You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: tips.rs
    path of file: ./repos/bee/bee-api/bee-rest-api/src/routes/api/core/v2
    
    the code of the file until where you have to start completion: // Copyright 2020-2022 IOTA Stiftung
// SPDX-License-Identifier: Apache-2.0

use axum::{extract::Extension, routing::get, Router};
use bee_block::BlockId;

use crate::{
    error::ApiError, storage::StorageBackend, types::responses::TipsResponse, ApiArgsFullNode, CONFIRMED_THRESHOLD,
};

pub(crate) fn filter<B: StorageBacke
    
async fn tips<B: StorageBackend>(Extension(args): Extension<ApiArgsFullNode<B>>) -> Result<TipsResponse, ApiError> {
    if !args.tangle.is_confirmed_threshold(CONFIRMED_THRESHOLD) {
        return Err(ApiError::ServiceUnavailable("the node is not synchronized"));
    }
    match args.tangle.get_blocks_to_approve().await {
        Some(tips) => Ok(TipsResponse {
            tips: tips.iter().map(BlockId::to_string).collect(),
        }),
        None => Err(ApiError::ServiceUnavailable("no tips available")),
    }
}