refactor(network): declarative P2P capability advertisement via IP2PCapabilityResolver

src/Nethermind/Nethermind.Core.Test/Container/OrderedComponentsTests.cs

@@ -40,6 +40,20 @@ public void TestAddFirst()
         Assert.That(ctx.Resolve<Item[]>().Select(item => item.Name), Is.EqualTo(["1", "2", "3"]));
     }
 
+    [Test]
+    public void TestRemove()
+    {
+        // RemoveOrderedComponents drops every component of the given concrete type, keeping the rest in order
+        using IContainer ctx = new ContainerBuilder()
+            .AddLast<IItem>(_ => new Item("1"))
+            .AddLast<IItem>(_ => new OtherItem("2"))
+            .AddLast<IItem>(_ => new Item("3"))
+            .RemoveOrderedComponents<IItem, Item>()
+            .Build();
+
+        Assert.That(ctx.Resolve<IItem[]>().Select(item => item.Name), Is.EqualTo(["2"]));
+    }
+
     [Test]
     public void TestDisallowIndividualRegistration()
     {
@@ -112,6 +126,7 @@ protected override void Load(ContainerBuilder builder) =>
     }
     private interface IItem { string Name { get; } }
     private record Item(string Name) : IItem;
+    private record OtherItem(string Name) : IItem;
     private class CompositeItem(IItem[] items) : IItem
     {
         public IItem[] Items { get; } = items;

src/Nethermind/Nethermind.Core.Test/Modules/PseudoNetworkModule.cs

@@ -2,13 +2,9 @@
 // SPDX-License-Identifier: LGPL-3.0-only
 
 using Autofac;
-using Nethermind.Blockchain.Synchronization;
 using Nethermind.Consensus;
 using Nethermind.Logging;
-using Nethermind.Network;
 using Nethermind.Network.Config;
-using Nethermind.Network.Contract.P2P;
-using Nethermind.Stats.Model;
 
 namespace Nethermind.Core.Test.Modules;
 
@@ -21,25 +17,6 @@ protected override void Load(ContainerBuilder builder)
         builder
             .AddSingleton<IGossipPolicy>(Policy.FullGossip)
 
-            // TODO: LastNStateRootTracker
-
-            .AddAdvance<ProtocolsManager>(cfg =>
-            {
-                cfg
-                    .As<IProtocolsManager>()
-                    .SingleInstance()
-                    .OnActivating((m) =>
-                    {
-                        ProtocolsManager protocolManager = m.Instance;
-                        ISyncConfig syncConfig = m.Context.Resolve<ISyncConfig>();
-
-                        if (syncConfig.SnapServingEnabled == true || syncConfig.SnapSync)
-                        {
-                            protocolManager.AddSupportedCapability(new Capability(Protocol.Snap, 1));
-                        }
-                    });
-            })
-
             // Some config migration
             .AddDecorator<INetworkConfig>((ctx, networkConfig) =>
             {

src/Nethermind/Nethermind.Core/Container/OrderedComponents.cs

@@ -1,18 +1,21 @@
 // SPDX-FileCopyrightText: 2025 Demerzel Solutions Limited
 // SPDX-License-Identifier: LGPL-3.0-only
 
+using System;
 using System.Collections.Generic;
 
 namespace Nethermind.Core.Container;
 
 public class OrderedComponents<T>
 {
-    private IList<T> _components = [];
+    private readonly List<T> _components = [];
     public IEnumerable<T> Components => _components;
 
     public void AddLast(T item) => _components.Add(item);
 
     public void AddFirst(T item) => _components.Insert(0, item);
 
+    public void RemoveAll(Predicate<T> match) => _components.RemoveAll(match);
+
     public void Clear() => _components.Clear();
 }

src/Nethermind/Nethermind.Core/Container/OrderedComponentsContainerBuilderExtensions.cs

@@ -76,6 +76,23 @@ public static ContainerBuilder AddCompositeOrderedComponents<T, TComposite>(this
         return builder;
     }
 
