Parsing

Let’s have a look at the JSON response from Tileserver.

/index.json
[
  {
    "tilejson": "2.0.0",
    "name": "Basic preview",
    "attribution": "<a href=\"http://openmaptiles.org/\" target=\"_blank\">&copy; OpenMapTiles</a> <a href=\"http://www.openstreetmap.org/about/\" target=\"_blank\">&copy; OpenStreetMap contributors</a>",
    "minzoom": 0,
    "maxzoom": 20,
    "bounds": [8.275, 47.225, 8.8, 47.533],
    "format": "png",
    "type": "baselayer",
    "tiles": ["http://localhost:8081/styles/basic-preview/{z}/{x}/{y}.png"],
    "center": [8.537500000000001, 47.379000000000005, 11]
  },
  {
    "tiles": ["http://localhost:8081/data/v3/{z}/{x}/{y}.pbf"],
    "name": "OpenMapTiles",
    "format": "pbf",
    "basename": "zurich_switzerland.mbtiles",
    "id": "openmaptiles",
    "attribution": "<a href=\"http://openmaptiles.org/\" target=\"_blank\">&copy; OpenMapTiles</a> <a href=\"http://www.openstreetmap.org/about/\" target=\"_blank\">&copy; OpenStreetMap contributors</a>",
    "description": "https://openmaptiles.org",
    "minzoom": 0,
    "maxzoom": 14,
    "center": [8.5375, 47.379, 10],
    "bounds": [8.275, 47.225, 8.8, 47.533],
    "version": "3.3",
    "type": "overlay",
    "tilejson": "2.0.0"
  }
]

The first layer is an XYZ (see tiles template) PNG (format = 'png') layer that is intended as base map imagery (type = 'baselayer'). OpenSphere already supports XYZ layers and base map layers, so we can take advantage of a lot of code that already exists.

The second layer is a vector format, which we will ignore in this guide. The first JSON object is very similar to the layer config JSON needed to create XYZ layers. So all we have to do is translate it.

src/plugin/tileserver/tileserver.js
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goog.declareModuleId('plugin.tileserver.Tileserver');

import ConfigDescriptor from 'opensphere/src/os/data/configdescriptor.js';
import DataManager from 'opensphere/src/os/data/datamanager.js';
import {filterFalsey} from 'opensphere/src/os/fn/fn.js';
import {MAX_ZOOM, MIN_ZOOM} from 'opensphere/src/os/map/map.js';
import Request from 'opensphere/src/os/net/request.js';
import {EPSG3857, EPSG4326} from 'opensphere/src/os/proj/proj.js';
import BaseProvider from 'opensphere/src/os/ui/data/baseprovider.js';
import DescriptorNode from 'opensphere/src/os/ui/data/descriptornode.js';
import {createIconSet} from 'opensphere/src/os/ui/icons/index.js';
import IconsSVG from 'opensphere/src/os/ui/iconssvg.js';
import AbstractLoadingServer from 'opensphere/src/os/ui/server/abstractloadingserver.js';
import * as basemap from 'opensphere/src/plugin/basemap/basemap.js';

import {ID} from './index.js';

const {default: IDataProvider} = goog.requireType('os.data.IDataProvider');


/**
 * The Tileserver provider
 * @implements {IDataProvider}
 */
export default class Tileserver extends AbstractLoadingServer {
  /**
   * Constructor.
   */
  constructor() {
    super();
    this.providerType = ID;
  }

  /**
   * @inheritDoc
   */
  load(opt_ping) {
    super.load(opt_ping);

    // clear out any children we already have
    this.setChildren(null);

    // load the JSON
    new Request(this.getUrl()).getPromise().
        then(this.onLoad, this.onError, this).
        thenCatch(this.onError, this);
  }

  /**
   * @param {string} response
   * @protected
   */
  onLoad(response) {
    let layers;

    try {
      layers = JSON.parse(response);
    } catch (e) {
      this.onError('Malformed JSON');
      return;
    }

    if (!Array.isArray(layers)) {
      // not sure what we got but it isn't an array of layers
      this.onError('Expected an array of layers but got something else');
      return;
    }

    var children = /** @type {Array<!os.structs.ITreeNode>} */ (
      layers.map(this.toChildNode, this).filter(filterFalsey));
    this.setChildren(children);
    this.finish();
  }

