#4427: hGetBuf sometimes reads fewer bytes than required
------------------------+---------------------------------------------------
Reporter: rl | Owner:
Type: bug | Status: new
Priority: normal | Component: libraries/base
Version: 7.1 | Keywords:
Testcase: | Blockedby:
Os: Windows | Blocking:
Architecture: x86 | Failure: Incorrect result at runtime
------------------------+---------------------------------------------------
The attached program repeatedly calls `hGetBuf` and prints how much it
wanted to read and how many bytes `hGetBuf` returned. It should be run on
a sufficiently large file. On Cygwin, the last 4 lines of the output are:
{{{
4 4
608 523
4 4
300 300
}}}
Note that we requested 608 bytes but `hGetBuf` only returned 523 even
though we weren't at the end of file (since subsequent reads succeeded).
I suspect the bug is in `GHC.IO.Handle.Text.bufReadEmpty`, namely here:
{{{
loop :: FD -> Int -> Int -> IO Int
loop fd off bytes | bytes <= 0 = return off
}}}
It should probably return `so_far + off`.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4427>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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