+    /// <summary>
+    /// Remove all previously registered ordered components of type <typeparamref name="TImpl"/> for <typeparamref name="T"/>.
+    /// Useful when a plugin replaces a default component instead of layering on top of it
+    /// (e.g., XDC dropping the default eth/68 capability resolver).
+    /// </summary>
+    /// <remarks>
+    /// Like <see cref="ClearOrderedComponents{T}"/>, this relies on the removing decorator being registered
+    /// after the component it targets, which holds when a plugin module loads after the core module that
+    /// registered the default.
+    /// </remarks>
+    public static ContainerBuilder RemoveOrderedComponents<T, TImpl>(this ContainerBuilder builder) where TImpl : T =>
+        builder.AddDecorator<OrderedComponents<T>>((_, orderedComponents) =>
+        {
+            orderedComponents.RemoveAll(static item => item is TImpl);
+            return orderedComponents;
+        });
+
     /// <summary>
     /// Clear all previously registered ordered components for <typeparamref name="T"/>.
     /// Useful when a plugin needs to disable all ordered policies (e.g., Hive).

src/Nethermind/Nethermind.Init/Modules/NetworkModule.cs

@@ -67,7 +67,8 @@ protected override void Load(ContainerBuilder builder)
             .AddSingleton<IMessagePad, Handshake.Eip8MessagePad>()
             .AddSingleton<IProtocolValidator, ProtocolValidator>()
             .AddSingleton<IProtocolsManager, ProtocolsManager>()
-            .AddSingleton<SnapCapabilitySwitcher>()
+            .AddFirst<IP2PCapabilityResolver, DefaultP2PCapabilityResolver>()
+            .AddLast<IP2PCapabilityResolver, SnapP2PCapabilityResolver>()
 
             // Handshake
             .AddMessageSerializer<Handshake.AuthEip8Message, Handshake.AuthEip8MessageSerializer>()

src/Nethermind/Nethermind.Init/Steps/InitializeNetwork.cs

@@ -15,10 +15,8 @@
 using Nethermind.Logging;
 using Nethermind.Network;
 using Nethermind.Network.Config;
-using Nethermind.Network.Contract.P2P;
 using Nethermind.Network.Discovery.Discv4;
 using Nethermind.Network.Rlpx;
-using Nethermind.Stats.Model;
 using Nethermind.Synchronization;
 using Nethermind.Synchronization.Peers;
 
@@ -58,7 +56,6 @@ public class InitializeNetwork : IStep
     private readonly IEnode _enode;
     private readonly INethermindPlugin[] _plugins;
     private readonly Lazy<IProtocolsManager> _protocolsManager;
-    private readonly Lazy<SnapCapabilitySwitcher> _snapCapabilitySwitcher;
 
     private readonly NodeSourceToDiscV4Feeder _enrDiscoveryAppFeeder;
     private readonly ISyncConfig _syncConfig;
@@ -83,7 +80,6 @@ public InitializeNetwork(
         IEnode enode,
         INethermindPlugin[] plugins,
         Lazy<IProtocolsManager> protocolsManager,
-        Lazy<SnapCapabilitySwitcher> snapCapabilitySwitcher,
         INetworkConfig networkConfig,
         ISyncConfig syncConfig,
         IInitConfig initConfig,
@@ -104,7 +100,6 @@ ILogManager logManager
         _enode = enode;
         _plugins = plugins;
         _protocolsManager = protocolsManager;
-        _snapCapabilitySwitcher = snapCapabilitySwitcher;
         _networkConfig = networkConfig;
         _syncConfig = syncConfig;
         _initConfig = initConfig;
@@ -151,12 +146,6 @@ await InitPeer().ContinueWith(initPeerTask =>
             }
         });
 
-        if (_syncConfig.SnapSync && _syncConfig.SnapServingEnabled != true)
-        {
-            _snapCapabilitySwitcher.Value.EnableSnapCapabilityUntilSynced();
-        }
-        else if (_logger.IsDebug) _logger.Debug("Skipped enabling snap capability");
-
         if (cancellationToken.IsCancellationRequested)
         {
             return;
@@ -258,12 +247,9 @@ private Task StartSync()
 
     protected virtual async Task InitPeer()
     {
-        IProtocolsManager protocolsManager = _protocolsManager.Value;
+        // Force creation so the protocols manager subscribes to session events before the RLPx listener starts.
+        _ = _protocolsManager.Value;
 
