connamara · gbirchmeier · Jul 6, 2026 · Jul 5, 2026 · Jul 6, 2026 · Jul 6, 2026
diff --git a/AcceptanceTest/cfg/at_40.cfg b/AcceptanceTest/cfg/at_40.cfg
@@ -11,6 +11,9 @@ TargetCompID=TW
 ResetOnLogon=Y 
 FileStorePath=store
 
-[SESSION] 
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
+
+[SESSION]
 BeginString=FIX.4.0 
 DataDictionary=spec\fix\FIX40.xml 
diff --git a/AcceptanceTest/cfg/at_41.cfg b/AcceptanceTest/cfg/at_41.cfg
@@ -9,7 +9,11 @@ EndTime=00:00:00
 SenderCompID=ISLD 
 TargetCompID=TW 
 ResetOnLogon=Y 
-FileStorePath=store 
+FileStorePath=store
+
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
+
 [SESSION] 
 BeginString=FIX.4.1 
 DataDictionary=spec\fix\FIX41.xml 
diff --git a/AcceptanceTest/cfg/at_42.cfg b/AcceptanceTest/cfg/at_42.cfg
@@ -9,7 +9,11 @@ EndTime=00:00:00
 SenderCompID=ISLD 
 TargetCompID=TW 
 ResetOnLogon=Y 
-FileStorePath=store 
+FileStorePath=store
+
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
+
 [SESSION] 
 BeginString=FIX.4.2 
 DataDictionary=spec\fix\FIX42.xml 
diff --git a/AcceptanceTest/cfg/at_42.misc.cfg b/AcceptanceTest/cfg/at_42.misc.cfg
@@ -17,6 +17,10 @@ FileStorePath=store
 EnableLastMsgSeqNumProcessed=Y
 MaxMessagesInResendRequest=2500
 SendLogoutBeforeDisconnectFromTimeout=Y
+
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
+
 [SESSION] 
 BeginString=FIX.4.2 
 DataDictionary=spec\fix\FIX42.xml 
diff --git a/AcceptanceTest/cfg/at_43.cfg b/AcceptanceTest/cfg/at_43.cfg
@@ -9,7 +9,11 @@ EndTime=00:00:00
 SenderCompID=ISLD 
 TargetCompID=TW 
 ResetOnLogon=Y 
-FileStorePath=store 
+FileStorePath=store
+
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
+
 [SESSION] 
 BeginString=FIX.4.3 
 DataDictionary=spec\fix\FIX43.xml 
diff --git a/AcceptanceTest/cfg/at_44.cfg b/AcceptanceTest/cfg/at_44.cfg
@@ -9,7 +9,11 @@ EndTime=00:00:00
 SenderCompID=ISLD 
 TargetCompID=TW 
 ResetOnLogon=Y 
-FileStorePath=store 
+FileStorePath=store
+
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
+
 [SESSION] 
 BeginString=FIX.4.4 
 DataDictionary=spec\fix\FIX44.xml 
diff --git a/AcceptanceTest/cfg/at_44_enhancedresend.cfg b/AcceptanceTest/cfg/at_44_enhancedresend.cfg
@@ -11,6 +11,9 @@ TargetCompID=TW
 ResetOnLogon=Y
 FileStorePath=store
 
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
+
 # All these settings needed for EnhancedResend
 # See README-EnhancedResend.md for details
 RequiresOrigSendingTime=N

diff --git a/AcceptanceTest/cfg/at_44_noreset.cfg b/AcceptanceTest/cfg/at_44_noreset.cfg
@@ -9,7 +9,11 @@ EndTime=00:00:00
 SenderCompID=ISLD 
 TargetCompID=TW 
 ResetOnLogon=N
-FileStorePath=store 
+FileStorePath=store
+
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
+
 [SESSION] 
 BeginString=FIX.4.4 
 DataDictionary=spec\fix\FIX44.xml 
diff --git a/AcceptanceTest/cfg/at_50.cfg b/AcceptanceTest/cfg/at_50.cfg
@@ -9,7 +9,11 @@ EndTime=00:00:00
 SenderCompID=ISLD 
 TargetCompID=TW 
 ResetOnLogon=Y 
-FileStorePath=store 
+FileStorePath=store
+
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
+
 [SESSION]
 BeginString=FIXT.1.1
 DefaultApplVerID=FIX.5.0

