Documentation
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Overview ¶
Package sdnv encodes and decodes Self-Delimiting Numeric Values.
An SDNV packs an unsigned integer into as few octets as it needs. The top bit of each octet says whether another follows: set means "more to come", clear means "this is the last one". The value is the 7 low bits of each octet concatenated, most significant first.
0x7F -> 01111111 one octet 0x80 -> 10000001 00000000 two octets 0x4234 -> 10000001 10000100 00110100 three octets
The scheme comes from ASN.1 Object Identifier encoding. Two protocols in this library use it for nearly every variable-length field: LTP (RFC 5326 clause 1.6 item 20) and Bundle Protocol version 6 (RFC 5050 clause 4.1). It lives in its own package so neither has to carry a private copy, the same way pkg/crc serves the checksum users.
Index ¶
Constants ¶
const MaxEncodedSize = 10
MaxEncodedSize is the widest SDNV this package produces or accepts: ten octets, which is what a full 64-bit value needs at 7 bits per octet.
Variables ¶
var ( // ErrDataTooShort indicates the input ended mid-value, with every octet // so far having its continuation bit set. ErrDataTooShort = errors.New("sdnv: data ended before the value did") // ErrOverflow indicates a value too large for a uint64. ErrOverflow = errors.New("sdnv: value does not fit in 64 bits") // ErrTooLong indicates an encoding running past MaxEncodedSize octets. // RFC 6256 clause 3.2 allows leading zero-padding octets (0x80), so an encoding // this long is not necessarily a value overflow, but this package caps // what it will read at ten octets, the width a canonical 64-bit value // needs, and refuses longer inputs with this distinct error. ErrTooLong = errors.New("sdnv: encoding is longer than the 10-octet maximum") )
Functions ¶
func AppendEncode ¶
AppendEncode appends the SDNV encoding of v to dst and returns the extended slice. Use it to build a segment without an allocation per field.
func Decode ¶
Decode reads one SDNV from the front of data, returning the value and the number of octets consumed.
A value wider than 64 bits is an error rather than a silent wrap. So is an input that runs out while the continuation bit is still set.
func DecodeFrom ¶
func DecodeFrom(r io.ByteReader) (uint64, error)
DecodeFrom reads one SDNV from r, one octet at a time. It reads no further than the end of the value.
func DecodeN ¶
DecodeN reads count consecutive SDNVs from the front of data, returning the values and the total octets consumed. It is the common case when a segment carries a run of adjacent SDNV fields.
func EncodedSize ¶
EncodedSize returns how many octets Encode will produce for v.
Types ¶
This section is empty.
Source Files