MDEV-37633 Connect UDF functions push empty string warning.

BsonGet_String and JsonGet_String with a NULL argument
push an empty string warning which is the default contents
of g->Message.

In push_warning in the server, there is a Debug assertion
that the string doesn't end in \n. This looks before
the last null of the string, which in this case is
before the buffer. This results in a UBSAN error as
its a pointer overflow/underflow.

Correct by adding an "Argument is NULL" as the warning
message.

Also corrected the JsonGet_String to error if the Value
failed to allocate a buffer in its constructor.

Author: grooverdan

storage/connect/bsonudf.cpp

@@ -294,8 +294,11 @@ my_bool BJNX::ParseJpath(PGLOBAL g)
 	if (Parsed)
 		return false;                       // Already done
 	else if (!Jpath)
+	{
 		//	Jpath = Name;
+		snprintf(g->Message, sizeof(g->Message), MSG(ARG_IS_NULL));
 		return true;
+	}
 
 	if (trace(1))
 		htrc("ParseJpath %s\n", SVP(Jpath));

storage/connect/encas.h

@@ -318,3 +318,4 @@
     case MSG_XPATH_CNTX_ERR:  p = "Unable to create new XPath context";                      break;
     case MSG_XPATH_EVAL_ERR:  p = "Unable to evaluate xpath location '%s'";                  break;
     case MSG_XPATH_NOT_SUPP:  p = "Unsupported Xpath for column %s";                         break;
+    case MSG_ARG_IS_NULL:     p = "Argument is NULL";                                        break;

storage/connect/engmsg.h

@@ -324,3 +324,4 @@
 #define MSG_XPATH_EVAL_ERR  "Unable to evaluate xpath location '%s'"
 #define MSG_XPATH_NOT_SUPP  "Unsupported Xpath for column %s"
 #define MSG_ZERO_DIVIDE     "Zero divide in expression"
+#define MSG_ARG_IS_NULL     "Argument is NULL"

storage/connect/jsonudf.cpp

@@ -98,7 +98,10 @@ my_bool JSNX::SetJpath(PGLOBAL g, char *path, my_bool jb)
 {
 	// Check Value was allocated
 	if (!Value)
+	{
+		snprintf(g->Message, sizeof(g->Message), MSG(NO_MEMORY));
 		return true;
+	}
 
 	Value->SetNullable(true);
 	Jpath = path;
@@ -217,8 +220,11 @@ my_bool JSNX::ParseJpath(PGLOBAL g)
 	if (Parsed)
 		return false;                       // Already done
 	else if (!Jpath)
+	{
 		//	Jpath = Name;
+		snprintf(g->Message, sizeof(g->Message), MSG(ARG_IS_NULL));
 		return true;
+	}
 
 	if (trace(1))
 		htrc("ParseJpath %s\n", SVP(Jpath));

storage/connect/msgid.h

@@ -324,3 +324,4 @@
 #define MSG_FIX_OVFLW_TIMES    522
 #define MSG_FIX_UNFLW_ADD      523
 #define MSG_FIX_UNFLW_TIMES    524
+#define MSG_ARG_IS_NULL        525

storage/connect/mysql-test/connect/r/bson_udf.result

@@ -352,7 +352,7 @@ SELECT BsonGet_String(NULL json_, NULL);
 BsonGet_String(NULL json_, NULL)
 NULL
 Warnings:
-Warning	1105	
+Warning	1105	Argument is NULL
 /* NULL WARNING */
 SELECT department, BsonGet_String(Bson_Make_Object(department, Bson_Array_Grp(salary) "Json_salaries"),'salaries.[+]') Sumsal FROM t3 GROUP BY department;
 department	Sumsal

storage/connect/mysql-test/connect/r/json_udf.result

@@ -346,7 +346,7 @@ SELECT JsonGet_String(NULL json_, NULL);
 JsonGet_String(NULL json_, NULL)
 NULL
 Warnings:
-Warning	1105	
+Warning	1105	Argument is NULL
 SELECT department, JsonGet_String(Json_Make_Object(department, Json_Array_Grp(salary) "Json_salaries"),'salaries.[+]') Sumsal FROM t3 GROUP BY department;
 department	Sumsal
 0021	28500.000000