  /**
   * @param {Object<string, *>} layer The layer JSON
   * @return {?DescriptorNode} The child node for the provider
   * @protected
   */
  toChildNode(layer) {
    if (!layer['tilejson']) {
      return null;
    }

    if (!/^(png|jpe?g|gif)$/i.test(layer['format'])) {
      // not our format
      return null;
    }

    var id = this.getId() + BaseProvider.ID_DELIMITER + layer['name'];

    var config = {
      'type': 'XYZ',
      'id': id,
      'title': layer['name'],
      'urls': layer['tiles'],
      'extent': layer['bounds'],
      'extentProjection': EPSG4326,
      'icons': createIconSet(id, [IconsSVG.TILES], [], [255, 255, 255, 1]),
      'projection': EPSG3857,
      'minZoom': Math.max(MIN_ZOOM, layer['minzoom']),
      'maxZoom': Math.min(MAX_ZOOM, layer['maxzoom']),
      'attributions': [layer['attribution']],
      'provider': this.getLabel(),
      // this delays enabling the descriptor on startup until this provider marks it as ready
      'delayUpdateActive': true
    };

    if (layer['type'] === 'baselayer') {
      config['baseType'] = config['type'];
      config['type'] = basemap.ID;
      config['layerType'] = basemap.LAYER_TYPE;
      config['noClear'] = true;
    }

    var descriptor = /** @type {ConfigDescriptor} */ (DataManager.getInstance().getDescriptor(id));
    if (!descriptor) {
      descriptor = new ConfigDescriptor();
    }

    descriptor.setBaseConfig(config);

    // add the descriptor to the data manager
    DataManager.getInstance().addDescriptor(descriptor);

    // mark the descriptor as ready if the user had it enabled previously
    descriptor.updateActiveFromTemp();

    var node = new DescriptorNode();
    node.setDescriptor(descriptor);

    return node;
  }

  /**
   * @param {*} e
   * @protected
   */
  onError(e) {
    var msg = Array.isArray(e) ? e.join(' ') : e.toString();
    this.setErrorMessage(msg);
  }
}

Let’s test it.

test/plugin/tileserver/tileserver.test.js
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goog.require('goog.Promise');
goog.require('os.data.ConfigDescriptor');
goog.require('os.net.Request');
goog.require('os.ui.data.BaseProvider');
goog.require('plugin.tileserver');
goog.require('plugin.tileserver.Tileserver');

describe('plugin.tileserver.Tileserver', function() {
  const Promise = goog.module.get('goog.Promise');
  const {default: ConfigDescriptor} = goog.module.get('os.data.ConfigDescriptor');
  const {default: Request} = goog.module.get('os.net.Request');
  const {default: BaseProvider} = goog.module.get('os.ui.data.BaseProvider');

  const {ID} = goog.module.get('plugin.tileserver');
  const {default: Tileserver} = goog.module.get('plugin.tileserver.Tileserver');

  it('should configure properly', function() {
    var p = new Tileserver();
    var conf = {
      type: ID,
      label: 'Test Server',
      url: 'http://localhost/doesnotexist.json'
    };

    p.configure(conf);

    expect(p.getLabel()).toBe(conf.label);
    expect(p.getUrl()).toBe(conf.url);
  });

  it('should load valid JSON', function() {
    var p = new Tileserver();
    p.setUrl('/something');

    // we're going to spy on the getPromise method and return a promise resolving
    // to valid JSON
    spyOn(Request.prototype, 'getPromise').andReturn(Promise.resolve('[]'));

    spyOn(p, 'onLoad').andCallThrough();
    spyOn(p, 'onError').andCallThrough();

    runs(function() {
      p.load();
    });

    waitsFor(function() {
      return p.onLoad.calls.length;
    });

    runs(function() {
      expect(p.onLoad).toHaveBeenCalled();
      expect(p.onError).not.toHaveBeenCalled();
    });
  });

  it('should error on invalid JSON', function() {
    var p = new Tileserver();
    p.setUrl('/something');

    // we're going to spy on the getPromise method and return a promise resolving
    // to invalid JSON
    spyOn(Request.prototype, 'getPromise').andReturn(Promise.resolve('[wut'));

    spyOn(p, 'onLoad').andCallThrough();
    spyOn(p, 'onError').andCallThrough();

    runs(function() {
      p.load();
    });

    waitsFor(function() {
      return p.onLoad.calls.length;
    });

    runs(function() {
      expect(p.onLoad).toHaveBeenCalled();
      expect(p.onError).toHaveBeenCalled();
    });
  });

  it('should error on request error', function() {
    var p = new Tileserver();
    p.setUrl('/something');

    // we're going to spy on the getPromise method and return a promise rejecting
    // with errors
    spyOn(Request.prototype, 'getPromise').andReturn(
        // request rejects with arrays of all errors that occurred
        Promise.reject(['something awful happend']));

    spyOn(p, 'onLoad').andCallThrough();
    spyOn(p, 'onError').andCallThrough();

    runs(function() {
      p.load();
    });

    waitsFor(function() {
      return p.onError.calls.length;
    });

    runs(function() {
      expect(p.onLoad).not.toHaveBeenCalled();
      expect(p.onError).toHaveBeenCalled();
    });
  });

  it('should ignore JSON that is not an array', function() {
    var p = new Tileserver();
    p.setUrl('/something');

