libio/tst-fgetc-after-eof.c

   1 /* Bug 1190: EOF conditions are supposed to be sticky.
   2    Copyright (C) 2018 Free Software Foundation.
   3    Copying and distribution of this file, with or without modification,
   4    are permitted in any medium without royalty provided the copyright
   5    notice and this notice are preserved. This file is offered as-is,
   6    without any warranty.  */
   7
   8 /* ISO C1999 specification of fgetc:
   9
  10        #include <stdio.h>
  11        int fgetc (FILE *stream);
  12
  13    Description
  14
  15      If the end-of-file indicator for the input stream pointed to by
  16      stream is not set and a next character is present, the fgetc
  17      function obtains that character as an unsigned char converted to
  18      an int and advances the associated file position indicator for
  19      the stream (if defined).
  20
  21    Returns
  22
  23      If the end-of-file indicator for the stream is set, or if the
  24      stream is at end-of-file, the end-of-file indicator for the
  25      stream is set and the fgetc function returns EOF. Otherwise, the
  26      fgetc function returns the next character from the input stream
  27      pointed to by stream. If a read error occurs, the error indicator
  28      for the stream is set and the fgetc function returns EOF.
  29
  30    The requirement to return EOF "if the end-of-file indicator for the
  31    stream is set" was new in C99; the language in the 1989 edition of
  32    the standard was ambiguous.  Historically, BSD-derived Unix always
  33    had the C99 behavior, whereas in System V fgetc would attempt to
  34    call read() again before returning EOF again.  Prior to version 2.28,
  35    glibc followed the System V behavior even though this does not
  36    comply with C99.
  37
  38    See
  39    <https://sourceware.org/bugzilla/show_bug.cgi?id=1190>,
  40    <https://sourceware.org/bugzilla/show_bug.cgi?id=19476>,
  41    and the thread at
  42    <https://sourceware.org/ml/libc-alpha/2012-09/msg00343.html>
  43    for more detail.  */
  44
  45 #include <support/tty.h>
  46 #include <support/check.h>
  47
  48 #include <fcntl.h>
  49 #include <stdio.h>
  50 #include <stdlib.h>
  51 #include <string.h>
  52 #include <unistd.h>
  53
  54 #define XWRITE(fd, s, msg) do {                         \
  55     if (write (fd, s, sizeof s - 1) != sizeof s - 1)    \
  56       {                                                 \
  57         perror ("write " msg);                          \
  58         return 1;                                       \
  59       }                                                 \
  60   } while (0)
  61
  62 int
  63 do_test (void)
  64 {
  65   /* The easiest way to set up the conditions under which you can
  66      notice whether the end-of-file indicator is sticky, is with a
  67      pseudo-tty.  This is also the case which applications are most
  68      likely to care about.  And it avoids any question of whether and
  69      how it is legitimate to access the same physical file with two
  70      independent FILE objects.  */
  71   int outer_fd, inner_fd;
  72   FILE *fp;
  73
  74   support_openpty (&outer_fd, &inner_fd, 0, 0, 0);
  75   fp = fdopen (inner_fd, "r+");
  76   if (!fp)
  77     {
  78       perror ("fdopen");
  79       return 1;
  80     }
  81
  82   XWRITE (outer_fd, "abc\n\004", "first line + EOF");
  83   TEST_COMPARE (fgetc (fp), 'a');
  84   TEST_COMPARE (fgetc (fp), 'b');
  85   TEST_COMPARE (fgetc (fp), 'c');
  86   TEST_COMPARE (fgetc (fp), '\n');
  87   TEST_COMPARE (fgetc (fp), EOF);
  88
  89   TEST_VERIFY_EXIT (feof (fp));
  90   TEST_VERIFY_EXIT (!ferror (fp));
  91
  92   XWRITE (outer_fd, "d\n", "second line");
  93
  94   /* At this point, there is a new full line of input waiting in the
  95      kernelside input buffer, but we should still observe EOF from
  96      stdio, because the end-of-file indicator has not been cleared.  */
  97   TEST_COMPARE (fgetc (fp), EOF);
  98
  99   /* Clearing EOF should reveal the next line of input.  */
 100   clearerr (fp);
 101   TEST_COMPARE (fgetc (fp), 'd');
 102   TEST_COMPARE (fgetc (fp), '\n');
 103
 104   fclose (fp);
 105   close (outer_fd);
 106   return 0;
 107 }
 108
 109 #include <support/test-driver.c>