fixes #4653

src/posts/parse.js

@@ -1,10 +1,14 @@
-
 'use strict';
 
+var nconf = require('nconf'),
+	url = require('url');
+
 var cache = require('./cache');
 var plugins = require('../plugins');
 var translator = require('../../public/src/modules/translator');
 
+var urlRegex = /href="([^"]+)"/g;
+
 module.exports = function(Posts) {
 
 	Posts.parsePost = function(postData, callback) {
@@ -26,6 +30,7 @@ module.exports = function(Posts) {
 			}
 
 			data.postData.content = translator.escape(data.postData.content);
+			data.postData.content = Posts.relativeToAbsolute(data.postData.content);
 
 			if (global.env === 'production' && data.postData.pid) {
 				cache.set(data.postData.pid, data.postData.content);
@@ -40,4 +45,29 @@ module.exports = function(Posts) {
 
 		plugins.fireHook('filter:parse.signature', {userData: userData, uid: uid}, callback);
 	};
+
+	Posts.relativeToAbsolute = function(content) {
+		// Turns relative links in post body to absolute urls
+		var parsed, current, absolute;
+
+		while ((current=urlRegex.exec(content)) !== null) {
+			if (current[1]) {
+				parsed = url.parse(current[1]);
+
+				if (!parsed.protocol) {
+					if (current[1].startsWith('/')) {
+						// Internal link
+						absolute = nconf.get('url') + current[1];
+					} else {
+						// External link
+						absolute = '//' + current[1];
+					}
+
+					content = content.slice(0, current.index + 6) + absolute + content.slice(current.index + 6 + current[1].length);
+				}
+			}
+		}
+
+		return content;
+	};
 };

src/topics/follow.js

@@ -171,7 +171,7 @@ module.exports = function(Topics) {
 								pid: postData.pid,
 								subject: '[' + (meta.config.title || 'NodeBB') + '] ' + title,
 								intro: '[[notifications:user_posted_to, ' + postData.user.username + ', ' + titleEscaped + ']]',
-								postBody: postData.content.replace(/"\/\//g, '"http://'),
+								postBody: postData.content.replace(/"\/\//g, '"https://'),
 								site_title: meta.config.title || 'NodeBB',
 								username: data.userData.username,
 								userslug: data.userData.userslug,