Add flags to NatsMsg and JetStream Request (#652)

* Add flags to NatsMsg

* Code comments for msg size

* Format

* Fix warnings

* Keep 503 header

* Format

* JetStream TryJSRequestAsync

* Format

* Fix tests

* Refactor JetStream method results to use NatsResult

* Refactor NatsMsg size and flags handling in tests and class

* Refactor JSON document deserialization

* Refactor NatsJSContext error handling logic.

Reordered error checks in `NatsJSContext.cs` to prioritize handling `HasNoResponders` and `null` data conditions early. Modified flag checks in `NatsMsg.cs` for `IsEmpty` and `HasNoResponders` by directly using bitwise operations instead of enum comparisons.

* Fix memory leak by disposing JsonDocument properly

* Skip slow tests for unique NUID generation

src/NATS.Client.Core/NatsMsg.cs

@@ -1,9 +1,18 @@
 using System.Buffers;
 using System.Diagnostics.CodeAnalysis;
+using System.Xml.Linq;
 using NATS.Client.Core.Internal;
 
 namespace NATS.Client.Core;
 
+[Flags]
+public enum NatsMsgFlags : byte
+{
+    None = 0,
+    Empty = 1,
+    NoResponders = 2,
+}
+
 /// <summary>
 /// This interface provides an optional contract when passing
 /// messages to processing methods which is usually helpful in
@@ -103,12 +112,6 @@ public interface INatsMsg<T>
 /// <summary>
 /// NATS message structure as defined by the protocol.
 /// </summary>
-/// <param name="Subject">The destination subject to publish to.</param>
-/// <param name="ReplyTo">The reply subject that subscribers can use to send a response back to the publisher/requester.</param>
-/// <param name="Size">Message size in bytes.</param>
-/// <param name="Headers">Pass additional information using name-value pairs.</param>
-/// <param name="Data">Serializable data object.</param>
-/// <param name="Connection">NATS connection this message is associated to.</param>
 /// <typeparam name="T">Specifies the type of data that may be sent to the NATS Server.</typeparam>
 /// <remarks>
 /// <para>Connection property is used to provide reply functionality.</para>
@@ -119,20 +122,120 @@ public interface INatsMsg<T>
 /// </code>
 /// </para>
 /// </remarks>
-public readonly record struct NatsMsg<T>(
-    string Subject,
-    string? ReplyTo,
-    int Size,
-    NatsHeaders? Headers,
-    T? Data,
-    INatsConnection? Connection) : INatsMsg<T>
+public readonly record struct NatsMsg<T> : INatsMsg<T>
 {
+    /*
+          2               30
+        +--+------------------------------+
+        |EN|          Message Size        |
+        +--+------------------------------+
+        E: Empty flag
+        N: No responders flag
+
+        # Size is 30 bits:
+        Max Size: 1,073,741,823 (0x3FFFFFFF / 00111111111111111111111111111111)
+        Uint.Max: 4,294,967,295
+         Int.Max: 2,147,483,647
+             8mb:     8,388,608
+     */
+    private readonly uint _flagsAndSize;
+
+    /// <summary>
+    /// NATS message structure as defined by the protocol.
+    /// </summary>
+    /// <param name="subject">The destination subject to publish to.</param>
+    /// <param name="replyTo">The reply subject that subscribers can use to send a response back to the publisher/requester.</param>
+    /// <param name="size">Message size in bytes.</param>
+    /// <param name="headers">Pass additional information using name-value pairs.</param>
+    /// <param name="data">Serializable data object.</param>
+    /// <param name="connection">NATS connection this message is associated to.</param>
+    /// <param name="flags">Message flags to indicate no responders and empty payloads.</param>
+    /// <remarks>
+    /// <para>Connection property is used to provide reply functionality.</para>
+    /// <para>
+    /// Message size is calculated using the same method NATS server uses:
+    /// <code lang="C#">
+    /// int size = subject.Length + replyTo.Length + headers.Length + payload.Length;
+    /// </code>
+    /// </para>
+    /// </remarks>
+    public NatsMsg(
+        string subject,
+        string? replyTo,
+        int size,
+        NatsHeaders? headers,
+        T? data,
+        INatsConnection? connection,
+        NatsMsgFlags flags = default)
+    {
+        Subject = subject;
+        ReplyTo = replyTo;
+        _flagsAndSize = ((uint)flags << 30) | (uint)(size & 0x3FFFFFFF);
+        Headers = headers;
+        Data = data;
+        Connection = connection;
+    }
+
     /// <inheritdoc />
     public NatsException? Error => Headers?.Error;
 
