Responding to the list.. ---------- Forwarded message ---------- From: Benjamin Edwards Date: 11 August 2012 17:37 Subject: Re: [Haskell-cafe] hGetContents Illegal byte sequence / ghc-pkg To: David McBride Thank you Gents, Most useful. One thing that had escaped me is that of course, even if hGetContents and friends are respecting *my* locale, I have a binary distro and the package database probably isn't in my locale. I will try and find that. Thanks, Ben On 11 August 2012 15:26, David McBride wrote:

I had this same problem a couple weeks ago when trying to install virthualenv and I don't really understand it got into a bad state, but the way I solved it was by fixing the locale settings on my gentoo machine so that I'm using UTF8. That just involved a few changes in /etc and then the problem went away.

On Sat, Aug 11, 2012 at 7:13 AM, Benjamin Edwards wrote:

...

Hello café,

I have a program that is crashing, and I have no idea why:

module Main where

import System.Process (readProcessWithExitCode)

main :: IO () main = do _ <- readProcessWithExitCode "ghc-pkg" ["describe", "hoopl"] "" putStrLn "Should never get here"

this is using the process package from hackage. The program crashes with

minimal-test: fd:5: hGetContents: invalid argument (invalid byte sequence) minimal-test: thread blocked indefinitely in an MVar operation

inspecting the source of readProcessWithExitCode yields an obvious explanation to the MVar problem, but I don't understand why hGetContents is so offended.

For the lazy it is defined as follows:

readProcessWithExitCode :: FilePath -- ^ command to run -> [String] -- ^ any arguments -> String -- ^ standard input -> IO (ExitCode,String,String) -- ^ exitcode, stdout, stderr readProcessWithExitCode cmd args input = do (Just inh, Just outh, Just errh, pid) <- createProcess (proc cmd args){ std_in = CreatePipe, std_out = CreatePipe, std_err = CreatePipe }

outMVar <- newEmptyMVar

-- fork off a thread to start consuming stdout out <- hGetContents outh _ <- forkIO $ C.evaluate (length out) >> putMVar outMVar ()

-- fork off a thread to start consuming stderr err <- hGetContents errh _ <- forkIO $ C.evaluate (length err) >> putMVar outMVar ()

-- now write and flush any input when (not (null input)) $ do hPutStr inh input; hFlush inh hClose inh -- done with stdin

-- wait on the output takeMVar outMVar takeMVar outMVar hClose outh hClose errh

-- wait on the process ex <- waitForProcess pid

return (ex, out, err)

Now having looked at the source of ghc-pkg it is dumping it's output using putStr and friends, so that should be using my local encoding on the system, right? and so should hGetContents in my program..?

Now, for the curious: the reason I care is that this problem has effectively prevented me from using virthualenv. Sadness and woe.

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