specifier: add helper for escaping '%' characters to avoid making them subject for expansion

This is ultimately just a wrapper around strreplace(), but it makes
things a bit more self-descriptive.

src/shared/specifier.c

@@ -32,6 +32,7 @@
 #include "macro.h"
 #include "specifier.h"
 #include "string-util.h"
+#include "strv.h"
 
 /*
  * Generic infrastructure for replacing %x style specifiers in
@@ -191,3 +192,32 @@ int specifier_kernel_release(char specifier, void *data, void *userdata, char **
         *ret = n;
         return 0;
 }
+
+int specifier_escape_strv(char **l, char ***ret) {
+        char **z, **p, **q;
+
+        assert(ret);
+
+        if (strv_isempty(l)) {
+                *ret = NULL;
+                return 0;
+        }
+
+        z = new(char*, strv_length(l)+1);
+        if (!z)
+                return -ENOMEM;
+
+        for (p = l, q = z; *p; p++, q++) {
+
+                *q = specifier_escape(*p);
+                if (!*q) {
+                        strv_free(z);
+                        return -ENOMEM;
+                }
+        }
+
+        *q = NULL;
+        *ret = z;
+
+        return 0;
+}

src/shared/specifier.h

@@ -20,6 +20,8 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 ***/
 
+#include "string-util.h"
+
 typedef int (*SpecifierCallback)(char specifier, void *data, void *userdata, char **ret);
 
 typedef struct Specifier {
@@ -36,3 +38,9 @@ int specifier_machine_id(char specifier, void *data, void *userdata, char **ret)
 int specifier_boot_id(char specifier, void *data, void *userdata, char **ret);
 int specifier_host_name(char specifier, void *data, void *userdata, char **ret);
 int specifier_kernel_release(char specifier, void *data, void *userdata, char **ret);
+
+static inline char* specifier_escape(const char *string) {
+        return strreplace(string, "%", "%%");
+}
+
+int specifier_escape_strv(char **l, char ***ret);

src/test/meson.build

@@ -249,6 +249,10 @@ tests += [
          [],
          []],
 
+        [['src/test/test-specifier.c'],
+         [],
+         []],
+
         [['src/test/test-string-util.c'],
          [],
          []],

src/test/test-specifier.c

@@ -0,0 +1,66 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+/***
+  This file is part of systemd.
+
+  Copyright 2017 Lennart Poettering
+
+  systemd 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.
+
+  systemd 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 systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include "alloc-util.h"
+#include "log.h"
+#include "specifier.h"
+#include "string-util.h"
+#include "strv.h"
+
+static void test_specifier_escape_one(const char *a, const char *b) {
+        _cleanup_free_ char *x = NULL;
+
+        x = specifier_escape(a);
+        assert_se(streq_ptr(x, b));
+}
+
+static void test_specifier_escape(void) {
+        test_specifier_escape_one(NULL, NULL);
+        test_specifier_escape_one("", "");
+        test_specifier_escape_one("%", "%%");
+        test_specifier_escape_one("foo bar", "foo bar");
+        test_specifier_escape_one("foo%bar", "foo%%bar");
+        test_specifier_escape_one("%%%%%", "%%%%%%%%%%");
+}
+
+static void test_specifier_escape_strv_one(char **a, char **b) {
+        _cleanup_strv_free_ char **x = NULL;
+
+        assert_se(specifier_escape_strv(a, &x) >= 0);
+        assert_se(strv_equal(x, b));
+}
+
+static void test_specifier_escape_strv(void) {
+        test_specifier_escape_strv_one(NULL, NULL);
+        test_specifier_escape_strv_one(STRV_MAKE(NULL), STRV_MAKE(NULL));
+        test_specifier_escape_strv_one(STRV_MAKE(""), STRV_MAKE(""));
+        test_specifier_escape_strv_one(STRV_MAKE("foo"), STRV_MAKE("foo"));
+        test_specifier_escape_strv_one(STRV_MAKE("%"), STRV_MAKE("%%"));
+        test_specifier_escape_strv_one(STRV_MAKE("foo", "%", "foo%", "%foo", "foo%foo", "quux", "%%%"), STRV_MAKE("foo", "%%", "foo%%", "%%foo", "foo%%foo", "quux", "%%%%%%"));
+}
+
+int main(int argc, char *argv[]) {
+        log_set_max_level(LOG_DEBUG);
+
+        test_specifier_escape();
+        test_specifier_escape_strv();
+
+        return 0;
+}