+    /// <summary>The destination subject to publish to.</summary>
+    public string Subject { get; init; }
+
+    /// <summary>The reply subject that subscribers can use to send a response back to the publisher/requester.</summary>
+    public string? ReplyTo { get; init; }
+
+    /// <summary>Message size in bytes.</summary>
+    public int Size
+    {
+        // Extract the lower 30 bits
+        get => (int)(_flagsAndSize & 0x3FFFFFFF);
+
+        // Clear the lower 30 bits and set the new number
+        init
+        {
+            // Mask the input value to fit within 30 bits (clear upper bits)
+            var numberPart = (uint)(value & 0x3FFFFFFF);
+
+            // Clear the lower 30 bits and set the new number value
+            // Preserve the flags, update the number
+            _flagsAndSize = (_flagsAndSize & 0xC0000000) | numberPart;
+        }
+    }
+
+    public NatsMsgFlags Flags
+    {
+        // Extract the two leftmost bits (31st and 30th bit)
+        // Mask with 0b11 to get two bits
+        get => (NatsMsgFlags)((_flagsAndSize >> 30) & 0b11);
+
+        init
+        {
+            // Clear the current flag bits (set to 0) and then set the new flag value
+            var flagsPart = (uint)value << 30;
+            _flagsAndSize = (_flagsAndSize & 0x3FFFFFFF) | flagsPart;
+        }
+    }
+
+    /// <summary>Pass additional information using name-value pairs.</summary>
+    public NatsHeaders? Headers { get; init; }
+
+    /// <summary>Serializable data object.</summary>
+    public T? Data { get; init; }
+
+    /// <summary>NATS connection this message is associated to.</summary>
+    public INatsConnection? Connection { get; init; }
+
+    public bool IsEmpty => (_flagsAndSize & 0x40000000) != 0;
+
+    public bool HasNoResponders => (_flagsAndSize & 0x80000000) != 0;
+
     /// <inheritdoc />
     public void EnsureSuccess()
     {
+        if (HasNoResponders)
+            throw new NatsNoRespondersException();
+
         if (Error != null)
             throw Error;
     }
@@ -197,6 +300,17 @@ public ValueTask ReplyAsync<TReply>(NatsMsg<TReply> msg, INatsSerialize<TReply>?
         return Connection.PublishAsync(msg with { Subject = ReplyTo }, serializer, opts, cancellationToken);
     }
 
+    public void Deconstruct(out string subject, out string? replyTo, out int size, out NatsHeaders? headers, out T? data, out INatsConnection? connection, out NatsMsgFlags flags)
+    {
+        subject = Subject;
+        replyTo = ReplyTo;
+        size = Size;
+        headers = Headers;
+        data = Data;
+        connection = Connection;
+        flags = Flags;
+    }
+
     internal static NatsMsg<T> Build(
         string subject,
         string? replyTo,
@@ -207,6 +321,16 @@ internal static NatsMsg<T> Build(
         INatsDeserialize<T> serializer)
     {
         NatsHeaders? headers = null;
+        var flags = NatsMsgFlags.None;
+
+        if (payloadBuffer.Length == 0)
+        {
+            flags |= NatsMsgFlags.Empty;
+            if (NatsSubBase.IsHeader503(headersBuffer))
+            {
+                flags |= NatsMsgFlags.NoResponders;
+            }
+        }
 
         if (headersBuffer != null)
         {
@@ -277,7 +401,7 @@ internal static NatsMsg<T> Build(
             }
         }
 
-        return new NatsMsg<T>(subject, replyTo, (int)size, headers, data, connection);
+        return new NatsMsg<T>(subject, replyTo, (int)size, headers, data, connection, flags);
     }
 
     [MemberNotNull(nameof(Connection))]

src/NATS.Client.Core/NatsResult.cs

@@ -0,0 +1,38 @@
+using System.Runtime.CompilerServices;
+
+namespace NATS.Client.Core;
+
+public readonly struct NatsResult<T>
+{
+    private readonly T? _value;
+    private readonly Exception? _error;
+
+    public NatsResult(T value)
+    {
+        _value = value;
+        _error = null;
+    }
+
+    public NatsResult(Exception error)
+    {
+        _value = default;
+        _error = error;
+    }
+
+    public T Value => _value ?? ThrowValueIsNotSetException();
+
+    public Exception Error => _error ?? ThrowErrorIsNotSetException();
+
+    public bool Success => _error == null;
+
+    public static implicit operator NatsResult<T>(T value) => new(value);
+
+    public static implicit operator NatsResult<T>(Exception error) => new(error);
+
+    private static T ThrowValueIsNotSetException() => throw CreateInvalidOperationException("Result value is not set");
+
+    private static Exception ThrowErrorIsNotSetException() => throw CreateInvalidOperationException("Result error is not set");
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static Exception CreateInvalidOperationException(string message) => new InvalidOperationException(message);
+}

src/NATS.Client.Core/NatsSubBase.cs

@@ -271,7 +271,7 @@ public virtual async ValueTask ReceiveAsync(string subject, string? replyTo, Rea
         {
             switch (Opts)
             {
-            case { ThrowIfNoResponders: true } when headersBuffer is { Length: >= 12 } && headersBuffer.Value.Slice(8, 4).ToSpan().SequenceEqual(NoRespondersHeaderSequence):
+            case { ThrowIfNoResponders: true } when IsHeader503(headersBuffer):
                 SetException(new NatsNoRespondersException());
                 return;
             case { StopOnEmptyMsg: true }:
@@ -311,6 +311,10 @@ public virtual async ValueTask ReceiveAsync(string subject, string? replyTo, Rea
         }
     }
 
+    internal static bool IsHeader503(ReadOnlySequence<byte>? headersBuffer) =>
+        headersBuffer is { Length: >= 12 }
+        && headersBuffer.Value.Slice(8, 4).ToSpan().SequenceEqual(NoRespondersHeaderSequence);
+
     internal void ClearException() => Interlocked.Exchange(ref _exception, null);
 
     /// <summary>

src/NATS.Client.JetStream/Internal/NatsJSJsonDocumentSerializer.cs

@@ -0,0 +1,12 @@
+using System.Buffers;
+using System.Text.Json;
+using NATS.Client.Core;
+
+namespace NATS.Client.JetStream.Internal;
+
+internal sealed class NatsJSJsonDocumentSerializer : INatsDeserialize<JsonDocument>
+{
+    public static readonly NatsJSJsonDocumentSerializer Default = new();
+
+    public JsonDocument? Deserialize(in ReadOnlySequence<byte> buffer) => buffer.Length == 0 ? default : JsonDocument.Parse(buffer);
+}