nimbus-eth2/beacon_chain/ssz/navigator.nim

133 lines
4.4 KiB
Nim

{.push raises: [Defect].}
{.pragma: raisesssz, raises: [Defect, MalformedSszError, SszSizeMismatchError].}
import
stew/[ptrops, objects], stew/ranges/ptr_arith,
./bytes_reader, ./types, ./spec_types
export bytes_reader, types
type
MemRange* = object
startAddr*: ptr byte
length*: int
SszNavigator*[T] = object
m: MemRange
func sszMount*(data: openArray[byte], T: type): SszNavigator[T] =
let startAddr = unsafeAddr data[0]
SszNavigator[T](m: MemRange(startAddr: startAddr, length: data.len))
template sszMount*(data: MemRange, T: type): SszNavigator[T] =
SszNavigator[T](m: data)
template getMemRange*(n: SszNavigator): MemRange =
# Please note that this accessor was created intentionally.
# We don't want to expose the `m` field, because the navigated
# type may have a field by that name. We wan't any dot field
# access to be redirected to the navigated type.
# For this reason, this template should always be used with
# the function call syntax `getMemRange(n)`.
n.m
template checkBounds(m: MemRange, offset: int) =
if offset > m.length:
raise newException(MalformedSszError, "Malformed SSZ")
template toOpenArray(m: MemRange): auto =
makeOpenArray(m.startAddr, m.length)
func navigateToField*[T](n: SszNavigator[T],
fieldName: static string,
FieldType: type): SszNavigator[FieldType] {.raisesssz.} =
mixin toSszType
type SszFieldType = type toSszType(declval FieldType)
const boundingOffsets = getFieldBoundingOffsets(T, fieldName)
checkBounds(n.m, boundingOffsets[1])
when isFixedSize(SszFieldType):
SszNavigator[FieldType](m: MemRange(
startAddr: offset(n.m.startAddr, boundingOffsets[0]),
length: boundingOffsets[1] - boundingOffsets[0]))
else:
template readOffset(off): int =
int fromSszBytes(uint32, makeOpenArray(offset(n.m.startAddr, off),
sizeof(uint32)))
let
startOffset = readOffset boundingOffsets[0]
endOffset = when boundingOffsets[1] == -1: n.m.length
else: readOffset boundingOffsets[1]
if endOffset < startOffset or endOffset > n.m.length:
raise newException(MalformedSszError, "Incorrect offset values")
SszNavigator[FieldType](m: MemRange(
startAddr: offset(n.m.startAddr, startOffset),
length: endOffset - startOffset))
template `.`*[T](n: SszNavigator[T], field: untyped): auto =
type RecType = T
type FieldType = type(default(RecType).field)
navigateToField(n, astToStr(field), FieldType)
func indexVarSizeList(m: MemRange, idx: int): MemRange {.raisesssz.} =
template readOffset(pos): int =
int fromSszBytes(uint32, makeOpenArray(offset(m.startAddr, pos), offsetSize))
let offsetPos = offsetSize * idx
checkBounds(m, offsetPos + offsetSize)
let firstOffset = readOffset 0
let listLen = firstOffset div offsetSize
if idx >= listLen:
# TODO: Use a RangeError here?
# This would require the user to check the `len` upfront
raise newException(MalformedSszError, "Indexing past the end")
let elemPos = readOffset offsetPos
checkBounds(m, elemPos)
let endPos = if idx < listLen - 1:
let nextOffsetPos = offsetPos + offsetSize
# TODO. Is there a way to remove this bounds check?
checkBounds(m, nextOffsetPos + offsetSize)
readOffset(offsetPos + nextOffsetPos)
else:
m.length
MemRange(startAddr: m.startAddr.offset(elemPos), length: endPos - elemPos)
template indexList(n, idx, T: untyped): untyped =
type R = T
mixin toSszType
type ElemType = type toSszType(declval R)
when isFixedSize(ElemType):
const elemSize = fixedPortionSize(ElemType)
let elemPos = idx * elemSize
checkBounds(n.m, elemPos + elemSize)
SszNavigator[R](m: MemRange(startAddr: offset(n.m.startAddr, elemPos),
length: elemSize))
else:
SszNavigator[R](m: indexVarSizeList(n.m, idx))
template `[]`*[T](n: SszNavigator[seq[T]], idx: int): SszNavigator[T] =
indexList n, idx, T
template `[]`*[R, T](n: SszNavigator[array[R, T]], idx: int): SszNavigator[T] =
indexList(n, idx, T)
func `[]`*[T](n: SszNavigator[T]): T {.raisesssz.} =
mixin toSszType, fromSszBytes
type SszRepr = type toSszType(declval T)
when type(SszRepr) is type(T) or T is List:
readSszValue(toOpenArray(n.m), result)
else:
fromSszBytes(T, toOpenArray(n.m))
converter derefNavigator*[T](n: SszNavigator[T]): T {.raisesssz.} =
n[]