archive_read_open1 hangs indefinitely

[vanessa...@iohk.io]

Hi all,

I have been trying to get lazy streaming with libarchive working in Haskell. My code follows:

-- | Lazily stream a 'BSL.ByteString'
bslToArchive :: BSL.ByteString -> IO (Ptr Archive)
bslToArchive bs = do
    a <- archive_read_new
    void $ archive_read_support_format_all a
    bsChunksRef <- newIORef bsChunks
    rc <- mkReadCallback (readBSL bsChunksRef)
    cc <- mkCloseCallback (\_ ptr -> free ptr $> archiveOk)
    nothingPtr <- mallocBytes 0
    sequence_ [ archive_read_set_read_callback a rc
              , archive_read_set_close_callback a cc
              , archive_read_set_callback_data a nothingPtr
              -- this is where it hangs indefinitely
              , archive_read_open1 a
              ]
    pure a
    where readBSL bsRef _ _ dataPtr = do
                bs' <- readIORef bsRef
                case bs' of
                    [] -> pure 0
                    (x:_) -> do
                        modifyIORef bsRef tail
                        useAsCStringLen x $ \(charPtr, sz) ->
                            poke dataPtr charPtr $>
                            fromIntegral sz
          bsChunks = BSL.toChunks bs

Unfortunately, this hangs indefinitely upon the call to archive_read_open1(I know this from print-debugging). Somewhat curiously, memory consumption remains constant and CPU usage remains low though nothing happens.

I have a feeling I have done something wrong: are there any known circumstances in which a call to archive_read_open1 will result in an infinite loop that consumes no CPU?

The full code is here https://github.com/vmchale/libarchive if interested. 

Thanks,
Vanessa McHale

[Vanessa McHale]

Upon further investigation, it appears that the Haskell functions to create function pointers are somehow fucked (hence the indefinite hanging with no CPU use). Thus, I do not believe it is triggered by any infinite loop in archive_read_open1 itself.

Cheers,
Vanessa McHale

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