diff --git a/ActivityPubPlugin.php b/ActivityPubPlugin.php
index 4319080..72436c2 100644
--- a/ActivityPubPlugin.php
+++ b/ActivityPubPlugin.php
@@ -1,5 +1,4 @@
 <?php
-require_once __DIR__ . DIRECTORY_SEPARATOR . "utils" . DIRECTORY_SEPARATOR . "postman.php";
 /**
  * GNU social - a federating social network
  *
@@ -30,6 +29,11 @@ if (!defined ('GNUSOCIAL')) {
         exit (1);
 }
 
+// Import required files by the plugin
+require_once __DIR__ . DIRECTORY_SEPARATOR . "utils" . DIRECTORY_SEPARATOR . "discoveryhints.php";
+require_once __DIR__ . DIRECTORY_SEPARATOR . "utils" . DIRECTORY_SEPARATOR . "explorer.php";
+require_once __DIR__ . DIRECTORY_SEPARATOR . "utils" . DIRECTORY_SEPARATOR . "postman.php";
+
 /**
  * @category  Plugin
  * @package   GNUsocial
@@ -40,6 +44,50 @@ if (!defined ('GNUSOCIAL')) {
  */
 class ActivityPubPlugin extends Plugin
 {
+        /**
+         * Get remote user's ActivityPub_profile via a identifier
+         * (https://www.w3.org/TR/activitypub/#obj-id)
+         *
+         * @author GNU Social
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
+         * @param string $arg A remote user identifier
+         * @return Activitypub_profile|null Valid profile in success | null otherwise
+         */
+        protected function pull_remote_profile ($arg)
+        {
+            if (preg_match ('!^((?:\w+\.)*\w+@(?:\w+\.)*\w+(?:\w+\-\w+)*\.\w+)$!', $arg)) {
+                    // webfinger lookup
+                    try {
+                            return Activitypub_profile::ensure_web_finger ($arg);
+                    } catch (Exception $e) {
+                            common_log(LOG_ERR, 'Webfinger lookup failed for ' .
+                                                $arg . ': ' . $e->getMessage ());
+                    }
+            }
+
+            // Look for profile URLs, with or without scheme:
+            $urls = array ();
+            if (preg_match ('!^https?://((?:\w+\.)*\w+(?:\w+\-\w+)*\.\w+(?:/\w+)+)$!', $arg)) {
+                    $urls[] = $arg;
+            }
+            if (preg_match ('!^((?:\w+\.)*\w+(?:\w+\-\w+)*\.\w+(?:/\w+)+)$!', $arg)) {
+                    $schemes = array ('http', 'https');
+                    foreach ($schemes as $scheme) {
+                            $urls[] = "$scheme://$arg";
+                    }
+            }
+
+            foreach ($urls as $url) {
+                    try {
+                            return Activitypub_profile::get_from_uri ($url);
+                    } catch (Exception $e) {
+                            common_log(LOG_ERR, 'Profile lookup failed for ' .
+                                                $arg . ': ' . $e->getMessage ());
+                    }
+                }
+                return null;
+        }
+
         /**
          * Route/Reroute urls
          *
@@ -77,7 +125,7 @@ class ActivityPubPlugin extends Plugin
          * Plugin version information
          *
          * @param array $versions
-         * @return boolean true
+         * @return boolean hook true
          */
         public function onPluginVersion (array &$versions)
         {
@@ -94,6 +142,8 @@ class ActivityPubPlugin extends Plugin
 
         /**
          * Make sure necessary tables are filled out.
+         *
+         * @return boolean hook true
          */
         function onCheckSchema ()
         {
@@ -102,6 +152,251 @@ class ActivityPubPlugin extends Plugin
             return true;
         }
 
+            /********************************************************
+             *                   Discovery Events                   *
+             ********************************************************/
+
+        /**
+        * Webfinger matches: @user@example.com or even @user--one.george_orwell@1984.biz
+        *
+        * @author GNU Social
+        * @param   string  $text       The text from which to extract webfinger IDs
+        * @param   string  $preMention Character(s) that signals a mention ('@', '!'...)
