index.js

#!/usr/bin/env node

const Koa = require('koa')
const Router = require('@koa/router')
const multer = require('@koa/multer')
const logger = require('koa-logger')
const sendfile = require('koa-sendfile')
const mkdirp = require('mkdirp')
const fs = require('fs')
const { spawn } = require('child_process')
const { extname, basename, dirname } = require('path')
const FileType = require('file-type')

const port = 3001
const expireDelay = 30  // 30 seconds
const maxExpireDuration = 1 * 60 * 60  // 1 hour
const maxFileSize = 1024 * 1024 * 800  // 800 MB

const TYPE_EPUB = 'application/epub+zip'
const TYPE_MOBI = 'application/x-mobipocket-ebook'

const allowedTypes = [TYPE_EPUB, TYPE_MOBI, 'application/pdf', 'application/vnd.comicbook+zip', 'application/vnd.comicbook-rar', 'text/html', 'text/plain', 'application/zip', 'application/x-rar-compressed']
const allowedExtensions = ['epub', 'mobi', 'pdf', 'cbz', 'cbr', 'html', 'txt']

const keyChars = "3469ACEGHLMNPRTY"
const keyLength = 4

function randomKey () {
  const choices = Math.pow(keyChars.length, keyLength)
  const rnd = Math.floor(Math.random() * choices)

  return rnd.toString(keyChars.length).padStart(keyLength, '0').split('').map((chr) => {
    return keyChars[parseInt(chr, keyChars.length)]
  }).join('')
}

function removeKey (key) {
  console.log('Removing expired key', key)
  const info = app.context.keys.get(key)
  if (info) {
    clearTimeout(app.context.keys.get(key).timer)
    if (info.file) {
      console.log('Deleting file', info.file.path)
      fs.unlink(info.file.path, (err) => {
        if (err) console.error(err)
      })
      info.file = null
    }
    app.context.keys.delete(key)
  } else {
    console.log('Tried to remove non-existing key', key)
  }
}

function expireKey (key) {
  // console.log('key', key, 'will expire in', expireDelay, 'seconds')
  const info = app.context.keys.get(key)
  const timer = setTimeout(removeKey, expireDelay * 1000, key)
  if (info) {
    clearTimeout(info.timer)
    info.timer = timer
    info.alive = new Date()
  }
  return timer
}

function flash (ctx, data) {
  console.log(data)
  ctx.cookies.set('flash', encodeURIComponent(JSON.stringify(data)), {overwrite: true, httpOnly: false})
}

const app = new Koa()
app.context.keys = new Map()
app.use(logger())

const router = new Router()

const upload = multer({
  storage: multer.diskStorage({
    destination: function (req, file, cb) {
      cb(null, 'uploads')
    },
    filename: function (req, file, cb) {
      const uniqueSuffix = Date.now() + '-' + Math.floor(Math.random() * 1E9)
      cb(null, file.fieldname + '-' + uniqueSuffix + extname(file.originalname).toLowerCase())
    }
  }),
  limits: {
    fileSize: maxFileSize,
    files: 1
  },
  fileFilter: (req, file, cb) => {
    console.log('Incoming file:', file)
    const key = req.body.key.toUpperCase()
    if (!app.context.keys.has(key)) {
      console.error('FileFilter: Unknown key: ' + key)
      cb(null, false)
      return
    }
    if (!allowedTypes.includes(file.mimetype) || !allowedExtensions.includes(extname(file.originalname.toLowerCase()).substr(1))) {
      console.error('FileFilter: File is of an invalid type ', file)
      cb(null, false)
      return
    }
    cb(null, true)
  }
})

router.post('/generate', async ctx => {
  const agent = ctx.get('user-agent')

  let key = null
  let attempts = 0
  console.log('There are currently', ctx.keys.size, 'key(s) in use.')
  console.log('Generating unique key...', ctx.ip, agent)
  do {
    key = randomKey()
    if (attempts > ctx.keys.size) {
      console.error('Can\'t generate more keys, map is full.', attempts, ctx.keys.size)
      ctx.body = 'error'
      return
    }
    attempts++
  } while (ctx.keys.has(key))

  console.log('Generated key ' + key + ', '+attempts+' attempt(s)')

  const info = {
    created: new Date(),
    agent: agent,
    file: null
  }
  ctx.keys.set(key, info)
  expireKey(key)
  setTimeout(() => {
    // remove if it is the same object
    if(ctx.keys.get(key) === info) removeKey(key)
  }, maxExpireDuration * 1000)

  ctx.body = key
})

router.get('/download/:key', async ctx => {
  const key = ctx.params.key.toUpperCase()
  const info = ctx.keys.get(key)
  if (!info || !info.file) {
    return
  }
  if (info.agent !== ctx.get('user-agent')) {
    console.error("User Agent doesnt match: " + info.agent + " VS " + ctx.get('user-agent'))
    return
  }
  expireKey(key)
  console.log('Sending file', info.file.path)
  await sendfile(ctx, info.file.path)
  ctx.attachment(info.file.name)
})

router.post('/upload', upload.single('file'), async ctx => {
  const key = ctx.request.body.key.toUpperCase()

  if (ctx.request.file) {
    console.log('Uploaded file:', ctx.request.file)
  }

  if (!ctx.keys.has(key)) {
    flash(ctx, {
      message: 'Unknown key ' + key,
      success: false
    })
    ctx.redirect('back', '/')
    if (ctx.request.file) {
      fs.unlink(ctx.request.file.path, (err) => {
        if (err) console.error(err)
        else console.log('Removed file', ctx.request.file.path)
      })
    }
    return
  }