    // we're going to spy on the getPromise method and return a promise resolving
    // to valid JSON
    spyOn(Request.prototype, 'getPromise').andReturn(Promise.resolve('{}'));

    spyOn(p, 'onLoad').andCallThrough();
    spyOn(p, 'onError').andCallThrough();

    runs(function() {
      p.load();
    });

    waitsFor(function() {
      return p.onLoad.calls.length;
    });

    runs(function() {
      expect(p.onLoad).toHaveBeenCalled();
      expect(p.onError).toHaveBeenCalled();
    });
  });

  it('should parse Tileserver JSON', function() {
    var p = new Tileserver();
    p.setUrl('/something');

    // we're going to spy on the getPromise method and return a promise resolving to some Tileserver JSON
    spyOn(Request.prototype, 'getPromise').andReturn(Promise.resolve(JSON.stringify(
        [{
          tilejson: '2.0.0',
          name: 'Klokantech Basic',
          attribution: 'This is a test',
          minzoom: 0,
          maxzoom: 20,
          bounds: [8.275, 47.225, 8.8, 47.533],
          format: 'png',
          type: 'baselayer',
          tiles: ['http://localhost:8081/styles/klokantech-basic/{z}/{x}/{y}.png'],
          center: [8.537500000000001, 47.379000000000005, 11]
        }, {
          tilejson: '2.0.0',
          name: 'Klokantech Basic 2',
          attribution: 'This is a test',
          minzoom: 0,
          maxzoom: 20,
          bounds: [8.275, 47.225, 8.8, 47.533],
          format: 'png',
          tiles: ['http://localhost:8081/styles/klokantech-basic/{z}/{x}/{y}.png'],
          center: [8.537500000000001, 47.379000000000005, 11]
        }, {
          tilejson: '2.0.0',
          format: 'pbf'
        }, {
          something: true
        }]
    )));

    spyOn(p, 'onLoad').andCallThrough();
    spyOn(p, 'onError').andCallThrough();

    // add a config descriptor to the datamanager so that we can test updating on one of the layers
    var id = p.getId() + BaseProvider.ID_DELIMITER + 'Klokantech Basic';
    var descriptor = new ConfigDescriptor();
    descriptor.setBaseConfig({
      id: id
    });
    os.dataManager.addDescriptor(descriptor);

    runs(function() {
      p.load();
    });

    waitsFor(function() {
      return p.onLoad.calls.length;
    });

    runs(function() {
      expect(p.onLoad).toHaveBeenCalled();
      expect(p.onError).not.toHaveBeenCalled();
      expect(p.getChildren().length).toBe(2);
      expect(p.getChildren()[0].getLabel()).toBe('Klokantech Basic');
      expect(p.getChildren()[1].getLabel()).toBe('Klokantech Basic 2');
    });
  });
});

yarn test should result in a clean test run. Now let’s ensure that our descriptor type is registered in our plugin.

src/plugin/tileserver/tileserverplugin.js
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goog.declareModuleId('plugin.tileserver.TileserverPlugin');

import ConfigDescriptor from 'opensphere/src/os/data/configdescriptor.js';
import DataManager from 'opensphere/src/os/data/datamanager.js';
import ProviderEntry from 'opensphere/src/os/data/providerentry.js';
import AbstractPlugin from 'opensphere/src/os/plugin/abstractplugin.js';
import PluginManager from 'opensphere/src/os/plugin/pluginmanager.js';

import Tileserver from './tileserver.js';
import {ID} from './index.js';

/**
 * Provides Tileserver support
 */
export default class TileserverPlugin extends AbstractPlugin {
  /**
   * Constructor.
   */
  constructor() {
    super();
    this.id = ID;
    this.errorMessage = null;
  }

  /**
   * @inheritDoc
   */
  init() {
    const dm = DataManager.getInstance();
    dm.registerProviderType(new ProviderEntry(
        ID, // the type
        Tileserver, // the class
        'Tileserver', // the title
        'Tileserver layers' // the description
    ));

    dm.registerDescriptorType(ID, ConfigDescriptor);
  }
}

// add the plugin to the application
PluginManager.getInstance().addPlugin(new TileserverPlugin());

Since ConfigDescriptor is highly resuable, it is possible that several plugins make that same registration. That’s fine.

Now run the build and open up the debug instance again. This time the server should complete its loading and show a child node for the parsed layer. Toggling the child should enable the given layer, and the layer should persist on refresh.

We’ve got the provider working if added by an admin in config, but what about the user? Let’s handle that next.