3 files changed, 82 insertions, 15 deletions

diff --git a/src/basic/strv.c b/src/basic/strv.c
index 22f5402575..b2fe8d9d4e 100644
--- a/src/basic/strv.c
+++ b/src/basic/strv.c
@@ -403,27 +403,33 @@ char* strv_join_full(char * const *l, const char *separator, const char *prefix,
         return r;
 }
 
-int strv_push(char ***l, char *value) {
-        char **c;
-        size_t n;
+int strv_push_with_size(char ***l, size_t *n, char *value) {
+        /* n is a pointer to a variable to store the size of l.
+         * If not given (i.e. n is NULL or *n is SIZE_MAX), size will be calculated using strv_length().
+         * If n is not NULL, the size after the push will be returned.
+         * If value is empty, no action is taken and *n is not set. */
 
         if (!value)
                 return 0;
 
-        n = strv_length(*l);
+        size_t size = n ? *n : SIZE_MAX;
+        if (size == SIZE_MAX)
+                size = strv_length(*l);
 
         /* Check for overflow */
-        if (n > SIZE_MAX-2)
+        if (size > SIZE_MAX-2)
                 return -ENOMEM;
 
-        c = reallocarray(*l, GREEDY_ALLOC_ROUND_UP(n + 2), sizeof(char*));
+        char **c = reallocarray(*l, GREEDY_ALLOC_ROUND_UP(size + 2), sizeof(char*));
         if (!c)
                 return -ENOMEM;
 
-        c[n] = value;
-        c[n+1] = NULL;
+        c[size] = value;
+        c[size+1] = NULL;
 
         *l = c;
+        if (n)
+                *n = size + 1;
         return 0;
 }
 
@@ -484,10 +490,10 @@ int strv_insert(char ***l, size_t position, char *value) {
         return free_and_replace(*l, c);
 }
 
-int strv_consume(char ***l, char *value) {
+int strv_consume_with_size(char ***l, size_t *n, char *value) {
         int r;
 
-        r = strv_push(l, value);
+        r = strv_push_with_size(l, n, value);
         if (r < 0)
                 free(value);
 
@@ -529,7 +535,7 @@ int strv_prepend(char ***l, const char *value) {
         return strv_consume_prepend(l, v);
 }
 
-int strv_extend(char ***l, const char *value) {
+int strv_extend_with_size(char ***l, size_t *n, const char *value) {
         char *v;
 
         if (!value)
@@ -539,7 +545,7 @@ int strv_extend(char ***l, const char *value) {
         if (!v)
                 return -ENOMEM;
 
-        return strv_consume(l, v);
+        return strv_consume_with_size(l, n, v);
 }
 
 int strv_extend_front(char ***l, const char *value) {
diff --git a/src/basic/strv.h b/src/basic/strv.h
index b9563e8692..c567785cdb 100644
--- a/src/basic/strv.h
+++ b/src/basic/strv.h
@@ -35,18 +35,36 @@ size_t strv_length(char * const *l) _pure_;
 int strv_extend_strv(char ***a, char * const *b, bool filter_duplicates);
 int strv_extend_strv_concat(char ***a, char * const *b, const char *suffix);
 int strv_prepend(char ***l, const char *value);
-int strv_extend(char ***l, const char *value);
+
+/* _with_size() are lower-level functions where the size can be provided externally,
+ * which allows us to skip iterating over the strv to find the end, which saves
+ * a bit of time and reduces the complexity of appending from O(n²) to O(n). */
+
+int strv_extend_with_size(char ***l, size_t *n, const char *value);
+static inline int strv_extend(char ***l, const char *value) {
+        return strv_extend_with_size(l, NULL, value);
+}
+
 int strv_extendf(char ***l, const char *format, ...) _printf_(2,0);
 int strv_extend_front(char ***l, const char *value);
-int strv_push(char ***l, char *value);
+
+int strv_push_with_size(char ***l, size_t *n, char *value);
+static inline int strv_push(char ***l, char *value) {
+        return strv_push_with_size(l, NULL, value);
+}
 int strv_push_pair(char ***l, char *a, char *b);
+
 int strv_insert(char ***l, size_t position, char *value);
 
 static inline int strv_push_prepend(char ***l, char *value) {
         return strv_insert(l, 0, value);
 }
 
-int strv_consume(char ***l, char *value);
+int strv_consume_with_size(char ***l, size_t *n, char *value);
+static inline int strv_consume(char ***l, char *value) {
+        return strv_consume_with_size(l, NULL, value);
+}
+
 int strv_consume_pair(char ***l, char *a, char *b);
 int strv_consume_prepend(char ***l, char *value);
 
diff --git a/src/test/test-strv.c b/src/test/test-strv.c
index 331c277c35..b892396f05 100644
--- a/src/test/test-strv.c
+++ b/src/test/test-strv.c
@@ -601,6 +601,25 @@ TEST(strv_extend_strv) {
         assert_se(strv_length(n) == 4);
 }
 
+TEST(strv_extend_with_size) {
+        _cleanup_strv_free_ char **a = NULL;
+        size_t n = SIZE_MAX;
+
+        a = strv_new("test", "test1");
+        assert_se(a);
+
+        assert_se(strv_extend_with_size(&a, &n, "test2") >= 0);
+        assert_se(n == 3);
+        assert_se(strv_extend_with_size(&a, &n, "test3") >= 0);
+        assert_se(n == 4);
+
+        assert_se(streq(a[0], "test"));
+        assert_se(streq(a[1], "test1"));
+        assert_se(streq(a[2], "test2"));
+        assert_se(streq(a[3], "test3"));
+        assert_se(a[4] == NULL);
+}
+
 TEST(strv_extend) {
         _cleanup_strv_free_ char **a = NULL, **b = NULL;
 
@@ -746,6 +765,30 @@ TEST(strv_push_prepend) {
         assert_se(!a[5]);
 }
 
+TEST(strv_push_with_size) {
+        _cleanup_strv_free_ char **a = NULL;
+        size_t n = 0;
+        char *i, *j;
+
+        assert_se(i = strdup("foo"));
+        assert_se(strv_push_with_size(&a, &n, i) >= 0);
+        assert_se(n == 1);
+
+        assert_se(i = strdup("a"));
+        assert_se(j = strdup("b"));
+        assert_se(strv_push_with_size(&a, &n, i) >= 0);
+        assert_se(n == 2);
+        assert_se(strv_push_with_size(&a, &n, j) >= 0);
+        assert_se(n == 3);
+
+        assert_se(streq_ptr(a[0], "foo"));
+        assert_se(streq_ptr(a[1], "a"));
+        assert_se(streq_ptr(a[2], "b"));
+        assert_se(streq_ptr(a[3], NULL));
+
+        assert_se(n = strv_length(a));
+}
+
 TEST(strv_push) {
         _cleanup_strv_free_ char **a = NULL;
         char *i, *j;