purge.js

const fsp = require('fs').promises

async function purge(dir, pictureId) {
    const entries = await fsp.readdir(dir, { withFileTypes: true })
    let n = 0
    await Promise.all(entries.map(async (e) => {
        const path = `${dir}/${e.name}`
        if (e.isDirectory()) {
            n += await purge(path, pictureId)
        } else if (e.isFile()) {
            const buf = await fsp.readFile(path)
            const idOnCache = buf.slice(364, 396).toString()
            if (idOnCache === pictureId) {
                const copy = Buffer.from(buf)
                copy.writeIntLE(Math.floor(new Date() / 1000) - 1, 8, 6)
                copy.writeIntLE(0, 32, 6)
                await fsp.writeFile(path, copy)
                n++
            }
        }
    }))
    return n
}

async function handler(r) {
    const pictureId = r.uri.slice(r.uri.lastIndexOf('/') + 1)
    const n = await purge('/var/cache/nginx/kakeru', pictureId)
    r.return(200, `${n}`)
}

export default {handler}