string-util: add strextendn() helper

src/basic/string-util.c

@@ -891,6 +891,33 @@ oom:
         return -ENOMEM;
 }
 
+char *strextendn(char **x, const char *s, size_t l) {
+        assert(x);
+        assert(s || l == 0);
+
+        if (l == SIZE_MAX)
+                l = strlen_ptr(s);
+        else if (l > 0)
+                l = strnlen(s, l); /* ignore trailing noise */
+
+        if (l > 0 || !*x) {
+                size_t q;
+                char *m;
+
+                q = strlen_ptr(*x);
+                m = realloc(*x, q + l + 1);
+                if (!m)
+                        return NULL;
+
+                memcpy_safe(m + q, s, l);
+                m[q + l] = 0;
+
+                *x = m;
+        }
+
+        return *x;
+}
+
 char *strrep(const char *s, unsigned n) {
         char *r, *p;
         size_t l;

src/basic/string-util.h

@@ -186,6 +186,8 @@ char *strextend_with_separator_internal(char **x, const char *separator, ...) _s
 #define strextend_with_separator(x, separator, ...) strextend_with_separator_internal(x, separator, __VA_ARGS__, NULL)
 #define strextend(x, ...) strextend_with_separator_internal(x, NULL, __VA_ARGS__, NULL)
 
+char *strextendn(char **x, const char *s, size_t l);
+
 int strextendf_with_separator(char **x, const char *separator, const char *format, ...) _printf_(3,4);
 #define strextendf(x, ...) strextendf_with_separator(x, NULL, __VA_ARGS__)
 

src/test/test-string-util.c

@@ -1274,4 +1274,22 @@ TEST(version_is_valid) {
         assert_se(version_is_valid("6.2.12-300.fc38.x86_64"));
 }
 
+TEST(strextendn) {
+        _cleanup_free_ char *x = NULL;
+
+        assert_se(streq_ptr(strextendn(&x, NULL, 0), ""));
+        x = mfree(x);
+
+        assert_se(streq_ptr(strextendn(&x, "", 0), ""));
+        x = mfree(x);
+
+        assert_se(streq_ptr(strextendn(&x, "xxx", 3), "xxx"));
+        assert_se(streq_ptr(strextendn(&x, "xxx", 3), "xxxxxx"));
+        assert_se(streq_ptr(strextendn(&x, "...", 1), "xxxxxx."));
+        assert_se(streq_ptr(strextendn(&x, "...", 2), "xxxxxx..."));
+        assert_se(streq_ptr(strextendn(&x, "...", 3), "xxxxxx......"));
+        assert_se(streq_ptr(strextendn(&x, "...", 4), "xxxxxx........."));
+        x = mfree(x);
+}
+
 DEFINE_TEST_MAIN(LOG_DEBUG);