respect storageType on copy&paste

Instead of observing the clipboard, we first put the data URI into the
pad text, so it is uploaded by contentCollector.
When Etherpad starts using the Clipboard API we should use it too.

static/js/contentCollection.js

@@ -1,18 +1,47 @@
 'use strict';
 
+const {_isValid, uploadFile} = require('ep_image_upload/static/js/toolbar');
+
 // When an image is detected give it a lineAttribute
 // of Image with the URL to the iamge
 exports.collectContentImage = (hookName, {node, state: {lineAttributes}, tname}) => {
   if (tname === 'div' || tname === 'p') delete lineAttributes.img;
   if (tname !== 'img') return;
-  lineAttributes.img =
+  const imageData =
       // Client-side. This will also be used for server-side HTML imports once jsdom adds support
       // for HTMLImageElement.currentSrc.
       node.currentSrc ||
       // Server-side HTML imports using jsdom v16.6.0 (Etherpad v1.8.15).
       node.src ||
       // Server-side HTML imports using cheerio (Etherpad <= v1.8.14).
       (node.attribs && node.attribs.src);
+
+  if (typeof window !== 'undefined' && clientVars.ep_image_upload.storageType === 'local') {
+    if (/^http/.test(imageData)) {
+      // an uploaded image is copied, place a copy in the desired line
+      lineAttributes.img = imageData;
+      return;
+    }
+
+    const padeditor = require('ep_etherpad-lite/static/js/pad_editor').padeditor;
+
+    const match = imageData.match(/data:([^;]+);base64,(.*)/);
+    if (!match || !match[1] || !match[2]) return;
+
+    // decode from internal base64 rep
+    const decodedData = Uint8Array.from(window.atob(match[2]), (c) => c.charCodeAt(0));
+
+    // check if size is within limits and mime type is supported
+    const extension = _isValid({size: decodedData.length, type: match[1]});
+    if (!extension) return;
+
+    const blob = new Blob([decodedData], {type: match[1]});
+
+    // image.* is a temporary name not used on the server
+    uploadFile(padeditor, blob, `image.${extension}`);
+  } else {
+    lineAttributes.img = imageData;
+  }
 };
 
 exports.collectContentPre = (name, context) => {