nimbus-eth2/beacon_chain/ssz/dynamic_navigator.nim

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import
strutils, parseutils,
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faststreams/output_stream, json_serialization/writer,
../spec/datatypes,
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types, bytes_reader, navigator
export
navigator
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type
ObjKind = enum
Record
Indexable
LeafValue
FieldInfo = ref object
name: string
fieldType: TypeInfo
navigator: proc (m: MemRange): MemRange {. gcsafe
noSideEffect
raises: [Defect,
MalformedSszError] }
TypeInfo = ref object
case kind: ObjKind
of Record:
fields: seq[FieldInfo]
of Indexable:
elemType: TypeInfo
navigator: proc (m: MemRange, idx: int): MemRange {. gcsafe
noSideEffect
raises: [Defect,
MalformedSszError] }
else:
discard
jsonPrinter: proc (m: MemRange,
outStream: OutputStream,
pretty: bool) {.gcsafe.}
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DynamicSszNavigator* = object
m: MemRange
typ: TypeInfo
proc jsonPrinterImpl[T](m: MemRange, outStream: OutputStream, pretty: bool) =
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var typedNavigator = sszMount(m, T)
var jsonWriter = init(JsonWriter, outStream, pretty)
# TODO: it should be possible to serialize the navigator object
# without dereferencing it (to avoid the intermediate value).
writeValue(jsonWriter, typedNavigator[])
func findField(fields: seq[FieldInfo], name: string): FieldInfo =
# TODO: Replace this with a binary search?
# Will it buy us anything when there are only few fields?
for field in fields:
if field.name == name:
return field
func indexableNavigatorImpl[T](m: MemRange, idx: int): MemRange =
var typedNavigator = sszMount(m, T)
getMemRange(typedNavigator[idx])
func fieldNavigatorImpl[RecordType; FieldType;
fieldName: static string](m: MemRange): MemRange {.raises: [MalformedSszError].} =
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# TODO: Make sure this doesn't fail with a Defect when
# navigating to an inactive field in a case object.
var typedNavigator = sszMount(m, RecordType)
getMemRange navigateToField(typedNavigator, fieldName, FieldType)
func genTypeInfo(T: type): TypeInfo {.gcsafe.}
proc typeInfo*(T: type): TypeInfo =
let res {.global.} = genTypeInfo(T)
# TODO This will be safer if the RTTI object use only manually
# managed memory, but the `fields` sequence right now make
# things harder. We'll need to switch to a different seq type.
{.gcsafe, noSideEffect.}: res
func genTypeInfo(T: type): TypeInfo =
mixin toSszType, enumAllSerializedFields
type SszType = type(toSszType default(T))
result = when type(SszType) isnot T:
TypeInfo(kind: LeafValue)
elif T is object:
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var fields: seq[FieldInfo]
enumAllSerializedFields(T):
fields.add FieldInfo(name: fieldName,
fieldType: typeInfo(FieldType),
navigator: fieldNavigatorImpl[T, FieldType, fieldName])
TypeInfo(kind: Record, fields: fields)
elif T is seq|array:
TypeInfo(kind: Indexable,
elemType: typeInfo(ElemType(T)),
navigator: indexableNavigatorImpl[T])
else:
TypeInfo(kind: LeafValue)
result.jsonPrinter = jsonPrinterImpl[T]
func `[]`*(n: DynamicSszNavigator, idx: int): DynamicSszNavigator =
doAssert n.typ.kind == Indexable
DynamicSszNavigator(m: n.typ.navigator(n.m, idx), typ: n.typ.elemType)
func navigate*(n: DynamicSszNavigator, path: string): DynamicSszNavigator {.
raises: [Defect, ValueError, MalformedSszError] .} =
case n.typ.kind
of Record:
let fieldInfo = n.typ.fields.findField(path)
if fieldInfo == nil:
raise newException(KeyError, "Unrecogned field name: " & path)
return DynamicSszNavigator(m: fieldInfo.navigator(n.m),
typ: fieldInfo.fieldType)
of Indexable:
var idx: int
let consumed = parseInt(path, idx)
if consumed == 0 or idx < 0:
raise newException(KeyError, "Indexing should be done with natural numbers")
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return n[idx]
else:
doAssert false, "Navigation should be terminated once you reach a leaf value"
template navigatePathImpl(nav, iterabalePathFragments: untyped) =
result = nav
for pathFragment in iterabalePathFragments:
if pathFragment.len == 0:
continue
result = result.navigate(pathFragment)
if result.typ.kind == LeafValue:
return
func navigatePath*(n: DynamicSszNavigator, path: string): DynamicSszNavigator {.
raises: [Defect, ValueError, MalformedSszError] .} =
navigatePathImpl n, split(path, '/')
func navigatePath*(n: DynamicSszNavigator, path: openarray[string]): DynamicSszNavigator {.
raises: [Defect, ValueError, MalformedSszError] .} =
navigatePathImpl n, path
func init*(T: type DynamicSszNavigator,
bytes: openarray[byte], Navigated: type): T =
T(m: MemRange(startAddr: unsafeAddr bytes[0], length: bytes.len),
typ: typeInfo(Navigated))
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proc writeJson*(n: DynamicSszNavigator, outStream: OutputStream, pretty = true) =
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n.typ.jsonPrinter(n.m, outStream, pretty)
func toJson*(n: DynamicSszNavigator, pretty = true): string =
var outStream = memoryOutput()
{.noSideEffect.}:
# We are assuming that there are no side-effects here
# because we are using a `memoryOutput`. The computed
# side-effects are coming from the fact that the dynamic
# dispatch mechanisms used in faststreams may be reading
# from a file or a network device.
writeJson(n, outStream, pretty)
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outStream.getOutput(string)