+        * @return  array   The matching IDs (without $preMention) and each respective position in the given string.
+        */
+        static function extractWebfingerIds ($text, $preMention='@')
+        {
+                $wmatches = array ();
+                $result = preg_match_all ('/(?<!\S)'.preg_quote ($preMention, '/').'('.Nickname::WEBFINGER_FMT.')/',
+                                $text,
+                                $wmatches,
+                                PREG_OFFSET_CAPTURE);
+                if ($result === false) {
+                        common_log (LOG_ERR, __METHOD__ . ': Error parsing webfinger IDs from text (preg_last_error=='.preg_last_error ().').');
+                } elseif (count ($wmatches)) {
+                        common_debug (sprintf ('Found %d matches for WebFinger IDs: %s', count ($wmatches), _ve ($wmatches)));
+                }
+                return $wmatches[1];
+        }
+
+        /**
+         * Profile URL matches: @example.com/mublog/user
+         *
+         * @author GNU Social
+         * @param   string  $text       The text from which to extract URL mentions
+         * @param   string  $preMention Character(s) that signals a mention ('@', '!'...)
+         * @return  array   The matching URLs (without @ or acct:) and each respective position in the given string.
+         */
+        static function extractUrlMentions ($text, $preMention='@')
+        {
+                $wmatches = array ();
+                // In the regexp below we need to match / _before_ URL_REGEX_VALID_PATH_CHARS because it otherwise gets merged
+                // with the TLD before (but / is in URL_REGEX_VALID_PATH_CHARS anyway, it's just its positioning that is important)
+                $result = preg_match_all ('/(?:^|\s+)'.preg_quote ($preMention, '/').'('.URL_REGEX_DOMAIN_NAME.'(?:\/['.URL_REGEX_VALID_PATH_CHARS.']*)*)/',
+                                $text,
+                                $wmatches,
+                                PREG_OFFSET_CAPTURE);
+                if ($result === false) {
+                        common_log (LOG_ERR, __METHOD__ . ': Error parsing profile URL mentions from text (preg_last_error=='.preg_last_error ().').');
+                } elseif (count ($wmatches)) {
+                        common_debug(sprintf('Found %d matches for profile URL mentions: %s', count ($wmatches), _ve ($wmatches)));
+                }
+                return $wmatches[1];
+        }
+
+        /**
+         * Find any explicit remote mentions. Accepted forms:
+         *   Webfinger: @user@example.com
+         *   Profile link: @example.com/mublog/user
+         *
+         * @author GNU Social
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
+         * @param Profile $sender
+         * @param string $text input markup text
+         * @param array &$mention in/out param: set of found mentions
+         * @return boolean hook return value
+         */
+        function onEndFindMentions(Profile $sender, $text, &$mentions)
+        {
+                $matches = array();
+
+                foreach (self::extractWebfingerIds($text, '@') as $wmatch) {
+                        list($target, $pos) = $wmatch;
+                        $this->log(LOG_INFO, "Checking webfinger person '$target'");
+                        $profile = null;
+                        try {
+                                $aprofile = Activitypub_profile::ensure_web_finger($target);
+                                $profile = $aprofile->local_profile();
+                        } catch (Exception $e) {
+                                $this->log(LOG_ERR, "Webfinger check failed: " . $e->getMessage());
+                                continue;
+                        }
+                        assert ($profile instanceof Profile);
+
+                        $displayName = !empty ($profile->nickname) && mb_strlen ($profile->nickname) < mb_strlen ($target)
+                        ? $profile->getNickname ()   // TODO: we could do getBestName() or getFullname() here
+                        : $target;
+                        $url = $profile->getUri ();
+                        if (!common_valid_http_url ($url)) {
+                                $url = $profile->getUrl ();
+                        }
+                        $matches[$pos] = array('mentioned' => array ($profile),
+                                               'type' => 'mention',
+                                               'text' => $displayName,
+                                               'position' => $pos,
+                                               'length' => mb_strlen ($target),
+                                               'url' => $url);
+                }
+
+                foreach (self::extractUrlMentions ($text) as $wmatch) {
+                        list ($target, $pos) = $wmatch;
+                        $schemes = array('https', 'http');
+                        foreach ($schemes as $scheme) {
+                                $url = "$scheme://$target";
+                                $this->log(LOG_INFO, "Checking profile address '$url'");
+                                try {
+                                        $aprofile = Activitypub_profile::get_from_uri ($url);
+                                        $profile = $aprofile->local_profile();
+                                        $displayName = !empty ($profile->nickname) && mb_strlen ($profile->nickname) < mb_strlen ($target) ?
