seq: detect and report I/O errors immediately

Ensure I/O errors are detected (and terminate seq), preventing seq
from infloop (or running for long time with a large
range) upon write errors or ignored SIGPIPE. Examples:

     seq 1 inf > /dev/full             (seq_fast)
     seq 1.1 0.1 inf >/dev/full        (print_numbers)

* src/seq.c (io_error): A new function to diagnose appropriate
stdio errors and exit the program with failure status.
(seq_fast, print_numbers): Explicitly check for write errors
and terminate the program with diagnostic.
* tests/misc/seq-io-errors.sh: Test error detection with /dev/full.
* tests/misc/seq-epipe.sh: Test error detection with broken pipes.
* tests/local.mk: Add new tests.
* NEWS: Mention the fix.

1 files changed, 19 insertions, 5 deletions

diff --git a/src/seq.c b/src/seq.c
index de92bc278..1b9da40fb 100644
--- a/src/seq.c
+++ b/src/seq.c
@@ -278,6 +278,15 @@ long_double_format (char const *fmt, struct layout *layout)
       }
 }
 
+static void ATTRIBUTE_NORETURN
+io_error (void)
+{
+  /* FIXME: consider option to silently ignore errno=EPIPE */
+  error (0, errno, _("standard output"));
+  clearerr (stdout);
+  exit (EXIT_FAILURE);
+}
+
 /* Actually print the sequence of numbers in the specified range, with the
    given or default stepping and format.  */
 
@@ -295,7 +304,8 @@ print_numbers (char const *fmt, struct layout layout,
       for (i = 1; ; i++)
         {
           long double x0 = x;
-          printf (fmt, x);
+          if (printf (fmt, x) < 0)
+            io_error ();
           if (out_of_range)
             break;
           x = first + i * step;
@@ -336,10 +346,12 @@ print_numbers (char const *fmt, struct layout layout,
                 break;
             }
 
-          fputs (separator, stdout);
+          if (fputs (separator, stdout) == EOF)
+            io_error ();
         }
 
-      fputs (terminator, stdout);
+      if (fputs (terminator, stdout) == EOF)
+        io_error ();
     }
 }
 
@@ -506,14 +518,16 @@ seq_fast (char const *a, char const *b)
              output buffer so far, and reset to start of buffer.  */
           if (buf_end - (p_len + 1) < bufp)
             {
-              fwrite (buf, bufp - buf, 1, stdout);
+              if (fwrite (buf, bufp - buf, 1, stdout) != 1)
+                io_error ();
               bufp = buf;
             }
         }
 
       /* Write any remaining buffered output, and the terminator.  */
       *bufp++ = *terminator;
-      fwrite (buf, bufp - buf, 1, stdout);
+      if (fwrite (buf, bufp - buf, 1, stdout) != 1)
+        io_error ();
 
       IF_LINT (free (buf));
     }