为什么清空缓存后css文件错误_切图仔学后端-缓存

const cache = {
    maxAge:3600,
    expires:true,
    cacheControl: true,
    lastModified: true,
    etag: true
}
module.exports = cache

function refreshRes(stats, res) {
    const {maxAge, expires, cacheControl, lastModified, etag} = cache;
    if(expires) {
        res.setHeader('Expires', (new Date(Date.now() + maxAge*1000)).toUTCString());
    }
    if(cacheControl) {
        res.setHeader('Cache-Control', `public, max-age=${maxAge}`);
    }
    if(lastModified) {
        res.setHeader('Last-Modified', stats.mtime.toUTCString());
    }
    if(etag) {
        res.setHeader('ETag', generateETag(stats));
    }
}
 
function isFresh(source){
    refresh(source,res)
    const lastModified = req.headers['if-modified-since'];
    const etag = req.headers['if-none-match'];
    if(!lastModified && !etag) {
        return false;
    }
    if(lastModified && lastModified !== res.getHeader('Last-Modified')) {
        return false;
    }
    if(etag && etag !== res.getHeader('ETag')) {
        return false;
    }
    return true;
}
module.exports = isFresh

if(isFresh(resource, req, res)) {
    res.statusCode = 304;
    res.end();
    return;
}

class Cache {
    constructor(maxAge = 1000 * 60 * 30,max = 10) {
        this.maxAge = maxAge
        //保存缓存的 Map
        this.cache = new Map()
        //过期时间 Map
        this.ttl = new Map()
        this.max = max
    }
    getCache(key) {
        let ttl = this.ttl.get(key)
        if ((+new Date()) - ttl >= this.maxAge) {
            //过期了则删除
            this.deleteCache(key)
            return null
        } else {
            return this.cache.get(key)
        }
    }
    setCache(key, value) {
        this.cache.set(key) = value
        this.ttl.set(key) = +new Date()
    }
    deleteCache(key) {
        this.cache.delete(key)
        this.ttl.delete(key)
    }
}
 
module.exports = Cache

class Cache {
    constructor(maxAge = 1000 * 60 * 30, max = 10) {
        this.maxAge = maxAge
        //保存缓存的object
        this.cache = [];
        this.max = max
        //过期时间object
        this.ttl = new Map()
    }
    getCache(key) {
        let index = this.findIndex(key);
        if (index === -1) {
            return undefined;
        }
        if ((+new Date()) - this.ttl.get(key) >= this.maxAge) {
            this.deleteCache(key)
            return undefined
        } else {
            // 删除此元素后插入到数组第一项
            let value = this.cache[index].value;
            this.cache.splice(index, 1);
            this.cache.unshift({
                key,
                value,
            });
            return value;
        }
    }
    setCache(key, value) {
        let index = this.findIndex(key);
        // 已经存在，提升
        if (index > -1) {
            this.cache.splice(index, 1);
        } else if (this.cache.length >= this.capacity) {
            // 若已经到达最大限制，先淘汰一个最久没有使用的
            this.cache.pop();
        }
        this.cache.unshift({
            key,
            value
        });
        this.ttl[key] = +new Date()
    }
    deleteCache(key) {
        let index = this.cache.findIndex(key)
        if(index == -1)return
        //依次提升
        for (let i = index; i < this.cache.length - 1; i++) {
            this.cache[i] = this.cache[i + 1]
        }
        delete this.ttl[key]
    }
    findIndex(key) {
        return this.cache.findIndex(item => key === item.key)
    }
}
 
module.exports = Cache

const Memcached = require('memcached');
const memcached = new Memcached('localhost:11211');
 
class Cache {
    get(key) {
        return new Promise((resolve, reject) => {
            memcached.get(key, (err, data) => {
                if (err) {
                    reject(err)
                } else {
                    resolve(data)
                }
            })
        })
    }
    set(key, value, lifetime) {
        return new Promise((resolve, reject) => {
            memcached.set(key, value, lifetime, (err, data) => {
                if (err) {
                    reject(err)
                } else {
                    resolve(data)
                }
            })
        })
    }
}
 
 
const cache = new Cache()
async function test() {
    var json = {
        name: 'abc',
        age: 12,
        sa: 16
    }
    await cache.set('t', JSON.stringify(json), 0)
    const res = await cache.get('t')
    console.log(res)
}
test()

async getSubject(){
    let sql = `SELECT * FROM subject`
    let key = md5(sql)
    let data = await cache.get(key)
    let result
    if(!data){
        result = await db.table('subject').select()
        cache.set(key,JSON.stringify(result))
    }
    return result
}

function hash($key) {
    let md5Str = md5($key).substring(0, 8)
    let seed = 31
    let hash = 0
    for (let i = 0; i < 8; i++) {
        hash = hash * seed + md5Str[i].charCodeAt()
        i++
    }
    return hash & 0x7FFFFFFF
}

let servers = [{
    host: '192.168.1.12',
    port: 6397
}, {
    host: '192.168.1.20',
    port: 6397
}]
 
let key = 'key'
let value = 'value'
let config = servers[hash(key) % 2]
const memcached = new Memcached(config)