mcap

package module
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 Go to latest Published: Apr 23, 2025 License: MIT Imports: 16 Imported by: 21

README

mcap

Note: This library is experimental and will change without warning until finalization of the spec.

An experimental library for writing and reading MCAP files in go.

API reference

API documentation can be found here.

Documentation

Index

Constants

This section is empty.

Variables

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var ErrAttachmentDataSizeIncorrect = errors.New("attachment content length incorrect")

ErrAttachmentDataSizeIncorrect is returned when the length of a written attachment does not match the length supplied.

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var ErrBadOffset = errors.New("invalid offset")
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var ErrChunkTooLarge = errors.New("chunk exceeds configured maximum size")
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var ErrInvalidZeroOpcode = errors.New("invalid zero opcode")
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var ErrLengthOutOfRange = errors.New("length out of int32 range")
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var ErrMetadataNotFound = errors.New("metadata not found")
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var ErrNestedChunk = errors.New("detected nested chunk")

ErrNestedChunk indicates the lexer has detected a nested chunk.

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var ErrRecordTooLarge = errors.New("record exceeds configured maximum size")
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var ErrUnknownSchema = errors.New("unknown schema")

ErrUnknownSchema is returned when a schema ID is not known to the writer.

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var Magic = []byte{0x89, 'M', 'C', 'A', 'P', 0x30, '\r', '\n'}

Magic is the magic number for an MCAP file.

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var Version = "v1.7.2"

Version of the MCAP library.

Functions

func NewErrUnexpectedToken added in v1.7.0 

func NewErrUnexpectedToken(err error) error

func Range 

func Range(it MessageIterator, f func(*Schema, *Channel, *Message) error) error

Types

type Attachment 

type Attachment struct {
	LogTime    uint64
	CreateTime uint64
	Name       string
	MediaType  string
	DataSize   uint64
	Data       io.Reader
}

Attachment records contain auxiliary artifacts such as text, core dumps, calibration data, or other arbitrary data. Attachment records must not appear within a chunk.

type AttachmentIndex 

type AttachmentIndex struct {
	Offset     uint64
	Length     uint64
	LogTime    uint64
	CreateTime uint64
	DataSize   uint64
	Name       string
	MediaType  string
}

AttachmentIndex records contain the location of attachments in the file. An AttachmentIndex record exists for every Attachment in the file.

func ParseAttachmentIndex 

func ParseAttachmentIndex(buf []byte) (*AttachmentIndex, error)

ParseAttachmentIndex parses an attachment index record.

type AttachmentReader added in v0.3.0 

type AttachmentReader struct {
	LogTime    uint64
	CreateTime uint64
	Name       string
	MediaType  string
	DataSize   uint64
	// contains filtered or unexported fields
}

AttachmentReader represents an attachment for handling in a streaming manner.

func (*AttachmentReader) ComputedCRC added in v0.3.0 

func (ar *AttachmentReader) ComputedCRC() (uint32, error)

ComputedCRC discards any remaining data in the Data portion of the AttachmentReader, then returns the checksum computed from the fields of the attachment up to the CRC. If it is called before the data portion of the reader has been fully consumed, an error will be returned. If the AttachmentReader has been created with a crcReader that is instructed not to compute the CRC, this will return a CRC of zero.

func (*AttachmentReader) Data added in v0.3.0 

func (ar *AttachmentReader) Data() io.Reader

Data returns a reader over the data section of the attachment.

func (*AttachmentReader) ParsedCRC added in v0.3.0 

func (ar *AttachmentReader) ParsedCRC() (uint32, error)

ParsedCRC returns the CRC from the crc field of the record. It must be called after the data field has been handled. If ParsedCRC is called before the data reader is exhausted, an error is returned.

type Channel 

type Channel struct {
	ID              uint16
	SchemaID        uint16
	Topic           string
	MessageEncoding string
	Metadata        map[string]string
}

Channel records define encoded streams of messages on topics. Channel records are uniquely identified within a file by their channel ID. A Channel record must occur at least once in the file prior to any message referring to its channel ID. Any two channel records sharing a common ID must be identical.

