Added new StringJoin() utility function

The function joins a sequence of strings with an optional separator in
between the elements.

Ticket: None
Changelog: None
Signed-off-by: Lars Erik Wik <lars.erik.wik@northern.tech>

libutils/string_lib.c

@@ -1781,3 +1781,23 @@ bool StringMatchesOption(
     }
     return StringEqualN_IgnoreCase(supplied, longopt, length);
 }
+
+char *StringJoin(const Seq *const seq, const char *sep)
+{
+    assert(seq != NULL);
+
+    Writer *const writer = StringWriter();
+    const size_t len = SeqLength(seq);
+    for (size_t i = 0; i < len; i++)
+    {
+        if (i != 0 && sep != NULL)
+        {
+            WriterWrite(writer, sep);
+        }
+        const char *const str = SeqAt(seq, i);
+        WriterWrite(writer, str);
+    }
+
+    char *const data = StringWriterClose(writer);
+    return data;
+}

libutils/string_lib.h

@@ -322,4 +322,14 @@ void CanonifyNameInPlace(char *str);
 bool StringMatchesOption(
     const char *supplied, const char *longopt, const char *shortopt);
 
+/**
+ * @brief Join elements in sequence into a string
+ * @param[in] seq Sequence of strings to join
+ * @param[in] sep Separator between elements (can be NULL)
+ * @return The concatenation of the elements in sequence
+ * @note Sequence must contain only NUL-terminated strings, otherwise behavior
+ *       is undefined
+ */
+char *StringJoin(const Seq *seq, const char *sep);
+
 #endif

tests/unit/string_lib_test.c

@@ -1470,6 +1470,43 @@ static void test_StringMatchesOption(void)
     assert_true(StringMatchesOption("--host", "--hosts", "-H"));
 }
 
+static void test_StringJoin(void)
+{
+    const char *argv[] = { "one", "two", "three" };
+    const int argc = sizeof(argv) / sizeof(argv[0]);
+
+    Seq *seq = SeqFromArgv(argc, argv);
+
+    char *actual = StringJoin(seq, NULL);
+    assert_string_equal(actual, "onetwothree");
+    free(actual);
+
+    actual = StringJoin(seq, "");
+    assert_string_equal(actual, "onetwothree");
+    free(actual);
+
+    actual = StringJoin(seq, ", ");
+    assert_string_equal(actual, "one, two, three");
+    free(actual);
+
+    SeqDestroy(seq);
+    seq = SeqNew(0, NULL);
+
+    actual = StringJoin(seq, NULL);
+    assert_string_equal(actual, "");
+    free(actual);
+
+    actual = StringJoin(seq, "");
+    assert_string_equal(actual, "");
+    free(actual);
+
+    actual = StringJoin(seq, ", ");
+    assert_string_equal(actual, "");
+    free(actual);
+
+    SeqDestroy(seq);
+}
+
 int main()
 {
     PRINT_TEST_BANNER();
@@ -1564,6 +1601,7 @@ int main()
         unit_test(test_StrCatDelim),
 
         unit_test(test_StringMatchesOption),
+        unit_test(test_StringJoin),
     };
 
     return run_tests(tests);