les: historical data garbage collection (#19570)

This change introduces garbage collection for the light client. Historical
chain data is deleted periodically. If you want to disable the GC, use
the --light.nopruning flag.

core/rawdb/accessors_chain_test.go

@@ -23,6 +23,7 @@ import (
 	"io/ioutil"
 	"math/big"
 	"os"
+	"reflect"
 	"testing"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -424,3 +425,35 @@ func TestAncientStorage(t *testing.T) {
 		t.Fatalf("invalid td returned")
 	}
 }
+
+func TestCanonicalHashIteration(t *testing.T) {
+	var cases = []struct {
+		from, to uint64
+		limit    int
+		expect   []uint64
+	}{
+		{1, 8, 0, nil},
+		{1, 8, 1, []uint64{1}},
+		{1, 8, 10, []uint64{1, 2, 3, 4, 5, 6, 7}},
+		{1, 9, 10, []uint64{1, 2, 3, 4, 5, 6, 7, 8}},
+		{2, 9, 10, []uint64{2, 3, 4, 5, 6, 7, 8}},
+		{9, 10, 10, nil},
+	}
+	// Test empty db iteration
+	db := NewMemoryDatabase()
+	numbers, _ := ReadAllCanonicalHashes(db, 0, 10, 10)
+	if len(numbers) != 0 {
+		t.Fatalf("No entry should be returned to iterate an empty db")
+	}
+	// Fill database with testing data.
+	for i := uint64(1); i <= 8; i++ {
+		WriteCanonicalHash(db, common.Hash{}, i)
+		WriteTd(db, common.Hash{}, i, big.NewInt(10)) // Write some interferential data
+	}
+	for i, c := range cases {
+		numbers, _ := ReadAllCanonicalHashes(db, c.from, c.to, c.limit)
+		if !reflect.DeepEqual(numbers, c.expect) {
+			t.Fatalf("Case %d failed, want %v, got %v", i, c.expect, numbers)
+		}
+	}
+}