func ParseChannel 

func ParseChannel(buf []byte) (*Channel, error)

ParseChannel parses a channel record.

type Chunk 

type Chunk struct {
	MessageStartTime uint64
	MessageEndTime   uint64
	UncompressedSize uint64
	UncompressedCRC  uint32
	Compression      string
	Records          []byte
}

Chunk records each contain a batch of Schema, Channel, and Message records. The batch of records contained in a chunk may be compressed or uncompressed. All messages in the chunk must reference channels recorded earlier in the file (in a previous chunk or earlier in the current chunk).

func ParseChunk 

func ParseChunk(buf []byte) (*Chunk, error)

ParseChunk parses a chunk record.

type ChunkIndex 

type ChunkIndex struct {
	MessageStartTime    uint64
	MessageEndTime      uint64
	ChunkStartOffset    uint64
	ChunkLength         uint64
	MessageIndexOffsets map[uint16]uint64
	MessageIndexLength  uint64
	Compression         CompressionFormat
	CompressedSize      uint64
	UncompressedSize    uint64
}

ChunkIndex records contain the location of a Chunk record and its associated MessageIndex records. A ChunkIndex record exists for every Chunk in the file.

func ParseChunkIndex 

func ParseChunkIndex(buf []byte) (*ChunkIndex, error)

ParseChunkIndex parses a chunk index record.

type CompressionFormat 

type CompressionFormat string

CompressionFormat represents a supported chunk compression format. 

const (
	// CompressionZSTD represents zstd compression.
	CompressionZSTD CompressionFormat = "zstd"
	// CompressionLZ4 represents lz4 compression.
	CompressionLZ4 CompressionFormat = "lz4"
	// CompressionNone represents no compression.
	CompressionNone CompressionFormat = ""
)

func (CompressionFormat) String 

func (c CompressionFormat) String() string

String converts a compression format to a string for display.

type CompressionLevel added in v1.0.1 

type CompressionLevel int
const (
	// Default is the default "pretty fast" compression option.
	// This is roughly equivalent to the default Zstandard mode (level 3).
	CompressionLevelDefault CompressionLevel = iota

	// Fastest will choose the fastest reasonable compression. This is roughly
	// equivalent to the fastest LZ4/Zstandard modes.
	CompressionLevelFastest

	// Better will yield better compression than the default.
	// For zstd, this is about level 7-8 with ~ 2x-3x the default CPU usage.
	CompressionLevelBetter

	// Best will choose the best available compression option. This will offer the
	// best compression no matter the CPU cost.
	CompressionLevelBest
)

type CustomCompressor added in v1.0.4 

type CustomCompressor interface {
	Compressor() ResettableWriteCloser
	Compression() CompressionFormat
}

func NewCustomCompressor added in v1.0.4 

func NewCustomCompressor(compression CompressionFormat, compressor ResettableWriteCloser) CustomCompressor

NewCustomCompressor returns a structure that may be supplied to writer options as a custom chunk compressor.

type DataEnd 

type DataEnd struct {
	DataSectionCRC uint32
}

DataEnd indicates the end of the data section.

func ParseDataEnd 

func ParseDataEnd(buf []byte) (*DataEnd, error)

ParseDataEnd parses a data end record.

type ErrBadMagic 

type ErrBadMagic struct {
	// contains filtered or unexported fields
}

ErrBadMagic indicates invalid magic bytes were detected.

func (*ErrBadMagic) Error added in v0.3.0 

func (e *ErrBadMagic) Error() string

func (*ErrBadMagic) Is added in v1.3.1 

func (e *ErrBadMagic) Is(err error) bool

type ErrTruncatedRecord added in v0.3.0 

type ErrTruncatedRecord struct {
	// contains filtered or unexported fields
}

ErrTruncatedRecord indicates not enough data was available to parse a certain record.

func (*ErrTruncatedRecord) Error added in v0.3.0 

func (e *ErrTruncatedRecord) Error() string

func (*ErrTruncatedRecord) Unwrap added in v0.3.0 

func (e *ErrTruncatedRecord) Unwrap() error

type ErrUnexpectedToken added in v1.7.0 

type ErrUnexpectedToken struct {
	// contains filtered or unexported fields
}

ErrUnexpectedToken indicated when an unexpected token was found in an MCAP file.

