%
% (c) The GRASP/AQUA Project, Glasgow University, 1994
%
\subsection[seekFile.lc]{hSeek and hIsSeekable Runtime Support}

\begin{code}

#include "rtsdefs.h"
#include "stgio.h"

#ifdef HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif

#ifdef HAVE_SYS_STAT_H
#include <sys/stat.h>
#endif

StgInt
seekFile(fp, whence, size, d)
StgAddr fp;
StgInt whence;
StgInt size;
StgByteArray d;
{
    struct stat sb;
    long int offset;

    /*
     * We need to snatch the offset out of an MP_INT.  The bits are there sans sign,
     * which we pick up from our size parameter.  If abs(size) is greater than 1,
     * this integer is just too big.
     */

    switch (size) {
    case -1:
	offset = -*(StgInt *) d;
	break;
    case 0:
	offset = 0;
	break;
    case 1:
	offset = *(StgInt *) d;
	break;
    default:
	ghc_errtype = ERR_INVALIDARGUMENT;
	ghc_errstr = "offset out of range";
	return -1;
    }

    /* Try to find out the file type & size for a physical file */
    while (fstat(fileno((FILE *) fp), &sb) < 0) {
	/* highly unlikely */
	if (errno != EINTR) {
	    cvtErrno();
	    stdErrno();
	    return -1;
	}
    }
    if (S_ISREG(sb.st_mode)) {
	/* Verify that we are not seeking beyond end-of-file */
	int posn;

	switch (whence) {
	case SEEK_SET:
	    posn = offset;
	    break;
	case SEEK_CUR:
	    while ((posn = ftell((FILE *) fp)) == -1) {
		/* the possibility seems awfully remote */
		if (errno != EINTR) {
		    cvtErrno();
		    stdErrno();
		    return -1;
		}
	    }
	    posn += offset;
	    break;
	case SEEK_END:
	    posn = sb.st_size + offset;
	    break;
	}
	if (posn > sb.st_size) {
	    ghc_errtype = ERR_INVALIDARGUMENT;
	    ghc_errstr = "seek position beyond end of file";
	    return -1;
	}
    } else if (S_ISFIFO(sb.st_mode)) {
	ghc_errtype = ERR_UNSUPPORTEDOPERATION;
	ghc_errstr = "can't seek on a pipe";
	return -1;
    } else {
        ghc_errtype = ERR_UNSUPPORTEDOPERATION;
        ghc_errstr = "can't seek on a device";
        return -1;
    }
    while (fseek((FILE *) fp, offset, whence) != 0) {
	if (errno != EINTR) {
	    cvtErrno();
	    stdErrno();
	    return -1;
	}
    }
    return 0;
}

StgInt
seekFileP(fp)
StgAddr fp;
{
    struct stat sb;

    /* Try to find out the file type */
    while (fstat(fileno((FILE *) fp), &sb) < 0) {
	/* highly unlikely */
	if (errno != EINTR) {
	    cvtErrno();
	    stdErrno();
	    return -1;
	}
    }
    /* Regular files are okay */
    if (S_ISREG(sb.st_mode)) {
	return 1;
    } 
    /* For now, everything else is not */
    else {
	return 0;
    }
}

\end{code}