perf(grpc): O(1) unconstrained bulk fast path, direct filtered-command build, cache eviction, capacity hints

src/ZB.MOM.WW.MxGateway.Server/Grpc/MxAccessGatewayService.cs

@@ -461,6 +461,14 @@ public sealed class MxAccessGatewayService(
         string? correlationId,
         CancellationToken cancellationToken)
     {
+        // An identity with no read constraints allows every tag, so the per-item enforcer call below
+        // can only answer "allowed" — the whole loop (and the plan it would build) is dead work.
+        // Returning null is exactly what the denied.Count == 0 exit below returns.
+        if (!constraintEnforcer.HasReadConstraints(identity))
+        {
+            return null;
+        }
+
         Dictionary<int, SubscribeResult> denied = [];
         List<string> allowed = [];
         for (int index = 0; index < tagAddresses.Count; index++)
@@ -491,16 +499,23 @@ public sealed class MxAccessGatewayService(
             return null;
         }
 
-        MxCommand filtered = command.Clone();
-        if (filtered.Kind == MxCommandKind.AddItemBulk)
+        // Build the filtered command directly instead of cloning the original and clearing it:
+        // the clone deep-copied every denied address only to drop it. The payload's other fields
+        // (server_handle) are copied across explicitly. Nothing aliases the request here — these
+        // bulk payloads carry only strings — and the worker-bound graph is still the unaliased copy
+        // MapCommand makes.
+        MxCommand filtered = new() { Kind = command.Kind };
+        if (command.Kind == MxCommandKind.AddItemBulk)
         {
-            filtered.AddItemBulk.TagAddresses.Clear();
-            filtered.AddItemBulk.TagAddresses.Add(allowed);
+            AddItemBulkCommand payload = new() { ServerHandle = command.AddItemBulk.ServerHandle };
+            payload.TagAddresses.Add(allowed);
+            filtered.AddItemBulk = payload;
         }
         else
         {
-            filtered.SubscribeBulk.TagAddresses.Clear();
-            filtered.SubscribeBulk.TagAddresses.Add(allowed);
+            SubscribeBulkCommand payload = new() { ServerHandle = command.SubscribeBulk.ServerHandle };
+            payload.TagAddresses.Add(allowed);
+            filtered.SubscribeBulk = payload;
         }
 
         return new SubscribeBulkConstraintPlan(filtered, tagAddresses.Count, denied, allowed.Count > 0);
@@ -517,6 +532,11 @@ public sealed class MxAccessGatewayService(
         // Mirrors FilterTagBulkAsync but produces BulkReadResult denial entries
         // so the reply payload merges into BulkReadReply.Results, not
         // BulkSubscribeReply.Results.
+        if (!constraintEnforcer.HasReadConstraints(identity))
+        {
+            return null;
+        }
+
         Dictionary<int, BulkReadResult> denied = [];
         List<string> allowed = [];
         for (int index = 0; index < tagAddresses.Count; index++)
@@ -548,9 +568,14 @@ public sealed class MxAccessGatewayService(
             return null;
         }
 
-        MxCommand filtered = command.Clone();
-        filtered.ReadBulk.TagAddresses.Clear();
-        filtered.ReadBulk.TagAddresses.Add(allowed);
+        MxCommand filtered = new() { Kind = command.Kind };
+        ReadBulkCommand payload = new()
+        {
+            ServerHandle = command.ReadBulk.ServerHandle,
+            TimeoutMs = command.ReadBulk.TimeoutMs,
+        };
+        payload.TagAddresses.Add(allowed);
+        filtered.ReadBulk = payload;
 
         return new ReadBulkConstraintPlan(filtered, tagAddresses.Count, denied, allowed.Count > 0);
     }
@@ -572,6 +597,11 @@ public sealed class MxAccessGatewayService(
         // Parameterising on TEntry + getItemHandle keeps a single filter
         // routine for all four and avoids duplicating CheckWriteHandleAsync
         // calls.
+        if (!constraintEnforcer.HasWriteConstraints(identity))
+        {
+            return null;
+        }
+
         Dictionary<int, BulkWriteResult> denied = [];
         List<TEntry> allowed = [];
         for (int index = 0; index < entries.Count; index++)
@@ -609,33 +639,70 @@ public sealed class MxAccessGatewayService(
             return null;
         }
 
