adding get_query_function

Author: Cedric Boudinet

src/modbus.c

@@ -1856,6 +1856,16 @@ int modbus_get_header_length(modbus_t *ctx)
     return ctx->backend->header_length;
 }
 
+int modbus_get_query_function(modbus_t *ctx, const uint8_t * req)
+{
+    if (ctx == NULL) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    return req[ctx->backend->header_length];
+}
+
 int modbus_enable_quirks(modbus_t *ctx, uint32_t quirks_mask)
 {
     if (ctx == NULL) {

src/modbus.h

@@ -206,6 +206,7 @@ MODBUS_API int
 modbus_set_indication_timeout(modbus_t *ctx, uint32_t to_sec, uint32_t to_usec);
 
 MODBUS_API int modbus_get_header_length(modbus_t *ctx);
+int modbus_get_query_function(modbus_t *ctx, const uint8_t * req);
 
 MODBUS_API int modbus_connect(modbus_t *ctx);
 MODBUS_API void modbus_close(modbus_t *ctx);