Add block tree ancestor binding

kernel/block_tree_entry.go

@@ -50,6 +50,17 @@ func (bi *BlockTreeEntry) Equals(other *BlockTreeEntry) bool {
 	return C.btck_block_tree_entry_equals(bi.ptr, other.ptr) != 0
 }
 
+// Ancestor returns the ancestor block tree entry at the given height.
+//
+// Returns nil if height is negative or greater than this entry's height.
+func (bi *BlockTreeEntry) Ancestor(height int32) *BlockTreeEntry {
+	if height < 0 || height > bi.Height() {
+		return nil
+	}
+	ptr := C.btck_block_tree_entry_get_ancestor(bi.ptr, C.int32_t(height))
+	return &BlockTreeEntry{ptr: check(ptr)}
+}
+
 // GetHeader returns the block header associated with this block tree entry.
 func (bi *BlockTreeEntry) GetHeader() *BlockHeader {
 	return newBlockHeader(C.btck_block_tree_entry_get_block_header(bi.ptr), true)

kernel/block_tree_entry_test.go

@@ -63,6 +63,29 @@ func TestBlockTreeEntry(t *testing.T) {
 		}
 	})
 
+	t.Run("Ancestor", func(t *testing.T) {
+		entry2 := chain.GetByHeight(2)
+		if entry2 == nil {
+			t.Fatal("Entry at height 2 is nil")
+		}
+
+		for _, height := range []int32{0, 1, 2} {
+			ancestor := entry2.Ancestor(height)
+			if ancestor == nil {
+				t.Fatalf("Ancestor(%d) returned nil", height)
+			}
+			if got := ancestor.Height(); got != height {
+				t.Fatalf("Ancestor(%d) height = %d, want %d", height, got, height)
+			}
+		}
+
+		for _, height := range []int32{-1, 3} {
+			if ancestor := entry2.Ancestor(height); ancestor != nil {
+				t.Fatalf("Ancestor(%d) returned height %d, want nil", height, ancestor.Height())
+			}
+		}
+	})
+
 	t.Run("GetHeader", func(t *testing.T) {
 		// Get genesis block entry
 		genesisEntry := chain.GetByHeight(0)