Add support for Direct Get API with key in subject

src/NATS.Client.KeyValueStore/NatsKVContext.cs

@@ -19,15 +19,30 @@ public enum NatsKVStorageType
 /// </summary>
 public class NatsKVContext : INatsKVContext
 {
-    private const string KvStreamNamePrefix = "KV_";
+    internal const string KvStreamNamePrefix = "KV_";
     private static readonly int KvStreamNamePrefixLen = KvStreamNamePrefix.Length;
     private static readonly Regex ValidBucketRegex = new(pattern: @"\A[a-zA-Z0-9_-]+\z", RegexOptions.Compiled);
+    private readonly NatsKVOpts _opts;
 
     /// <summary>
     /// Create a new Key Value Store context
     /// </summary>
     /// <param name="context">JetStream context</param>
-    public NatsKVContext(INatsJSContext context) => JetStreamContext = context;
+    /// <param name="opts">Context options</param>
+    public NatsKVContext(INatsJSContext context, NatsKVOpts opts)
+    {
+        JetStreamContext = context;
+        _opts = opts;
+    }
+
+    /// <summary>
+    /// Create a new Key Value Store context
+    /// </summary>
+    /// <param name="context">JetStream context</param>
+    public NatsKVContext(INatsJSContext context)
+        : this(context, NatsKVOpts.Default)
+    {
+    }
 
     /// <inheritdoc />
     public INatsJSContext JetStreamContext { get; }
@@ -45,7 +60,7 @@ public async ValueTask<INatsKVStore> CreateStoreAsync(NatsKVConfig config, Cance
 
         var stream = await JetStreamContext.CreateStreamAsync(streamConfig, cancellationToken);
 
-        return new NatsKVStore(config.Bucket, JetStreamContext, stream);
+        return new NatsKVStore(config.Bucket, JetStreamContext, stream, _opts);
     }
 
     /// <inheritdoc />
@@ -61,7 +76,7 @@ public async ValueTask<INatsKVStore> GetStoreAsync(string bucket, CancellationTo
         }
 
         // TODO: KV mirror
-        return new NatsKVStore(bucket, JetStreamContext, stream);
+        return new NatsKVStore(bucket, JetStreamContext, stream, _opts);
     }
 
     /// <inheritdoc />
@@ -73,7 +88,7 @@ public async ValueTask<INatsKVStore> UpdateStoreAsync(NatsKVConfig config, Cance
 
         var stream = await JetStreamContext.UpdateStreamAsync(streamConfig, cancellationToken);
 
-        return new NatsKVStore(config.Bucket, JetStreamContext, stream);
+        return new NatsKVStore(config.Bucket, JetStreamContext, stream, _opts);
     }
 
     /// <inheritdoc />
@@ -85,7 +100,7 @@ public async ValueTask<INatsKVStore> CreateOrUpdateStoreAsync(NatsKVConfig confi
 
         var stream = await JetStreamContext.CreateOrUpdateStreamAsync(streamConfig, cancellationToken);
 
-        return new NatsKVStore(config.Bucket, JetStreamContext, stream);
+        return new NatsKVStore(config.Bucket, JetStreamContext, stream, _opts);
     }
 
     /// <inheritdoc />
@@ -251,3 +266,10 @@ private static StreamConfig CreateStreamConfig(NatsKVConfig config)
         return streamConfig;
     }
 }
+
+public class NatsKVOpts
+{
+    public static readonly NatsKVOpts Default = new();
+
+    public bool UseDirectGetApiWithKeysInSubject { get; init; }
+}

src/NATS.Client.KeyValueStore/NatsKVStore.cs

@@ -56,14 +56,18 @@ public class NatsKVStore : INatsKVStore
     private static readonly NatsKVException KeyCannotStartOrEndWithPeriodException = new("Key cannot start or end with a period");
     private static readonly NatsKVException KeyContainsInvalidCharactersException = new("Key contains invalid characters");
     private readonly INatsJSStream _stream;
+    private readonly NatsKVOpts _opts;
     private readonly string _kvBucket;
+    private readonly string _streamName;
 
