From e36b28ab6a70f94d7060249dd13f6f545e2155a6 Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Fri, 27 Dec 2024 12:51:45 +0300
Subject: [PATCH] capability: add ArchivalNode, fix #3776

This will be used to differentiate full history nodes from state only. Currently
it's just a definition, we can not use it safely on current networks because
nodes will refuse this Version, so actual code using the attribute will be
added in newer versions.

Signed-off-by: Roman Khimov <roman@nspcc.ru>
---
 pkg/network/capability/capability.go      | 18 ++++++++++++++++++
 pkg/network/capability/capability_test.go | 12 ++++++++++++
 pkg/network/capability/type.go            |  5 +++++
 pkg/network/payload/version_test.go       |  4 ++++
 4 files changed, 39 insertions(+)

diff --git a/pkg/network/capability/capability.go b/pkg/network/capability/capability.go
index bc0fa101d3..21f0bc7900 100644
--- a/pkg/network/capability/capability.go
+++ b/pkg/network/capability/capability.go
@@ -64,6 +64,8 @@ type Capability struct {
 func (c *Capability) DecodeBinary(br *io.BinReader) {
 	c.Type = Type(br.ReadB())
 	switch c.Type {
+	case ArchivalNode:
+		c.Data = &Archival{}
 	case FullNode:
 		c.Data = &Node{}
 	case TCPServer, WSServer:
@@ -115,6 +117,22 @@ func (s *Server) EncodeBinary(bw *io.BinWriter) {
 	bw.WriteU16LE(s.Port)
 }
 
+// Archival represents an archival node that stores all blocks.
+type Archival struct{}
+
+// DecodeBinary implements io.Serializable.
+func (a *Archival) DecodeBinary(br *io.BinReader) {
+	var zero = br.ReadB() // Zero-length byte array as per Unknown.
+	if zero != 0 {
+		br.Err = errors.New("archival capability with non-zero data")
+	}
+}
+
+// EncodeBinary implements io.Serializable.
+func (a *Archival) EncodeBinary(bw *io.BinWriter) {
+	bw.WriteB(0)
+}
+
 // Unknown represents an unknown capability with some data. Other nodes can
 // decode it even if they can't interpret it. This is not expected to be used
 // for sending data directly (proper new types should be used), but it allows
diff --git a/pkg/network/capability/capability_test.go b/pkg/network/capability/capability_test.go
index 52649f9a84..62ef988118 100644
--- a/pkg/network/capability/capability_test.go
+++ b/pkg/network/capability/capability_test.go
@@ -4,6 +4,7 @@ import (
 	"testing"
 
 	"github.com/nspcc-dev/neo-go/internal/testserdes"
+	"github.com/stretchr/testify/require"
 )
 
 func TestUnknownEncodeDecode(t *testing.T) {
@@ -13,3 +14,14 @@ func TestUnknownEncodeDecode(t *testing.T) {
 	)
 	testserdes.EncodeDecodeBinary(t, &u, &ud)
 }
+
+func TestArchivalEncodeDecode(t *testing.T) {
+	var (
+		a  = Archival{}
+		ad Archival
+	)
+	testserdes.EncodeDecodeBinary(t, &a, &ad)
+
+	var bad = []byte{0x02, 0x55, 0xaa} // Two-byte var-encoded string.
+	require.Error(t, testserdes.DecodeBinary(bad, &ad))
+}
diff --git a/pkg/network/capability/type.go b/pkg/network/capability/type.go
index a20336e40a..161a49f548 100644
--- a/pkg/network/capability/type.go
+++ b/pkg/network/capability/type.go
@@ -10,6 +10,11 @@ const (
 	WSServer Type = 0x02
 	// FullNode represents a node that has complete current state.
 	FullNode Type = 0x10
+	// ArchivalNode represents a node that stores full block history.
+	// These nodes can be used for P2P synchronization from genesis
+	// (FullNode can cut the tail and may not respond to requests for
+	// old (wrt MaxTraceableBlocks) blocks).
+	ArchivalNode Type = 0x11
 
 	// 0xf0-0xff are reserved for private experiments.
 	ReservedFirst Type = 0xf0
diff --git a/pkg/network/payload/version_test.go b/pkg/network/payload/version_test.go
index a18ac3d329..45315e6980 100644
--- a/pkg/network/payload/version_test.go
+++ b/pkg/network/payload/version_test.go
@@ -29,6 +29,10 @@ func TestVersionEncodeDecode(t *testing.T) {
 				Port: wsPort,
 			},
 		},
+		{
+			Type: capability.ArchivalNode,
+			Data: &capability.Archival{},
+		},
 		{
 			Type: 0xff,
 			Data: &capability.Unknown{},