Use RESP3 Null in a lot of places where it's appropriate given right protocol version and fix PUNSUBSCRIBE (microsoft#1125)

* Write RESP3 null in many cases where RESP2 null was sent despite protocol version.

* Write a response in punsubscribe where no subscriptions exist

---------

Co-authored-by: prvyk <github@privatemail.fastmailbox.net>
Co-authored-by: Badrish Chandramouli <badrishc@microsoft.com>

Author: prvyk

libs/server/Resp/ACLCommands.cs

@@ -432,8 +432,7 @@ private bool NetworkAclGetUser()
 
                 if (user is null)
                 {
-                    while (!RespWriteUtils.TryWriteNull(ref dcurr, dend))
-                        SendAndReset();
+                    WriteNull();
                 }
                 else
                 {

libs/server/Resp/BasicCommands.cs

@@ -1161,8 +1161,7 @@ private bool NetworkCOMMAND_INFO()
                     }
                     else
                     {
-                        while (!RespWriteUtils.TryWriteNull(ref dcurr, dend))
-                            SendAndReset();
+                        WriteNull();
                     }
                 }
             }

libs/server/Resp/ClientCommands.cs

@@ -501,8 +501,7 @@ private bool NetworkCLIENTGETNAME()
 
             if (string.IsNullOrEmpty(this.clientName))
             {
-                while (!RespWriteUtils.TryWriteNull(ref dcurr, dend))
-                    SendAndReset();
+                WriteNull();
             }
             else
             {

libs/server/Resp/Objects/ListCommands.cs

@@ -407,8 +407,7 @@ private bool ListBlockingMove(ArgSlice srcKey, ArgSlice dstKey, ArgSlice srcDir,
 
             if (!result.Found)
             {
-                while (!RespWriteUtils.TryWriteNull(ref dcurr, dend))
-                    SendAndReset();
+                WriteNull();
             }
             else
             {
@@ -779,8 +778,7 @@ private bool ListMove<TGarnetApi>(ref TGarnetApi storageApi)
                     }
                     else
                     {
-                        while (!RespWriteUtils.TryWriteNull(ref dcurr, dend))
-                            SendAndReset();
+                        WriteNull();
                     }
 
                     break;
@@ -823,8 +821,7 @@ private bool ListRightPopLeftPush<TGarnetApi>(ref TGarnetApi storageApi)
                     }
                     else
                     {
-                        while (!RespWriteUtils.TryWriteNull(ref dcurr, dend))
-                            SendAndReset();
+                        WriteNull();
                     }
 
                     break;
@@ -994,8 +991,7 @@ private unsafe bool ListBlockingPopMultiple()
 
             if (!result.Found)
             {
-                while (!RespWriteUtils.TryWriteNull(ref dcurr, dend))
-                    SendAndReset();
+                WriteNull();
                 return true;
             }
 

libs/server/Resp/Objects/SortedSetCommands.cs

@@ -483,8 +483,7 @@ private unsafe bool SortedSetMPop<TGarnetApi>(ref TGarnetApi storageApi)
                     if (pairs == null || pairs.Length == 0)
                     {
                         // No elements found
-                        while (!RespWriteUtils.TryWriteNull(ref dcurr, dend))
-                            SendAndReset();
+                        WriteNull();
                     }
                     else
                     {
@@ -1568,8 +1567,7 @@ private unsafe bool SortedSetBlockingPop(RespCommand command)
 
             if (!result.Found)
             {
-                while (!RespWriteUtils.TryWriteNull(ref dcurr, dend))
-                    SendAndReset();
+                WriteNull();
             }
             else
             {
@@ -1675,8 +1673,7 @@ private unsafe bool SortedSetBlockingMPop()
 
             if (!result.Found)
             {
-                while (!RespWriteUtils.TryWriteNull(ref dcurr, dend))
-                    SendAndReset();
+                WriteNull();
                 return true;
             }
 

libs/server/Resp/PubSubCommands.cs

@@ -284,8 +284,9 @@ private bool NetworkUNSUBSCRIBE()
                         SendAndReset();
                     while (!RespWriteUtils.TryWriteBulkString("unsubscribe"u8, ref dcurr, dend))
                         SendAndReset();
-                    while (!RespWriteUtils.TryWriteNull(ref dcurr, dend))
-                        SendAndReset();
+
+                    WriteNull();
+
                     while (!RespWriteUtils.TryWriteInt32(numActiveChannels, ref dcurr, dend))
                         SendAndReset();
                 }
@@ -360,6 +361,20 @@ private bool NetworkPUNSUBSCRIBE()
                         SendAndReset();
                 }
 
+                if (channels.Count == 0)
+                {
+                    while (!RespWriteUtils.TryWriteArrayLength(3, ref dcurr, dend))
+                        SendAndReset();
+
+                    while (!RespWriteUtils.TryWriteBulkString("punsubscribe"u8, ref dcurr, dend))
+                        SendAndReset();
+
+                    WriteNull();
+
+                    while (!RespWriteUtils.TryWriteInt32(0, ref dcurr, dend))
+                        SendAndReset();
+                }
+
                 if (numActiveChannels == 0)
                     isSubscriptionSession = false;
 

libs/server/Resp/RespServerSession.cs

@@ -1192,6 +1192,21 @@ private void WriteDirectLarge(ReadOnlySpan<byte> src)
             }
         }
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void WriteNull()
+        {
+            if (respProtocolVersion == 3)
+            {
+                while (!RespWriteUtils.TryWriteResp3Null(ref dcurr, dend))
+                    SendAndReset();
+            }
+            else
+            {
+                while (!RespWriteUtils.TryWriteNull(ref dcurr, dend))
+                    SendAndReset();
+            }
+        }
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private void Send(byte* d)
         {