[erlang-bugs] prim_file bug

[Gunilla Arendt]

Thanks, Martin.

/ Gunilla

Martin Bjorklund wrote:
> Reading 0 bytes from a raw file returns eof, instead of {ok, []} or
> {ok, <<>>}.
> 
> (non-raw file works, and the man page says that it should return {ok,
> ...}.)
> 
> 
> Eshell V5.5.1  (abort with ^G)
> 1> {ok, F} = file:open("README", [read,raw]).
> {ok,{file_descriptor,prim_file,{#Port<0.101>,5}}}
> 2> file:read(F, 0).
> eof
> 3> {ok, G} = file:open("README", [read]).    
> {ok,<0.38.0>}
> 4> file:read(G, 0).                     
> {ok,[]}
> 
> 
> 
> Tested in R10B-10 and R11B-1.
> 
> 
> Here's a patch, but I'm not 100% sure it's correct.
> 
> 
> 
> Index: prim_file.erl
> ===================================================================
> --- prim_file.erl       (revision 6046)
> +++ prim_file.erl       (working copy)
> @@ -296,7 +296,7 @@
>  read(#file_descriptor{module = ?MODULE, data = {Port, _}}, Size)
>    when is_integer(Size), 0 =< Size, Size < ?LARGEFILESIZE ->
>      case drv_command(Port, <<?FILE_READ, Size:64>>) of
> -       {ok, {0, _Data}} ->
> +       {ok, {0, _Data}} when Size =/= 0 ->
>             eof;
>         {ok, 0} ->
>             eof;
> 
> 
> 
> Index: efile_drv.c
> ===================================================================
> --- efile_drv.c (revision 6046)
> +++ efile_drv.c (working copy)
> @@ -2170,11 +2170,13 @@
>             reply_posix_error(desc, EBADF);
>             goto done;
>         }
> +/*
>         if (size == 0) {
>             reply_Uint(desc, size);
>             goto done;
>         }
> -       if (desc->read_size >= size) {
> +*/
> +       if (desc->read_size > 0 && desc->read_size >= size) {
>             /* We already have all data */
>             TRACE_C('D');
>             reply_data(desc, desc->read_binp, desc->read_offset, size);
> 
> 
> 
> /martin