-        MxCommand filtered = command.Clone();
-        ReplaceWriteBulkEntries(filtered, allowed);
-        return new WriteBulkConstraintPlan(filtered, entries.Count, denied, allowed.Count > 0);
+        return new WriteBulkConstraintPlan(
+            BuildFilteredWriteBulkCommand(command, allowed),
+            entries.Count,
+            denied,
+            allowed.Count > 0);
     }
 
-    private static void ReplaceWriteBulkEntries<TEntry>(MxCommand command, IReadOnlyList<TEntry> allowed)
+    /// <summary>
+    ///     Builds the allowed-only bulk-write command. The allowed entries are carried over by
+    ///     reference rather than deep-cloned: the caller only reads this command (TrackCommandReply),
+    ///     and the copy the worker mutates and owns is the one <c>MapCommand</c> clones — the same
+    ///     no-aliasing boundary as before. Cloning the whole command here and clearing it copied
+    ///     every denied entry's payload (including <c>WriteSecured</c> values) for nothing.
+    /// </summary>
+    /// <typeparam name="TEntry">The per-family bulk-write entry message type.</typeparam>
+    /// <param name="command">The original command, read for its kind and payload scalars.</param>
+    /// <param name="allowed">The entries that survived constraint filtering, in original order.</param>
+    /// <returns>A command of the same kind carrying only the allowed entries.</returns>
+    private static MxCommand BuildFilteredWriteBulkCommand<TEntry>(MxCommand command, IReadOnlyList<TEntry> allowed)
         where TEntry : class
     {
+        MxCommand filtered = new() { Kind = command.Kind };
         switch (command.Kind)
         {
             case MxCommandKind.WriteBulk:
-                command.WriteBulk.Entries.Clear();
-                command.WriteBulk.Entries.Add((IEnumerable<WriteBulkEntry>)allowed);
-                break;
-            case MxCommandKind.Write2Bulk:
-                command.Write2Bulk.Entries.Clear();
-                command.Write2Bulk.Entries.Add((IEnumerable<Write2BulkEntry>)allowed);
-                break;
-            case MxCommandKind.WriteSecuredBulk:
-                command.WriteSecuredBulk.Entries.Clear();
-                command.WriteSecuredBulk.Entries.Add((IEnumerable<WriteSecuredBulkEntry>)allowed);
-                break;
-            case MxCommandKind.WriteSecured2Bulk:
-                command.WriteSecured2Bulk.Entries.Clear();
-                command.WriteSecured2Bulk.Entries.Add((IEnumerable<WriteSecured2BulkEntry>)allowed);
+            {
+                WriteBulkCommand payload = new() { ServerHandle = command.WriteBulk.ServerHandle };
+                payload.Entries.Add((IEnumerable<WriteBulkEntry>)allowed);
+                filtered.WriteBulk = payload;
                 break;
             }
+
+            case MxCommandKind.Write2Bulk:
+            {
+                Write2BulkCommand payload = new() { ServerHandle = command.Write2Bulk.ServerHandle };
+                payload.Entries.Add((IEnumerable<Write2BulkEntry>)allowed);
+                filtered.Write2Bulk = payload;
+                break;
+            }
+
+            case MxCommandKind.WriteSecuredBulk:
+            {
+                WriteSecuredBulkCommand payload = new() { ServerHandle = command.WriteSecuredBulk.ServerHandle };
+                payload.Entries.Add((IEnumerable<WriteSecuredBulkEntry>)allowed);
+                filtered.WriteSecuredBulk = payload;
+                break;
+            }
+
+            case MxCommandKind.WriteSecured2Bulk:
+            {
+                WriteSecured2BulkCommand payload = new() { ServerHandle = command.WriteSecured2Bulk.ServerHandle };
+                payload.Entries.Add((IEnumerable<WriteSecured2BulkEntry>)allowed);
+                filtered.WriteSecured2Bulk = payload;
+                break;
+            }
+
+            default:
+                // Only the four bulk-write kinds above reach FilterWriteBulkAsync, so this is
+                // unreachable; keep the previous behaviour (the unmodified command) rather than
+                // emitting a payload-less one if that ever stops holding.
+                return command.Clone();
+        }
+
+        return filtered;
     }
 
