Catching decompression errors

[mayeranalytics]

I can't quite figure out how to catch decompression errors. I'd expect the usual mechanisms, try or catch, to work. But LzmaRet Exceptions thrown by decompress cannot be caught. Here's my example (create a jumbled.xz file with silly content):

{-# LANGUAGE OverloadedStrings #-}
module Main where

import qualified Codec.Compression.Lzma as Lzma
import           Control.Exception      (catch)
import qualified Data.ByteString.Lazy   as BSL

readXz :: FilePath -> IO BSL.ByteString
readXz f = do
    let params = Lzma.defaultDecompressParams {Lzma.decompressMemLimit = maxBound}
    Lzma.decompressWith params <$> BSL.readFile f

handleErr :: Lzma.LzmaRet -> IO BSL.ByteString
handleErr e = do
    print e
    return ""

main :: IO ()
main = do
    a <- catch (readXz "jumbled.xz") handleErr
    print a

This will not fail gracefully. What am I missing, here?

[hvr]

A transformer acting on lazy bytestrings and returning a lazy bytestring simply has no ability to signal errors in a well-defined way. This is a fundamental issue w/ lazy ByteStrings. Also BSL.readFile suffers from this issue: some I/O errors may result in exceptions being injected into lazy bytestring chunks.

If you need the ability to handle errors in a well-defined way you should use the incremental api, e.g. compressIO or compressST; or alternatively take a look at the streaming framework bindings mentioned at http://hackage.haskell.org/package/lzma.