error_functions.c

/*************************************************************************\
*                  Copyright (C) Michael Kerrisk, 2016.                   *
*                                                                         *
* This program is free software. You may use, modify, and redistribute it *
* under the terms of the GNU Lesser General Public License as published   *
* by the Free Software Foundation, either version 3 or (at your option)   *
* any later version. This program is distributed without any warranty.    *
* See the files COPYING.lgpl-v3 and COPYING.gpl-v3 for details.           *
\*************************************************************************/

/* Listing 3-3 */

/* error_functions.c

   Some standard error handling routines used by various programs.
*/
#include <stdarg.h>
#include "error_functions.h"
#include "tlpi_hdr.h"
#include "ename.c.inc"          /* Defines ename and MAX_ENAME */

#ifdef __GNUC__                 /* Prevent 'gcc -Wall' complaining  */
__attribute__ ((__noreturn__))  /* if we call this function as last */
#endif                          /* statement in a non-void function */
static void
terminate(Boolean useExit3)
{
    char *s;

    /* Dump core if EF_DUMPCORE environment variable is defined and
       is a nonempty string; otherwise call exit(3) or _exit(2),
       depending on the value of 'useExit3'. */

    s = getenv("EF_DUMPCORE");

    if (s != NULL && *s != '\0')
        abort();
    else if (useExit3)
        exit(EXIT_FAILURE);
    else
        _exit(EXIT_FAILURE);
}

/* Diagnose 'errno' error by:

      * outputting a string containing the error name (if available
        in 'ename' array) corresponding to the value in 'err', along
        with the corresponding error message from strerror(), and

      * outputting the caller-supplied error message specified in
        'format' and 'ap'. */

static void
outputError(Boolean useErr, int err, Boolean flushStdout,
        const char *format, va_list ap)
{
#define BUF_SIZE 500
    char buf[BUF_SIZE], userMsg[BUF_SIZE], errText[BUF_SIZE];

    vsnprintf(userMsg, BUF_SIZE, format, ap);

    if (useErr)
        snprintf(errText, BUF_SIZE, " [%s %s]",
                (err > 0 && err <= MAX_ENAME) ?
                ename[err] : "?UNKNOWN?", strerror(err));
    else
        snprintf(errText, BUF_SIZE, ":");

    snprintf(buf, BUF_SIZE, "ERROR%s %s\n", errText, userMsg);

    if (flushStdout)
        fflush(stdout);       /* Flush any pending stdout */
    fputs(buf, stderr);
    fflush(stderr);           /* In case stderr is not line-buffered */
}

/* Display error message including 'errno' diagnostic, and
   return to caller */

void
errMsg(const char *format, ...)
{
    va_list argList;
    int savedErrno;

    savedErrno = errno;       /* In case we change it here */

    va_start(argList, format);
    outputError(TRUE, errno, TRUE, format, argList);
    va_end(argList);

    errno = savedErrno;
}

/* Display error message including 'errno' diagnostic, and
   terminate the process */

void
errExit(const char *format, ...)
{
    va_list argList;

    va_start(argList, format);
    outputError(TRUE, errno, TRUE, format, argList);
    va_end(argList);

    terminate(TRUE);
}

/* Display error message including 'errno' diagnostic, and
   terminate the process by calling _exit().

   The relationship between this function and errExit() is analogous
   to that between _exit(2) and exit(3): unlike errExit(), this
   function does not flush stdout and calls _exit(2) to terminate the
   process (rather than exit(3), which would cause exit handlers to be
   invoked).

   These differences make this function especially useful in a library
   function that creates a child process that must then terminate
   because of an error: the child must terminate without flushing
   stdio buffers that were partially filled by the caller and without
   invoking exit handlers that were established by the caller. */

void
err_exit(const char *format, ...)
{
    va_list argList;

    va_start(argList, format);
    outputError(TRUE, errno, FALSE, format, argList);
    va_end(argList);

    terminate(FALSE);
}

/* The following function does the same as errExit(), but expects
   the error number in 'errnum' */

void
errExitEN(int errnum, const char *format, ...)
{
    va_list argList;

    va_start(argList, format);
    outputError(TRUE, errnum, TRUE, format, argList);
    va_end(argList);

    terminate(TRUE);
}

/* Print an error message (without an 'errno' diagnostic) */

void
fatal(const char *format, ...)
{
    va_list argList;

    va_start(argList, format);
    outputError(FALSE, 0, TRUE, format, argList);
    va_end(argList);

    terminate(TRUE);
}

/* Print a command usage error message and terminate the process */

void
usageErr(const char *format, ...)
{
    va_list argList;

    fflush(stdout);           /* Flush any pending stdout */

    fprintf(stderr, "Usage: ");
    va_start(argList, format);
    vfprintf(stderr, format, argList);
    va_end(argList);

    fflush(stderr);           /* In case stderr is not line-buffered */
    exit(EXIT_FAILURE);
}

/* Diagnose an error in command-line arguments and
   terminate the process */

void
cmdLineErr(const char *format, ...)
{
    va_list argList;

    fflush(stdout);           /* Flush any pending stdout */

    fprintf(stderr, "Command-line usage error: ");
    va_start(argList, format);
    vfprintf(stderr, format, argList);
    va_end(argList);

    fflush(stderr);           /* In case stderr is not line-buffered */
    exit(EXIT_FAILURE);
}