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.

2 files changed, 53 insertions, 0 deletions

diff --git a/tests/local.mk b/tests/local.mk
index 815dc6fdd..26aef504f 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -277,6 +277,7 @@ all_tests =					\
   tests/misc/groups-version.sh			\
   tests/misc/head-c.sh				\
   tests/misc/head-pos.sh			\
+  tests/misc/head-write-error.sh		\
   tests/misc/md5sum.pl				\
   tests/misc/md5sum-bsd.sh			\
   tests/misc/md5sum-newline.pl			\
diff --git a/tests/misc/head-write-error.sh b/tests/misc/head-write-error.sh
new file mode 100755
index 000000000..22ecf993e
--- /dev/null
+++ b/tests/misc/head-write-error.sh
@@ -0,0 +1,52 @@
+#!/bin/sh
+# Ensure we diagnose and not continue writing to
+# the output if we get a write error.
+
+# Copyright (C) 2014 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ head
+
+if ! test -w /dev/full || ! test -c /dev/full; then
+  skip_ '/dev/full is required'
+fi
+
+# We can't use /dev/zero as that's bypassed in the --lines case
+# due to lseek() indicating it has a size of zero.
+yes | head -c10M > bigseek || framework_failure_
+
+# This is the single output diagnostic expected,
+# (without the possibly varying :strerror(ENOSPC) suffix).
+printf '%s\n' "head: error writing 'standard output'" > exp
+
+# Memory is bounded in these cases
+for item in lines bytes; do
+  for N in 0 1; do
+    # pipe case
+    yes | timeout 10s head --$item=-$N > /dev/full 2> errt && fail=1
+    test $? = 124 && fail=1
+    sed 's/\(head:.*\):.*/\1/' errt > err
+    compare exp err || fail=1
+
+    # seekable case
+    timeout 10s head --$item=-$N bigseek > /dev/full 2> errt && fail=1
+    test $? = 124 && fail=1
+    sed 's/\(head:.*\):.*/\1/' errt > err
+    compare exp err || fail=1
+  done
+done
+
+Exit $fail