diff --git a/AcceptanceTest/cfg/at_50_sp1.cfg b/AcceptanceTest/cfg/at_50_sp1.cfg
@@ -9,7 +9,11 @@ EndTime=00:00:00
 SenderCompID=ISLD 
 TargetCompID=TW 
 ResetOnLogon=Y 
-FileStorePath=store 
+FileStorePath=store
+
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
+
 [SESSION]
 BeginString=FIXT.1.1
 DefaultApplVerID=FIX.5.0SP1

diff --git a/AcceptanceTest/cfg/at_50_sp2.cfg b/AcceptanceTest/cfg/at_50_sp2.cfg
@@ -9,7 +9,11 @@ EndTime=00:00:00
 SenderCompID=ISLD 
 TargetCompID=TW 
 ResetOnLogon=Y 
-FileStorePath=store 
+FileStorePath=store
+
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
+
 [SESSION]
 BeginString=FIXT.1.1
 DefaultApplVerID=FIX.5.0SP2

diff --git a/Examples/Executor/executor.cfg b/Examples/Executor/executor.cfg
@@ -13,6 +13,9 @@ ScreenLogShowIncoming=Y
 ScreenLogShowOutgoing=Y
 ScreenLogShowEvents=Y
 
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
+
 [SESSION]
 BeginString=FIX.4.0
 SenderCompID=EXECUTOR

diff --git a/Examples/Executor/executor_ssl.cfg b/Examples/Executor/executor_ssl.cfg
@@ -14,6 +14,8 @@ ScreenLogShowIncoming=Y
 ScreenLogShowOutgoing=Y
 ScreenLogShowEvents=Y
 
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
 
 SSLEnable=Y
 # It is recommended to install the certificate and refer to it by name instead of using filename + password

diff --git a/Examples/SimpleAcceptor/simpleacc.cfg b/Examples/SimpleAcceptor/simpleacc.cfg
@@ -10,6 +10,9 @@ ResetOnLogon=Y
 ResetOnLogout=Y
 ResetOnDisconnect=Y
 
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
+
 [SESSION]
 BeginString=FIX.4.0
 SenderCompID=SIMPLE

diff --git a/Examples/SimpleAcceptor/simpleacc_ssl.cfg b/Examples/SimpleAcceptor/simpleacc_ssl.cfg
@@ -17,6 +17,9 @@ SSLCertificatePassword=QuickFixn-TestServer
 SSLCACertificate=QuickFixn-TestCA.cer
 SSLCheckCertificateRevocation=N
 
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
+
 [SESSION]
 BeginString=FIX.4.0
 SenderCompID=SIMPLE

diff --git a/Examples/Standalone/SerilogLog/Serilog.cfg b/Examples/Standalone/SerilogLog/Serilog.cfg
@@ -14,6 +14,9 @@ LogoutTimeout=5
 ResetOnLogon=Y
 HeartBtInt=10
 
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
+
 [SESSION]
 BeginString=FIX.4.0
 SenderCompID=CLIENT1

diff --git a/Examples/TradeClient/tradeclient.cfg b/Examples/TradeClient/tradeclient.cfg
@@ -11,6 +11,9 @@ SocketConnectPort=5001
 SocketIgnoreProxy=Y
 ResetOnDisconnect=Y
 
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
+
 FileLogPath=log
 ScreenLogShowIncoming=Y
 ScreenLogShowOutgoing=Y

diff --git a/Examples/TradeClient/tradeclient_ssl.cfg b/Examples/TradeClient/tradeclient_ssl.cfg
@@ -10,6 +10,9 @@ SocketConnectHost=127.0.0.1
 SocketConnectPort=5001
 SSLEnable=Y
 
+# In message logs, replace non-visible SOH with this character
+FieldSeparatorInMessageLogs=|
+
 FileLogPath=log
 ScreenLogShowIncoming=Y
 ScreenLogShowOutgoing=Y

diff --git a/QuickFIXn/Session.cs b/QuickFIXn/Session.cs
@@ -226,6 +226,8 @@ public TimePrecision TimeStampPrecision
     public int[] RedactFieldsInLogs { get; set; } = [];
     public string RedactionLogText { get; set; } = "<redacted>";
 
