switched to modbus_new_tcp_pi

README.md

@@ -56,9 +56,7 @@ where:
 
     for Modbus Encapsulated (RTU over TCP): 
     IPv4 of Modbus gate, for example: `enc://192.168.1.1`  
-    TCP port may also be redefined (from Modbus default 502) if needed: `enc://192.168.1.1:5000`
-
-    Note: DNS names are not supported for TCP and RTU over TCP
+    TCP port may also be redefined (from Modbus default 502) if needed: `enc://192.168.1.1:5000`  
 
     for Modbus RTU over serial:
     Serial connection parameters in a form of:  

src/modbus.c

@@ -449,30 +449,34 @@ void create_modbus_context(char *con_string, modbus_t **ctx_out, int *lock_requi
 
 		char host[100];
 		int  port = MODBUS_TCP_DEFAULT_PORT;
+		char port_str[10];
 
 		if (strncmp(con_string, "enc://", strlen("enc://")) == 0)
 		{
 			*lock_required_out = 1;
 			con_string += strlen("enc://");
 			sscanf(con_string, "%99[^:]:%99d[^\n]", host, &port);
+			sprintf(port_str, "%d", port);
 			*lock_key = hash(host) % NSEMS;
-			*ctx_out = modbus_new_rtutcp(host, port);
+			*ctx_out = modbus_new_rtutcp_pi(host, port_str);
 		}
 		else if (strncmp(con_string, "tcp://", strlen("tcp://")) == 0)
 		{
 			*lock_required_out = 0;
 			con_string += strlen("tcp://");
 			sscanf(con_string, "%99[^:]:%99d[^\n]", host, &port);
+			sprintf(port_str, "%d", port);
 			*lock_key = hash(host) % NSEMS;
-			*ctx_out = modbus_new_tcp(host, port);
+			*ctx_out = modbus_new_tcp_pi(host, port_str);
 		}
 		else
 		{	// try Modbus TCP
 
 			*lock_required_out = 0;
 			sscanf(con_string, "%99[^:]:%99d[^\n]", host, &port);
+			sprintf(port_str, "%d", port);
 			*lock_key = hash(host) % NSEMS;
-			*ctx_out = modbus_new_tcp(host, port);
+			*ctx_out = modbus_new_tcp_pi(host, port_str);
 		}
 	}
 

tests/test_00modbus_connection_string.py

@@ -6,6 +6,8 @@ class TestModbusConnectionString(object):
 
     host = "172.16.238.2:5020"
     host_rtutcp = "172.16.238.2:5021"
+    host_dns = "modbus-server:5020"
+    host_rtutcp_dns = "modbus-server:5021"
 
     # test enc:// (rtu over tcp)
 
@@ -18,6 +20,16 @@ def test_modbus_tcp(self):
         key = "modbus_read[tcp://"+self.host+",1,1,3,uint16]"
         assert zabbix_get(key) == '49677'
 
+    # test enc:// (rtu over tcp) using hostname
+    def test_modbus_test_rtutcp_dns(self):
+        key = "modbus_read[enc://"+self.host_rtutcp_dns+",1,0,3,uint16]"
+        assert zabbix_get(key) == '49807'
+
+    # test tcp:// (plain tcp) using hostname
+    def test_modbus_tcp_dns(self):
+        key = "modbus_read[tcp://"+self.host_dns+",1,1,3,uint16]"
+        assert zabbix_get(key) == '49677'
+
     # test serial /dev/ttyS0
     @pytest.mark.skip("implement this first")
     def test_modbus_serial(self, host):