Etag Implementation

libs/common/RespReadUtils.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Buffers.Text;
+using System.Diagnostics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Text;
@@ -377,6 +378,46 @@ public static bool TryRead64Int(out long number, ref byte* ptr, byte* end, out b
             return true;
         }
 
+        /// <summary>
+        /// Given a buffer check if the value is nil ($-1\r\n)
+        /// If the value is nil it advances the buffer forward
+        /// </summary>
+        /// <param name="ptr">The starting position in the RESP string. Will be advanced if parsing is successful.</param>
+        /// <param name="end">The current end of the RESP string.</param>
+        /// <param name="unexpectedToken"></param>
+        /// <returns>True if value is nil on the buffer, false if the value on buffer is not nil</returns>
+        public static bool ReadNil(ref byte* ptr, byte* end, out byte? unexpectedToken)
+        {
+            unexpectedToken = null;
+            if (end - ptr < 5)
+            {
+                return false;
+            }
+
+            ReadOnlySpan<byte> ptrNext5Bytes = new ReadOnlySpan<byte>(ptr, 5);
+            ReadOnlySpan<byte> expectedNilRepr = "$-1\r\n"u8;
+            if (!ptrNext5Bytes.SequenceEqual(expectedNilRepr))
+            {
+                for (int i = 0; i < 5; i++)
+                {
+                    // first place where the sequence differs we have found the unexpected token
+                    if (expectedNilRepr[i] != ptrNext5Bytes[i])
+                    {
+                        // move the pointer to the unexpected token
+                        ptr += i;
+                        unexpectedToken = ptrNext5Bytes[i];
+                        return false;
+                    }
+                }
+                // If the sequence is not equal we shouldn't even reach this because atleast one byte should have mismatched
+                Debug.Assert(false);
+                return false;
+            }
+
+            ptr += 5;
+            return true;
+        }
+
         /// <summary>
         /// Tries to read a RESP array length header from the given ASCII-encoded RESP string
         /// and, if successful, moves the given ptr to the end of the length header.

libs/server/API/GarnetApi.cs

@@ -103,8 +103,8 @@ public GarnetStatus SET_Conditional(ref SpanByte key, ref SpanByte input)
             => storageSession.SET_Conditional(ref key, ref input, ref context);
 
         /// <inheritdoc />
-        public GarnetStatus SET_Conditional(ref SpanByte key, ref SpanByte input, ref SpanByteAndMemory output)
-            => storageSession.SET_Conditional(ref key, ref input, ref output, ref context);
+        public GarnetStatus SET_Conditional(ref SpanByte key, ref SpanByte input, ref SpanByteAndMemory output, RespCommand cmd)
+            => storageSession.SET_Conditional(ref key, ref input, ref output, ref context, cmd);
 
         /// <inheritdoc />
         public GarnetStatus SET(ArgSlice key, Memory<byte> value)

libs/server/API/GarnetStatus.cs

@@ -23,6 +23,10 @@ public enum GarnetStatus : byte
         /// <summary>
         /// Wrong type
         /// </summary>
-        WRONGTYPE
+        WRONGTYPE,
+        /// <summary>
+        /// ETAG mismatch result for an etag based command 
+        /// </summary>
+        ETAGMISMATCH,
     }
 }

libs/server/API/IGarnetApi.cs

@@ -27,7 +27,7 @@ public interface IGarnetApi : IGarnetReadApi, IGarnetAdvancedApi
         /// <summary>
         /// SET Conditional
         /// </summary>
-        GarnetStatus SET_Conditional(ref SpanByte key, ref SpanByte input, ref SpanByteAndMemory output);
+        GarnetStatus SET_Conditional(ref SpanByte key, ref SpanByte input, ref SpanByteAndMemory output, RespCommand cmd);
 
         /// <summary>
         /// SET

libs/server/InputHeader.cs

@@ -26,6 +26,13 @@ enum RespInputFlags : byte
         /// Expired
         /// </summary>
         Expired = 128,
+
+        /// <summary>
+        /// Flag indicating if a SET operation should retain the etag of the previous value if it exists.
+        /// This is used for conditional setting.
+        /// </summary>
+        RetainEtag = 129,
+
     }
 
     /// <summary>
@@ -100,6 +107,17 @@ internal ListOperation ListOp
         /// </summary>
         internal unsafe void SetSetGetFlag() => flags |= RespInputFlags.SetGet;
 
+        /// <summary>
+        /// Set "RetainEtag" flag, used to update the old etag of a key after conditionally setting it
+        /// </summary>
+        internal unsafe void SetRetainEtagFlag() => flags |= RespInputFlags.RetainEtag;
+
+        /// <summary>
+        /// Check if the RetainEtagFlag is set
+        /// </summary>
+        /// <returns></returns>
+        internal unsafe bool CheckRetainEtagFlag() => (flags & RespInputFlags.RetainEtag) != 0;
+
         /// <summary>
         /// Check if record is expired, either deterministically during log replay,
         /// or based on current time in normal operation.