-    internal NatsKVStore(string bucket, INatsJSContext context, INatsJSStream stream)
+    internal NatsKVStore(string bucket, INatsJSContext context, INatsJSStream stream, NatsKVOpts opts)
     {
         Bucket = bucket;
         JetStreamContext = context;
         _stream = stream;
+        _opts = opts;
         _kvBucket = $"$KV.{Bucket}.";
+        _streamName = NatsKVContext.KvStreamNamePrefix + Bucket;
     }
 
     /// <inheritdoc />
@@ -333,7 +337,19 @@ public async ValueTask<NatsResult<NatsKVEntry<T>>> TryGetEntryAsync<T>(string ke
 
         if (_stream.Info.Config.AllowDirect)
         {
-            var direct = await _stream.GetDirectAsync<T>(request, serializer, cancellationToken);
+            NatsMsg<T> direct;
+            if (_opts.UseDirectGetApiWithKeysInSubject)
+            {
+                direct = await JetStreamContext.Connection.RequestAsync<object, T>(
+                    subject: $"{JetStreamContext.Opts.Prefix}.DIRECT.GET.{_streamName}.{keySubject}",
+                    data: null,
+                    replySerializer: serializer,
+                    cancellationToken: cancellationToken);
+            }
+            else
+            {
+                direct = await _stream.GetDirectAsync<T>(request, serializer, cancellationToken);
+            }
 
             if (direct is { Headers: { } headers } msg)
             {

tests/NATS.Client.KeyValueStore.Tests/DirectGetTest.cs

@@ -0,0 +1,63 @@
+using NATS.Client.Core.Tests;
+
+namespace NATS.Client.KeyValueStore.Tests;
+
+public class DirectGetTest(ITestOutputHelper output)
+{
+    [Fact]
+    public async Task API_subject_test()
+    {
+        await using var server = await NatsServer.StartJSAsync();
+        var (nats1, proxy) = server.CreateProxiedClientConnection();
+        await using var nats = nats1;
+
+        var js = new NatsJSContext(nats);
+
+        var cts = new CancellationTokenSource(TimeSpan.FromSeconds(10));
+        var cancellationToken = cts.Token;
+
+        // default
+        {
+            var kv = new NatsKVContext(js);
+
+            var store = await kv.CreateStoreAsync(new NatsKVConfig("b1"), cancellationToken);
+            await store.PutAsync("x", 1, cancellationToken: cancellationToken);
+            await store.PutAsync("x", 2, cancellationToken: cancellationToken);
+
+            await proxy.FlushFramesAsync(nats);
+
+            var entry = await store.GetEntryAsync<int>("x", cancellationToken: cancellationToken);
+            Assert.Equal(2, entry.Value);
+
+            var proto = proxy.ClientFrames[0].Message;
+            Assert.StartsWith("PUB $JS.API.DIRECT.GET.KV_b1 _INBOX.", proto);
+            Assert.EndsWith("""␍␊{"last_by_subj":"$KV.b1.x"}""", proto);
+            foreach (var proxyFrame in proxy.ClientFrames)
+            {
+                output.WriteLine(proxyFrame.Message);
+            }
+        }
+
+        // key in api subject
+        {
+            var kv = new NatsKVContext(js, new NatsKVOpts { UseDirectGetApiWithKeysInSubject = true });
+
+            var store = await kv.CreateStoreAsync(new NatsKVConfig("b1"), cancellationToken);
+            await store.PutAsync("x", 1, cancellationToken: cancellationToken);
+            await store.PutAsync("x", 2, cancellationToken: cancellationToken);
+
+            await proxy.FlushFramesAsync(nats);
+
+            var entry = await store.GetEntryAsync<int>("x", cancellationToken: cancellationToken);
+            Assert.Equal(2, entry.Value);
+
+            var proto = proxy.ClientFrames[0].Message;
+            Assert.StartsWith("PUB $JS.API.DIRECT.GET.KV_b1.$KV.b1.x _INBOX.", proto);
+            Assert.EndsWith(""" 0␍␊""", proto);
+            foreach (var proxyFrame in proxy.ClientFrames)
+            {
+                output.WriteLine(proxyFrame.Message);
+            }
+        }
+    }
+}