fix(img): move img requests out of web workers

Due to iOS Cordova WKWebView limitations, ion-img is not able to use
web workers for XMLHttpRequests.

src/components/img/img-loader.ts

@@ -1,83 +1,166 @@
-import { Injectable } from '@angular/core';
 
-import { Config } from '../../config/config';
-import { removeArrayItem } from '../../util/util';
-
-
-@Injectable()
 export class ImgLoader {
-  private wkr: Worker;
-  private callbacks: Function[] = [];
-  private ids = 0;
-  private url: string;
+  private imgs: ImgData[] = [];
 
-  constructor(config: Config) {
-    this.url = config.get('imgWorkerUrl', IMG_WORKER_URL);
+  load(src: string, useCache: boolean, callback: ImgLoadCallback) {
+    // see if we already have image data for this src
+    let img = this.imgs.find(i => i.src === src);
+
+    if (img && img.datauri && useCache) {
+      // we found image data, and it's cool if we use the cache
+      // so let's respond with the cached data
+      callback(200, null, img.datauri);
+      return;
     }
 
-  load(src: string, cache: boolean, callback: Function) {
-    if (src) {
-      (<any>callback).id = this.ids++;
-      this.callbacks.push(callback);
-      this.worker().postMessage(JSON.stringify({
-        id: (<any>callback).id,
-        src: src,
-        cache: cache
-      }));
-    }
+    // so no cached image data, so we'll
+    // need to do a new http request
+
+    if (img && img.xhr && img.xhr.readyState !== 4) {
+      // looks like there's already an active http request going on
+      // for this same source, so let's just add another listener
+      img.xhr.addEventListener('load', (xhrEvent) => {
+        onXhrLoad(callback, xhrEvent, useCache, img, this.imgs);
+      });
+      img.xhr.addEventListener('error', (xhrErrorEvent) => {
+        onXhrError(callback, img, xhrErrorEvent);
+      });
+      return;
     }
 
-  cancelLoad(callback: Function) {
-    removeArrayItem(this.callbacks, callback);
+    if (!img) {
+      // no image data yet, so let's create it
+      img = { src: src };
+      this.imgs.push(img);
+    }
+
+    // ok, let's do a full request for the image
+    img.xhr = new XMLHttpRequest();
+    img.xhr.open('GET', src, true);
+    img.xhr.responseType = 'arraybuffer';
+
+    // add the listeners if it loaded or errored
+    img.xhr.addEventListener('load', (xhrEvent) => {
+      onXhrLoad(callback, xhrEvent, useCache, img, this.imgs);
+    });
+    img.xhr.addEventListener('error', (xhrErrorEvent) => {
+      onXhrError(callback, img, xhrErrorEvent);
+    });
+
+    // awesome, let's kick off the request
+    img.xhr.send();
   }
 
   abort(src: string) {
-    if (src) {
-      this.worker().postMessage(JSON.stringify({
-        src: src,
-        type: 'abort'
-      }));
+    const img = this.imgs.find(i => i.src === src);
+    if (img && img.xhr && img.xhr.readyState !== 4) {
+      // we found the image data and there's an active
+      // http request, so let's abort the request
+      img.xhr.abort();
+      img.xhr = null;
     }
   }
 
-  private worker() {
-    if (!this.wkr) {
-      // create the worker
-      this.wkr = new Worker(this.url);
-
-      // create worker onmessage handler
-      this.wkr.onmessage = (ev: MessageEvent) => {
-        // we got something back from the web worker
-        // let's emit this out to everyone listening
-        const msg: ImgResponseMessage = JSON.parse(ev.data);
-        const callback = this.callbacks.find(cb => (<any>cb).id === msg.id);
-        if (callback) {
-          callback(msg);
-          removeArrayItem(this.callbacks, callback);
-        }
-      };
-
-      // create worker onerror handler
-      this.wkr.onerror = (ev: ErrorEvent) => {
-        console.error(`ImgLoader, worker ${ev.type} ${ev.message ? ev.message : ''}`);
-        this.callbacks.length = 0;
-        this.wkr.terminate();
-        this.wkr = null;
-      };
-    }
-
-    // return that hard worker
-    return this.wkr;
-  }
-
 }
 
-const IMG_WORKER_URL = 'build/ion-img-worker.js';
 
