From ebf3da6280f1f60a1990bbc534b8bd945798f028 Mon Sep 17 00:00:00 2001
From: Michael Croes <mycroes@gmail.com>
Date: Wed, 19 Jul 2023 23:29:11 +0200
Subject: [PATCH] refactor: Extract WriteS7Header

---
 S7.Net/PLCHelpers.cs | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/S7.Net/PLCHelpers.cs b/S7.Net/PLCHelpers.cs
index 97623cc..ce5f6d2 100644
--- a/S7.Net/PLCHelpers.cs
+++ b/S7.Net/PLCHelpers.cs
@@ -20,6 +20,16 @@ namespace S7.Net
             stream.Write(new byte[] { 0x02, 0xf0, 0x80 });
         }
 
+        private static void WriteS7Header(System.IO.MemoryStream stream, byte messageType, int parameterLength, int dataLength)
+        {
+            stream.Write(0x32); // S7 protocol ID
+            stream.Write(messageType); // Message type
+            stream.Write(new byte[] { 0x00, 0x00 }); // Reserved
+            stream.Write(new byte[] { 0x00, 0x00 }); // PDU ref
+            stream.Write(Word.ToByteArray((ushort) parameterLength));
+            stream.Write(Word.ToByteArray((ushort) dataLength));
+        }
+
         /// <summary>
         /// Creates the header to read bytes from the PLC
         /// </summary>
@@ -30,10 +40,9 @@ namespace S7.Net
             // Header size 19, 12 bytes per item
             WriteTpktHeader(stream, 19 + (12 * amount));
             WriteDateHeader(stream);
-            stream.Write(new byte[] { 0x32, 0x01, 0x00, 0x00, 0x00, 0x00 });
-            //data part size
-            stream.Write(Word.ToByteArray((ushort)(2 + (amount * 12))));
-            stream.Write(new byte[] { 0x00, 0x00, 0x04 });
+            WriteS7Header(stream, 0x01, 2 + amount * 12, 0);
+            // Function code: read request
+            stream.Write(0x04);
             //amount of requests
             stream.WriteByte((byte)amount);
         }