nimbus-eth2/beacon_chain/ssz/navigator.nim

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import
stew/objects, stew/ranges/ptr_arith,
./types, ./bytes_reader
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 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] =
mixin toSszType
type SszFieldType = type toSszType(default FieldType)
const boundingOffsets = getFieldBoundingOffsets(T, fieldName)
checkBounds(n.m, boundingOffsets[1])
when isFixedSize(SszFieldType):
SszNavigator[FieldType](m: MemRange(
startAddr: shift(n.m.startAddr, boundingOffsets[0]),
length: boundingOffsets[1] - boundingOffsets[0]))
else:
template readOffset(offset): int =
int fromSszBytes(uint32, makeOpenArray(shift(n.m.startAddr, offset),
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: shift(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 `[]`*[T](n: SszNavigator[T]): T =
readSszValue(toOpenArray(n.m), T)
converter derefNavigator*[T](n: SszNavigator[T]): T =
n[]