head,tail: consistently diagnose write errors

If we can't output more data, we should immediately
diagnose the issue and exit rather than consuming all
of input (in some cases).

* src/tail.c (xwrite_stdout): Also diagnose the case where
only some data is written.  Also clearerr() to avoid the
redundant less specific error from atexit (close_stdout);
* src/head.c (xwrite_stdout): Copy this new function from tail,
and use it to write all output.
* tests/misc/head-write-error.sh: A new test to ensure we
exit immediately on write error.
* tests/local.mk: Reference the new test.

1 files changed, 14 insertions, 7 deletions

diff --git a/src/tail.c b/src/tail.c
index a5268c2c6..5ff738df8 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -339,13 +339,6 @@ pretty_name (struct File_spec const *f)
   return (STREQ (f->name, "-") ? _("standard input") : f->name);
 }
 
-static void
-xwrite_stdout (char const *buffer, size_t n_bytes)
-{
-  if (n_bytes > 0 && fwrite (buffer, 1, n_bytes, stdout) == 0)
-    error (EXIT_FAILURE, errno, _("write error"));
-}
-
 /* Record a file F with descriptor FD, size SIZE, status ST, and
    blocking status BLOCKING.  */
 
@@ -385,6 +378,20 @@ write_header (const char *pretty_filename)
   first_file = false;
 }
 
+/* Write N_BYTES from BUFFER to stdout.
+   Exit immediately on error with a single diagnostic.  */
+
+static void
+xwrite_stdout (char const *buffer, size_t n_bytes)
+{
+  if (n_bytes > 0 && fwrite (buffer, 1, n_bytes, stdout) < n_bytes)
+    {
+      clearerr (stdout); /* To avoid redundant close_stdout diagnostic.  */
+      error (EXIT_FAILURE, errno, _("error writing %s"),
+             quote ("standard output"));
+    }
+}
+
 /* Read and output N_BYTES of file PRETTY_FILENAME starting at the current
    position in FD.  If N_BYTES is COPY_TO_EOF, then copy until end of file.
    If N_BYTES is COPY_A_BUFFER, then copy at most one buffer's worth.