func (*ErrUnexpectedToken) Error added in v1.7.0 

func (e *ErrUnexpectedToken) Error() string

func (*ErrUnexpectedToken) Is added in v1.7.0 

func (e *ErrUnexpectedToken) Is(target error) bool
type Footer struct {
	SummaryStart       uint64
	SummaryOffsetStart uint64
	SummaryCRC         uint32
}

Footer records contain end-of-file information. MCAP files must end with a Footer record.

func ParseFooter 

func ParseFooter(buf []byte) (*Footer, error)

ParseFooter parses a footer record. 

type Header struct {
	Profile string
	Library string
}

Header is the first record in an MCAP file.

func ParseHeader 

func ParseHeader(buf []byte) (*Header, error)

ParseHeader parses a header record.

type Info 

type Info struct {
	Statistics        *Statistics
	Channels          map[uint16]*Channel
	Schemas           map[uint16]*Schema
	ChunkIndexes      []*ChunkIndex
	MetadataIndexes   []*MetadataIndex
	AttachmentIndexes []*AttachmentIndex
	Header            *Header
	Footer            *Footer
}

Info represents the result of an "info" operation, for gathering information from the summary section of a file.

func (*Info) ChannelCounts 

func (i *Info) ChannelCounts() map[string]uint64

ChannelCounts counts the number of messages on each channel in an Info.

type Lexer 

type Lexer struct {
	// contains filtered or unexported fields
}

Lexer is a low-level reader for mcap files that emits tokenized byte strings without parsing or interpreting them, except in the case of chunks, which may be optionally de-chunked.

func NewLexer 

func NewLexer(r io.Reader, opts ...*LexerOptions) (*Lexer, error)

NewLexer returns a new lexer for the given reader.

func (*Lexer) Close added in v0.4.0 

func (l *Lexer) Close()

Close the lexer.

func (*Lexer) Next 

func (l *Lexer) Next(p []byte) (TokenType, []byte, error)

Next returns the next token from the lexer as a byte array. The result will be sliced out of the provided buffer `p`, if p has adequate space. If p does not have adequate space, a new buffer with sufficient size is allocated for the result.

type LexerOptions 

type LexerOptions struct {
	// SkipMagic instructs the lexer not to perform validation of the leading magic bytes.
	SkipMagic bool
	// ValidateChunkCRC instructs the lexer to validate CRC checksums for
	// chunks.
	ValidateChunkCRCs bool
	// ComputeAttachmentCRCs instructs the lexer to compute CRCs for any
	// attachments parsed from the file. Consumers should only set this to true
	// if they intend to validate those CRCs in their attachment callback.
	ComputeAttachmentCRCs bool
	// EmitChunks instructs the lexer to emit chunk records without de-chunking.
	// It is incompatible with ValidateCRC.
	EmitChunks bool
	// EmitChunks instructs the lexer to emit TokenInvalidChunk rather than TokenError when CRC
	// validation fails.
	EmitInvalidChunks bool
	// MaxDecompressedChunkSize defines the maximum size chunk the lexer will
	// decompress. Chunks larger than this will result in an error.
	MaxDecompressedChunkSize int
	// MaxRecordSize defines the maximum size record the lexer will read.
	// Records larger than this will result in an error.
	MaxRecordSize int
	// AttachmentCallback is a function to execute on attachments encountered in the file.
	AttachmentCallback func(*AttachmentReader) error
	// Decompressors are custom decompressors. Chunks matching the supplied
	// compression format will be decompressed with the provided
	// ResettableReader instead of the default implementation.
	Decompressors map[CompressionFormat]ResettableReader
}

LexerOptions holds options for the lexer.

type Message 

type Message struct {
	ChannelID   uint16
	Sequence    uint32
	LogTime     uint64
	PublishTime uint64
	Data        []byte
}

Message records encode a single timestamped message on a channel. The message encoding and schema must match that of the Channel record corresponding to the message's channel ID.

