route_guide_server.js

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'use strict';

var fs = require('fs');
var parseArgs = require('minimist');
var path = require('path');
var _ = require('underscore');
var grpc = require('..');
var examples = grpc.load(__dirname + '/route_guide.proto').examples;

var Server = grpc.buildServer([examples.RouteGuide.service]);

var COORD_FACTOR = 1e7;

/**
 * For simplicity, a point is a record type that looks like
 * {latitude: number, longitude: number}, and a feature is a record type that
 * looks like {name: string, location: point}. feature objects with name===''
 * are points with no feature.
 */

/**
 * List of feature objects at points that have been requested so far.
 */
var feature_list = [];

/**
 * Get a feature object at the given point.
 * @param {point} point The point to check
 * @return {feature} The feature object at the point. Note that an empty name
 *     indicates no feature
 */
function checkFeature(point) {
  var feature;
  // Check if there is already a feature object for the given point
  for (var i = 0; i < feature_list.length; i++) {
    feature = feature_list[i];
    if (feature.location.latitude === point.latitude &&
        feature.location.longitude === point.longitude) {
      return feature;
    }
  }
  var name = '';
  feature = {
    name: name,
    location: point
  };
  return feature;
}

/**
 * getFeature request handler. Gets a request with a point, and responds with a
 * feature object indicating whether there is a feature at that point.
 * @param {EventEmitter} call Call object for the handler to process
 * @param {function(Error, feature)} callback Response callback
 */
function getFeature(call, callback) {
  callback(null, checkFeature(call.request));
}

/**
 * listFeatures request handler. Gets a request with two points, and responds
 * with a stream of all features in the bounding box defined by those points.
 * @param {Writable} call Writable stream for responses with an additional
 *     request property for the request value.
 */
function listFeatures(call) {
  var lo = call.request.lo;
  var hi = call.request.hi;
  var left = _.min([lo.longitude, hi.longitude]);
  var right = _.max([lo.longitude, hi.longitude]);
  var top = _.max([lo.latitude, hi.latitude]);
  var bottom = _.min([lo.latitude, hi.latitude]);
  // For each feature, check if it is in the given bounding box
  _.each(feature_list, function(feature) {
    if (feature.name === '') {
      return;
    }
    if (feature.location.longitude >= left &&
        feature.location.longitude <= right &&
        feature.location.latitude >= bottom &&
        feature.location.latitude <= top) {
      call.write(feature);
    }
  });
  call.end();
}

/**
 * Calculate the distance between two points using the "haversine" formula.
 * This code was taken from http://www.movable-type.co.uk/scripts/latlong.html.
 * @param start The starting point
 * @param end The end point
 * @return The distance between the points in meters
 */
function getDistance(start, end) {
  function toRadians(num) {
    return num * Math.PI / 180;
  }
  var lat1 = start.latitude / COORD_FACTOR;
  var lat2 = end.latitude / COORD_FACTOR;
  var lon1 = start.longitude / COORD_FACTOR;
  var lon2 = end.longitude / COORD_FACTOR;
  var R = 6371000; // metres
  var φ1 = toRadians(lat1);
  var φ2 = toRadians(lat2);
  var Δφ = toRadians(lat2-lat1);
  var Δλ = toRadians(lon2-lon1);

  var a = Math.sin(Δφ/2) * Math.sin(Δφ/2) +
      Math.cos(φ1) * Math.cos(φ2) *
      Math.sin(Δλ/2) * Math.sin(Δλ/2);
  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));

  return R * c;
}

/**
 * recordRoute handler. Gets a stream of points, and responds with statistics
 * about the "trip": number of points, number of known features visited, total
 * distance traveled, and total time spent.
 * @param {Readable} call The request point stream.
 * @param {function(Error, routeSummary)} callback The callback to pass the
 *     response to
 */
function recordRoute(call, callback) {
  var point_count = 0;
  var feature_count = 0;
  var distance = 0;
  var previous = null;
  // Start a timer
  var start_time = process.hrtime();
  call.on('data', function(point) {
    point_count += 1;
    if (checkFeature(point).name !== '') {
      feature_count += 1;
    }
    /* For each point after the first, add the incremental distance from the
     * previous point to the total distance value */
    if (previous !== null) {
      distance += getDistance(previous, point);
    }
    previous = point;
  });
  call.on('end', function() {
    callback(null, {
      point_count: point_count,
      feature_count: feature_count,
      // Cast the distance to an integer
      distance: Math.floor(distance),
      // End the timer
      elapsed_time: process.hrtime(start_time)[0]
    });
  });
}

var route_notes = {};

/**
 * Turn the point into a dictionary key.
 * @param {point} point The point to use
 * @return {string} The key for an object
 */
function pointKey(point) {
  return point.latitude + ' ' + point.longitude;
}

/**
 * routeChat handler. Receives a stream of message/location pairs, and responds
 * with a stream of all previous messages at each of those locations.
 * @param {Duplex} call The stream for incoming and outgoing messages
 */
function routeChat(call) {
  call.on('data', function(note) {
    var key = pointKey(note.location);
    /* For each note sent, respond with all previous notes that correspond to
     * the same point */
    if (route_notes.hasOwnProperty(key)) {
      _.each(route_notes[key], function(note) {
        call.write(note);
      });
    } else {
      route_notes[key] = [];
    }
    // Then add the new note to the list
    route_notes[key].push(JSON.parse(JSON.stringify(note)));
  });
  call.on('end', function() {
    call.end();
  });
}

/**
 * Get a new server with the handler functions in this file bound to the methods
 * it serves.
 * @return {Server} The new server object
 */
function getServer() {
  return new Server({
    'examples.RouteGuide' : {
      getFeature: getFeature,
      listFeatures: listFeatures,
      recordRoute: recordRoute,
      routeChat: routeChat
    }
  });
}

if (require.main === module) {
  // If this is run as a script, start a server on an unused port
  var routeServer = getServer();
  routeServer.bind('0.0.0.0:50051');
  var argv = parseArgs(process.argv, {
    string: 'db_path'
  });
  fs.readFile(path.resolve(argv.db_path), function(err, data) {
    if (err) {
      throw err;
    }
    feature_list = JSON.parse(data);
    routeServer.listen();
  });
}

exports.getServer = getServer;