Patch from Dirk Reusch to change the port number at init in TCP.

include/modbus/modbus.h

@@ -23,7 +23,7 @@
 #include <termios.h>
 #include <arpa/inet.h>
 
-#define MODBUS_TCP_PORT      502
+#define MODBUS_TCP_DEFAULT_PORT 502
 
 #define HEADER_LENGTH_RTU         0
 #define PRESET_QUERY_SIZE_RTU     6
@@ -130,6 +130,8 @@ typedef struct {
         int debug;
         /* IP address */
         char ip[16];
+        /* TCP port */
+        uint16_t port;
         /* Header length used for offset */
         int header_length;
         /* Checksum size RTU = 2 and TCP = 0 */
@@ -203,10 +205,17 @@ int report_slave_id(modbus_param_t *mb_param, int slave,
 void modbus_init_rtu(modbus_param_t *mb_param, char *device,
                      int baud, char *parity, int data_bit,
                      int stop_bit);
+                     
 /* Initialises a parameters structure for TCP
-   - ip : "192.168.0.5" */
-void modbus_init_tcp(modbus_param_t *mb_param, char *ip_address);
+   - ip : "192.168.0.5" 
+   - port : 1099
 
+   Set the port to MODBUS_TCP_DEFAULT_PORT to use the default one
+   (502). It's convenient to use a port number greater than or equal
+   to 1024 because it's not necessary to be root to use this port
+   number.
+*/
+void modbus_init_tcp(modbus_param_t *mb_param, char *ip_address, uint16_t port);
 
 /* Sets up a serial port for RTU communications to modbus or a TCP
    connexion */

src/modbus.c

@@ -1151,11 +1151,18 @@ void modbus_init_rtu(modbus_param_t *mb_param, char *device,
         mb_param->checksum_size = CHECKSUM_SIZE_RTU;
 }
 
-/* Initialises the modbus_param_t structure for TCP */
-void modbus_init_tcp(modbus_param_t *mb_param, char *ip)
+/* Initialises the modbus_param_t structure for TCP.
+
+   Set the port to MODBUS_TCP_DEFAULT_PORT to use the default one
+   (502). It's convenient to use a port number greater than or equal
+   to 1024 because it's not necessary to be root to use this port
+   number.
+*/
+void modbus_init_tcp(modbus_param_t *mb_param, char *ip, uint16_t port)
 {
         memset(mb_param, 0, sizeof(modbus_param_t));
         strncpy(mb_param->ip, ip, sizeof(char)*16);
+        mb_param->port = port;
         mb_param->type_com = TCP;
         mb_param->header_length = HEADER_LENGTH_TCP;
         mb_param->checksum_size = CHECKSUM_SIZE_TCP;
@@ -1423,7 +1430,7 @@ static int modbus_connect_tcp(modbus_param_t *mb_param)
         struct sockaddr_in addr;
 
         addr.sin_family = AF_INET;
-        addr.sin_port = htons(MODBUS_TCP_PORT);
+        addr.sin_port = htons(mb_param->port);
         addr.sin_addr.s_addr = inet_addr(mb_param->ip);
 
         mb_param->fd = socket(AF_INET, SOCK_STREAM, 0);
@@ -1544,9 +1551,8 @@ int modbus_init_listen_tcp(modbus_param_t *mb_param)
         socklen_t addrlen;
 
         addr.sin_family = AF_INET;
-        /* The modbus port is < 1024
-           This program must be made setuid root. */
-        addr.sin_port = htons(MODBUS_TCP_PORT);
+        /* If the modbus port is < to 1024, we need the setuid root. */
+        addr.sin_port = htons(mb_param->port);
         addr.sin_addr.s_addr = INADDR_ANY;
         memset(&(addr.sin_zero), '\0', 8);
 

src/test-modbus-master.c

@@ -45,7 +45,7 @@ int main(void)
 /*      modbus_init_rtu(&mb_param, "/dev/ttyS0", 19200, "none", 8, 1); */
 
         /* TCP */
-        modbus_init_tcp(&mb_param, "169.254.7.104");
+        modbus_init_tcp(&mb_param, "127.0.0.1", 1502);
         modbus_set_debug(&mb_param, TRUE);
       
         modbus_connect(&mb_param);

src/test-modbus-slave.c

@@ -36,11 +36,12 @@ int main(void)
         int ret;
         int i;
 
-        modbus_init_tcp(&mb_param, "127.0.0.1");
+        modbus_init_tcp(&mb_param, "127.0.0.1", 1502);
         modbus_set_debug(&mb_param, TRUE);
 
         modbus_mapping_new(&mb_mapping,
-                           nb_coil_status, nb_input_status, nb_input_registers, nb_holding_registers);
+                           nb_coil_status, nb_input_status,
+                           nb_input_registers, nb_holding_registers);
 
         /* Examples from PI_MODBUS_300.pdf */