private CompletableFuture<Map<BlockHeader, List<TransactionReceipt>>> processResponse(
      final Map<BlockHeader, List<TransactionReceipt>> responseData) {
    receipts.putAll(responseData);

    if (isComplete()) {
      result.complete(receipts);
    }

    return CompletableFuture.completedFuture(responseData);
  }
Given a set of headers, repeatedly requests the receipts for those blocks.
ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/sync/tasks/GetReceiptsForHeadersTask.java