data-provider-temporary/examples/node_modules/detect-port-alt/lib/detect-port.js

Library that helps with server-to-client synchronization of data

'use strict'

const debug = require('debug')('detect-port')
const net = require('net')
const address = require('address')

module.exports = (port, host, callback) => {
  if (typeof port === 'function') {
    callback = port
    port = null
  } else if (typeof host === 'function') {
    callback = host
    host = null
  }
  port = parseInt(port) || 0
  let maxPort = port + 10
  if (maxPort > 65535) {
    maxPort = 65535
  }
  debug('detect free port between [%s, %s)', port, maxPort)
  if (typeof callback === 'function') {
    return tryListen(host, port, maxPort, callback)
  }
  // promise
  return new Promise((resolve, reject) => {
    tryListen(host, port, maxPort, (error, realPort) => {
      if (error) {
        reject(error);
      } else {
        resolve(realPort);
      }
    })
  })
}

function tryListen(host, port, maxPort, callback) {
  function handleError() {
    port++
    if (port >= maxPort) {
      debug(
        'port: %s >= maxPort: %s, give up and use random port',
        port,
        maxPort
      )
      port = 0
      maxPort = 0
    }
    tryListen(host, port, maxPort, callback)
  }

  // 1. check specified host (or null)
  listen(port, host, (err, realPort) => {
    // ignore random listening
    if (port === 0) {
      return callback(err, realPort)
    }

    if (err) {
      return handleError(err)
    }

    // 2. check default host
    listen(port, null, err => {
      if (err) {
        return handleError(err)
      }

      // 3. check localhost
      listen(port, 'localhost', err => {
        if (err) {
          return handleError(err)
        }

        // 4. check current ip
        listen(port, address.ip(), (err, realPort) => {
          if (err) {
            return handleError(err)
          }

          callback(null, realPort)
        })
      })
    })
  })
}

function listen(port, hostname, callback) {
  const server = new net.Server()

  server.on('error', err => {
    debug('listen %s:%s error: %s', hostname, port, err)
    server.close()
    return callback(err)
  })

  server.listen(port, hostname, () => {
    port = server.address().port
    server.close()
    debug('get free %s:%s', hostname, port)
    return callback(null, port)
  })
}