feat: add jetstream consumer api lifecycle

src/NATS.Server/JetStream/Api/Handlers/ConsumerApiHandlers.cs

@@ -0,0 +1,72 @@
+using System.Text.Json;
+using NATS.Server.JetStream.Models;
+
+namespace NATS.Server.JetStream.Api.Handlers;
+
+public static class ConsumerApiHandlers
+{
+    private const string CreatePrefix = "$JS.API.CONSUMER.CREATE.";
+    private const string InfoPrefix = "$JS.API.CONSUMER.INFO.";
+
+    public static JetStreamApiResponse HandleCreate(string subject, ReadOnlySpan<byte> payload, ConsumerManager consumerManager)
+    {
+        var parsed = ParseSubject(subject, CreatePrefix);
+        if (parsed == null)
+            return JetStreamApiResponse.NotFound(subject);
+
+        var (stream, durableName) = parsed.Value;
+        var config = ParseConfig(payload);
+        if (string.IsNullOrWhiteSpace(config.DurableName))
+            config.DurableName = durableName;
+
+        return consumerManager.CreateOrUpdate(stream, config);
+    }
+
+    public static JetStreamApiResponse HandleInfo(string subject, ConsumerManager consumerManager)
+    {
+        var parsed = ParseSubject(subject, InfoPrefix);
+        if (parsed == null)
+            return JetStreamApiResponse.NotFound(subject);
+
+        var (stream, durableName) = parsed.Value;
+        return consumerManager.GetInfo(stream, durableName);
+    }
+
+    private static (string Stream, string Durable)? ParseSubject(string subject, string prefix)
+    {
+        if (!subject.StartsWith(prefix, StringComparison.Ordinal))
+            return null;
+
+        var remainder = subject[prefix.Length..];
+        var split = remainder.Split('.', 2, StringSplitOptions.RemoveEmptyEntries);
+        if (split.Length != 2)
+            return null;
+
+        return (split[0], split[1]);
+    }
+
+    private static ConsumerConfig ParseConfig(ReadOnlySpan<byte> payload)
+    {
+        if (payload.IsEmpty)
+            return new ConsumerConfig();
+
+        try
+        {
+            using var doc = JsonDocument.Parse(payload.ToArray());
+            var root = doc.RootElement;
+            var config = new ConsumerConfig();
+
+            if (root.TryGetProperty("durable_name", out var durableEl))
+                config.DurableName = durableEl.GetString() ?? string.Empty;
+
+            if (root.TryGetProperty("filter_subject", out var filterEl))
+                config.FilterSubject = filterEl.GetString();
+
+            return config;
+        }
+        catch (JsonException)
+        {
+            return new ConsumerConfig();
+        }
+    }
+}