+    public char FieldSeparatorInMessageLogs { get; set; } = Message.SOH;
+
     #endregion
 
     internal Session(
@@ -375,7 +377,7 @@ public bool Send(string message)
                        }))
                 {
                     Log.Log(MessagesLogLevel, LogEventIds.OutgoingMessage, "{Message}",
-                        LogAssist.RedactSensitiveFields(message, RedactFieldsInLogs, RedactionLogText));
+                        LogAssist.PrepareFixMessageForLog(message, this));
                 }
             }
 
@@ -549,13 +551,13 @@ private void NextMessage(string msgStr)
                        }))
                 {
                     Log.Log(MessagesLogLevel, LogEventIds.IncomingMessage, "{Message}",
-                        LogAssist.RedactSensitiveFields(msgStr, RedactFieldsInLogs, RedactionLogText));
+                        LogAssist.PrepareFixMessageForLog(msgStr, this));
                 }
             }
         } catch (Exception)
         {
             Log.Log(MessagesLogLevel, LogEventIds.IncomingMessage, "{Message}",
-                LogAssist.RedactSensitiveFields(msgStr, RedactFieldsInLogs, RedactionLogText));
+                LogAssist.PrepareFixMessageForLog(msgStr, this));
         }
 
         MessageBuilder msgBuilder = new MessageBuilder(

diff --git a/QuickFIXn/SessionFactory.cs b/QuickFIXn/SessionFactory.cs
@@ -166,6 +166,8 @@ public Session Create(SessionID sessionId, SettingsDictionary settings)
             session.RedactFieldsInLogs = settings.GetIntArray(SessionSettings.REDACT_FIELDS_IN_LOGS);
         if (settings.Has(SessionSettings.REDACTION_LOG_TEXT))
             session.RedactionLogText = settings.GetString(SessionSettings.REDACTION_LOG_TEXT);
+        if (settings.Has(SessionSettings.FIELD_SEPARATOR_IN_MESSAGE_LOGS))
+            session.FieldSeparatorInMessageLogs = settings.GetChar(SessionSettings.FIELD_SEPARATOR_IN_MESSAGE_LOGS);
 
         return session;
     }

diff --git a/QuickFIXn/SessionSettings.cs b/QuickFIXn/SessionSettings.cs
@@ -75,6 +75,7 @@ public class SessionSettings
     public const string CME_ENHANCED_RESEND = "CmeEnhancedResend";
     public const string REDACT_FIELDS_IN_LOGS = "RedactFieldsInLogs";
     public const string REDACTION_LOG_TEXT = "RedactionLogText";
+    public const string FIELD_SEPARATOR_IN_MESSAGE_LOGS = "FieldSeparatorInMessageLogs";
 
     public const string SSL_ENABLE = "SSLEnable";
     public const string SSL_SERVERNAME = "SSLServerName";

diff --git a/QuickFIXn/SettingsDictionary.cs b/QuickFIXn/SettingsDictionary.cs
@@ -72,6 +72,16 @@ public String GetString(string key, bool capitalize)
         return capitalize ? s.ToUpperInvariant() : s;
     }
 
+    public char GetChar(string key)
+    {
+        string s = GetString(key);
+        if (string.IsNullOrEmpty(s))
+            throw new ConfigError($"Value is empty for key: {key}");
+        if (s.Length > 1)
+            throw new ConfigError($"Value is not a char for key: {key}");
+        return s[0];
+    }
+
     public int GetInt(string key)
     {
         try

diff --git a/QuickFIXn/SocketReader.cs b/QuickFIXn/SocketReader.cs
@@ -137,8 +137,7 @@ private void OnMessageFound(string msg)
                 if (_qfSession.HasResponder)
                 {
                     _qfSession.Log.Log(LogLevel.Information, LogEventIds.IncomingMessage, "{Message}",
-                        LogAssist.RedactSensitiveFields(
-                            msg, _qfSession.RedactFieldsInLogs, _qfSession.RedactionLogText));
+                        LogAssist.PrepareFixMessageForLog(msg, _qfSession));
                     _qfSession.Log.Log(LogLevel.Error,
                         "Multiple logons/connections for this session are not allowed ({Endpoint})",
                         _tcpClient.Client.RemoteEndPoint);

diff --git a/QuickFIXn/Util/LogAssist.cs b/QuickFIXn/Util/LogAssist.cs
@@ -3,9 +3,34 @@
 
 namespace QuickFix.Util;
 