func ParseMessage 

func ParseMessage(buf []byte) (*Message, error)

ParseMessage parses a message record.

func (*Message) PopulateFrom added in v1.4.0 

func (m *Message) PopulateFrom(buf []byte, copyData bool) error

PopulateFrom populates the fields of a Message struct from the message data slice.

type MessageIndex 

type MessageIndex struct {
	ChannelID uint16
	Records   []MessageIndexEntry
	// contains filtered or unexported fields
}

MessageIndex records allow readers to locate individual records within a chunk by timestamp. A sequence of Message Index records occurs immediately after each chunk. Exactly one Message Index record must exist in the sequence for every channel on which a message occurs inside the chunk.

func ParseMessageIndex 

func ParseMessageIndex(buf []byte) (*MessageIndex, error)

ParseMessageIndex parses a message index record.

func (*MessageIndex) Add 

func (idx *MessageIndex) Add(timestamp uint64, offset uint64)

Add an entry to the message index.

func (*MessageIndex) Entries 

func (idx *MessageIndex) Entries() []MessageIndexEntry

Entries lists the entries in the message index.

func (*MessageIndex) IsEmpty added in v1.0.1 

func (idx *MessageIndex) IsEmpty() bool

func (*MessageIndex) Reset 

func (idx *MessageIndex) Reset()

Reset resets the MessageIndex to an empty state, to enable reuse.

type MessageIndexEntry 

type MessageIndexEntry struct {
	Timestamp uint64
	Offset    uint64
}

type MessageIterator 

type MessageIterator interface {
	// Deprecated: use NextInto to avoid repeatedly heap-allocating Message structs while iterating.
	Next([]byte) (*Schema, *Channel, *Message, error)
	// NextInto returns the next message from the MCAP. If the returned error is io.EOF,
	// this signals the end of the MCAP.
	// If `msg` is not nil, NextInto will populate it with new data and
	// return the same pointer, re-using or resizing `msg.Data` as needed.
	// If `msg` is nil, NextInto will allocate and return a new Message on the heap.
	NextInto(msg *Message) (*Schema, *Channel, *Message, error)
}

type Metadata 

type Metadata struct {
	Name     string
	Metadata map[string]string
}

Metadata records contain arbitrary user data in key-value pairs.

func ParseMetadata 

func ParseMetadata(buf []byte) (*Metadata, error)

ParseMetadata parses a metadata record.

type MetadataIndex 

type MetadataIndex struct {
	Offset uint64
	Length uint64
	Name   string
}

MetadataIndex records each contain the location of a metadata record within the file.

func ParseMetadataIndex 

func ParseMetadataIndex(buf []byte) (*MetadataIndex, error)

ParseMetadataIndex parses a metadata index record.

type OpCode 

type OpCode byte
const (
	OpReserved        OpCode = 0x00
	OpHeader          OpCode = 0x01
	OpFooter          OpCode = 0x02
	OpSchema          OpCode = 0x03
	OpChannel         OpCode = 0x04
	OpMessage         OpCode = 0x05
	OpChunk           OpCode = 0x06
	OpMessageIndex    OpCode = 0x07
	OpChunkIndex      OpCode = 0x08
	OpAttachment      OpCode = 0x09
	OpAttachmentIndex OpCode = 0x0A
	OpStatistics      OpCode = 0x0B
	OpMetadata        OpCode = 0x0C
	OpMetadataIndex   OpCode = 0x0D
	OpSummaryOffset   OpCode = 0x0E
	OpDataEnd         OpCode = 0x0F
)

func (OpCode) String 

func (c OpCode) String() string

type ReadOpt added in v1.1.0 

type ReadOpt func(*ReadOptions) error

func After deprecated added in v1.1.0 

func After(start int64) ReadOpt

After limits messages yielded by the reader to those with log times after this timestamp.

