eth/filters: honor context cancellation in bor block-log range scan

eth/filters/bor_filter.go

@@ -128,6 +128,16 @@ func (f *BorBlockLogsFilter) unindexedLogs(ctx context.Context, end uint64) ([]*
 	sprintLength := f.borConfig.CalculateSprint(uint64(f.begin))
 
 	for ; f.begin <= int64(end); f.begin = f.begin + int64(sprintLength) {
+		// Honor context cancellation (client disconnect or deadline) so a large
+		// range scan stops promptly instead of holding an RPC worker busy with
+		// work whose result the caller will never read. Mirrors the check in
+		// upstream go-ethereum eth/filters/filter.go's unindexedLogs.
+		select {
+		case <-ctx.Done():
+			return logs, ctx.Err()
+		default:
+		}
+
 		header, err := f.backend.HeaderByNumber(ctx, rpc.BlockNumber(f.begin))
 		if header == nil || err != nil {
 			return logs, err

eth/filters/bor_filter_test.go

@@ -1,13 +1,18 @@
 package filters
 
 import (
+	"context"
+	"errors"
 	"math/big"
+	"sync/atomic"
 	"testing"
+	"time"
 
 	"github.com/ethereum/go-ethereum/common"
 	types "github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/crypto"
 	"github.com/ethereum/go-ethereum/params"
+	"github.com/ethereum/go-ethereum/rpc"
 
 	"go.uber.org/mock/gomock"
 )
@@ -154,6 +159,92 @@ func TestBorFilters(t *testing.T) {
 	}
 }
 
+// newCancellationTestFilter builds a bor range filter wired to a mock backend
+// that counts per-block header reads inside the scan loop, returning the filter
+// and a pointer to that counter. A test can then assert the loop bailed out
+// early (counter == 0) instead of scanning the whole range. Only the per-block
+// reads are counted: the single pre-loop head lookup uses rpc.LatestBlockNumber
+// (negative), while loop reads use the concrete, non-negative block number.
+func newCancellationTestFilter(t *testing.T) (*BorBlockLogsFilter, *int32) {
+	t.Helper()
+
+	ctrl := gomock.NewController(t)
+	t.Cleanup(ctrl.Finish)
+
+	db := NewMockDatabase(ctrl)
+	backend := NewMockBackend(ctrl)
+
+	loopBlockReads := new(int32)
+	backend.EXPECT().ChainDb().Return(db).AnyTimes()
+	backend.EXPECT().HeaderByNumber(gomock.Any(), gomock.Any()).
+		DoAndReturn(func(_ context.Context, number rpc.BlockNumber) (*types.Header, error) {
+			if number >= 0 {
+				atomic.AddInt32(loopBlockReads, 1)
+			}
+			return newTestHeader(1), nil
+		}).AnyTimes()
+	backend.EXPECT().GetBorBlockReceipt(gomock.Any(), gomock.Any()).Return(nil, nil).AnyTimes()
+
+	// Range large enough that an unguarded loop would iterate hundreds of times.
+	filter := NewBorBlockLogsRangeFilter(backend, params.TestChainConfig.Bor, 0, 4000, []common.Address{addr}, nil)
+
+	return filter, loopBlockReads
+}
+
+// TestBorFilterHonorsContextCancellation asserts that a range scan stops as soon
+// as the request context is cancelled (e.g. the RPC client disconnected, or a
+// deadline fired) instead of scanning the whole range and keeping an RPC worker
+// busy with work whose result nobody will read. This mirrors the cancellation
+// check upstream go-ethereum performs in eth/filters/filter.go's unindexedLogs.
+func TestBorFilterHonorsContextCancellation(t *testing.T) {
+	t.Parallel()
+
+	filter, loopBlockReads := newCancellationTestFilter(t)
+
+	// Cancel up-front: a scan that honors cancellation must bail out before
+	// doing any per-block work.
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	logs, err := filter.Logs(ctx)
+
+	if !errors.Is(err, context.Canceled) {
+		t.Fatalf("expected context.Canceled, got err=%v (loop ran %d block reads, ignoring cancellation)",
+			err, atomic.LoadInt32(loopBlockReads))
+	}
+	if got := atomic.LoadInt32(loopBlockReads); got != 0 {
+		t.Fatalf("expected 0 in-loop block reads after honoring cancellation, got %d", got)
+	}
+	if len(logs) != 0 {
+		t.Fatalf("expected no logs on a cancelled scan, got %d", len(logs))
+	}
+}
+
+// TestBorFilterHonorsContextDeadline asserts the scan also stops once the
+// context deadline has passed. Because the loop now observes the context, any
+// deadline attached upstream (an operator-configured RPC timeout, or a deadline
+// the caller sets) bounds the scan -- previously the loop ran to completion
+// regardless of the deadline.
+func TestBorFilterHonorsContextDeadline(t *testing.T) {
+	t.Parallel()
+
+	filter, loopBlockReads := newCancellationTestFilter(t)
+
+	// Deadline already in the past: the scan must stop before any per-block work.
+	ctx, cancel := context.WithDeadline(context.Background(), time.Now().Add(-time.Hour))
+	defer cancel()
+
+	_, err := filter.Logs(ctx)
+
+	if !errors.Is(err, context.DeadlineExceeded) {
+		t.Fatalf("expected context.DeadlineExceeded, got err=%v (loop ran %d block reads, ignoring the deadline)",
+			err, atomic.LoadInt32(loopBlockReads))
+	}
+	if got := atomic.LoadInt32(loopBlockReads); got != 0 {
+		t.Fatalf("expected 0 in-loop block reads after honoring the deadline, got %d", got)
+	}
+}
+
 func TestBorFilters_SkipOnBeginAtStateSync(t *testing.T) {
 	t.Parallel()