From d1405ec1857b8c03c6a96bf1b6ba14fc4f2c16a7 Mon Sep 17 00:00:00 2001
From: Simon Lin <simonlin@google.com>
Date: Wed, 10 Nov 2021 00:11:30 +0800
Subject: [PATCH] [dnssd-server] fix TXT RR format when TXT length is zero
 (#7141)

---
 src/core/net/dnssd_server.cpp | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/core/net/dnssd_server.cpp b/src/core/net/dnssd_server.cpp
index c3ac14d1f..7e6ba2a5d 100644
--- a/src/core/net/dnssd_server.cpp
+++ b/src/core/net/dnssd_server.cpp
@@ -488,17 +488,25 @@ Error Server::AppendTxtRecord(Message &         aMessage,
                               uint32_t          aTtl,
                               NameCompressInfo &aCompressInfo)
 {
-    Error     error = kErrorNone;
-    TxtRecord txtRecord;
+    Error         error = kErrorNone;
+    TxtRecord     txtRecord;
+    const uint8_t kEmptyTxt = 0;
 
     SuccessOrExit(error = AppendInstanceName(aMessage, aInstanceName, aCompressInfo));
 
     txtRecord.Init();
     txtRecord.SetTtl(aTtl);
-    txtRecord.SetLength(aTxtLength);
+    txtRecord.SetLength(aTxtLength > 0 ? aTxtLength : sizeof(kEmptyTxt));
 
     SuccessOrExit(error = aMessage.Append(txtRecord));
-    error = aMessage.AppendBytes(aTxtData, aTxtLength);
+    if (aTxtLength > 0)
+    {
+        error = aMessage.AppendBytes(aTxtData, aTxtLength);
+    }
+    else
+    {
+        error = aMessage.Append(kEmptyTxt);
+    }
 
 exit:
     return error;