Deprecated: the int64 argument does not permit the full range of possible message timestamps, use AfterNanos instead.

func AfterNanos added in v1.3.0 

func AfterNanos(start uint64) ReadOpt

AfterNanos limits messages yielded by the reader to those with log times after this timestamp.

func Before deprecated added in v1.1.0 

func Before(end int64) ReadOpt

Before limits messages yielded by the reader to those with log times before this timestamp.

Deprecated: the int64 argument does not permit the full range of possible message timestamps, use BeforeNanos instead.

func BeforeNanos added in v1.3.0 

func BeforeNanos(end uint64) ReadOpt

BeforeNanos limits messages yielded by the reader to those with log times before this timestamp.

func InOrder added in v1.1.0 

func InOrder(order ReadOrder) ReadOpt

func UsingIndex added in v1.1.0 

func UsingIndex(useIndex bool) ReadOpt

func WithMetadataCallback added in v1.1.0 

func WithMetadataCallback(callback func(*Metadata) error) ReadOpt

func WithTopics added in v1.1.0 

func WithTopics(topics []string) ReadOpt

type ReadOptions added in v1.1.0 

type ReadOptions struct {
	// Deprecated: use StartNanos instead
	Start int64
	// Deprecated: use EndNanos instead
	End      int64
	Topics   []string
	UseIndex bool
	Order    ReadOrder

	MetadataCallback func(*Metadata) error

	StartNanos uint64
	EndNanos   uint64
}

func (*ReadOptions) Finalize added in v1.3.0 

func (ro *ReadOptions) Finalize()

type ReadOrder added in v1.1.0 

type ReadOrder int
const (
	FileOrder           ReadOrder = 0
	LogTimeOrder        ReadOrder = 1
	ReverseLogTimeOrder ReadOrder = 2
)

type Reader 

type Reader struct {
	// contains filtered or unexported fields
}

func NewReader 

func NewReader(r io.Reader) (*Reader, error)

func (*Reader) Close added in v0.4.0 

func (r *Reader) Close()

Close the reader.

func (*Reader) GetAttachmentReader added in v1.1.0 

func (r *Reader) GetAttachmentReader(offset uint64) (*AttachmentReader, error)

GetAttachmentReader returns an attachment reader located at the specific offset. The reader must be consumed before the base reader is used again.

func (*Reader) GetMetadata added in v1.1.0 

func (r *Reader) GetMetadata(offset uint64) (*Metadata, error)

func (*Reader) Header added in v0.2.0 

func (r *Reader) Header() *Header

Get the Header record from this MCAP.

func (*Reader) Info 

func (r *Reader) Info() (*Info, error)

Info scans the summary section to form a structure describing characteristics of the underlying mcap file.

func (*Reader) Messages 

func (r *Reader) Messages(
	opts ...ReadOpt,
) (MessageIterator, error)

type ResettableReader added in v1.0.4 

type ResettableReader interface {
	io.Reader
	Reset(io.Reader) error
}

ResettableReadCloser implements io.ReadCloser and adds a Reset method.

type ResettableWriteCloser added in v1.0.4 

type ResettableWriteCloser interface {
	io.WriteCloser
	Reset(io.Writer)
}

ResettableWriteCloser implements io.WriteCloser and adds a Reset method.

type Schema 

type Schema struct {
	ID       uint16
	Name     string
	Encoding string
	Data     []byte
}

A Schema record defines an individual schema. Schema records are uniquely identified within a file by their schema ID. A Schema record must occur at least once in the file prior to any Channel referring to its ID. Any two schema records sharing a common ID must be identical.

func ParseSchema 

func ParseSchema(buf []byte) (*Schema, error)

ParseSchema parses a schema record.

type Statistics 

type Statistics struct {
	MessageCount         uint64
	SchemaCount          uint16
	ChannelCount         uint32
	AttachmentCount      uint32
	MetadataCount        uint32
	ChunkCount           uint32
	MessageStartTime     uint64
	MessageEndTime       uint64
	ChannelMessageCounts map[uint16]uint64
}

Statistics records contain summary information about recorded data. The statistics record is optional, but the file should contain at most one.

func ParseStatistics 

func ParseStatistics(buf []byte) (*Statistics, error)

ParseStatistics parses a statistics record.