     private async Task<BulkConstraintPlan?> FilterHandleBulkAsync(
@@ -647,6 +714,11 @@ public sealed class MxAccessGatewayService(
         string? correlationId,
         CancellationToken cancellationToken)
     {
+        if (!constraintEnforcer.HasReadConstraints(identity))
+        {
+            return null;
+        }
+
         Dictionary<int, SubscribeResult> denied = [];
         List<int> allowed = [];
         for (int index = 0; index < itemHandles.Count; index++)
@@ -677,9 +749,10 @@ public sealed class MxAccessGatewayService(
             return null;
         }
 
-        MxCommand filtered = command.Clone();
-        filtered.AdviseItemBulk.ItemHandles.Clear();
-        filtered.AdviseItemBulk.ItemHandles.Add(allowed);
+        MxCommand filtered = new() { Kind = command.Kind };
+        AdviseItemBulkCommand payload = new() { ServerHandle = command.AdviseItemBulk.ServerHandle };
+        payload.ItemHandles.Add(allowed);
+        filtered.AdviseItemBulk = payload;
 
         return new SubscribeBulkConstraintPlan(filtered, itemHandles.Count, denied, allowed.Count > 0);
     }

src/ZB.MOM.WW.MxGateway.Server/Security/Authentication/GatewayApiKeyIdentityMapper.cs

@@ -19,10 +19,35 @@ namespace ZB.MOM.WW.MxGateway.Server.Security.Authentication;
 /// </remarks>
 public static class GatewayApiKeyIdentityMapper
 {
-    private const int MaxCachedConstraintBlobs = 1024;
+    /// <summary>
+    ///     Maximum number of parsed constraint blobs retained in <see cref="ConstraintCache"/>.
+    ///     Blobs are admin-controlled (one per API key), so the cap is only a memory backstop for a
+    ///     store with an unusually large number of distinct constrained keys.
+    /// </summary>
+    internal const int MaxCachedConstraintBlobs = 1024;
+
+    /// <summary>
+    ///     Bounded parsed-constraints cache keyed by the raw constraints JSON. The blob is parsed
+    ///     once per authenticated RPC otherwise, so this keeps the JSON parse off the hot path.
+    ///     Beyond <see cref="MaxCachedConstraintBlobs"/> entries the oldest insertion is evicted
+    ///     rather than the cache refusing new entries — a hard stop at the cap would leave every key
+    ///     admitted after it re-parsing its blob on every RPC for the process lifetime. Eviction is
+    ///     approximate (FIFO over insertion order, not true LRU) because only the bound matters.
+    /// </summary>
     private static readonly ConcurrentDictionary<string, ApiKeyConstraints> ConstraintCache =
         new(StringComparer.Ordinal);
 
+    /// <summary>
+    ///     Insertion-order queue used to evict the oldest cache entry once the cache exceeds
+    ///     <see cref="MaxCachedConstraintBlobs"/>. Keeping it separate leaves
+    ///     <see cref="ConstraintCache"/> reads lock-free; the lock guards only the eviction path.
+    /// </summary>
+    private static readonly ConcurrentQueue<string> InsertionOrder = new();
+    private static readonly object EvictionLock = new();
+
+    /// <summary>Current cache size, exposed for tests asserting the cap is honoured.</summary>
+    internal static int CurrentCacheSize => ConstraintCache.Count;
+
     private static ApiKeyConstraints DeserializeConstraints(string? constraintsJson)
     {
         if (string.IsNullOrWhiteSpace(constraintsJson))
@@ -36,12 +61,36 @@ public static class GatewayApiKeyIdentityMapper
         }
 
