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bytestring: incorrect documentation for hGetContents

    • Closed Issue created by kmcallister @trac-kmcallister

    (I guess this is the ByteString bug tracker? This copies an email I sent directly to Don Stewart and Duncan Coutts.)

    The current documentation [1] for Data.ByteString.hGetContents says:

    "As with hGet, the string representation in the file is assumed to be ISO-8859-1."

    This confuses me -- why would ByteString care what the "string representation" of a file is, or that it even has one?

    Perhaps it's for the benefit of this function's appearance in ByteString.Char8. But the caveats of that module are widely documented throughout, and it's a hack that most people shouldn't use. I think the docs for hGetContents should reflect the "main" module and its intended use on possibly opaque binary data.

    Don Stewart suggested that this is "a property of the underlying handle", but I have confirmed that ByteString is insensitive to the handle's designated encoding.

    $ cat test-bytestring-handle-encoding.hs
import System.IO

import qualified Data.ByteString as B

test :: TextEncoding -> IO ()
test enc = do
    hdl <- openFile "snowman" ReadMode
    hSetEncoding hdl enc
    B.hGetContents hdl >>= (print . B.unpack)
    hClose hdl

main :: IO ()
main = do
    test utf8
    test utf32
    test latin1

$ ghc -V
The Glorious Glasgow Haskell Compilation System, version 7.0.4
$ ghc-pkg list bytestring
/var/lib/ghc/package.conf.d
  bytestring-0.9.1.10
$ echo -ne '\xe2\x98\x83' > snowman
$ hexdump -C snowman
00000000  e2 98 83                                          |...|
00000003
$ runhaskell test-bytestring-handle-encoding.hs
[226,152,131]
[226,152,131]
[226,152,131]

    [1] http://hackage.haskell.org/packages/archive/bytestring/0.9.2.0/doc/html/Data-ByteString.html#v:hGetContents

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