-export interface ImgResponseMessage {
-  id: number;
+function onXhrLoad(callback: ImgLoadCallback, ev: any, useCache: boolean, img: ImgData, imgs: ImgData[]) {
+  if (!callback) {
+    return;
+  }
+
+  // the http request has been loaded
+  // create a rsp object to send back to the main thread
+  const status: number = ev.target.status;
+  let datauri: string = null;
+
+  if (status === 200) {
+    // success!!
+    // now let's convert the response arraybuffer data into a datauri
+    datauri = getDataUri(ev.target.getResponseHeader('Content-Type'), ev.target.response);
+
+    if (useCache) {
+      // if the image was successfully downloaded
+      // and this image is allowed to be cached
+      // then let's add it to our image data for later use
+      img.datauri = datauri;
+      img.len = datauri.length;
+
+      // let's loop through all our cached data and if we go
+      // over our limit then let's clean it out a bit
+      // oldest data should go first
+      var cacheSize = 0;
+      for (var i = imgs.length - 1; i >= 0; i--) {
+        cacheSize += imgs[i].len;
+        if (cacheSize > CACHE_LIMIT) {
+          console.debug(`img-loader, clear: ${imgs[i].src}, len: ${imgs[i].len}`);
+          imgs.splice(i, 1);
+        }
+      }
+    }
+  }
+
+  // fire the callback with what we've learned today
+  callback(status, null, datauri);
+}
+
+
+function onXhrError(callback: ImgLoadCallback, imgData: ImgData, err: ErrorEvent) {
+  // darn, we got an error!
+  callback && callback(0, (err.message || ''), null);
+  imgData.xhr = null;
+}
+
+
+function getDataUri(contentType, arrayBuffer): string {
+  // take arraybuffer and content type and turn it into
+  // a datauri string that can be used by <img>
+  const rtn: string[] = ['data:' + contentType + ';base64,'];
+
+  const bytes = new Uint8Array(arrayBuffer);
+  const byteLength = bytes.byteLength;
+  const byteRemainder = byteLength % 3;
+  const mainLength = byteLength - byteRemainder;
+  let i, a, b, c, d, chunk;
+
+  for (i = 0; i < mainLength; i = i + 3) {
+    chunk = (bytes[i] << 16) | (bytes[i + 1] << 8) | bytes[i + 2];
+    a = (chunk & 16515072) >> 18;
+    b = (chunk & 258048) >> 12;
+    c = (chunk & 4032) >> 6;
+    d = chunk & 63;
+    rtn.push(ENCODINGS[a] + ENCODINGS[b] + ENCODINGS[c] + ENCODINGS[d]);
+  }
+
+  if (byteRemainder === 1) {
+    chunk = bytes[mainLength];
+    a = (chunk & 252) >> 2;
+    b = (chunk & 3) << 4;
+    rtn.push(ENCODINGS[a] + ENCODINGS[b] + '==');
+
+  } else if (byteRemainder === 2) {
+    chunk = (bytes[mainLength] << 8) | bytes[mainLength + 1];
+    a = (chunk & 64512) >> 10;
+    b = (chunk & 1008) >> 4;
+    c = (chunk & 15) << 2;
+    rtn.push(ENCODINGS[a] + ENCODINGS[b] + ENCODINGS[c] + '=');
+  }
+
+  return rtn.join('');
+}
+
+// used by the setData function
+const ENCODINGS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
+
+const CACHE_LIMIT = 1381855 * 20;
+
+export interface ImgData {
   src: string;
-  status?: number;
-  data?: string;
-  msg?: string;
+  datauri?: string;
+  len?: number;
+  xhr?: XMLHttpRequest;
+}
+
+export type ImgLoadCallback = {
+  (status: number, msg: string, datauri: string): void;
 }

src/components/img/img.ts

@@ -2,7 +2,7 @@ import { ChangeDetectionStrategy, Component, ElementRef, Input, NgZone, OnDestro
 
 import { Content } from '../content/content';
 import { DomController } from '../../util/dom-controller';
-import { ImgLoader, ImgResponseMessage } from './img-loader';
+import { ImgLoader, ImgLoadCallback } from './img-loader';
 import { isPresent, isTrueProperty } from '../../util/util';
 import { Platform } from '../../platform/platform';
 
@@ -134,7 +134,7 @@ export class Img implements OnDestroy {
   /** @internal */
   _cache: boolean = true;
   /** @internal */
-  _cb: Function;
+  _cb: ImgLoadCallback;
   /** @internal */
   _bounds: any;
   /** @internal */
@@ -235,9 +235,9 @@ export class Img implements OnDestroy {
         console.debug(`request ${this._src} ${Date.now()}`);
         this._requestingSrc = this._src;
 
-        // create a callback for when we get data back from the web worker
-        this._cb = (msg: ImgResponseMessage) => {
-          this._loadResponse(msg);
+        this._cb = (status, msg, datauri) => {
+          this._loadResponse(status, msg, datauri);
+          this._cb = null;
         };
 
         // post the message to the web worker
@@ -263,18 +263,18 @@ export class Img implements OnDestroy {
     }
   }
 
-  private _loadResponse(msg: ImgResponseMessage) {
+  private _loadResponse(status: number, msg: string, datauri: string) {
     this._requestingSrc = null;
 
-    if (msg.status === 200) {
+    if (status === 200) {
       // success :)
-      this._tmpDataUri = msg.data;
+      this._tmpDataUri = datauri;
       this.update();
 
     } else {
       // error :(
-      if (msg.status) {
-        console.error(`img, status: ${msg.status} ${msg.msg}`);
+      if (status) {
+        console.error(`img, status: ${status} ${msg}`);
       }
       this._renderedSrc = this._tmpDataUri = null;
       this._dom.write(() => {
@@ -413,7 +413,6 @@ export class Img implements OnDestroy {
    * @private
    */
   ngOnDestroy() {
-    this._ldr.cancelLoad(this._cb);
     this._cb = null;
     this._content && this._content.removeImg(this);
   }

src/components/img/test/img.spec.ts

@@ -2,7 +2,7 @@ import { ElementRef, Renderer } from '@angular/core';
 import { Content } from '../../content/content';
 import { Img } from '../img';
 import { ImgLoader } from '../img-loader';
-import { mockConfig, mockContent, MockDomController, mockElementRef, mockPlatform, mockRenderer, mockZone } from '../../../util/mock-providers';
+import { mockContent, MockDomController, mockElementRef, mockPlatform, mockRenderer, mockZone } from '../../../util/mock-providers';
 import { Platform } from '../../../platform/platform';
 
 
@@ -79,7 +79,7 @@ describe('Img', () => {
 
   beforeEach(() => {
     content = mockContent();
-    ldr = new ImgLoader(mockConfig());
+    ldr = new ImgLoader();
     elementRef = mockElementRef();
     renderer = mockRenderer();
     platform = mockPlatform();