         ApiKeyConstraints parsed = ApiKeyConstraintSerializer.Deserialize(constraintsJson);
-        if (ConstraintCache.Count < MaxCachedConstraintBlobs)
+
+        // GetOrAdd returns whichever instance is in the cache after the call, so concurrent parsers
+        // of the same blob converge on one instance; it also avoids the TryAdd-then-read race where
+        // the key could be evicted between a failed TryAdd and the read back.
+        ApiKeyConstraints result = ConstraintCache.GetOrAdd(constraintsJson, parsed);
+        if (ReferenceEquals(result, parsed))
         {
-            ConstraintCache.TryAdd(constraintsJson, parsed);
+            // We were the inserter — track for FIFO eviction and bound the cache.
+            InsertionOrder.Enqueue(constraintsJson);
+            EvictIfOverCapacity();
         }
 
-        return parsed;
+        return result;
+    }
+
+    private static void EvictIfOverCapacity()
+    {
+        if (ConstraintCache.Count <= MaxCachedConstraintBlobs)
+        {
+            return;
+        }
+
+        // Serialize eviction so two threads do not race past the cap together.
+        lock (EvictionLock)
+        {
+            while (ConstraintCache.Count > MaxCachedConstraintBlobs && InsertionOrder.TryDequeue(out string? oldest))
+            {
+                ConstraintCache.TryRemove(oldest, out _);
+            }
+        }
     }
 
     /// <summary>

src/ZB.MOM.WW.MxGateway.Server/Security/Authorization/ConstraintEnforcer.cs

@@ -16,6 +16,14 @@ public sealed class ConstraintEnforcer(
     IGalaxyHierarchyCache cache,
     IAuditWriter auditWriter) : IConstraintEnforcer
 {
+    /// <inheritdoc />
+    public bool HasReadConstraints(ApiKeyIdentity? identity) =>
+        identity?.EffectiveConstraints.HasReadConstraints ?? false;
+
+    /// <inheritdoc />
+    public bool HasWriteConstraints(ApiKeyIdentity? identity) =>
+        identity?.EffectiveConstraints.HasWriteConstraints ?? false;
+
     /// <inheritdoc />
     public Task<ConstraintFailure?> CheckReadTagAsync(
         ApiKeyIdentity? identity,
@@ -211,7 +219,25 @@ public sealed class ConstraintEnforcer(
             return true;
         }
 
-        return subtreeGlobs.Any(glob => GalaxyGlobMatcher.IsMatch(containedPath, glob))
-            || tagGlobs.Any(glob => GalaxyGlobMatcher.IsMatch(tagAddress, glob));
+        // Plain index loops rather than Any(lambda): this runs once per item of every bulk
+        // read/write, and the closures the lambdas capture (containedPath / tagAddress) allocate a
+        // display class plus a delegate per call. Same short-circuit order, same result.
+        for (int i = 0; i < subtreeGlobs.Count; i++)
+        {
+            if (GalaxyGlobMatcher.IsMatch(containedPath, subtreeGlobs[i]))
+            {
+                return true;
+            }
+        }
+
+        for (int i = 0; i < tagGlobs.Count; i++)
+        {
+            if (GalaxyGlobMatcher.IsMatch(tagAddress, tagGlobs[i]))
+            {
+                return true;
+            }
+        }
+
+        return false;
     }
 }

src/ZB.MOM.WW.MxGateway.Server/Security/Authorization/IConstraintEnforcer.cs

@@ -5,6 +5,30 @@ namespace ZB.MOM.WW.MxGateway.Server.Security.Authorization;
 
