Fixed validation logic in PaymentOrder generator

Author: codebude

QRCoder/PayloadGenerator.cs

@@ -2512,6 +2512,13 @@ public override string ToString()
 
             public byte[] ToBytes()
             {
+                //Setup byte encoder
+                //Encode return string as byte[] with correct CharacterSet
+#if !NET35_OR_GREATER
+                Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
+#endif
+                var cp = this.characterSet.ToString().Replace("_", "-");
+
                 //Calculate the seperator
                 separator = DetermineSeparator();
 
@@ -2523,21 +2530,19 @@ public byte[] ToBytes()
                     $"{separator}BIC={mFields.BIC}" +
                     $"{separator}CorrespAcc={mFields.CorrespAcc}";
 
+                //Check length of mandatory field block (-8 => Removing service data block bytes from ret length)
+                int bytesMandatoryLen = Encoding.Convert(Encoding.UTF8, Encoding.GetEncoding(cp), Encoding.UTF8.GetBytes(ret)).Length - 8;
+                if (bytesMandatoryLen > 300)
+                    throw new RussiaPaymentOrderException($"Data too long. Mandatory data must not exceed 300 bytes, but actually is {bytesMandatoryLen} bytes long. Remove additional data fields or shorten strings/values.");
+
+
                 //Add optional fields, if filled
                 var optionalFieldsList = GetOptionalFieldsAsList();
                 if (optionalFieldsList.Count > 0)
                     ret += $"|{string.Join("|", optionalFieldsList.ToArray())}";
                 ret += separator;
 
-                //Encode return string as byte[] with correct CharacterSet
-#if !NET35_OR_GREATER
-                Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
-#endif
-                var cp = this.characterSet.ToString().Replace("_", "-");
-                byte[] bytesOut = Encoding.Convert(Encoding.UTF8, Encoding.GetEncoding(cp), Encoding.UTF8.GetBytes(ret));
-                if (bytesOut.Length > 300)
-                    throw new RussiaPaymentOrderException($"Data too long. Payload must not exceed 300 bytes, but actually is {bytesOut.Length} bytes long. Remove additional data fields or shorten strings/values.");
-                return bytesOut;
+                return Encoding.Convert(Encoding.UTF8, Encoding.GetEncoding(cp), Encoding.UTF8.GetBytes(ret));
             }