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nim-libp2p-experimental
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nim-libp2p-experimental/libp2p/varint.nim

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## Nim-Libp2p
## Copyright (c) 2018 Status Research & Development GmbH
## Licensed under either of
## * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
## * MIT license ([LICENSE-MIT](LICENSE-MIT))
## at your option.
## This file may not be copied, modified, or distributed except according to
## those terms.
## This module implements Variable Integer `VARINT`.
## This module supports two variants of variable integer
## - Google ProtoBuf varint, which is able to encode full uint64 number and
## maximum size of encoded value is 10 octets (bytes).
## https://developers.google.com/protocol-buffers/docs/encoding#varints
## - LibP2P varint, which is able to encode only 63bits of uint64 number and
## maximum size of encoded value is 9 octets (bytes).
## https://github.com/multiformats/unsigned-varint
import bitops
type
VarintStatus* {.pure.} = enum
Error,
Success,
Overflow,
Incomplete,
Overlong,
Overrun
PB* = object
## Use this type to specify Google ProtoBuf's varint encoding
LP* = object
## Use this type to specify LibP2P varint encoding
PBSomeUVarint* = uint | uint64 | uint32
PBSomeSVarint* = int | int64 | int32
PBSomeVarint* = PBSomeUVarint | PBSomeSVarint
LPSomeUVarint* = uint | uint64 | uint32 | uint16 | uint8
LPSomeVarint* = LPSomeUVarint
SomeVarint* = PBSomeVarint | LPSomeVarint
SomeUVarint* = PBSomeUVarint | LPSomeUVarint
VarintError* = object of CatchableError
proc vsizeof*(x: SomeVarint): int {.inline.} =
## Returns number of bytes required to encode integer ``x`` as varint.
if x == cast[type(x)](0):
result = 1
else:
result = (fastLog2(x) + 1 + 7 - 1) div 7
proc getUVarint*[T: PB|LP](vtype: typedesc[T],
pbytes: openarray[byte],
outlen: var int,
outval: var SomeUVarint): VarintStatus =
## Decode `unsigned varint` from buffer ``pbytes`` and store it to ``outval``.
## On success ``outlen`` will be set to number of bytes processed while
## decoding `unsigned varint`.
##
## If array ``pbytes`` is empty, ``Incomplete`` error will be returned.
##
## If there not enough bytes available in array ``pbytes`` to decode `unsigned
## varint`, ``Incomplete`` error will be returned.
##
## If encoded value can produce integer overflow, ``Overflow`` error will be
## returned.
##
## Google ProtoBuf
## When decoding 10th byte of Google Protobuf's 64bit integer only 1 bit from
## byte will be decoded, all other bits will be ignored. When decoding 5th
## byte of 32bit integer only 4 bits from byte will be decoded, all other bits
## will be ignored.
##
## LibP2P
## When decoding 5th byte of 32bit integer only 4 bits from byte will be
## decoded, all other bits will be ignored.
when vtype is PB:
const MaxBits = byte(sizeof(outval) * 8)
else:
when sizeof(outval) == 8:
const MaxBits = 63'u8
else:
const MaxBits = byte(sizeof(outval) * 8)
var shift = 0'u8
result = VarintStatus.Incomplete
outlen = 0
outval = cast[type(outval)](0)
for i in 0..<len(pbytes):
let b = pbytes[i]
if shift >= MaxBits:
result = VarintStatus.Overflow
outlen = 0
outval = cast[type(outval)](0)
break
else:
outval = outval or (cast[type(outval)](b and 0x7F'u8) shl shift)
shift += 7
inc(outlen)
if (b and 0x80'u8) == 0'u8:
result = VarintStatus.Success
break
if result == VarintStatus.Incomplete:
outlen = 0
outval = cast[type(outval)](0)
when vtype is LP:
if result == VarintStatus.Success:
if outlen != vsizeof(outval):
outval = cast[type(outval)](0)
