From 4b773b91307715d016c84542037cbfbc16dbdcfa Mon Sep 17 00:00:00 2001
From: Mike Yuan <me@yhndnzj.com>
Date: Mon, 10 Feb 2025 19:03:08 +0100
Subject: [PATCH] string-util: introduce strprepend() helper

(cherry picked from commit b40694f5fc21317af617f37bb03304c84ca993c8)

Related: RHEL-143028
---
 src/basic/string-util.c     | 14 ++++++++++++++
 src/basic/string-util.h     |  2 ++
 src/test/test-string-util.c | 13 +++++++++++++
 3 files changed, 29 insertions(+)

diff --git a/src/basic/string-util.c b/src/basic/string-util.c
index 7122d5145e..6d490e7444 100644
--- a/src/basic/string-util.c
+++ b/src/basic/string-util.c
@@ -46,6 +46,20 @@ char* first_word(const char *s, const char *word) {
         return (char*) nw;
 }
 
+char* strprepend(char **x, const char *s) {
+        assert(x);
+
+        if (isempty(s) && *x)
+                return *x;
+
+        char *p = strjoin(strempty(s), *x);
+        if (!p)
+                return NULL;
+
+        free_and_replace(*x, p);
+        return *x;
+}
+
 char* strnappend(const char *s, const char *suffix, size_t b) {
         size_t a;
         char *r;
diff --git a/src/basic/string-util.h b/src/basic/string-util.h
index a1592b6e6d..7ce26b30f9 100644
--- a/src/basic/string-util.h
+++ b/src/basic/string-util.h
@@ -106,6 +106,8 @@ static inline const char* empty_or_dash_to_null(const char *p) {
 
 char* first_word(const char *s, const char *word) _pure_;
 
+char* strprepend(char **x, const char *s);
+
 char* strnappend(const char *s, const char *suffix, size_t length);
 
 char* strjoin_real(const char *x, ...) _sentinel_;
diff --git a/src/test/test-string-util.c b/src/test/test-string-util.c
index b692af6cc0..0474f3a162 100644
--- a/src/test/test-string-util.c
+++ b/src/test/test-string-util.c
@@ -1335,6 +1335,19 @@ TEST(strextendn) {
         x = mfree(x);
 }
 
+TEST(strprepend) {
+        _cleanup_free_ char *x = NULL;
+
+        ASSERT_STREQ(strprepend(&x, NULL), "");
+        x = mfree(x);
+
+        ASSERT_STREQ(strprepend(&x, ""), "");
+
+        ASSERT_STREQ(strprepend(&x, "xxx"), "xxx");
+        ASSERT_STREQ(strprepend(&x, "bar"), "barxxx");
+        ASSERT_STREQ(strprepend(&x, "foo"), "foobarxxx");
+}
+
 TEST(strlevenshtein) {
         assert_se(strlevenshtein(NULL, NULL) == 0);
         assert_se(strlevenshtein("", "") == 0);