code: function vhost (hostname, handle) {
    if (!hostname) {
      throw new TypeError('argument hostname is required')
    }
  
    if (!handle) {
      throw new TypeError('argument handle is required')
    }
  
    if (typeof handle !== 'function') {
      throw new TypeError('argument handle must be a function')
    }
  
    // create regular expression for hostname
    var regexp = hostregexp(hostname)
  
    return function vhost (req, res, next) {
      var vhostdata = vhostof(req, regexp)
  
      if (!vhostdata) {
        return next()
      }
  
      // populate
      req.vhost = vhostdata
  
      // handle
      handle(req, res, next)
    }
  }
docs: Create a vhost middleware.
  
  @param {string|RegExp} hostname
  @param {function} handle
  @return {Function}
  @public