-        if (_syncConfig.SnapServingEnabled == true)
-        {
-            protocolsManager.AddSupportedCapability(new Capability(Protocol.Snap, 1));
-        }
         if (!_networkConfig.DisableDiscV4DnsFeeder)
         {
             // Feed some nodes into discoveryApp in case all bootnodes is faulty.
@@ -275,7 +261,7 @@ protected virtual async Task InitPeer()
             await plugin.InitNetworkProtocol();
         }
 
-        // Capabilities must be finalized before the RLPx listener accepts peers. Otherwise
+        // Capabilities must be resolved before the RLPx listener accepts peers. Otherwise
         // early sessions can negotiate only the default ETH version and never upgrade.
         await _rlpxPeer.Init();
 

src/Nethermind/Nethermind.JsonRpc.Test/Modules/TestRpcBlockchain.cs

@@ -233,6 +233,7 @@ await base.Build(builder =>
                 Substitute.For<IProtocolValidator>(),
                 Substitute.For<INetworkStorage>(),
                 Array.Empty<IProtocolHandlerFactory>(),
+                [new DefaultP2PCapabilityResolver()],
                 LimboLogs.Instance
             );
 

src/Nethermind/Nethermind.Merge.AuRa/AuRaMergePlugin.cs

@@ -17,6 +17,7 @@
 using Nethermind.Consensus.Withdrawals;
 using Nethermind.Config;
 using Nethermind.Core;
+using Nethermind.Core.Container;
 using Nethermind.Core.Specs;
 using Nethermind.Evm.TransactionProcessing;
 using Nethermind.Logging;
@@ -25,6 +26,7 @@
 using Nethermind.Merge.Plugin;
 using Nethermind.Merge.Plugin.BlockProduction;
 using Nethermind.Merge.Plugin.Handlers;
+using Nethermind.Network;
 using Nethermind.Specs.ChainSpecStyle;
 
 namespace Nethermind.Merge.AuRa
@@ -80,6 +82,8 @@ public class AuRaMergeModule : Module
         protected override void Load(ContainerBuilder builder) => builder
                 .AddModule(new BaseMergePluginModule())
 
+                .AddLast<IP2PCapabilityResolver, MergeP2PCapabilityResolver>()
+
                 // Aura (non merge) use `BlockProducerStarter` directly.
                 .AddSingleton<IBlockProducerTxSourceFactory, AuRaMergeBlockProducerTxSourceFactory>()
 

src/Nethermind/Nethermind.Merge.Plugin.Test/MergeP2PCapabilityResolverTests.cs

@@ -0,0 +1,48 @@
+// SPDX-FileCopyrightText: 2026 Demerzel Solutions Limited
+// SPDX-License-Identifier: LGPL-3.0-only
+
+using System.Collections.Generic;
+using Nethermind.Consensus;
+using Nethermind.Network.Contract.P2P;
+using Nethermind.Stats.Model;
+using NSubstitute;
+using NUnit.Framework;
+
+namespace Nethermind.Merge.Plugin.Test;
+
+[Parallelizable(ParallelScope.All)]
+public class MergeP2PCapabilityResolverTests
+{
+    [TestCase(false, false, false, TestName = "Pre-merge: not advertised")]
+    [TestCase(true, false, true, TestName = "Transition finished (post-merge restart): advertised")]
+    [TestCase(false, true, true, TestName = "Live merge: terminal block reached before transition finished: advertised")]
+    [TestCase(true, true, true, TestName = "Both: advertised")]
+    public void Resolve_advertises_post_merge_eth_capabilities_once_post_merge(bool transitionFinished, bool hasReachedTerminalBlock, bool expected)
+    {
+        IPoSSwitcher poSSwitcher = Substitute.For<IPoSSwitcher>();
+        poSSwitcher.TransitionFinished.Returns(transitionFinished);
+        poSSwitcher.HasEverReachedTerminalBlock().Returns(hasReachedTerminalBlock);
+        using MergeP2PCapabilityResolver resolver = new(poSSwitcher);
+
+        HashSet<Capability> capabilities = [];
+        resolver.Resolve(capabilities);
+
+        Assert.That(capabilities.Contains(new Capability(Protocol.Eth, 69)), Is.EqualTo(expected));
+        Assert.That(capabilities.Contains(new Capability(Protocol.Eth, 70)), Is.EqualTo(expected));
+        Assert.That(capabilities.Contains(new Capability(Protocol.Eth, 71)), Is.EqualTo(expected));
+    }
+
+    [Test]
+    public void Raises_Changed_when_terminal_block_reached()
+    {
+        IPoSSwitcher poSSwitcher = Substitute.For<IPoSSwitcher>();
+        using MergeP2PCapabilityResolver resolver = new(poSSwitcher);
+
+        bool changed = false;
+        resolver.Changed += () => changed = true;
+
+        poSSwitcher.TerminalBlockReached += Raise.Event();
+
+        Assert.That(changed, Is.True);
+    }
+}

