lib/cache/base.js

// Copyright (c) 2018, Compiler Explorer Authors
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
//     * Redistributions of source code must retain the above copyright notice,
//       this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above copyright
//       notice, this list of conditions and the following disclaimer in the
//       documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.

const crypto = require('crypto'),
    logger = require('../logger').logger;

const HashVersion = 'Compiler Explorer Cache Version 1';

class BaseCache {
    constructor(name) {
        this.name = name;
        this.gets = 0;
        this.hits = 0;
        this.puts = 0;
    }

    stats() {
        return {hits: this.hits, puts: this.puts, gets: this.gets};
    }

    statString() {
        const pc = this.gets ? (100 * this.hits) / this.gets : 0;
        const misses = this.gets - this.hits;
        return `${this.puts} puts; ${this.gets} gets, ${this.hits} hits, ${misses} misses (${pc.toFixed(2)}%)`;
    }

    report() {
        logger.info(`${this.name}: cache stats: ${this.statString()}`);
    }

    static hash(object) {
        // See https://stackoverflow.com/questions/899574/which-is-best-to-use-typeof-or-instanceof/6625960#6625960
        const asString = (typeof(object) === 'string') ? object : JSON.stringify(object);
        return crypto.createHmac('sha256', HashVersion)
            .update(asString)
            .digest('hex');
    }

    get(key) {
        this.gets++;
        return this.getInternal(key)
            .then(result => {
                if (result.hit) {
                    this.hits++;
                }
                return result;
            });
    }

    put(key, value, creator) {
        if (!(value instanceof Buffer))
            value = new Buffer(value);
        this.puts++;
        return this.putInternal(key, value, creator);
    }

    // eslint-disable-next-line no-unused-vars
    getInternal(key) {
        return Promise.reject("should be implemented in subclass");
    }

    // eslint-disable-next-line no-unused-vars
    putInternal(key, value, creator) {
        return Promise.reject("should be implemented in subclass");
    }
}

module.exports = BaseCache;