type SummaryOffset 

type SummaryOffset struct {
	GroupOpcode OpCode
	GroupStart  uint64
	GroupLength uint64
}

SummaryOffset records contain the location of records within the summary section. Each SummaryOffset record corresponds to a group of summary records with a common opcode.

func ParseSummaryOffset 

func ParseSummaryOffset(buf []byte) (*SummaryOffset, error)

ParseSummaryOffset parses a summary offset record.

type TokenType 

type TokenType int

TokenType encodes a type of token from the lexer. 

const (
	// TokenHeader represents a header token.
	TokenHeader TokenType = iota
	// TokenFooter represents a footer token.
	TokenFooter
	// TokenSchema represents a schema token.
	TokenSchema
	// TokenChannel represents a channel token.
	TokenChannel
	// TokenMessage represents a message token.
	TokenMessage
	// TokenChunk represents a chunk token.
	TokenChunk
	// TokenMessageIndex represents a message index token.
	TokenMessageIndex
	// TokenChunkIndex represents a chunk index token.
	TokenChunkIndex
	// TokenAttachmentIndex represents an attachment index token.
	TokenAttachmentIndex
	// TokenStatistics represents a statistics token.
	TokenStatistics
	// TokenMetadata represents a metadata token.
	TokenMetadata
	// TokenSummaryOffset represents a summary offset token.
	TokenMetadataIndex
	// TokenDataEnd represents a data end token.
	TokenSummaryOffset
	// 	TokenError represents an error token.
	TokenDataEnd
	// TokenError represents an error token.
	TokenError
	// TokenInvalidChunk represents a chunk token that failed CRC validation.
	TokenInvalidChunk
)

func (TokenType) String 

func (t TokenType) String() string

String converts a token type to its string representation.

type Writer 

type Writer struct {
	// Statistics collected over the course of the recording.
	Statistics *Statistics
	// ChunkIndexes created over the course of the recording.
	ChunkIndexes []*ChunkIndex
	// AttachmentIndexes created over the course of the recording.
	AttachmentIndexes []*AttachmentIndex
	// MetadataIndexes created over the course of the recording.
	MetadataIndexes []*MetadataIndex
	// contains filtered or unexported fields
}

Writer is a writer for the MCAP format.

func NewWriter 

func NewWriter(w io.Writer, opts *WriterOptions) (*Writer, error)

NewWriter returns a new MCAP writer.

func (*Writer) Close 

func (w *Writer) Close() error

Close the writer by closing the active chunk and writing the summary section.

func (*Writer) Offset 

func (w *Writer) Offset() uint64

Offset returns the current offset of the writer, or the size of the written file if called after Close().

func (*Writer) WriteAttachment 

func (w *Writer) WriteAttachment(a *Attachment) error

WriteAttachment writes an attachment to the output. Attachment records contain auxiliary artifacts such as text, core dumps, calibration data, or other arbitrary data. Attachment records must not appear within a chunk.

func (*Writer) WriteAttachmentIndex 

func (w *Writer) WriteAttachmentIndex(idx *AttachmentIndex) error

WriteAttachmentIndex writes an attachment index record to the output. An Attachment Index record contains the location of an attachment in the file. An Attachment Index record exists for every Attachment record in the file.

func (*Writer) WriteChannel 

func (w *Writer) WriteChannel(c *Channel) error

WriteChannel writes a channel info record to the output. Channel Info records are uniquely identified within a file by their channel ID. A Channel Info record must occur at least once in the file prior to any message referring to its channel ID.

func (*Writer) WriteChunkIndex added in v1.0.2 

func (w *Writer) WriteChunkIndex(idx *ChunkIndex) error

WriteChunkIndex writes a chunk index record to the output.

func (*Writer) WriteDataEnd 

func (w *Writer) WriteDataEnd(e *DataEnd) error

WriteDataEnd writes a data end record to the output. A Data End record indicates the end of the data section.

func (*Writer) WriteFooter 

func (w *Writer) WriteFooter(f *Footer) error

WriteFooter writes a footer record to the output. A Footer record contains end-of-file information. It must be the last record in the file. Readers using the index to read the file will begin with by reading the footer and trailing magic.