-public class LogAssist
+internal class LogAssist
 {
-    public static string RedactSensitiveFields(string msg, int[] tagsToRedact, string redactionText = "<redacted>")
+    internal static string PrepareFixMessageForLog(string msg, Session sesh)
+    {
+        if (string.IsNullOrEmpty(msg) || string.IsNullOrEmpty(msg))
+            return msg;
+        if (sesh.RedactFieldsInLogs.Length > 0)
+            msg = RedactSensitiveFields(msg, sesh.RedactFieldsInLogs, sesh.RedactionLogText);
+        msg = SwapFieldSeparator(msg, sesh.FieldSeparatorInMessageLogs);
+
+        return msg;
+    }
+
+    internal static string SwapFieldSeparator(string msg, char newSeparator)
+    {
+        if (newSeparator == Message.SOH)
+            return msg;
+        return msg.Replace(Message.SOH, newSeparator);
+    }
+
+    /// <summary>
+    /// Don't call this after SwapFieldSeparator!
+    /// </summary>
+    /// <param name="msg"></param>
+    /// <param name="tagsToRedact"></param>
+    /// <param name="redactionText"></param>
+    /// <returns></returns>
+    internal static string RedactSensitiveFields(string msg, int[] tagsToRedact, string redactionText = "<redacted>")
     {
         // This long text processor is much faster than Regex.
         // Since this is used on every message log, it needs to be fast.

diff --git a/README.md b/README.md
@@ -48,7 +48,7 @@ To run a specific suite, use ``--filter``, e.g.
 * `dotnet test --filter Fix44Test AcceptanceTest`
 (`Fix44Test` is the `TestCaseSource` function in Fix44.cs)
 
-AcceptanceTest logs are output to `bin/Debug/net8.0/log`.
+AcceptanceTest logs are output to `bin/Debug/net<NN>/log`.
 
 
 Credits

diff --git a/RELEASE_NOTES.md b/RELEASE_NOTES.md
@@ -48,10 +48,10 @@ What's New
 * **There are breaking changes between 1.10 and 1.11!  Please review the 1.11.0 notes below.**
 
 
-### v1.15.0
+### upcoming for v1.15.0
 * #1021 - remove .NET 8 support; remove expired deprecations (gbirchmeier)
 * #1015 - rework DateOnlyField/TimeOnlyField to be backed by DateOnly/TimeOnly types instead of DateTime (gbirchmeier)
-
+* #1023 - new config setting "FieldSeparatorInMessageLogs" (gbirchmeier)
 
 
 ### v1.14.1

diff --git a/UnitTests/SessionTestBase.cs b/UnitTests/SessionTestBase.cs
@@ -33,14 +33,17 @@ public void BaseSetup()
         var logFactory = new LogFactoryAdapter(new NullLogFactory());
 
         // acceptor
-        _session = new QuickFix.Session(false, _application, new MemoryStoreFactory(), _sessionId,
-            new QuickFix.DataDictionaryProvider(),new QuickFix.SessionSchedule(_config), 0, logFactory, new QuickFix.DefaultMessageFactory(), "blah");
+        _session = new QuickFix.Session(false, _application, new MemoryStoreFactory(),
+            _sessionId, new QuickFix.DataDictionaryProvider(),new QuickFix.SessionSchedule(_config),
+            0, logFactory, new QuickFix.DefaultMessageFactory(), "blah");
         _session.SetResponder(_responder);
         _session.CheckLatency = false;
 
         // initiator
-        _session2 = new QuickFix.Session(true, _application, new MemoryStoreFactory(), new QuickFix.SessionID("FIX.4.2", "OTHER_SENDER", "OTHER_TARGET"),
-            new QuickFix.DataDictionaryProvider(), new QuickFix.SessionSchedule(_config), 0, logFactory, new QuickFix.DefaultMessageFactory(), "blah");
+        _session2 = new QuickFix.Session(true, _application, new MemoryStoreFactory(),
+            new QuickFix.SessionID("FIX.4.2", "OTHER_SENDER", "OTHER_TARGET"),
+            new QuickFix.DataDictionaryProvider(), new QuickFix.SessionSchedule(_config),
+            0, logFactory, new QuickFix.DefaultMessageFactory(), "blah");
         _session2.SetResponder(_responder);
         _session2.CheckLatency = false;