CFE-2139: Allowed modules to define empty lists

libpromises/evalfunction.c

@@ -10409,8 +10409,9 @@ void ModuleProtocol(EvalContext *ctx, const char *command, const char *line, int
 
         if (CheckID(name))
         {
-            Rlist *list = RlistParseString(content);
-            if (!list)
+            /* An empty list is NULL too, so check the return value */
+            Rlist *list = NULL;
+            if (!RlistParseString(content, &list))
             {
                 Log(LOG_LEVEL_ERR, "Module protocol could not parse variable %s's data content %s", name, content);
             }

libpromises/rlist.c

@@ -828,6 +828,12 @@ static int LaunchParsingMachine(const char *str, Rlist **newlist)
                     BufferClear(buf);
                     current_state = ST_ELM2;
                 }
+                else if (CLASS_BRA2(*s))
+                {
+                    /* "{}" -- a closing brace before any element. Has to come
+                     * before the catch-all below. */
+                    current_state = ST_PRECLOSED;
+                }
                 else if (CLASS_ANY1(*s))
                 {
                     current_state = ST_ERROR;
@@ -955,19 +961,26 @@ static int LaunchParsingMachine(const char *str, Rlist **newlist)
 clean:
     BufferDestroy(buf);
     RlistDestroy(*newlist);
+    *newlist = NULL;
     assert(ret != 0);
     return ret;
 }
 
-Rlist *RlistParseString(const char *string)
+/**
+ * @brief Parse a list in the format used by the module protocol, e.g. { "a", "b" }
+ * @param string String to parse
+ * @param[out] newlist The parsed list, NULL for the empty list "{}"
+ * @return Whether the string was parsed successfully
+ *
+ * An empty list parses fine and gives NULL, so check the return value.
+ */
+bool RlistParseString(const char *string, Rlist **newlist)
 {
-    Rlist *newlist = NULL;
-    if (LaunchParsingMachine(string, &newlist))
-    {
-        return NULL;
-    }
+    assert(newlist != NULL);
 
-    return newlist;
+    *newlist = NULL;
+
+    return (LaunchParsingMachine(string, newlist) == 0);
 }
 
 /*******************************************************************/

libpromises/rlist.h

@@ -80,7 +80,7 @@ char *RlistScalarValueSafe(const Rlist *rlist);
 FnCall *RlistFnCallValue(const Rlist *rlist);
 Rlist *RlistRlistValue(const Rlist *rlist);
 Rlist *RlistParseShown(const char *string);
-Rlist *RlistParseString(const char *string);
+bool RlistParseString(const char *string, Rlist **newlist);
 Rlist *RlistKeyIn(Rlist *list, const char *key);
 Rlist *RlistKeyIn_IgnoreCase(Rlist *list, const char *key);
 int RlistLen(const Rlist *start);

tests/acceptance/08_commands/01_modules/module_allows_empty_lists.cf

@@ -14,9 +14,12 @@ body common control
 bundle agent test
 {
   meta:
+    "description" -> { "CFE-2139", "redmine7577" }
+      string => "Test that modules are allowed to emit empty lists";
+
     "test_soft_fail"
-      string => "any",
-      meta => { "redmine7577" };
+      string => "windows",
+      meta => { "ENT-10257" };
 
   commands:
     "$(G.cat)"

tests/unit/rlist_test.c

@@ -292,6 +292,11 @@ static struct ParseRoulette
     char *str;
 } PR[] =
 {
+        /*Empty list */
+    {
+    0, "{}"},
+    {
+    0, "{ }"},
         /*Simple */
     {
     1, "{\"a\"}"},
@@ -567,7 +572,7 @@ static void test_new_parser_success()
     int i = 0;
     while (PR[i].nfields != -1)
     {
-        list = RlistParseString(PR[i].str);
+        assert_true(RlistParseString(PR[i].str, &list));
         assert_int_equal(PR[i].nfields, RlistLen(list));
         if (list != NULL)
         {
@@ -583,7 +588,7 @@ static void test_new_parser_failure()
     Rlist *list = NULL;
     while (PFR[i] != NULL)
     {
-        list = RlistParseString(PFR[i]);
+        assert_false(RlistParseString(PFR[i], &list));
         assert_true(RlistLast(list) == NULL);
         if(list) RlistDestroy(list);
         i++;