/* eread.c -- Copyright 1994, 1996 Liam R. E. Quin.  All Rights Reserved.
 * This code is NOT in the public domain.
 * See the file COPYRIGHT for full details.
 */

/* $Id: eread.c,v 1.4 1996/05/14 16:36:33 lee Exp $
 * Error checking version of read(), taken from Liam Quin's
 * unreleased error handling library and stripped down somewhat.
 */

#include "globals.h"
#include "error.h"

#include <stdio.h>

#include <errno.h>
#ifdef HAVE_STRING_H
# include <string.h>
#else
# include <strings.h>
#endif

#include <sys/types.h>
#ifdef HAVE_FCNTL_H
# ifdef HAVE_SYSV_FCNTL_H
#  include <sys/stat.h>
# endif
# include <fcntl.h>
#endif
#ifdef HAVE_UNISTD_H
# include <unistd.h>
#endif

#ifdef HAVE_STDLIB_H
# include <stdlib.h>
#endif

#include "lqutil.h"

/* <Function>
 *   <Name>LQU_Eread
 *   <Class>Utilities/Files
 *   <Purpose>
 *      This routine provides an error-checking wrapper around the
 *	read(2) system call.  If the underlying read() returns -1,
 *	a diagnostic message is printed using by calling Error at the
 *	given Severity (bitwise or'd with E_SYS if appropriate).
 *	The message includes What, which should be a
 *	short, succinct summary of the purpose of the file, and Name,
 *	which is normally given as the name of the file, but could be
 *	any string.
 *   <Returns>
 *      the number of bytes read on success, or -1 on an error.
 *	If E_FATAL was given, LQU_Eread does not return after an error.
 *   <Example>
 *	nBytesRead = LQU_Eread(E_FATAL, "passwd", "list of users", 0, p, 12);
 *   </Example>
 *   <Notes>
 *	<P>There are several error flags, such as E_BUG, that include E_FATAL.
 *	See <error.h> for the current list.</P>
 *	<P>The example does not need to check to see whether nBytesRead is
 *	less than 0, since in that case the program would exit.  LQU_Eread can,
 *	however, return a number other than ByteCount, just as the underlying
 *	system call read(2) can, and in the same circumstances.  The caller
 *	of LQU_Eread should therefore check that the expected number of bytes
 *	were returned.</P>
 *   </Notes>
 * </Function>
 */
API int
LQU_Eread(Severity, Name, What, fd, Buffer, ByteCount)
    int Severity;
    CONST char *Name;
    CONST char *What;
    int fd;
    char *Buffer;
    int ByteCount;
{
    int Result;
    int e;

    errno = 0;

    Result = read(fd, Buffer, ByteCount);

    if (Result >= 0) {
	return Result;
    }

    /* Save errno so we can restore it again after printing an error message,
     * in case Error() changes it:
     */
    e = errno;
    if (!Name) {
	Name = "[null filename]";
	Severity |= E_BUG;
    }
    if (!What) {
	What = "[null description]";
	Severity |= E_BUG;
    }

    if (fd < 0) {
	Error(Severity|E_BUG,
	    "%s (%s) - LQE_read(): file descriptor %d invalid",
	    Name, What,
	    fd
	);

	errno = e;
	return -1;
    }

    switch (errno) {
#ifdef EBADF
    case EBADF:
	Error(Severity|E_BUG|E_SYS,
	    "%s (%s): LQE_read: %d is not an open file descriptor",
	    Name, What,
	    fd
	);
	errno = e;
	return -1;
#endif

#ifdef EWOULDBLOCK
    case EWOULDBLOCK:
	/* BSD style non-blocking I/O -- this isn't an error condition */
	return Result;
#else
    /* don't trap both EAGAIN and EWOULDBLOCK,
     * since they are often the same error number!
     */
# ifdef EAGAIN
    case EAGAIN:
#  ifdef O_NONBLOCK
	/* POSIX style non-blocking I/O -- this also isn't an error. */
	return Result;
#  else
	Error(Severity|E_SYS,
	    "%s (%s): LQE_read(fd=%d): unexpected error (EAGAIN)"
	    Name, What, fd
	);
	errno = e;
	return Result;
#  endif
# endif
#endif

#ifdef EBADMSG
    case EBADMSG: /* say what?  this is unlikely at best! */
	Error(Severity|E_SYS,
	    "%s (%s): LQE_read(fd=%d): Stream data corrupted? ",
	    Name, What, fd
	);
	errno = e;
	return Result;
#endif

#ifdef EFAULT
    case EFAULT:
	Error(Severity|E_SYS|E_BUG,
	    "%s (%s): LQE_read(fd=%d): Buffer (0x%x) outside valid memory",
	    Name, What, fd, Buffer
	);
	errno = e;
	return Result;
#endif

#ifdef EINTR
    case EINTR:
	Error(Severity|E_SYS,
	    "%s (%s): LQE_read(fd=%d): system call interrupted by signal",
	    Name, What, fd
	);
	errno = e;
	return Result;
#endif

#ifdef EINVAL
    case EINVAL:
	Error(Severity|E_SYS,
	    "%s (%s): LQE_read(fd=%d): file position is negative",
	    Name, What, fd
	);
	errno = e;
	return Result;
#endif

#ifdef EIO
    case EIO:
	Error(Severity|E_SYS,
	    "%s (%s): LQE_read(fd=%d): physical I/O error, or attempt\n\
%s: to read from a terminal in a backgrounded process",
	    Name, What, fd,
	    Name
	);
	errno = e;
	return Result;
#endif

#ifdef EISDIR
    case EISDIR:
	Error(Severity|E_SYS,
	    "%s (%s): LQE_read(fd=%d): Can't read a network-mounted directory",
	    Name, What, fd
	);
	errno = e;
	return Result;
#endif

    }

    Error(Severity|E_SYS, "%s (%s) - LQE_read(): couldn't read %d bytes",
	Name, What, ByteCount
    );

    errno = e;
    return Result;
}