Merge pull request #13863 from ahocevar/tile-error-handling

Fix reloading tiles in case of an error with tile.load()

src/ol/ImageTile.js

@@ -112,7 +112,40 @@ class ImageTile extends Tile {
   }
 
   /**
-   * Load not yet loaded URI.
+   * Load the image or retry if loading previously failed.
+   * Loading is taken care of by the tile queue, and calling this method is
+   * only needed for preloading or for reloading in case of an error.
+   *
+   * To retry loading tiles on failed requests, use a custom `tileLoadFunction`
+   * that checks for error status codes and reloads only when the status code is
+   * 408, 429, 500, 502, 503 and 504, and only when not too many retries have been
+   * made already:
+   *
+   * ```js
+   * const retryCodes = [408, 429, 500, 502, 503, 504];
+   * const retries = {};
+   * source.setTileLoadFunction((tile, src) => {
+   *   const image = tile.getImage();
+   *   fetch(src)
+   *     .then((response) => {
+   *       if (retryCodes.includes(response.status)) {
+   *         retries[src] = (retries[src] || 0) + 1;
+   *         if (retries[src] <= 3) {
+   *           setTimeout(() => tile.load(), retries[src] * 1000);
+   *         }
+   *         return Promise.reject();
+   *       }
+   *       return response.blob();
+   *     })
+   *     .then((blob) => {
+   *       const imageUrl = URL.createObjectURL(blob);
+   *       image.src = imageUrl;
+   *       setTimeout(() => URL.revokeObjectURL(imageUrl), 5000);
+   *     })
+   *     .catch(() => tile.setState(3)); // error
+   * });
+   * ```
+   *
    * @api
    */
   load() {

src/ol/Tile.js

@@ -142,7 +142,12 @@ class Tile extends EventTarget {
   /**
    * Called by the tile cache when the tile is removed from the cache due to expiry
    */
-  release() {}
+  release() {
+    if (this.state === TileState.ERROR) {
+      // to remove the `change` listener on this tile in `ol/TileQueue#handleTileChange`
+      this.setState(TileState.EMPTY);
+    }
+  }
 
   /**
    * @return {string} Key.

src/ol/TileCache.js

@@ -5,6 +5,13 @@ import LRUCache from './structs/LRUCache.js';
 import {fromKey, getKey} from './tilecoord.js';
 
 class TileCache extends LRUCache {
+  clear() {
+    while (this.getCount() > 0) {
+      this.pop().release();
+    }
+    super.clear();
+  }
+
   /**
    * @param {!Object<string, boolean>} usedTiles Used tiles.
    */

src/ol/TileQueue.js

@@ -86,7 +86,9 @@ class TileQueue extends PriorityQueue {
       state === TileState.ERROR ||
       state === TileState.EMPTY
     ) {
-      tile.removeEventListener(EventType.CHANGE, this.boundHandleTileChange_);
+      if (state !== TileState.ERROR) {
+        tile.removeEventListener(EventType.CHANGE, this.boundHandleTileChange_);
+      }
       const tileKey = tile.getKey();
       if (tileKey in this.tilesLoadingKeys_) {
         delete this.tilesLoadingKeys_[tileKey];

src/ol/renderer/canvas/TileLayer.js

@@ -129,10 +129,7 @@ class CanvasTileLayerRenderer extends CanvasLayerRenderer {
     const tileSource = tileLayer.getSource();
     let tile = tileSource.getTile(z, x, y, pixelRatio, projection);
     if (tile.getState() == TileState.ERROR) {
-      if (!tileLayer.getUseInterimTilesOnError()) {
-        // When useInterimTilesOnError is false, we consider the error tile as loaded.
-        tile.setState(TileState.LOADED);
-      } else if (tileLayer.getPreload() > 0) {
+      if (tileLayer.getUseInterimTilesOnError() && tileLayer.getPreload() > 0) {
         // Preloaded tiles for lower resolutions might have finished loading.
         this.newTiles_ = true;
       }

src/ol/source/TileEventType.js

@@ -22,7 +22,9 @@ export default {
   TILELOADEND: 'tileloadend',
 
   /**
-   * Triggered if tile loading results in an error.
+   * Triggered if tile loading results in an error. Note that this is not the
+   * right place to re-fetch tiles. See {@link module:ol/ImageTile~ImageTile#load}
+   * for details.
    * @event module:ol/source/Tile.TileSourceEvent#tileloaderror
    * @api
    */