Read the file as bytestring and write this bytestring to the file: problem on a network drive

Question

Consider the following simple Haskell program, which reads a file as a byte string and writes the tmp.tmp file from this byte:

 module Main where import System.Environment import qualified Data.ByteString.Lazy as B main :: IO () main = do [file] <- getArgs bs <- B.readFile file action <- B.writeFile "tmp.tmp" bs putStrLn "done" 

It is compiled into an executable file called tmptmp .

I have two hard drives on my computer: drive C and drive U , and this one is a network drive, and this network drive is offline.

Now try tmptmp .

When I run it from C , there is no problem; I run it two times lower, the first time with a file in C , and the second time with a file in U :

 C:\HaskellProjects\imagelength> tmptmp LICENSE done C:\HaskellProjects\imagelength> tmptmp U:\Data\ztemp\test.xlsx done 

Now I run it from U , with a file on drive C , no problem:

 U:\Data\ztemp> tmptmp C:\HaskellProjects\imagelength\LICENSE done 

The problem occurs when I run it from U with a file on U disk:

 U:\Data\ztemp> tmptmp test.xlsx tmptmp: tmp.tmp: openBinaryFile: resource busy (file is locked) 

If in my program I use strict bytes rather than lazy bytes (replacing Data.ByteString.Lazy with Data.ByteString ), this problem no longer occurs.

I would like to understand that. Any explanation? (I would especially like to know how to solve this problem, but still use lazy bytes)

EDIT

To be more precise, a problem still arises with this program:

 import qualified Data.ByteString as SB import qualified Data.ByteString.Lazy as LB main :: IO () main = do [file] <- getArgs bs <- LB.readFile file action <- SB.writeFile "tmp.tmp" (LB.toStrict bs) putStrLn "done" 

while the problem disappears with:

  bs <- SB.readFile file action <- LB.writeFile "tmp.tmp" (LB.fromStrict bs) 

It seems that the cause of the problem is readFile laziness.