std.zlib

zlib (RFC 1950), decompressed: DEFLATE data between a header of two bytes and the Adler-32 of what it holds, as Go’s compress/zlib reads it. A stream made with a preset dictionary is not read. Import it by a name, import std.zlib as Zlib.

import bytes as Bytes
import std.flate as Flate
import std.zlib as Zlib

-- | >>> greeting
-- | Right "hello"
greeting : Either Flate.CorruptInput String
greeting = case Zlib.decompress b["x", 1, 1, 5, 0, 250, 255, "hello", 6, ",", 2, 21] of
  Right out -> Right (show out)
  Left e -> Left e

decompress

decompress : Bytes -> Either Flate.CorruptInput Bytes

The zlib stream the bytes begin with, decompressed, its checksum checked; any bytes after it are not looked at. Where it is wrong, the byte of the input where it went wrong, and what is wrong.

>>> decompress b["x", 156, 203, "H", 205, 201, 201, 215, "Q", 200, "@", 162, 20, 1, "K", 30, 6, 246]
Right b["hello, hello, hello!"]
>>> decompress b["x", 1, 1, 5, 0, 250, 255, "hello", 6, ",", 2, 21]
Right b["hello"]
>>> decompress b["x", 156, 3, 0, 0, 0, 0, 1]
Right b[]
>>> decompress b["x", 156, 203, "H", 205, 201, 201, 215, "Q", 200, "@", 162, 20, 1, "K", 30, 6, 246, "xyz"]
Right b["hello, hello, hello!"]

(a header not checked by its 5 bits, another method than DEFLATE, a window over 32 KB, a preset dictionary; DEFLATE data that is wrong; a checksum not the data’s; too few bytes)

>>> decompress b["x", 157, 203, "H", 205, 201, 201, 215, "Q", 200, "@", 162, 20, 1, "K", 30, 6, 246]
Left { offset = 0, message = "incorrect header check" }
>>> decompress b["y", 24, 3, 0, 0, 0, 0, 1]
Left { offset = 0, message = "unknown compression method" }
>>> decompress b[136, 28, 3, 0, 0, 0, 0, 1]
Left { offset = 0, message = "invalid window size" }
>>> decompress b["x ", 203, "H", 205, 201, 201, 215, "Q", 200, "@", 162, 20, 1, "K", 30, 6, 246]
Left { offset = 1, message = "preset dictionary not supported" }
>>> decompress b["x", 156, 7]
Left { offset = 2, message = "invalid block type 3" }
>>> decompress b["x", 156, 203, "H", 205, 201, 201, 215, "Q", 200, "@", 162, 20, 1, "K", 30, 6, 247]
Left { offset = 14, message = "incorrect data check" }
>>> decompress b["x", 156, 203, "H", 205, 201, 201, 215, "Q", 200, "@", 162, 20, 1, "K", 30]
Left { offset = 16, message = "unexpected end of input" }
>>> decompress b["x"]
Left { offset = 1, message = "unexpected end of input" }