koa1-server-timing/index.js

Koa1 Server Timinig header generation middleware

const assert = require('assert');

function getSlug(str) {
    if (typeof str !== 'string') return '';
    return str.toLowerCase().trim().replace(/\s+/g, '-').replace(/[^a-z-]/g, '');
}

module.exports = function ({ total } = { total: process.env.NODE_ENV !== 'production' }) {
    return function * (next) {
        const ctx = this;
        // attaching timings object to state
        ctx.state.timings = {
            all: new Map(),
            startSpan(spanDesc, spanSlug = getSlug(spanDesc)) {
                assert.ok(!this.all.has(spanSlug), 'This span is running already, name muse be unique!');
                assert.ok(spanSlug.length, 'Either slug or description must be non-empy');
                this.all.set(spanSlug, { start: process.hrtime(), desc: spanDesc || '' });
                return spanSlug;
            },
            stopSpan(spanName) {
                const key = this.all.has(spanName) ? spanName : getSlug(spanName);
                assert.ok(this.all.has(key), 'Span to stop is not found!');
                assert.ok('start' in this.all.get(key), 'Span to stop were never started!');
                const timing = this.all.get(key);
                timing.stop = process.hrtime(timing.start);
            }
        };

        // if we need total, then start it now
        if (total) ctx.state.timings.startSpan('total');

        // letting other things pass now
        yield next;

        // Terminate all spans that wasn't explicitely terminated
        ctx.state.timings.all.forEach(timing => { if (!timing.stop) timing.stop = process.hrtime(timing.start); });

        // constructing headers array
        const metrics = [];
        for (const [key, { stop: [sec, nanosec], desc }] of ctx.state.timings.all) {
            const dur = (sec * 1000 + nanosec / 1000000).toFixed(2);
            metrics.push(`${key};dur=${dur}${desc.length && key !== desc ? `;desc="${desc}"` : ''}`);
        }

        // Adding our headers now
        if (metrics.length) ctx.append('Server-Timing', metrics.join(', '));
    }
}