On 2004-12-05, David Roundy
On Sat, Dec 04, 2004 at 05:42:30PM -0600, John Goerzen wrote: The FileArchive.GZip module is interesting, but I'm not sure I care for the interface. Wouldn't it be better for
decompress :: String -> (String, Maybe GZipError)
to be
decompress :: [Word8] -> Either GZipError [Word8]
The reason it doesn't use Either GZipError String is this: There are two places where there could be a problem. First, when reading the header (not a GZip file, etc.) Secondly, if the CRC-32 of the extracted data did not match the stored CRC-32 value. To validate this part, we must first inflate all the data and calculate the CRC-32 along the way. If the return type is an Either, then this will force the system to buffer the entire file in memory and check the CRC-32 before returning anything. In other words, the laziness is lost. As for [Word8] vs. String, I'm not sure what the advantages of using a Word8 instead of a Char are. I presume a slight performance benefit? The String seemed to be handy, given hGetContents and hPutStr.
And I'm not sure how hDecompress works. Could we use this with a pipe to read a gzipped file, or does it have to be able to synchronously write the entire file to the output handle?
Yes, you could do that.
What I'd really like would be
openGZippedFile :: IOMode -> FilePath -> IO Handle
Yes, me too. Though from what I can tell, that is impossible, or at least it's impossible to do in Haskell.
And of course, speed is an issue, so an optional zlib backend would be double-nice (or a really well-optimized decompressor). For now, I guess I'll stick with my tried and true (and butt ugly) zlib ffi interface, which uses threads and pipes to implement a gzOpenFile.
Ahh. I suppose one could do that, but that sounds nasty. But you're right, I would like to see good Haskell bindings for both zlib and the bzip2 library.
Actually, I see that compression is not implemented either...
I haven't found any Deflate implementation for Haskell yet. -- John