support: Implement support_quote_string

diff --git a/support/Makefile b/support/Makefile
index 2b663fbbfa..a2536980d1 100644
--- a/support/Makefile
+++ b/support/Makefile
@@ -58,6 +58,7 @@  libsupport-routines = \
   support_openpty \
   support_paths \
   support_quote_blob \
+  support_quote_string \
   support_record_failure \
   support_run_diff \
   support_shared_allocate \
@@ -196,6 +197,7 @@  tests = \
   tst-support_capture_subprocess \
   tst-support_format_dns_packet \
   tst-support_quote_blob \
+  tst-support_quote_string \
   tst-support_record_failure \
   tst-test_compare \
   tst-test_compare_blob \
diff --git a/support/support.h b/support/support.h
index 9418cd11ef..835e7173eb 100644
--- a/support/support.h
+++ b/support/support.h
@@ -69,6 +69,11 @@  void support_write_file_string (const char *path, const char *contents);
    the result).  */
 char *support_quote_blob (const void *blob, size_t length);
 
+/* Quote the contents of the at STR, in such a way that the result
+   string can be included in a C literal (in single/double quotes,
+   without putting the quotes into the result).  */
+char *support_quote_string (const char *str);
+
 /* Returns non-zero if the file descriptor is a regular file on a file
    system which supports holes (that is, seeking and writing does not
    allocate storage for the range of zeros).  FD must refer to a
diff --git a/support/support_quote_string.c b/support/support_quote_string.c
new file mode 100644
index 0000000000..d324371b13
--- /dev/null
+++ b/support/support_quote_string.c
@@ -0,0 +1,26 @@ 
+/* Quote a string so that it can be used in C literals.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <string.h>
+#include <support/support.h>
+
+char *
+support_quote_string (const char *str)
+{
+  return support_quote_blob (str, strlen (str));
+}
diff --git a/support/tst-support_quote_string.c b/support/tst-support_quote_string.c
new file mode 100644
index 0000000000..3c004759b7
--- /dev/null
+++ b/support/tst-support_quote_string.c
@@ -0,0 +1,60 @@ 
+/* Test the support_quote_string function.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <support/check.h>
+#include <support/support.h>
+#include <string.h>
+#include <stdlib.h>
+
+static int
+do_test (void)
+{
+  char *p = support_quote_string ("");
+  TEST_COMPARE (strlen (p), 0);
+  free (p);
+  p = support_quote_string ("X");
+  TEST_COMPARE (strlen (p), 1);
+  TEST_COMPARE (p[0], 'X');
+  free (p);
+
+  /* Check escaping of backslash-escaped characters, and lack of
+     escaping for other shell meta-characters.  */
+  p = support_quote_string ("$()*?`@[]{}~\'\"X");
+  TEST_COMPARE (strcmp (p, "$()*?`@[]{}~\\'\\\"X"), 0);
+  free (p);
+
+  /* Check lack of escaping for letters and digits.  */
+#define LETTERS_AND_DIGTS                       \
+  "abcdefghijklmnopqrstuvwxyz"                  \
+  "ABCDEFGHIJKLMNOPQRSTUVWXYZ"                  \
+  "0123456789"
+  p = support_quote_string (LETTERS_AND_DIGTS "@");
+  TEST_COMPARE (strcmp (p, LETTERS_AND_DIGTS "@"), 0);
+  free (p);
+
+  /* Check escaping of control characters and other non-printable
+     characters.  */
+  p = support_quote_string ("\r\n\t\a\b\f\v\1\177\200\377@");
+  TEST_COMPARE (strcmp (p, "\\r\\n\\t\\a\\b\\f\\v\\001"
+                        "\\177\\200\\377@"), 0);
+  free (p);
+
+  return 0;
+}
+
+#include <support/test-driver.c>