src/Nethermind/Nethermind.Merge.Plugin.Test/MergePluginTests.cs

@@ -21,13 +21,11 @@
 using Nethermind.Logging;
 using Nethermind.Merge.Plugin.BlockProduction;
 using Nethermind.Network;
-using Nethermind.Network.Contract.P2P;
 using Nethermind.Runner.Ethereum.Modules;
 using Nethermind.Runner.Test.Ethereum;
 using Nethermind.Serialization.Json;
 using Nethermind.Specs.ChainSpecStyle;
 using Nethermind.Specs.Test.ChainSpecStyle;
-using Nethermind.Stats.Model;
 using NUnit.Framework;
 using NSubstitute;
 
@@ -198,48 +196,6 @@ public async Task Initializes_correctly()
         Assert.That(blockProducer, Is.InstanceOf<MergeBlockProducer>());
     }
 
-    [Test]
-    public async Task InitNetworkProtocol_adds_post_merge_eth_capabilities_when_transition_finished()
-    {
-        IPoSSwitcher poSSwitcher = Substitute.For<IPoSSwitcher>();
-        poSSwitcher.TransitionFinished.Returns(true);
-
-        await using IContainer container = BuildContainer(configure: builder => builder
-            .RegisterInstance(poSSwitcher)
-            .As<IPoSSwitcher>());
-        INethermindApi api = container.Resolve<INethermindApi>();
-        await _consensusPlugin!.Init(api);
-        await _plugin.Init(api);
-
-        api.ProtocolsManager!.ClearReceivedCalls();
-        await _plugin.InitNetworkProtocol();
-
-        AssertPostMergeEthCapabilitiesAdded(api);
-    }
-
-    [Test]
-    public async Task InitNetworkProtocol_delays_post_merge_eth_capabilities_until_terminal_block()
-    {
-        IPoSSwitcher poSSwitcher = Substitute.For<IPoSSwitcher>();
-        poSSwitcher.TransitionFinished.Returns(false);
-
-        await using IContainer container = BuildContainer(configure: builder => builder
-            .RegisterInstance(poSSwitcher)
-            .As<IPoSSwitcher>());
-        INethermindApi api = container.Resolve<INethermindApi>();
-        await _consensusPlugin!.Init(api);
-        await _plugin.Init(api);
-
-        api.ProtocolsManager!.ClearReceivedCalls();
-        await _plugin.InitNetworkProtocol();
-
-        api.ProtocolsManager!.DidNotReceive().AddSupportedCapability(Arg.Any<Capability>());
-
-        poSSwitcher.TerminalBlockReached += Raise.Event();
-
-        AssertPostMergeEthCapabilitiesAdded(api);
-    }
-
     [Test]
     public async Task Init_registers_gas_limit_calculator_for_testing_rpc_module()
     {
@@ -301,13 +257,4 @@ public async Task InitDisableJsonRpcUrlWithNoEngineUrl()
         Assert.That(jsonRpcConfig.EnabledModules, Is.Empty);
         Assert.That(jsonRpcConfig.AdditionalRpcUrls, Is.EqualTo(new[] { "http://localhost:8551|http;ws|net;eth;subscribe;web3;engine;client" }));
     }
-
-    private static void AssertPostMergeEthCapabilitiesAdded(INethermindApi api)
-    {
-        IProtocolsManager protocolsManager = api.ProtocolsManager!;
-
-        protocolsManager.Received(1).AddSupportedCapability(new Capability(Protocol.Eth, 69));
-        protocolsManager.Received(1).AddSupportedCapability(new Capability(Protocol.Eth, 70));
-        protocolsManager.Received(1).AddSupportedCapability(new Capability(Protocol.Eth, 71));
-    }
 }