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varints: remove (#195)

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Jacek Sieka 2023-06-12 11:42:27 +02:00 committed by GitHub
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2
README.md
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@ -25,12 +25,12 @@ respective folders
- `bitops2` - an updated version of `bitops.nim`, filling in gaps in original code
- `byteutils` - utilities that make working with the Nim `byte` type convenient
- `endians2` - utilities for converting to and from little / big endian integers
- `leb128` - utilities for working with LEB128-based formats (such as the varint style found in protobuf)
- `objects` - get an object's base type at runtime, as a string
- `ptrops` - pointer arithmetic utilities
- `result` - friendly, exception-free value-or-error returns, similar to `Option[T]`, from [nim-result](https://github.com/arnetheduck/nim-result/)
- `shims` - backports of nim `devel` code to the stable version that Status is using
- `sequtils2` - extensions to the `sequtils` module for working conveniently with `seq`
- `varints` - helpers for working with variable length integers
## Layout

240
stew/varints.nim
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@ -1,240 +0,0 @@
## This module implements Variable Integer `VARINT`.
{.deprecated: "use leb128 or a higher level decoder".}
# There are better variations on this module around:
# * stew/leb128 implements the core varint encoding
# * nim-protobuf-serialization and nim-libp2p contain higher-level protobuf
# varint encoding/decoding
#
# This module has a couple of problems as written:
# * Name conflict with std/varints which implements a _different_ varint
# encoding (sqlite-style)
# * the `Stream` interface in this file is underdefined (ie there's a hidden
# implicit dependency on nim-serialization - the stateful byte-by-byte
# decoder should likely be moved there instead
# * The signed integer support is biased towards casting, whereas the most
# "common" way of encoding signed integers in protobuf is "zig-zag" which
# whose support is missing - above all, biasing towards one of the two signed
# integer formats is error-prone
# * there is no detection of overlong sequences
# * overflows in high bits of nibble are not detected
import
bitops2
type
VarintFlavour* = enum
ProtoBuf
LibP2P
VarintState* {.pure.} = enum
Incomplete,
Done,
Overflow
VarintParser*[IntType; flavour: static VarintFlavour] = object
## This stateful object can be used to parse varints.
##
## Type parameters:
##
## * `IntType` - The output type the parser will try to read
## * `flavour` - The type of varint encoding.
##
## The following encodings are supported:
##
## * `ProtoBuf`
##
## The encoding used by Google ProtoBuf.
## It's able to encode a full uint64 number and the maximum
## encoded size is 10 octets (bytes).
##
## 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`
##
## Encoding used by the LibP2P project.
## It ca encode only lower 63 bits of a uint64 number with a
## maximum size for the encoded value of 9 octets (bytes).
##
## When decoding 5th byte of 32bit integer only 4 bits from
## byte will be decoded, all other bits will be ignored.
##
## Usage protocol:
##
## This object is initialized with the default zero-initialization.
## Proceed to calling `feedByte` one or multiple times and then obtain
## the result with `getResult`.
##
shift: uint8
when IntType is int64|uint64:
res: uint64
else:
res: uint32
when defined(debug):
state: VarintState
VarintBuffer* = object
bytes*: array[10, byte]
totalBytesWritten*: int
func write*(buf: var VarintBuffer, b: byte) =
buf.bytes[buf.totalBytesWritten] = b
inc buf.totalBytesWritten
template writtenBytes*(buf: VarintBuffer): auto =
buf.bytes.toOpenArray(0, buf.totalBytesWritten - 1)
func maxBits(T: type VarintParser): uint8 {.compileTime.} =
when T.flavour == ProtoBuf:
uint8(sizeof(T.IntType) * 8)
elif sizeof(T.IntType) == 8:
uint8(63)
else:
uint(sizeof(T.IntType) * 8)
func feedByte*(p: var VarintParser, b: byte): VarintState =
## Supplies the next input byte to the varint parser.
## The return value is one of the following:
##
## * `Incomplete`
## More input bytes must be supplied.
##
## * `Done`
## The varint has been read to completion.
## Use `parser.getResult` to obtain it.
##
## * `Overflow`
## The maximum number of bits in the parser output value
## has been exceed. The supplied input can be considered invalid.
##
const maxShift = maxBits type(p)
if p.shift >= maxShift:
return Overflow
p.res = p.res or (p.IntType(b and 0x7F'u8) shl p.shift)
p.shift += 7
if (b and 0x80'u8) == 0'u8:
when defined(debug): p.state = Done
Done
else:
Incomplete
func getResult*[IntType, F](p: VarintParser[IntType, F]): IntType {.inline.} =
## Returns the final result of the varint parsing.
## This function must be called after a previous call to `parser.feedByte`
## has returned the state `Done`. The result of calling the function at
## any other time is undefined.
when defined(debug):
doAssert p.state == Done
when result is SomeSignedInt:
type UIntType = type(p.res)
if p.res and UIntType(1) != UIntType(0):
cast[p.IntType](not (p.res shr 1))
else:
cast[p.IntType](p.res shr 1)
else:
p.res
func readVarint*(input: openArray[byte],
outVal: var SomeInteger,
flavour: static VarintFlavour = ProtoBuf): int =
## Reads a varint from a buffer and stores it in `outVal`.
## The return value indicates the number of bytes read.
## If the buffer doesn't hold a valid varint value, the
## function will return 0.
var
parser: VarintParser[type(outVal), flavour]
pos = 0
while pos < input.len:
case parser.feedByte(input[pos])
of Incomplete:
inc pos
of Done:
outVal = parser.getResult
return pos + 1
of Overflow:
return 0
func readVarint*[Stream](input: var Stream,
T: type SomeInteger,
flavour: static VarintFlavour = ProtoBuf): T =
## Reads a varint from a stream (e.g. fastreams.InputStream) and returns it.
##
## The following exceptions may be raised:
##
## * `EOFError`
## The end of the stream was reached before the varint
## was completely read.
##
## * `ValueError`
## The stream contained an invalid varint value.
var parser: VarintParser[T, flavour]
while not input.eof:
case parser.feedByte(input.read)
of Done:
return parser.getResult
of Overflow:
raise newException(ValueError, "Failed to read a varint")
of Incomplete:
continue
raise newException(EOFError, "Failed to read a varint")
proc writeVarintImpl[Stream](s: var Stream, x: SomeUnsignedInt) {.inline.} =
mixin write
if x <= 0x7F:
s.write byte(x and 0xFF)
else:
var x = x
while true:
var nextByte = byte((x and 0x7F) or 0x80)
x = x shr 7
if x == 0:
nextByte = nextByte and 0x7F
s.write nextByte
return
else:
s.write nextByte
proc writeVarint*[Stream](s: var Stream, x: SomeInteger,
flavour: static VarintFlavour = ProtoBuf) {.inline.} =
## Writes a varint to a stream (e.g. faststreams.OutputStream)
when x is SomeSignedInt:
type UInt = (when sizeof(x) == 8: uint64
elif sizeof(x) == 4: uint32
else: uint16)
let x = if x < 0: not(cast[UInt](x) shl 1)
else: cast[UInt](x) shl 1
when flavour == LibP2P and sizeof(x) == 8:
doAssert(x.getBitBE(0) == false)
s.writeVarintImpl x
func vsizeof*(x: SomeInteger): int {.inline.} =
## Returns number of bytes required to encode integer ``x`` as varint.
if x == 0: 1
else: (log2trunc(x) + 1 + 7 - 1) div 7
template varintBytes*(x: SomeInteger,
flavour: static VarintFlavour = ProtoBuf): untyped =
var buf: VarintBuffer
buf.writeVarint(x, flavour)
# TODO: toOpenArray doesn't work here for some reason, so we must
# use the less optimal approach of allocating a sequence copy.
# buf.bytes.toOpenArray(0, buf.totalBytesWritten - 1)
buf.bytes[0 .. buf.totalBytesWritten - 1]

