README
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Raptor code over User Datagram Protocol
RC-UDP implements Raptor Coding over UDP transport protocol with tunable overhead.
The package provides two utilities - a RC-UDP Reader (Client) and a RC-UDP Writer (Server). Message encoding/decoding is based on the Raptor fountain code (also called the R10 code) from RFC 5053.
Naming convention
In this package a message means the complete data blob to be transmitted on the wire.
Packet is the UDP packet which includes a single block of the message.
Blocks are the segments which a message is encoded to.
Writer
rcudp.Writer(...) function is a UDP client that uses gofountain Raptor Code encoder to split a message into source blocks. An encoded block together with metadata is marshalled into a UDP packet with following structure:
MessageID 8 bytes
NumSourceSymbols 2 bytes
PaddingSize 2 bytes
TransferLength 4 bytes
BlockID 4 bytes
BlockData 1452 bytes
Note that overall size of a packet is up to 1472 (=1500-8-20) bytes. (default MTU size minus UDP Header size minus IPv4 header size)
The size of a complete wire message is TransferLength - PaddingSize. A limitation is that the code supports a maximum of 8192 source blocks. With current BlockData size of 1452, the maximum length of a message that can be transmitted is 1452*8192 (~11.89 MB)
NumSourceSymbols - K. Must be in the range [4, 8192] (inclusive). This is how many source symbols the input message will be divided into.
Tuning
backoffTimeout (config.go) - defines delay before each UDP socket write. This is intended to reduce the load on both sender and recv udp buffers.
writeBufferSize (config.go) - UDP Sender buffer size can be up to net.core.wmem_max (Linux)
redundancyFactor input param - defines the count of additional encoded blocks to be generated and sent
Reader
UDPReader is a UDP server that collects Raptor fountain code blocks from the wire and makes attempts to decode (recover) the complete and original message. It correlates blocks by MessageID. When a message is decoded, its processing is delegated to the MessageCollector (a callback).
Tuning
staleTimeout - The size of the time-window within which a message should be completely received and decoded. Out of this time-window, the message is marked as stale and deleted.
readBufferSize - UDP Recv buffer size can be up to net.core.rmem_max (Linux)
Documentation
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Index ¶
Constants ¶
const (
// BcastHeightPos is position in packet binary of height byte.
BcastHeightPos = 20
)
const (
// BlockSize - max length of an encoding symbol that can fit into a single wire packet.
BlockSize = maxUDPLength - 8 - 2 - 2 - 4 - 4 - 8
)
Variables ¶
var ( // ErrTooLargeUDP packet cannot fit into default MTU of 1500. ErrTooLargeUDP = errors.New("packet cannot fit into default MTU of 1500") )
Functions ¶
func CompileRaptorRFC5053 ¶ added in v0.4.3
func CompileRaptorRFC5053(height byte, message []byte, redundancyFactor uint8) ([]byte, [][]byte, error)
CompileRaptorRFC5053 compiles raptorRFC5053 blocks from message with a specified redundancyFactor. In Kadcast, one could compile blocks once but send them to multiple delegates.
Types ¶
type Decoder ¶
type Decoder struct {
// contains filtered or unexported fields
}
Decoder is based on fountain.newRaptorDecoder.
func NewDecoder ¶
NewDecoder creates a wrapper decoder of fountain.Decoder.
type Encoder ¶
type Encoder struct {
SymbolAlignmentSize uint16
// output parameters.
PaddingSize uint16
NumSourceSymbols int
// contains filtered or unexported fields
}
Encoder is wrapper around Raptor RFC5053 from gofountain.EncodeLTBlocks.
func NewEncoder ¶
func NewEncoder(message []byte, maxPacketSize uint16, redundancyFactor uint8, symbolAlignmentSize uint16) (*Encoder, error)
NewEncoder creates a Raptor RFC5053 wrapper.
func (*Encoder) GenerateBlocks ¶
GenerateBlocks encodes raptor codes. NB: This method is destructive to the w.message array.
func (*Encoder) TransferLength ¶
TransferLength is the number of message plus calculated padding.
type MessageCollector ¶
MessageCollector callback to be run on a newly decoded message.
type Packet ¶
type Packet struct {
NumSourceSymbols uint16
PaddingSize uint16
// contains filtered or unexported fields
}
Packet is the UDP packet that consists of encoding symbol data unit and raptor-specific data.
type UDPReader ¶
type UDPReader struct {
// contains filtered or unexported fields
}
UDPReader that supports decoding Raptor codes packets.
func NewUDPReader ¶
func NewUDPReader(lAddr *net.UDPAddr, h MessageCollector) (*UDPReader, error)
NewUDPReader instantiate a UDP reader of raptor code packets.
Source Files