  if (!ctx.request.file || ctx.request.file.size === 0) {
    flash(ctx, {
      message: 'Invalid file submitted',
      success: false,
      key: key
    })
    ctx.redirect('back', '/')
    if (ctx.request.file) {
      fs.unlink(ctx.request.file.path, (err) => {
        if (err) console.error(err)
        else console.log('Removed file', ctx.request.file.path)
      })
    }
    return
  }

  const mimetype = ctx.request.file.mimetype

  const type = await FileType.fromFile(ctx.request.file.path)

  if (!type || !allowedTypes.includes(type.mime)) {
    flash(ctx, {
      message: 'Uploaded file is of an invalid type: ' + ctx.request.file.originalname + ' (' + (type? type.mime : 'unknown mimetype') + ')',
      success: false,
      key: key
    })
    ctx.redirect('back', '/')
    fs.unlink(ctx.request.file.path, (err) => {
      if (err) console.error(err)
      else console.log('Removed file', ctx.request.file.path)
    })
    return
  }

  const info = ctx.keys.get(key)
  expireKey(key)

  let data = null
  let filename = ctx.request.file.originalname
  let conversion = null

  if (mimetype === TYPE_EPUB && info.agent.includes('Kindle')) {
    // convert to .mobi
    conversion = 'kindlegen'
    const outname = ctx.request.file.path.replace(/\.epub$/i, '.mobi')
    filename = filename.replace(/\.kepub\.epub$/i, '.epub').replace(/\.epub$/i, '.mobi')

    data = await new Promise((resolve, reject) => {
      const kindlegen = spawn('kindlegen', [basename(ctx.request.file.path), '-dont_append_source', '-c1', '-o', basename(outname)], {
        stdio: 'inherit',
        cwd: dirname(ctx.request.file.path)
      })
      kindlegen.once('close', (code) => {
        fs.unlink(ctx.request.file.path, (err) => {
          if (err) console.error(err)
          else console.log('Removed file', ctx.request.file.path)
        })
        fs.unlink(ctx.request.file.path.replace(/\.epub$/i, '.mobi8'), (err) => {
          if (err) console.error(err)
          else console.log('Removed file', ctx.request.file.path.replace(/\.epub$/i, '.mobi8'))
        })
        if (code !== 0) {
          console.warn('kindlegen error code ' + code)
        }

        resolve(outname)
      })
    })

  } else if (mimetype === TYPE_EPUB && info.agent.includes('Kobo') && ctx.request.body.kepubify) {
    // convert to Kobo EPUB
    conversion = 'kepubify'
    const outname = ctx.request.file.path.replace(/\.epub$/i, '.kepub.epub')
    filename = filename.replace(/\.kepub\.epub$/i, '.epub').replace(/\.epub$/i, '.kepub.epub')

    data = await new Promise((resolve, reject) => {
      const kepubify = spawn('kepubify', ['-v', '-u', '-o', basename(outname), basename(ctx.request.file.path)], {
        stdio: 'inherit',
        cwd: dirname(ctx.request.file.path)
      })
      kepubify.once('close', (code) => {
        fs.unlink(ctx.request.file.path, (err) => {
          if (err) console.error(err)
          else console.log('Removed file', ctx.request.file.path)
        })
        if (code !== 0) {
          reject('kepubify error code ' + code)
          return
        }

        resolve(outname)
      })
    })
  } else {
    // No conversion
    data = ctx.request.file.path
  }

  expireKey(key)
  if (info.file && info.file.path) {
    await new Promise((resolve, reject) => fs.unlink(info.file.path, (err) => {
      if (err) return reject(err)
      else console.log('Removed previously uploaded file', info.file.path)
      resolve()
    }))
  }
  info.file = {
    name: filename,
    path: data,
    // size: ctx.request.file.size,
    uploaded: new Date()
  }

  flash(ctx, {
    message: 'Upload successful!<br/>'+(conversion ? ' Ebook was converted with ' + conversion + ' and sent' : ' Sent')+' to '+(info.agent.includes('Kobo') ? 'a Kobo device.' : (info.agent.includes('Kindle') ? 'a Kindle device.' : 'a device.'))+'<br/>Filename: ' + filename,
    success: true,
    key: key
  })
  ctx.redirect('back', '/')
})

router.delete('/file/:key', async ctx => {
  const key = ctx.params.key.toUpperCase()
  const info = ctx.keys.get(key)
  if (!info) {
    ctx.throw(400, 'Unknown key: ' + key)
  }
  info.file = null
  ctx.body = 'ok'
})

router.get('/status/:key', async ctx => {
  const key = ctx.params.key.toUpperCase()
  const info = ctx.keys.get(key)
  if (!info) {
    ctx.body = {error: 'Unknown key'}
    return
  }
  if (info.agent !== ctx.get('user-agent')) {
    // don't send this error to client
    console.error("User Agent doesnt match: " + info.agent + " VS " + ctx.get('user-agent'))
    return
  }
  expireKey(key)
  ctx.body = {
    alive: info.alive,
    file: info.file ? {
      name: info.file.name,
      // size: info.file.size
    } : null
  }
})

router.get('/style.css', async ctx => {
  await sendfile(ctx, 'style.css')
})

router.get('/receive', async ctx => {
  await sendfile(ctx, 'download.html')
})

router.get('/', async ctx => {
  const agent = ctx.get('user-agent')
  console.log(ctx.ip, agent)
  await sendfile(ctx, agent.includes('Kobo') || agent.includes('Kindle')? 'download.html' : 'upload.html')
})


app.use(router.routes())
app.use(router.allowedMethods())

fs.rm('uploads', {recursive: true}, (err) => {
  if (err) throw err
  mkdirp('uploads').then (() => {
    app.listen(port)
    console.log('server is listening on port ' + port)
  })
})