Link Previews

js/modules/link_previews.js

@@ -0,0 +1,176 @@
+/* global URL */
+
+const he = require('he');
+const LinkifyIt = require('linkify-it');
+
+const linkify = LinkifyIt();
+const { concatenateBytes, getViewOfArrayBuffer } = require('./crypto');
+
+module.exports = {
+  assembleChunks,
+  findLinks,
+  getChunkPattern,
+  getDomain,
+  getTitleMetaTag,
+  getImageMetaTag,
+  isLinkInWhitelist,
+  isMediaLinkInWhitelist,
+};
+
+const SUPPORTED_DOMAINS = [
+  'youtube.com',
+  'www.youtube.com',
+  'm.youtube.com',
+  'youtu.be',
+  'reddit.com',
+  'www.reddit.com',
+  'm.reddit.com',
+  'imgur.com',
+  'www.imgur.com',
+  'm.imgur.com',
+  'instagram.com',
+  'www.instagram.com',
+  'm.instagram.com',
+];
+function isLinkInWhitelist(link) {
+  try {
+    const url = new URL(link);
+
+    if (url.protocol !== 'https:') {
+      return false;
+    }
+
+    if (!url.pathname || url.pathname.length < 2) {
+      return false;
+    }
+
+    const lowercase = url.host.toLowerCase();
+    if (!SUPPORTED_DOMAINS.includes(lowercase)) {
+      return false;
+    }
+
+    return true;
+  } catch (error) {
+    return false;
+  }
+}
+
+const SUPPORTED_MEDIA_DOMAINS = /^([^.]+\.)*(ytimg.com|cdninstagram.com|redd.it|imgur.com)$/i;
+function isMediaLinkInWhitelist(link) {
+  try {
+    const url = new URL(link);
+
+    if (url.protocol !== 'https:') {
+      return false;
+    }
+
+    if (!url.pathname || url.pathname.length < 2) {
+      return false;
+    }
+
+    if (!SUPPORTED_MEDIA_DOMAINS.test(url.host)) {
+      return false;
+    }
+
+    return true;
+  } catch (error) {
+    return false;
+  }
+}
+
+const META_TITLE = /<meta\s+property="og:title"\s+content="([\s\S]+?)"\s*\/?\s*>/im;
+const META_IMAGE = /<meta\s+property="og:image"\s+content="([\s\S]+?)"\s*\/?\s*>/im;
+function _getMetaTag(html, regularExpression) {
+  const match = regularExpression.exec(html);
+  if (match && match[1]) {
+    return he.decode(match[1]).trim();
+  }
+
+  return null;
+}
+
+function getTitleMetaTag(html) {
+  return _getMetaTag(html, META_TITLE);
+}
+function getImageMetaTag(html) {
+  return _getMetaTag(html, META_IMAGE);
+}
+
+function findLinks(text) {
+  const matches = linkify.match(text || '') || [];
+  return matches.map(match => match.text);
+}
+
+function getDomain(url) {
+  try {
+    const urlObject = new URL(url);
+    return urlObject.hostname;
+  } catch (error) {
+    return null;
+  }
+}
+
+const MB = 1024 * 1024;
+const KB = 1024;
+
+function getChunkPattern(size) {
+  if (size > MB) {
+    return _getRequestPattern(size, MB);
+  } else if (size > 500 * KB) {
+    return _getRequestPattern(size, 500 * KB);
+  } else if (size > 100 * KB) {
+    return _getRequestPattern(size, 100 * KB);
+  } else if (size > 50 * KB) {
+    return _getRequestPattern(size, 50 * KB);
+  } else if (size > 10 * KB) {
+    return _getRequestPattern(size, 10 * KB);
+  } else if (size > KB) {
+    return _getRequestPattern(size, KB);
+  }
+
+  throw new Error(`getChunkPattern: Unsupported size: ${size}`);
+}
+
+function _getRequestPattern(size, increment) {
+  const results = [];
+
+  let offset = 0;
+  while (size - offset > increment) {
+    results.push({
+      start: offset,
+      end: offset + increment - 1,
+      overlap: 0,
+    });
+    offset += increment;
+  }
+
+  if (size - offset > 0) {
+    results.push({
+      start: size - increment,
+      end: size - 1,
+      overlap: increment - (size - offset),
+    });
+  }
+
+  return results;
+}
+
+function assembleChunks(chunkDescriptors) {
+  const chunks = chunkDescriptors.map((chunk, index) => {
+    if (index !== chunkDescriptors.length - 1) {
+      return chunk.data;
+    }
+
+    if (!chunk.overlap) {
+      return chunk.data;
+    }
+
+    return getViewOfArrayBuffer(
+      chunk.data,
+      chunk.overlap,
+      chunk.data.byteLength
+    );
+  });
+
+  return concatenateBytes(...chunks);
+}