BlockId = uint32

BlockSize = uint32

InputBlock {.requiresInit.} = object
  stream: Stream
  avail: int
  size: int

OutputBlock {.requiresInit.} = object
  stream: Stream
  lengthPos: int
  size: int

proc begin(b: var InputBlock): BlockId {....raises: [IOError, OSError],
    tags: [ReadIOEffect].}

proc begin(b: var OutputBlock; blockId: BlockId) {....raises: [IOError, OSError],
    tags: [WriteIOEffect].}

proc finish(b: var OutputBlock) {....raises: [IOError, OSError],
                                  tags: [WriteIOEffect].}

func init(T: typedesc[InputBlock]; stream: Stream): InputBlock

func init(T: typedesc[OutputBlock]; stream: Stream): OutputBlock

func isFinished(b: InputBlock): bool {....raises: [], tags: [].}

proc read[T: not openArray](b: var InputBlock; val: var T): bool

proc read[T](b: var InputBlock; buf: var openArray[T]): bool

proc readData(b: var InputBlock; data: pointer; size: Natural): bool {.
    ...raises: [IOError, OSError], tags: [ReadIOEffect].}

func size(ib: InputBlock): int {....raises: [], tags: [].}

func toBlockId(str: string): BlockId {.compileTime, ...raises: [], tags: [].}

proc write[T: not openArray](b: var OutputBlock; data: T)

proc write[T](b: var OutputBlock; data: openArray[T])

proc writeData(b: var OutputBlock; data: pointer; size: Natural) {.
    ...raises: [IOError, OSError], tags: [WriteIOEffect].}