feat: Support GetHeader in store (#2422)

Resolves #2419

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **New Features**
* Added the ability to retrieve a block header by height without
fetching full block data.
* **Tests**
* Introduced new tests to verify block header retrieval, including error
scenarios.
  * Enhanced mocking support for header retrieval in test environments.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: alpe

pkg/store/store.go

@@ -106,16 +106,10 @@ func (s *DefaultStore) SaveBlockData(ctx context.Context, header *types.SignedHe
 
 // GetBlockData returns block header and data at given height, or error if it's not found in Store.
 func (s *DefaultStore) GetBlockData(ctx context.Context, height uint64) (*types.SignedHeader, *types.Data, error) {
-	headerBlob, err := s.db.Get(ctx, ds.NewKey(getHeaderKey(height)))
-	if err != nil {
-		return nil, nil, fmt.Errorf("failed to load block header: %w", err)
-	}
-	header := new(types.SignedHeader)
-	err = header.UnmarshalBinary(headerBlob)
+	header, err := s.GetHeader(ctx, height)
 	if err != nil {
-		return nil, nil, fmt.Errorf("failed to unmarshal block header: %w", err)
+		return nil, nil, err
 	}
-
 	dataBlob, err := s.db.Get(ctx, ds.NewKey(getDataKey(height)))
 	if err != nil {
 		return nil, nil, fmt.Errorf("failed to load block data: %w", err)
@@ -159,6 +153,19 @@ func (s *DefaultStore) GetSignatureByHash(ctx context.Context, hash []byte) (*ty
 	return s.GetSignature(ctx, height)
 }
 
+// GetHeader returns the header at the given height or error if it's not found in Store.
+func (s *DefaultStore) GetHeader(ctx context.Context, height uint64) (*types.SignedHeader, error) {
+	headerBlob, err := s.db.Get(ctx, ds.NewKey(getHeaderKey(height)))
+	if err != nil {
+		return nil, fmt.Errorf("load block header: %w", err)
+	}
+	header := new(types.SignedHeader)
+	if err = header.UnmarshalBinary(headerBlob); err != nil {
+		return nil, fmt.Errorf("unmarshal block header: %w", err)
+	}
+	return header, nil
+}
+
 // GetSignature returns signature for a block with given block header hash, or error if it's not found in Store.
 func (s *DefaultStore) GetSignature(ctx context.Context, height uint64) (*types.Signature, error) {
 	signatureData, err := s.db.Get(ctx, ds.NewKey(getSignatureKey(height)))

pkg/store/store_test.go

@@ -314,6 +314,7 @@ func TestMetadata(t *testing.T) {
 	require.Error(err)
 	require.Nil(v)
 }
+
 func TestGetBlockDataErrors(t *testing.T) {
 	t.Parallel()
 	chainID := "TestGetBlockDataErrors"
@@ -333,15 +334,15 @@ func TestGetBlockDataErrors(t *testing.T) {
 			name:      "header get error",
 			mock:      &mockBatchingDatastore{Batching: mustNewInMem(), getError: mockErr("get header")},
 			prepare:   func(_ context.Context, _ *mockBatchingDatastore) {}, // nothing to pre-seed
-			expectSub: "failed to load block header",
+			expectSub: "load block header",
 		},
 		{
 			name: "header unmarshal error",
 			mock: &mockBatchingDatastore{Batching: mustNewInMem(), unmarshalErrorOnCall: 1},
 			prepare: func(ctx context.Context, m *mockBatchingDatastore) {
 				_ = m.Put(ctx, ds.NewKey(getHeaderKey(header.Height())), []byte("garbage"))
 			},
-			expectSub: "failed to unmarshal block header",
+			expectSub: "unmarshal block header",
 		},
 		{
 			name: "data get error",
@@ -561,3 +562,54 @@ func TestGetMetadataError(t *testing.T) {
 	require.Contains(err.Error(), mockErrGet.Error())
 	require.Contains(err.Error(), fmt.Sprintf("failed to get metadata for key '%s'", key))
 }
+
+func TestGetHeader(t *testing.T) {
+	t.Parallel()
+	chainID := "TestGetHeader"
+	header, _ := types.GetRandomBlock(1, 0, chainID)
+	headerBlob, _ := header.MarshalBinary()
+
+	mockErr := func(msg string) error { return fmt.Errorf("mock %s error", msg) }
+
+	cases := map[string]struct {
+		mock    *mockBatchingDatastore
+		prepare func(context.Context, *mockBatchingDatastore)
+		expErr  string
+	}{
+		"all good": {
+			mock: &mockBatchingDatastore{Batching: mustNewInMem()},
+			prepare: func(ctx context.Context, db *mockBatchingDatastore) {
+				_ = db.Put(ctx, ds.NewKey(getHeaderKey(header.Height())), headerBlob)
+			},
+		},
+		"db error": {
+			mock:    &mockBatchingDatastore{Batching: mustNewInMem(), getError: mockErr("get header")},
+			prepare: func(_ context.Context, _ *mockBatchingDatastore) {}, // nothing to pre-seed
+			expErr:  "load block header",
+		},
+		"unmarshal error": {
+			mock: &mockBatchingDatastore{Batching: mustNewInMem(), unmarshalErrorOnCall: 1},
+			prepare: func(ctx context.Context, m *mockBatchingDatastore) {
+				_ = m.Put(ctx, ds.NewKey(getHeaderKey(header.Height())), []byte("garbage"))
+			},
+			expErr: "unmarshal block header",
+		},
+	}
+
+	for name, tc := range cases {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+			s := New(tc.mock)
+			tc.prepare(t.Context(), tc.mock)
+
+			gotHeader, gotErr := s.GetHeader(t.Context(), header.Height())
+			if tc.expErr != "" {
+				require.Error(t, gotErr)
+				require.ErrorContains(t, gotErr, tc.expErr)
+				return
+			}
+			require.NoError(t, gotErr)
+			assert.Equal(t, header, gotHeader)
+		})
+	}
+}

pkg/store/types.go

@@ -22,6 +22,9 @@ type Store interface {
 	// GetBlockByHash returns block with given block header hash, or error if it's not found in Store.
 	GetBlockByHash(ctx context.Context, hash []byte) (*types.SignedHeader, *types.Data, error)
 
+	// GetHeader returns the header at the given height or error if it's not found in Store.
+	GetHeader(ctx context.Context, height uint64) (*types.SignedHeader, error)
+
 	// GetSignature returns signature for a block at given height, or error if it's not found in Store.
 	GetSignature(ctx context.Context, height uint64) (*types.Signature, error)
 	// GetSignatureByHash returns signature for a block with given block header hash, or error if it's not found in Store.