a11::data::Chunk Struct Reference

A unit of data: bytes plus optional descriptive metadata. More...

#include <cpp/a11/data/types.h>

Public Member Functions
size_t	ApproxBytes () const
	Estimate memory/wire weight for bounded-buffer accounting.
std::string	DebugString () const
	Return a concise representation suitable for logs and diagnostics.
std::string	GetMimetype () const
	Returns the metadata mimetype, or empty when unset.
bool	IsEmpty () const
	Whether the chunk carries no data, reference or object.
bool	IsNull () const
	Whether the chunk represents an explicit null value.
absl::Status	Validate () const
	Validate that payload, reference, and metadata fields are consistent.
bool	HasObject () const
	Whether this chunk is carrying a value rather than bytes.
absl::Status	Materialize ()
	Produces data from object, if it has not been produced yet.
absl::StatusOr< Bytes >	ToMsgpack () const
	Encodes this chunk as MessagePack bytes.
absl::Status	ToMsgpackInto (MsgpackWriter *absl_nonnull writer) const
	Append this record's fields to an already-open writer.

Static Public Member Functions
static absl::StatusOr< Chunk >	FromMsgpack (std::string_view bytes)
	Decodes MessagePack bytes into a Chunk.

Public Attributes
std::optional< ChunkMetadata >	metadata {}
	Optional payload metadata.
std::string	ref {}
	Node id this chunk references, if not inline.
Bytes	data {}
	Inline byte payload.
std::shared_ptr< const ChunkObject >	object {}
	The value this chunk stands for, when its bytes have not been produced.

Friends
bool	operator== (const Chunk &, const Chunk &)=default
template<typename Sink >
void	AbslStringify (Sink &sink, const Chunk &value)

Detailed Description

A unit of data: bytes plus optional descriptive metadata.

A chunk holds its payload in data with an optional metadata describing it. Instead of inline data a chunk may instead carry a ref naming another node whose content it stands in for; such a reference must be resolved before the payload is used.

A third possibility exists and is local to one process: an object, whose bytes have not been produced because nothing has needed them. See a11::data::ChunkObject, and note the one invariant that matters to everybody else – an object-carrying chunk is not empty, even though data is, which is why IsEmpty() consults all three fields. A chunk that read as empty would read as a null stream terminator, and would end a stream that was only getting started.

Member Function Documentation

ApproxBytes()

size_t a11::data::Chunk::ApproxBytes

(

)

const

Estimate memory/wire weight for bounded-buffer accounting.

DebugString()

std::string a11::data::Chunk::DebugString

(

)

const

Return a concise representation suitable for logs and diagnostics.

FromMsgpack()

absl::StatusOr< Chunk > a11::data::Chunk::FromMsgpack ( std::string_view  bytes )

static

Decodes MessagePack bytes into a Chunk.

GetMimetype()

std::string a11::data::Chunk::GetMimetype

(

)

const

Returns the metadata mimetype, or empty when unset.

HasObject()

bool a11::data::Chunk::HasObject ( ) const

inline

Whether this chunk is carrying a value rather than bytes.

IsEmpty()

bool a11::data::Chunk::IsEmpty

(

)

const

Whether the chunk carries no data, reference or object.

IsNull()

bool a11::data::Chunk::IsNull

(

)

const

Whether the chunk represents an explicit null value.

Materialize()

absl::Status a11::data::Chunk::Materialize

(

)

Produces data from object, if it has not been produced yet.

Idempotent, and a no-op on a chunk that already has its bytes. Called at every boundary where bytes are required – a persisting store, an attached stream, a reader asking for a chunk – which is what keeps object an optimisation rather than a second representation everybody has to know about. The object is released afterwards, so the bytes become the single answer once they exist.

ToMsgpack()

absl::StatusOr< Bytes > a11::data::Chunk::ToMsgpack

(

)

const

Encodes this chunk as MessagePack bytes.

ToMsgpackInto()

absl::Status a11::data::Chunk::ToMsgpackInto

(

MsgpackWriter *absl_nonnull

writer

)

const

Append this record's fields to an already-open writer.

What ToMsgpack() is built from, and what a parent record calls through MsgpackWriter::PackRecord so that nesting costs no buffer of its own. Both produce the same bytes; this one avoids the intermediate string.

Assumes the record is already valid. Validate() recurses through nested records, so validating here as well would re-check every nested id once per ancestor level. ToMsgpack() validates the whole tree once and then calls this; a caller reaching for this directly should do the same, and any caller that got its record from FromMsgpack() already has.

Validate()

absl::Status a11::data::Chunk::Validate

(

)

const

Validate that payload, reference, and metadata fields are consistent.

Friends And Related Symbol Documentation

AbslStringify

template<typename Sink >

void AbslStringify ( Sink &  sink, const Chunk &  value  )

friend

operator==

bool operator== ( const Chunk &  , const Chunk &    )

friend

Member Data Documentation

data

Bytes a11::data::Chunk::data {}

Inline byte payload.

metadata

std::optional<ChunkMetadata> a11::data::Chunk::metadata {}

Optional payload metadata.

object

std::shared_ptr<const ChunkObject> a11::data::Chunk::object {}

The value this chunk stands for, when its bytes have not been produced.

Never crosses a process boundary: everything that sends, persists or hands out bytes calls Materialize() first, so a peer and a durable store see exactly what they saw before this field existed.

ref

std::string a11::data::Chunk::ref {}

Node id this chunk references, if not inline.

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The documentation for this struct was generated from the following files:

• cpp/a11/data/types.h
• cpp/a11/data/types.cc