[Rd] readBin on binary non-blocking connections (Windows & Unix differences/bugs)

[Gabor Grothendieck]

Ryacas uses non-blocking sockets and works across all platforms
but uses readLines/writeLines, rather than readBin, to communicate with
yacas.  You could look at its source code in case it brings anything to mind.

On Mon, May 18, 2009 at 1:40 PM, Jeff Ryan <jeff.a.ryan at gmail.com> wrote:
> R-devel:
>
> I am encountering a consistency issue using socketConnection and
> readBin with *non-blocking* connections on Unix and Windows XP (no
> Vista to test).
>
> I am a bit confused by the behavior of *non-blocking* connections
> under Windows specifically.  When calling readBin on a non-blocking
> connection when there is no data to read on the socket, the connection
> under Unix will return a vector of zero-length matching the type of
> the 'what' argument to the readBin call.
>
> The same call under Windows returns random data unless called with
> what=raw(), which instead returns an error.
>
>
> A simple example using two R processes to illustrate on one machine:
>
>
> #########################################################################
> # PROCESS 1 (Windows/Unix -- the same code for both):
> #########################################################################
>
> # Open the connection and don't write anything
>
> s <- socketConnection(port=7777, server=TRUE, blocking=TRUE,open="ab")
>
> #########################################################################
> # PROCESS 2 (Windows) use this to read:
> #########################################################################
>
> s <- socketConnection(port=7777,blocking=FALSE,open="ab")
> readBin(s, character())
> readBin(s, character())
> readBin(s, double())
> readBin(s, raw())
>
> # > readBin(s, character())
> # [1] "\020âƒ\001@ûƒ\001 $ƒ\001 $ƒ\001 $ƒ\001 $ƒ\001 $ƒ\001 $ƒ\001
> $ƒ\001 $ƒ\001 ...
> # > readBin(s, character())
> # [1] "X\n"
> # > readBin(s, double())
> # [1] 1.255609e-316
> # > readBin(s, raw())
> # Error in readBin(s, raw()) : negative length vectors are not allowed
>
> ##########################################################################
> # Using a *nix, the above works as I would expect
> #
> # PROCESS 2 (Unixes -- this example OSX 10.4, but is consistent on
> other flavors)
> #########################################################################
>
> s <- socketConnection(port=7777,blocking=FALSE, open="ab")
> readBin(s, character())
> readBin(s, raw())
> readBin(s, double())
>
> # > readBin(s, character())
> # character(0)
> # > readBin(s, raw())
> # raw(0)
> # > readBin(s, double())
> # numeric(0)
>
> Is this a bug in R or Windows?  Is there a workaround?  I would like
> to have readBin on non-blocking connections work consistently across
> platforms.  When data is present, both platforms behave consistently.
> Incidentally, the readBin calls in my program are not using R as the
> server, the above code is simply to illustrate the problem.
>
> The fact that the raw() returns an error on Windows seems to indicate
> that the error is able to be caught, and could be tested for.
>
> One other interesting point of note; the character() calls on Windows
> will return not just random data, but very non-random R type strings.
> Somehow non-allocated memory is being read.
>
>> readBin(s, character(),100)
>  [1] "X\n"
>  [2] "spatch"
>  [3] ""
>  [4] ""
>  [5] "X\n"
>  [6] "ssion"
>  [7] "\002"
>  [8] " $ƒ\001À|Ó\001\030[Ó\001°N¡\001°N¡\001 $ƒ\001\004"
>  [9] "H\024¢\001\f\025¢\001,œŒ\001\002\002"
>  [10] "è\026¢\001 $ƒ\001\005"
>  [11] ""
>  [12] "s.logical"
> ...
>  [75] "8}ò\001À~ò\001\020—ò\001 $ƒ\001Œ}ò\001 $ƒ\001ô–ò\001
> $ƒ\001¼–ò\001ˆ~ò\0014~ò\001Ø–ò\001È|ò\001€—ò\001¸—ò\001\034}ò\001œ—ò\001
> $ƒ\001¬|ò\001 \177ò\001"
>  [76] " $ƒ\001 $ƒ\001ˆ•ò\001\030•ò\001T”ò\001 $ƒ\001 $ƒ\001
> $ƒ\001¬“ò\0010–ò\001 $ƒ\001 $ƒ\001¼–ò\0014•ò\001
> \177ò\001X“ò\001\034”ò\001 $ƒ\001Œ”ò\001Ì’ò\001
> |ò\001\004“ò\001ä“ò\0010\177ò\001ø•ò\001è{ò\001<“ò\001
> $ƒ\001Ü•ò\001à}ò\001 “ò\001 $ƒ\001 $ƒ\001\024\177ò\001
> $ƒ\001t“ò\001¨”ò\001ü}ò\001 $ƒ\001 $ƒ\001t|ò\001 $ƒ\001
> $ƒ\001ô\177ò\001œ—ò\001ä|ò\001 |ò\001 $ƒ\001d—ò\001
> $ƒ\001è’ò\001x{ò\001 $ƒ\001"
>  [77] "' must be of length 1"
>
> This behavior has been noticed by me at least as early as 2.6, and is
> currently seen under 2.9.0.
>
> Thanks for any pointers,
> Jeff Ryan
>
>
> --
> Jeffrey Ryan
> jeffrey.ryan at insightalgo.com
>
> ia: insight algorithmics
> www.insightalgo.com
>
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