.

Parameters
lenThe length of data that should be trimmed.

Definition at line 456 of file buffer.h.

References isc_throw.

◆ writeData()

void isc::util::OutputBuffer::writeData ( const void *  data,
size_t  len 
)
inline

◆ writeUint16()

◆ writeUint16At()

void isc::util::OutputBuffer::writeUint16At ( uint16_t  data,
size_t  position 
)
inline

Write an unsigned 16-bit integer in host byte order at the specified position of the buffer in network byte order.

The buffer must have a sufficient room to store the given data at the given position, that is, pos + 2 < getLength(); otherwise an exception of class isc::OutOfRange will be thrown. Note also, that this method never extends the buffer.

Parameters
dataThe 16-bit integer to be written into the buffer.
positionThe beginning position in the buffer to write the data.

Definition at line 514 of file buffer.h.

References isc_throw.

Referenced by isc::dhcp::writeIpUdpHeader().

◆ writeUint32()

◆ writeUint64()

void isc::util::OutputBuffer::writeUint64 ( uint64_t  data)
inline

Write an unsigned 64-bit integer in host byte order into the buffer in network byte order.

Parameters
dataThe 64-bit integer to be written into the buffer.

Definition at line 539 of file buffer.h.

Referenced by isc::dhcp::Option6Auth::pack(), and isc::dhcp::Option6Auth::packHashInput().

◆ writeUint8()

◆ writeUint8At()

void isc::util::OutputBuffer::writeUint8At ( uint8_t  data,
size_t  position 
)
inline

Write an unsigned 8-bit integer into the buffer.

The position must be lower than the size of the buffer, otherwise an exception of class isc::OutOfRange will be thrown.

Parameters
dataThe 8-bit integer to be written into the buffer.
positionThe position in the buffer to write the data.

Definition at line 485 of file buffer.h.

References isc_throw.

Referenced by isc::perfdhcp::PktTransform::pack().


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