 public interface IConstraintEnforcer
 {
+    /// <summary>
+    ///     Gets a value indicating whether any read constraint applies to an identity at all, so a
+    ///     bulk caller can hoist the question out of its per-item loop.
+    /// </summary>
+    /// <param name="identity">The API key identity.</param>
+    /// <returns><see langword="true"/> when at least one read constraint applies; otherwise <see langword="false"/>.</returns>
+    /// <remarks>
+    ///     Every per-item <see cref="CheckReadTagAsync"/> / <see cref="CheckReadHandleAsync"/> call for
+    ///     an unconstrained identity allows the item, so skipping the loop removes work without
+    ///     changing a decision. The default implementation answers <see langword="true"/> — an
+    ///     implementation that does not model constraints (test doubles, allow-all enforcers) keeps
+    ///     being consulted per item rather than being silently bypassed.
+    /// </remarks>
+    bool HasReadConstraints(ApiKeyIdentity? identity) => true;
+
+    /// <summary>
+    ///     Gets a value indicating whether any write constraint applies to an identity at all, the
+    ///     write-side counterpart of <see cref="HasReadConstraints"/>.
+    /// </summary>
+    /// <param name="identity">The API key identity.</param>
+    /// <returns><see langword="true"/> when at least one write constraint applies; otherwise <see langword="false"/>.</returns>
+    /// <remarks>The same conservative default as <see cref="HasReadConstraints"/> applies.</remarks>
+    bool HasWriteConstraints(ApiKeyIdentity? identity) => true;
+
     /// <summary>Checks whether a read constraint is satisfied for a tag address.</summary>
     /// <param name="identity">The API key identity.</param>
     /// <param name="tagAddress">Tag address to check.</param>

src/ZB.MOM.WW.MxGateway.Server/Sessions/SparseArrayExpander.cs

@@ -120,6 +120,10 @@ internal static class SparseArrayExpander
             case MxDataType.Boolean:
             {
                 BoolArray values = new();
+
+                // Size the backing store once: the fill below adds exactly `length` elements,
+                // so without this the RepeatedField doubles its array log2(length) times.
+                values.Values.Capacity = length;
                 for (int i = 0; i < length; i++)
                 {
                     values.Values.Add(false);
@@ -137,6 +141,7 @@ internal static class SparseArrayExpander
             case MxDataType.Integer when UsesInt64(elements):
             {
                 Int64Array values = new();
+                values.Values.Capacity = length;
                 for (int i = 0; i < length; i++)
                 {
                     values.Values.Add(0L);
@@ -154,6 +159,7 @@ internal static class SparseArrayExpander
             case MxDataType.Integer:
             {
                 Int32Array values = new();
+                values.Values.Capacity = length;
                 for (int i = 0; i < length; i++)
                 {
                     values.Values.Add(0);
@@ -171,6 +177,7 @@ internal static class SparseArrayExpander
             case MxDataType.Float:
             {
                 FloatArray values = new();
+                values.Values.Capacity = length;
                 for (int i = 0; i < length; i++)
                 {
                     values.Values.Add(0f);
@@ -188,6 +195,7 @@ internal static class SparseArrayExpander
             case MxDataType.Double:
             {
                 DoubleArray values = new();
+                values.Values.Capacity = length;
                 for (int i = 0; i < length; i++)
                 {
                     values.Values.Add(0d);
@@ -205,6 +213,7 @@ internal static class SparseArrayExpander
             case MxDataType.String:
             {
                 StringArray values = new();
+                values.Values.Capacity = length;
                 for (int i = 0; i < length; i++)
                 {
                     values.Values.Add(string.Empty);
@@ -222,6 +231,7 @@ internal static class SparseArrayExpander
             case MxDataType.Time:
             {
                 TimestampArray values = new();
+                values.Values.Capacity = length;
                 for (int i = 0; i < length; i++)
                 {
                     values.Values.Add(new Timestamp { Seconds = 0, Nanos = 0 });

src/ZB.MOM.WW.MxGateway.Tests/Security/Authentication/CachingApiKeyVerifierTests.cs

@@ -8,10 +8,12 @@ using LibApiKeyIdentity = ZB.MOM.WW.Auth.Abstractions.ApiKeys.ApiKeyIdentity;
 namespace ZB.MOM.WW.MxGateway.Tests.Security.Authentication;
 
