feat(chain): block header validation (linkage, height, size)

Co-Authored-By: Charon <charon@lethean.io>

chain/validate.go

@@ -0,0 +1,59 @@
+// Copyright (c) 2017-2026 Lethean (https://lt.hn)
+//
+// Licensed under the European Union Public Licence (EUPL) version 1.2.
+// SPDX-License-Identifier: EUPL-1.2
+
+package chain
+
+import (
+	"bytes"
+	"fmt"
+
+	"forge.lthn.ai/core/go-blockchain/config"
+	"forge.lthn.ai/core/go-blockchain/types"
+	"forge.lthn.ai/core/go-blockchain/wire"
+)
+
+// ValidateHeader checks a block header before storage.
+// expectedHeight is the height at which this block would be stored.
+func (c *Chain) ValidateHeader(b *types.Block, expectedHeight uint64) error {
+	currentHeight, err := c.Height()
+	if err != nil {
+		return fmt.Errorf("validate: get height: %w", err)
+	}
+
+	// Height sequence check.
+	if expectedHeight != currentHeight {
+		return fmt.Errorf("validate: expected height %d but chain is at %d",
+			expectedHeight, currentHeight)
+	}
+
+	// Genesis block: prev_id must be zero.
+	if expectedHeight == 0 {
+		if !b.PrevID.IsZero() {
+			return fmt.Errorf("validate: genesis block has non-zero prev_id")
+		}
+		return nil
+	}
+
+	// Non-genesis: prev_id must match top block hash.
+	_, topMeta, err := c.TopBlock()
+	if err != nil {
+		return fmt.Errorf("validate: get top block: %w", err)
+	}
+	if b.PrevID != topMeta.Hash {
+		return fmt.Errorf("validate: prev_id %s does not match top block %s",
+			b.PrevID, topMeta.Hash)
+	}
+
+	// Block size check.
+	var buf bytes.Buffer
+	enc := wire.NewEncoder(&buf)
+	wire.EncodeBlock(enc, b)
+	if enc.Err() == nil && uint64(buf.Len()) > config.MaxBlockSize {
+		return fmt.Errorf("validate: block size %d exceeds max %d",
+			buf.Len(), config.MaxBlockSize)
+	}
+
+	return nil
+}

chain/validate_test.go

@@ -0,0 +1,123 @@
+// Copyright (c) 2017-2026 Lethean (https://lt.hn)
+//
+// Licensed under the European Union Public Licence (EUPL) version 1.2.
+// SPDX-License-Identifier: EUPL-1.2
+
+package chain
+
+import (
+	"testing"
+
+	store "forge.lthn.ai/core/go-store"
+	"forge.lthn.ai/core/go-blockchain/types"
+)
+
+func TestValidateHeader_Good_Genesis(t *testing.T) {
+	s, _ := store.New(":memory:")
+	defer s.Close()
+	c := New(s)
+
+	blk := &types.Block{
+		BlockHeader: types.BlockHeader{
+			MajorVersion: 1,
+			Timestamp:    1770897600,
+		},
+		MinerTx: testCoinbaseTx(0),
+	}
+
+	err := c.ValidateHeader(blk, 0)
+	if err != nil {
+		t.Fatalf("ValidateHeader genesis: %v", err)
+	}
+}
+
+func TestValidateHeader_Good_Sequential(t *testing.T) {
+	s, _ := store.New(":memory:")
+	defer s.Close()
+	c := New(s)
+
+	// Store block 0.
+	blk0 := &types.Block{
+		BlockHeader: types.BlockHeader{MajorVersion: 1, Timestamp: 1770897600},
+		MinerTx:     testCoinbaseTx(0),
+	}
+	hash0 := types.Hash{0x01}
+	c.PutBlock(blk0, &BlockMeta{Hash: hash0, Height: 0, Timestamp: 1770897600})
+
+	// Validate block 1.
+	blk1 := &types.Block{
+		BlockHeader: types.BlockHeader{
+			MajorVersion: 1,
+			Timestamp:    1770897720,
+			PrevID:       hash0,
+		},
+		MinerTx: testCoinbaseTx(1),
+	}
+
+	err := c.ValidateHeader(blk1, 1)
+	if err != nil {
+		t.Fatalf("ValidateHeader block 1: %v", err)
+	}
+}
+
+func TestValidateHeader_Bad_WrongPrevID(t *testing.T) {
+	s, _ := store.New(":memory:")
+	defer s.Close()
+	c := New(s)
+
+	blk0 := &types.Block{
+		BlockHeader: types.BlockHeader{MajorVersion: 1, Timestamp: 1770897600},
+		MinerTx:     testCoinbaseTx(0),
+	}
+	c.PutBlock(blk0, &BlockMeta{Hash: types.Hash{0x01}, Height: 0})
+
+	blk1 := &types.Block{
+		BlockHeader: types.BlockHeader{
+			MajorVersion: 1,
+			Timestamp:    1770897720,
+			PrevID:       types.Hash{0xFF}, // wrong
+		},
+		MinerTx: testCoinbaseTx(1),
+	}
+
+	err := c.ValidateHeader(blk1, 1)
+	if err == nil {
+		t.Fatal("expected error for wrong prev_id")
+	}
+}
+
+func TestValidateHeader_Bad_WrongHeight(t *testing.T) {
+	s, _ := store.New(":memory:")
+	defer s.Close()
+	c := New(s)
+
+	blk := &types.Block{
+		BlockHeader: types.BlockHeader{MajorVersion: 1, Timestamp: 1770897600},
+		MinerTx:     testCoinbaseTx(0),
+	}
+
+	// Chain is empty (height 0), but we pass expectedHeight=5.
+	err := c.ValidateHeader(blk, 5)
+	if err == nil {
+		t.Fatal("expected error for wrong height")
+	}
+}
+
+func TestValidateHeader_Bad_GenesisNonZeroPrev(t *testing.T) {
+	s, _ := store.New(":memory:")
+	defer s.Close()
+	c := New(s)
+
+	blk := &types.Block{
+		BlockHeader: types.BlockHeader{
+			MajorVersion: 1,
+			PrevID:       types.Hash{0xFF}, // genesis must have zero prev_id
+		},
+		MinerTx: testCoinbaseTx(0),
+	}
+
+	err := c.ValidateHeader(blk, 0)
+	if err == nil {
+		t.Fatal("expected error for genesis with non-zero prev_id")
+	}
+}