feat: implement /subz endpoint with account filter, test subject, and pagination

src/NATS.Server/Monitoring/MonitorServer.cs

@@ -15,6 +15,7 @@ public sealed class MonitorServer : IAsyncDisposable
     private readonly ILogger<MonitorServer> _logger;
     private readonly VarzHandler _varzHandler;
     private readonly ConnzHandler _connzHandler;
+    private readonly SubszHandler _subszHandler;
 
     public MonitorServer(NatsServer server, NatsOptions options, ServerStats stats, ILoggerFactory loggerFactory)
     {
@@ -29,6 +30,7 @@ public sealed class MonitorServer : IAsyncDisposable
 
         _varzHandler = new VarzHandler(server, options);
         _connzHandler = new ConnzHandler(server);
+        _subszHandler = new SubszHandler(server);
 
         _app.MapGet(basePath + "/", () =>
         {
@@ -75,15 +77,15 @@ public sealed class MonitorServer : IAsyncDisposable
             stats.HttpReqStats.AddOrUpdate("/leafz", 1, (_, v) => v + 1);
             return Results.Ok(new { });
         });
-        _app.MapGet(basePath + "/subz", () =>
+        _app.MapGet(basePath + "/subz", (HttpContext ctx) =>
         {
             stats.HttpReqStats.AddOrUpdate("/subz", 1, (_, v) => v + 1);
-            return Results.Ok(new { });
+            return Results.Ok(_subszHandler.HandleSubsz(ctx));
         });
-        _app.MapGet(basePath + "/subscriptionsz", () =>
+        _app.MapGet(basePath + "/subscriptionsz", (HttpContext ctx) =>
         {
             stats.HttpReqStats.AddOrUpdate("/subscriptionsz", 1, (_, v) => v + 1);
-            return Results.Ok(new { });
+            return Results.Ok(_subszHandler.HandleSubsz(ctx));
         });
         _app.MapGet(basePath + "/accountz", () =>
         {

src/NATS.Server/Monitoring/Subsz.cs

@@ -0,0 +1,45 @@
+using System.Text.Json.Serialization;
+
+namespace NATS.Server.Monitoring;
+
+/// <summary>
+/// Subscription information response. Corresponds to Go server/monitor.go Subsz struct.
+/// </summary>
+public sealed class Subsz
+{
+    [JsonPropertyName("server_id")]
+    public string Id { get; set; } = "";
+
+    [JsonPropertyName("now")]
+    public DateTime Now { get; set; }
+
+    [JsonPropertyName("num_subscriptions")]
+    public uint NumSubs { get; set; }
+
+    [JsonPropertyName("num_cache")]
+    public int NumCache { get; set; }
+
+    [JsonPropertyName("total")]
+    public int Total { get; set; }
+
+    [JsonPropertyName("offset")]
+    public int Offset { get; set; }
+
+    [JsonPropertyName("limit")]
+    public int Limit { get; set; }
+
+    [JsonPropertyName("subscriptions")]
+    public SubDetail[] Subs { get; set; } = [];
+}
+
+/// <summary>
+/// Options passed to Subsz() for filtering.
+/// </summary>
+public sealed class SubszOptions
+{
+    public int Offset { get; set; }
+    public int Limit { get; set; } = 1024;
+    public bool Subscriptions { get; set; }
+    public string Account { get; set; } = "";
+    public string Test { get; set; } = "";
+}

src/NATS.Server/Monitoring/SubszHandler.cs

@@ -0,0 +1,93 @@
+using Microsoft.AspNetCore.Http;
+using NATS.Server.Subscriptions;
+
+namespace NATS.Server.Monitoring;
+
+/// <summary>
+/// Handles /subz endpoint requests, returning subscription information.
+/// Corresponds to Go server/monitor.go handleSubsz.
+/// </summary>
+public sealed class SubszHandler(NatsServer server)
+{
+    public Subsz HandleSubsz(HttpContext ctx)
+    {
+        var opts = ParseQueryParams(ctx);
+        var now = DateTime.UtcNow;
+
+        // Collect subscriptions from all accounts (or filtered)
+        var allSubs = new List<Subscription>();
+        foreach (var account in server.GetAccounts())
+        {
+            if (!string.IsNullOrEmpty(opts.Account) && account.Name != opts.Account)
+                continue;
+            allSubs.AddRange(account.SubList.GetAllSubscriptions());
+        }
+
+        // Filter by test subject if provided
+        if (!string.IsNullOrEmpty(opts.Test))
+        {
+            allSubs = allSubs.Where(s => SubjectMatch.MatchLiteral(opts.Test, s.Subject)).ToList();
+        }
+
+        var total = allSubs.Count;
+        var numSubs = server.GetAccounts()
+            .Where(a => string.IsNullOrEmpty(opts.Account) || a.Name == opts.Account)
+            .Aggregate(0u, (sum, a) => sum + a.SubList.Count);
+        var numCache = server.GetAccounts()
+            .Where(a => string.IsNullOrEmpty(opts.Account) || a.Name == opts.Account)
+            .Sum(a => a.SubList.CacheCount);
+
+        SubDetail[] details = [];
+        if (opts.Subscriptions)
+        {
+            details = allSubs
+                .Skip(opts.Offset)
+                .Take(opts.Limit)
+                .Select(s => new SubDetail
+                {
+                    Subject = s.Subject,
+                    Queue = s.Queue ?? "",
+                    Sid = s.Sid,
+                    Msgs = Interlocked.Read(ref s.MessageCount),
+                    Max = s.MaxMessages,
+                    Cid = s.Client?.Id ?? 0,
+                })
+                .ToArray();
+        }
+
+        return new Subsz
+        {
+            Id = server.ServerId,
+            Now = now,
+            NumSubs = numSubs,
+            NumCache = numCache,
+            Total = total,
+            Offset = opts.Offset,
+            Limit = opts.Limit,
+            Subs = details,
+        };
+    }
+
+    private static SubszOptions ParseQueryParams(HttpContext ctx)
+    {
+        var q = ctx.Request.Query;
+        var opts = new SubszOptions();
+
+        if (q.TryGetValue("subs", out var subs))
+            opts.Subscriptions = subs == "true" || subs == "1" || subs == "detail";
+
+        if (q.TryGetValue("offset", out var offset) && int.TryParse(offset, out var o))
+            opts.Offset = o;
+
+        if (q.TryGetValue("limit", out var limit) && int.TryParse(limit, out var l))
+            opts.Limit = l;
+
+        if (q.TryGetValue("acc", out var acc))
+            opts.Account = acc.ToString();
+
+        if (q.TryGetValue("test", out var test))
+            opts.Test = test.ToString();
+
+        return opts;
+    }
+}