util: add a strv_join() helper function

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

src/libinput-util.c

@@ -535,3 +535,46 @@ strv_from_string(const char *in, const char *separators)
 
 	return strv;
 }
+
+/**
+ * Return a newly allocated string with all elements joined by the
+ * joiner, same as Python's string.join() basically.
+ * A strv of ["one", "two", "three", NULL] with a joiner of ", " results
+ * in "one, two, three".
+ *
+ * An empty strv ([NULL]) returns NULL, same for passing NULL as either
+ * argument.
+ *
+ * @param strv Input string arrray
+ * @param joiner Joiner between the elements in the final string
+ *
+ * @return A null-terminated string joining all elements
+ */
+char *
+strv_join(char **strv, const char *joiner)
+{
+	char **s;
+	char *str;
+	size_t slen = 0;
+	size_t count = 0;
+
+	if (!strv || !joiner)
+		return NULL;
+
+	s = strv;
+	for (s = strv, count = 0; *s; s++, count++) {
+		slen += strlen(*s);
+	}
+
+	slen += (count - 1) * strlen(joiner);
+
+	str = zalloc(slen + 1); /* trailing \0 */
+	for (s = strv; *s; s++) {
+		strcat(str, *s);
+		--count;
+		if (count > 0)
+			strcat(str, joiner);
+	}
+
+	return str;
+}

src/libinput-util.h

@@ -543,6 +543,7 @@ safe_atod(const char *str, double *val)
 }
 
 char **strv_from_string(const char *string, const char *separator);
+char *strv_join(char **strv, const char *separator);
 
 static inline void
 strv_free(char **strv) {

test/test-misc.c

@@ -1343,6 +1343,43 @@ START_TEST(kvsplit_double_test)
 }
 END_TEST
 
+struct strjoin_test {
+	char *strv[10];
+	const char *joiner;
+	const char *result;
+};
+
+START_TEST(strjoin_test)
+{
+	struct strjoin_test tests[] = {
+		{ { "one", "two", "three", NULL }, " ", "one two three" },
+		{ { "one", NULL }, "x", "one" },
+		{ { "one", "two", NULL }, "x", "onextwo" },
+		{ { "one", "two", NULL }, ",", "one,two" },
+		{ { "one", "two", NULL }, ", ", "one, two" },
+		{ { "one", "two", NULL }, "one", "oneonetwo" },
+		{ { "one", "two", NULL }, NULL, NULL },
+		{ { "", "", "", NULL }, " ", "  " },
+		{ { "a", "b", "c", NULL }, "", "abc" },
+		{ { "", "b", "c", NULL }, "x", "xbxc" },
+		{ { "", "", "", NULL }, "", "" },
+		{ { NULL }, NULL, NULL }
+	};
+	struct strjoin_test *t = tests;
+
+	while (t->strv[0]) {
+		char *str;
+		str = strv_join(t->strv, t->joiner);
+		if (t->result == NULL)
+			ck_assert_ptr_null(str);
+		else
+			ck_assert_str_eq(str, t->result);
+		free(str);
+		t++;
+	}
+}
+END_TEST
+
 static int open_restricted_leak(const char *path, int flags, void *data)
 {
 	return *(int*)data;
@@ -1580,6 +1617,7 @@ TEST_COLLECTION(misc)
 	litest_add_no_device("misc:parser", safe_atod_test);
 	litest_add_no_device("misc:parser", strsplit_test);
 	litest_add_no_device("misc:parser", kvsplit_double_test);
+	litest_add_no_device("misc:parser", strjoin_test);
 	litest_add_no_device("misc:time", time_conversion);
 
 	litest_add_no_device("misc:fd", fd_no_event_leak);