Added create response message functions

src/message.rs

@@ -53,6 +53,59 @@ impl Protocol300Message {
         }
     }
 
+    #[inline]
+    /// Creates a new `Protocol300message` used to respond to a message requesting data
+    /// 
+    /// # Arguments
+    /// * `data_address`: Address of the data to read
+    /// * `data`: Data which should be used to respond to the message
+    /// 
+    /// # Panics
+    /// Panics if the data vec is longer than 256 (u8), can never happen in protocol 300
+    pub fn new_read_response_message(data_address: u16, data: &[u8]) -> Self{
+        let message_identifier = MessageIdentifier::Response;
+        let function_code = FunctionCode::VirtualREAD;
+        let data_length = u8::try_from(data.len()).expect("Data should never be longer than 256");
+        let telegram_length: u8 = 5 + data_length;
+        let data = data.to_owned();
+        let checksum = calculate_checksum(telegram_length, message_identifier, function_code, data_address, data_length, &data);
+        Self {
+            telegram_length,
+            message_identifier,
+            function_code,
+            data_address,
+            data_length,
+            data,
+            checksum
+        }
+    }
+
+
+    #[inline]
+    /// Creates a new `Protocol300message` used to respond to a message writing data
+    /// 
+    /// # Arguments
+    /// * `data_address`: Address of the data to read
+    /// * `data`: Data which should be used to respond to the message
+    /// 
+    /// # Panics
+    /// Panics if the data vec is longer than 256 (u8), can never happen in protocol 300
+    pub fn new_write_response_message(data_address: u16, written_data_length: u8) -> Self{
+        let message_identifier = MessageIdentifier::Response;
+        let function_code = FunctionCode::VirtualWRITE;
+        let telegram_length: u8 = 5;
+        let checksum = calculate_checksum(telegram_length, message_identifier, function_code, data_address, written_data_length, &[]);
+        Self {
+            telegram_length,
+            message_identifier,
+            function_code,
+            data_address,
+            data_length: written_data_length,
+            data: vec![],
+            checksum
+        }
+    }
+
     #[inline]
     /// Creates a new `Protocol300message` used to write data to the device
     /// 
@@ -447,5 +500,19 @@ mod tests {
         assert_eq!(8_usize, expected_message.get_expected_return_telegram_length().unwrap());
     }
 
+    #[test]
+    fn create_read_response_message() {
+        let generated_message = Protocol300Message::new_read_response_message(0x5525, &[0x07, 0x01]).to_bytes();
+        let expected_message = vec![0x41, 0x07, 0x01, 0x01, 0x55, 0x25, 0x02, 0x07, 0x01, 0x8D];
+        assert_eq!(generated_message, expected_message);
+    }
+
+        #[test]
+    fn create_write_response_message() {
+        let generated_message = Protocol300Message::new_write_response_message(0x2323, 1).to_bytes();
+        let expected_message = vec![0x41, 0x05, 0x01, 0x02, 0x23, 0x23, 0x01, 0x4F];
+        assert_eq!(generated_message, expected_message);
+    }
+
 
 }