If opts.IncludeCRC is enabled, the CRC is expected to have been reset after the DataEnd record was written.

func (*Writer) WriteHeader 

func (w *Writer) WriteHeader(header *Header) error

WriteHeader writes a header record to the output.

func (*Writer) WriteMessage 

func (w *Writer) WriteMessage(m *Message) error

WriteMessage writes a message to the output. A message record encodes a single timestamped message on a channel. The message encoding and schema must match that of the channel info record corresponding to the message's channel ID.

func (*Writer) WriteMessageIndex 

func (w *Writer) WriteMessageIndex(idx *MessageIndex) error

WriteMessageIndex writes a message index record to the output. A Message Index record allows readers to locate individual message records within a chunk by their timestamp. A sequence of Message Index records occurs immediately after each chunk. Exactly one Message Index record must exist in the sequence for every channel on which a message occurs inside the chunk.

func (*Writer) WriteMetadata 

func (w *Writer) WriteMetadata(m *Metadata) error

WriteMetadata writes a metadata record to the output. A metadata record contains arbitrary user data in key-value pairs.

func (*Writer) WriteMetadataIndex 

func (w *Writer) WriteMetadataIndex(idx *MetadataIndex) error

WriteMetadataIndex writes a metadata index record to the output.

func (*Writer) WriteSchema 

func (w *Writer) WriteSchema(s *Schema) (err error)

WriteSchema writes a schema record to the output. Schema records are uniquely identified within a file by their schema ID. A Schema record must occur at least once in the file prior to any Channel Info referring to its ID. A unique identifier for this schema within the file. Must not be zero.

func (*Writer) WriteStatistics 

func (w *Writer) WriteStatistics(s *Statistics) error

WriteStatistics writes a statistics record to the output. A Statistics record contains summary information about the recorded data. The statistics record is optional, but the file should contain at most one.

func (*Writer) WriteSummaryOffset 

func (w *Writer) WriteSummaryOffset(s *SummaryOffset) error

WriteSummaryOffset writes a summary offset record to the output. A Summary Offset record contains the location of records within the summary section. Each Summary Offset record corresponds to a group of summary records with the same opcode.

type WriterOptions 

type WriterOptions struct {
	// IncludeCRC specifies whether to compute CRC checksums in the output.
	IncludeCRC bool
	// Chunked specifies whether the file should be chunk-compressed.
	Chunked bool
	// ChunkSize specifies a target chunk size for compressed chunks. This size
	// may be exceeded, for instance in the case of oversized messages.
	ChunkSize int64
	// Compression indicates the compression format to use for chunk compression.
	Compression CompressionFormat
	// CompressionLevel controls the speed vs. compression ratio tradeoff. The
	// exact interpretation of this value depends on the compression format.
	CompressionLevel CompressionLevel

	// SkipMessageIndexing skips the message and chunk indexes for a chunked
	// file.
	SkipMessageIndexing bool

	// SkipStatistics skips the statistics accounting.
	SkipStatistics bool

	// SkipRepeatedSchemas skips the schemas repeated at the end of the file
	SkipRepeatedSchemas bool

	// SkipRepeatedChannelInfos skips the channel infos repeated at the end of
	// the file
	SkipRepeatedChannelInfos bool

	// SkipAttachmentIndex skips indexing for attachments
	SkipAttachmentIndex bool

	// SkipMetadataIndex skips metadata index records.
	SkipMetadataIndex bool

	// SkipChunkIndex skips chunk index records.
	SkipChunkIndex bool

	// SkipSummaryOffsets skips summary offset records.
	SkipSummaryOffsets bool

	// OverrideLibrary causes the default header library to be overridden, not
	// appended to.
	OverrideLibrary bool

	// SkipMagic causes the writer to skip writing magic bytes at the start of
	// the file. This may be useful for writing a partial section of records.
	SkipMagic bool

	// Compressor is a custom compressor. If supplied it will take precedence
	// over the built-in ones.
	Compressor CustomCompressor
}

WriterOptions are options for the MCAP Writer.

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