alo

Documentation

Overview

Package alo implements a forward error correction scheme using Reed Solomon Erasure Coding. It segments the data into 1kb chunks in 16kb segments and contains a function for use in a network handler to process received packets

Index

• Constants
• Variables
• func Pieces(dLen, size int) (s int)
• func SegmentBytes(buf []byte, lim int) (out [][]byte)
• func ShardsPerRedundancy(nShards, redundancy int) int
• type PartialSegment
  • func (p PartialSegment) GetShardCount() (count int)
• type Partials
  • func NewPacket(firstShard []byte) (o *Partials, e error)
  • func (p *Partials) AddShard(newShard []byte) (e error)
  • func (p *Partials) Decode() (final []byte, e error)
  • func (p *Partials) GetRatio() (out float64)
  • func (p *Partials) HasAllDataShards() bool
  • func (p *Partials) HasMinimum() bool
  • func (p *Partials) IsDecoded() bool
• type Segments
• type ShardPrefix
  • func GetParams(data []byte) (p ShardPrefix, e error)
• type ShardedSegments
  • func GetShards(buf []byte, redundancy int) (out ShardedSegments)

Constants

const (
	SegmentSize = 2 << 13
	ShardSize   = 2 << 9
)

Variables

var F, E, W, I, D, T logg.LevelPrinter = logg.GetLogPrinterSet(subsystem)

Functions

func Pieces

func Pieces(dLen, size int) (s int)

Pieces computes the number of pieces based on a given chunk size

func SegmentBytes

func SegmentBytes(buf []byte, lim int) (out [][]byte)

SegmentBytes breaks a chunk of data into requested sized limit chunks

func ShardsPerRedundancy

func ShardsPerRedundancy(nShards, redundancy int) int

Types

type PartialSegment

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

PartialSegment is a max 16kb long segment with arbitrary redundancy parameters when all of the data segments are successfully received hasAll indicates the segment may be ready to reassemble

func (PartialSegment) GetShardCount

func (p PartialSegment) GetShardCount() (count int)

GetShardCount returns the number of shards already acquired

type Partials

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

Partials is a structure for storing a new inbound packet

func NewPacket

func NewPacket(firstShard []byte) (o *Partials, e error)

NewPacket creates a new structure to store a collection of incoming shards when the first of a new packet arrives

func (*Partials) AddShard

func (p *Partials) AddShard(newShard []byte) (e error)

AddShard adds a newly received shard to a Partials, ensuring that it has matching parameters (if the HMAC on the packet's wrapper passes it should be unless someone is playing silly buggers)

func (*Partials) Decode

func (p *Partials) Decode() (final []byte, e error)

Decode the received message if we have sufficient pieces

func (*Partials) GetRatio

func (p *Partials) GetRatio() (out float64)

GetRatio is used after the receive delay period expires to determine how successful a packet was. If it was exactly enough with no surplus, return 0, if there is more than the minimum, return the proportion compared to the total redundancy of the packet, if there is less, return a negative proportion versus the amount, -1 means zero received, and a fraction of 1 indicates the proportion that was received compared to the minimum

func (*Partials) HasAllDataShards

func (p *Partials) HasAllDataShards() bool

HasAllDataShards returns true if all data shards are present in a Partials

func (*Partials) HasMinimum

func (p *Partials) HasMinimum() bool

HasMinimum returns true if there may be enough data to decode

func (*Partials) IsDecoded

func (p *Partials) IsDecoded() bool

type Segments

type Segments [][]byte

type ShardPrefix

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

func GetParams

func GetParams(data []byte) (
	p ShardPrefix, e error,
)

GetParams reads the shard's prefix to provide the correct parameters for the RS codec the packet requires based on the prefix on a shard (presumably to create the codec when a new packet/group of shards arrives)

type ShardedSegments

type ShardedSegments []Segments

func GetShards

func GetShards(buf []byte, redundancy int) (out ShardedSegments)

GetShards returns a bundle of segments to be sent or stored in a 1kb segment size with redundancy shards added to each segment's shards that can reconstruct the original message by derivation via the available parity shards.