 /// <summary>
-/// Hot-path decorators. Covers both mechanisms: <see cref="CachingApiKeyVerifier"/>
-/// (read/verification coalescing plus revoke/rotate invalidation) and
+/// Hot-path decorators. Covers all three mechanisms: <see cref="CachingApiKeyVerifier"/>
+/// (read/verification coalescing plus revoke/rotate invalidation),
 /// <see cref="CoalescingMarkApiKeyStore"/> (the <c>last_used</c> write coalescing that keeps the
-/// per-RPC database write off the throughput ceiling).
+/// per-RPC database write off the throughput ceiling), and the constraint-blob cache inside
+/// <see cref="GatewayApiKeyIdentityMapper"/> (which keeps the per-RPC constraints JSON parse off
+/// the authenticated path).
 /// </summary>
 public sealed class CachingApiKeyVerifierTests
 {
@@ -245,6 +247,50 @@ public sealed class CachingApiKeyVerifierTests
         Assert.Equal(keyId, CachingApiKeyVerifier.TryParseKeyId($"Bearer mxgw_{keyId}_secret"));
     }
 
+    /// <summary>
+    ///     The mapper's constraint-blob cache is bounded by eviction, not by a hard stop at the cap:
+    ///     once it is full the oldest entry is dropped so a newly-seen blob is still cached. A cache
+    ///     that merely stopped accepting entries would re-parse every blob beyond the cap on every
+    ///     single RPC, forever. Asserted behaviourally through instance identity — a cached blob maps
+    ///     to the same <see cref="ApiKeyConstraints"/> instance, a re-parsed one does not.
+    /// </summary>
+    [Fact]
+    public void ToGatewayIdentity_ConstraintCacheOverCapacity_EvictsOldestAndKeepsCaching()
+    {
+        string firstJson = ConstraintsJson("Area_FifoProbe");
+        ApiKeyConstraints first = MapConstraints(firstJson);
+        Assert.Same(first, MapConstraints(firstJson));
+
+        // Push strictly more than the cap through the cache after the probe blob, so FIFO eviction
+        // is guaranteed to have reached it however full the (process-wide) cache already was.
+        for (int i = 0; i < GatewayApiKeyIdentityMapper.MaxCachedConstraintBlobs + 8; i++)
+        {
+            MapConstraints(ConstraintsJson($"Area_FifoFlood_{i}"));
+        }
+
+        Assert.True(
+            GatewayApiKeyIdentityMapper.CurrentCacheSize <= GatewayApiKeyIdentityMapper.MaxCachedConstraintBlobs,
+            $"cache grew to {GatewayApiKeyIdentityMapper.CurrentCacheSize} entries, past the {GatewayApiKeyIdentityMapper.MaxCachedConstraintBlobs} cap");
+
+        // Evicted, so the probe blob is parsed afresh...
+        ApiKeyConstraints reparsed = MapConstraints(firstJson);
+        Assert.NotSame(first, reparsed);
+        Assert.Equal(first.ReadSubtrees, reparsed.ReadSubtrees);
+
+        // ...and re-cached, rather than re-parsed on every later call.
+        Assert.Same(reparsed, MapConstraints(firstJson));
+    }
+
+    private static ApiKeyConstraints MapConstraints(string constraintsJson) =>
+        GatewayApiKeyIdentityMapper.ToGatewayIdentity(new LibApiKeyIdentity(
+            KeyId: "operator01",
+            DisplayName: "Operator Key",
+            Scopes: new HashSet<string>(StringComparer.Ordinal),
+            Constraints: constraintsJson)).EffectiveConstraints;
+
+    private static string ConstraintsJson(string readSubtree) =>
+        ApiKeyConstraintSerializer.Serialize(ApiKeyConstraints.Empty with { ReadSubtrees = [readSubtree] })!;
+
     private static MemoryCache NewCache() => new(new MemoryCacheOptions());
 
     private static ApiKeyVerification Success(string keyId) => new(