Websocket.header.err: def of bend-kit-websocket@0.4.0.0
Import: import bend-kit-websocket@0.4.0.0/websocket.bend as Websocket
Lines 394-398 of bend-kit-websocket@0.4.0.0/websocket.bend: https://jend.leeeet.dev/read.txt?path=bend-kit-websocket@0.4.0.0/websocket.bend&start_line=394&end_line=398

import Base

# A 64-bit length with a high word is over any U32 max, and is a control frame over 125.
def header.err(+masked: Bool, +b0: U32, +m: Bool, +hi: U32, +len: U32) -> Maybe<&1, U32 & String>:
  first(rules(U32.is_ne((b0 .&. 128 : U32), 0), ((b0 >> 4n) .&. 7 : U32), (b0 .&. 15 : U32), Bool.pick(U32, U32.is_eq(hi, 0), len, 4294967295)),
  first(reject(Bool.xor(m, masked), 1002, "mask bit does not match the peer's role"),
    reject(U32.is_ne(hi, 0), 1009, "frame over the size limit")))

Uses (14):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Bool
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Bool.pick
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Bool.xor
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Maybe
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Pair
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=String
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32.and
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32.is_eq
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32.is_ne
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32.shrn
  https://jend.leeeet.dev/definition.txt?path=bend-kit-websocket@0.4.0.0/websocket.bend&name=first
  https://jend.leeeet.dev/definition.txt?path=bend-kit-websocket@0.4.0.0/websocket.bend&name=reject
  https://jend.leeeet.dev/definition.txt?path=bend-kit-websocket@0.4.0.0/websocket.bend&name=rules