outlen = 0
result = VarintStatus.Overlong
proc putUVarint*[T: PB|LP](vtype: typedesc[T],
pbytes: var openarray[byte],
outlen: var int,
outval: SomeUVarint): VarintStatus =
## Encode `unsigned varint` ``outval`` and store it to array ``pbytes``.
##
## On success ``outlen`` will hold number of bytes (octets) used to encode
## unsigned integer ``v``.
##
## If there not enough bytes available in buffer ``pbytes``, ``Incomplete``
## error will be returned and ``outlen`` will be set to number of bytes
## required.
##
## Google ProtoBuf
## Maximum encoded length of 64bit integer is 10 octets.
## Maximum encoded length of 32bit integer is 5 octets.
##
## LibP2P
## Maximum encoded length of 63bit integer is 9 octets.
## Maximum encoded length of 32bit integer is 5 octets.
var buffer: array[10, byte]
var value = outval
var k = 0
when vtype is LP:
if sizeof(outval) == 8:
if (cast[uint64](outval) and 0x8000_0000_0000_0000'u64) != 0'u64:
result = Overflow
return
if value <= cast[type(outval)](0x7F):
buffer[0] = cast[byte](outval and 0xFF)
inc(k)
else:
while value != cast[type(outval)](0):
buffer[k] = cast[byte]((value and 0x7F) or 0x80)
value = value shr 7
inc(k)
buffer[k - 1] = buffer[k - 1] and 0x7F'u8
outlen = k
if len(pbytes) >= k:
copyMem(addr pbytes[0], addr buffer[0], k)
result = VarintStatus.Success
else:
result = VarintStatus.Overrun
proc getSVarint*(pbytes: openarray[byte], outsize: var int,
outval: var PBSomeSVarint): VarintStatus {.inline.} =
## Decode Google ProtoBuf's `signed varint` from buffer ``pbytes`` and store
## it to ``outval``. On success ``outlen`` will be set to number of bytes
## processed while decoding `signed varint`.
##
## If array ``pbytes`` is empty, ``Incomplete`` error will be returned.
##
## If there not enough bytes available in array ``pbytes`` to decode `signed
## varint`, ``Incomplete`` error will be returned.
##
## If encoded value can produce integer overflow, ``Overflow`` error will be
## returned.
##
## Note, when decoding 10th byte of 64bit integer only 1 bit from byte will be
## decoded, all other bits will be ignored. When decoding 5th byte of 32bit
## integer only 4 bits from byte will be decoded, all other bits will be
## ignored.
when sizeof(outval) == 8:
var value: uint64
else:
var value: uint32
result = PB.getUVarint(pbytes, outsize, value)
if result == VarintStatus.Success:
if (value and cast[type(value)](1)) != cast[type(value)](0):
outval = cast[type(outval)](not(value shr 1))
else:
outval = cast[type(outval)](value shr 1)
proc putSVarint*(pbytes: var openarray[byte], outsize: var int,
outval: PBSomeSVarint): VarintStatus {.inline.} =
## Encode Google ProtoBuf's `signed varint` ``outval`` and store it to array
## ``pbytes``.
##
## On success ``outlen`` will hold number of bytes (octets) used to encode
## unsigned integer ``v``.
##
## If there not enough bytes available in buffer ``pbytes``, ``Incomplete``
## error will be returned and ``outlen`` will be set to number of bytes
## required.
##
## Maximum encoded length of 64bit integer is 10 octets.
## Maximum encoded length of 32bit integer is 5 octets.
when sizeof(outval) == 8:
var value: uint64 =
if outval < 0:
not(cast[uint64](outval) shl 1)
else:
cast[uint64](outval) shl 1
else:
var value: uint32 =
if outval < 0:
not(cast[uint32](outval) shl 1)
else:
cast[uint32](outval) shl 1
result = PB.putUVarint(pbytes, outsize, value)
proc encodeVarint*(vtype: typedesc[PB],
value: PBSomeVarint): seq[byte] {.inline.} =
## Encode integer to Google ProtoBuf's `signed/unsigned varint` and returns
## sequence of bytes as result.
var outsize = 0
result = newSeqOfCap[byte](10)
when sizeof(value) == 4:
result.setLen(5)
else:
result.setLen(10)
when type(value) is PBSomeSVarint:
let res = putSVarint(result, outsize, value)
else:
let res = PB.putUVarint(result, outsize, value)
if res == VarintStatus.Success:
result.setLen(outsize)
else:
raise newException(VarintError, "Error '" & $res & "'")
proc encodeVarint*(vtype: typedesc[LP],
value: LPSomeVarint): seq[byte] {.inline.} =
## Encode integer to LibP2P `unsigned varint` and returns sequence of bytes
## as result.
var outsize = 0
result = newSeqOfCap[byte](9)
when sizeof(value) == 1:
result.setLen(2)
elif sizeof(value) == 2:
result.setLen(3)
elif sizeof(value) == 4:
result.setLen(5)
else:
result.setLen(9)
let res = LP.putUVarint(result, outsize, value)
if res == VarintStatus.Success:
result.setLen(outsize)
else:
raise newException(VarintError, "Error '" & $res & "'")
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