1
tests/all_tests.nim
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@ -34,5 +34,4 @@ import
test_templateutils,
test_results,
test_results2,
test_varints,
test_winacl

72
tests/test_varints.nim
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@ -1,72 +0,0 @@
# Copyright (c) 2019-2022 Status Research & Development GmbH
# Licensed and distributed under either of
# * MIT license: http://opensource.org/licenses/MIT
# * Apache License, Version 2.0: http://www.apache.org/licenses/LICENSE-2.0
# at your option. This file may not be copied, modified, or distributed except according to those terms.
{.used.}
import
unittest2, random,
../stew/[varints, byteutils]
const edgeValues = {
0'u64 : "00",
(1'u64 shl 7) - 1'u64 : "7f",
(1'u64 shl 7) : "8001",
(1'u64 shl 14) - 1'u64 : "ff7f",
(1'u64 shl 14) : "808001",
(1'u64 shl 21) - 1'u64 : "ffff7f",
(1'u64 shl 21) : "80808001",
(1'u64 shl 28) - 1'u64 : "ffffff7f",
(1'u64 shl 28) : "8080808001",
(1'u64 shl 35) - 1'u64 : "ffffffff7f",
(1'u64 shl 35) : "808080808001",
(1'u64 shl 42) - 1'u64 : "ffffffffff7f",
(1'u64 shl 42) : "80808080808001",
(1'u64 shl 49) - 1'u64 : "ffffffffffff7f",
(1'u64 shl 49) : "8080808080808001",
(1'u64 shl 56) - 1'u64 : "ffffffffffffff7f",
(1'u64 shl 56) : "808080808080808001",
(1'u64 shl 63) - 1'u64 : "ffffffffffffffff7f",
uint64(1'u64 shl 63) : "80808080808080808001",
0xFFFF_FFFF_FFFF_FFFF'u64 : "ffffffffffffffffff01"
}
suite "varints":
template roundtipTest(val) =
var s {.inject.}: VarintBuffer
s.writeVarint val
var roundtripVal: type(val)
let bytesRead = readVarint(s.bytes, roundtripVal)
check:
val == roundtripVal
bytesRead == s.totalBytesWritten
bytesRead == vsizeof(val)
test "[ProtoBuf] Success edge cases test":
for pair in edgeValues:
let (val, hex) = pair
roundtipTest val
check:
s.totalBytesWritten == hex.len div 2
toHex(s.writtenBytes) == hex
toHex(val.varintBytes) == hex
test "[ProtoBuf] random 64-bit values":
for i in 0..10000:
# TODO nim 1.0 random casts limits to int, so anything bigger will crash
# * sigh *
let v = rand(0'u64 .. cast[uint64](int.high))
roundtipTest v
test "[ProtoBuf] random 32-bit values":
for i in 0..10000:
# TODO nim 1.0 random casts limits to int, so anything bigger will crash
# * sigh *
let v = rand(0'u32 .. cast[uint32](int.high))
roundtipTest v
# TODO Migrate the rest of the LibP2P test cases