+                                        $profile->nickname : $target;
+                                        $matches[$pos] = array('mentioned' => array ($profile),
+                                                               'type' => 'mention',
+                                                               'text' => $displayName,
+                                                               'position' => $pos,
+                                                               'length' => mb_strlen ($target),
+                                                               'url' => $profile->getUrl());
+                                        break;
+                                } catch (Exception $e) {
+                                        $this->log(LOG_ERR, "Profile check failed: " . $e->getMessage());
+                                }
+                        }
+                }
+
+                foreach ($mentions as $i => $other) {
+                        // If we share a common prefix with a local user, override it!
+                        $pos = $other['position'];
+                        if (isset ($matches[$pos])) {
+                                $mentions[$i] = $matches[$pos];
+                                unset ($matches[$pos]);
+                        }
+                }
+                foreach ($matches as $mention) {
+                        $mentions[] = $mention;
+                }
+
+                return true;
+        }
+
+        /**
+         * Allow remote profile references to be used in commands:
+         *   sub update@status.net
+         *   whois evan@identi.ca
+         *   reply http://identi.ca/evan hey what's up
+         *
+         * @author GNU Social
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
+         * @param Command $command
+         * @param string $arg
+         * @param Profile &$profile
+         * @return hook return code
+         */
+        function onStartCommandGetProfile ($command, $arg, &$profile)
+        {
+                try {
+                        $aprofile = $this->pull_remote_profile ($arg);
+                        $profile = $aprofile->local_profile();
+                } catch (Exception $e) {
+                        // No remote ActivityPub profile found
+                        return true;
+                }
+
+                return false;
+        }
+
+        /**
+         * Profile URI for remote profiles.
+         *
+         * @author GNU Social
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
+         * @param Profile $profile
+         * @param string $uri in/out
+         * @return mixed hook return code
+         */
+        function onStartGetProfileUri ($profile, &$uri)
+        {
+                $aprofile = Activitypub_profile::getKV ('profile_id', $profile->id);
+                if ($aprofile instanceof Activitypub_profile) {
+                        $uri = $aprofile->get_uri ();
+                        return false;
+                }
+                return true;
+        }
+
+
+        /**
+         * Dummy string on AccountProfileBlock stating that ActivityPub is active
+         * this is more of a placeholder for eventual useful stuff ._.
+         *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
+         * @return void
+         */
+        function onEndShowAccountProfileBlock (HTMLOutputter $out, Profile $profile)
+        {
+                if ($profile->isLocal()) {
+                        return true;
+                }
+                try {
+                        $aprofile = Activitypub_profile::getKV ('profile_id', $profile->id);
+                } catch (NoResultException $e) {
+                        // Not a remote ActivityPub_profile! Maybe some other network
+                        // that has imported a non-local user (e.g.: OStatus)?
+                        return true;
+                }
+
+                $out->elementStart('dl', 'entity_tags activitypub_profile');
+                $out->element('dt', null, _m('ActivityPub'));
+                $out->element('dd', null, _m('Active'));
+                $out->elementEnd('dl');
+        }
+
+        /**
+         * Profile from URI.
+         *
+         * @author GNU Social
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
+         * @param string $uri
+         * @param Profile &$profile in/out param: Profile got from URI
+         * @return mixed hook return code
+         */
+        function onStartGetProfileFromURI ($uri, &$profile)
+        {
+                // Don't want to do Web-based discovery on our own server,
+                // so we check locally first. This duplicates the functionality
+                // in the Profile class, since the plugin always runs before
+                // that local lookup, but since we return false it won't run double.
+
+                $user = User::getKV ('uri', $uri);
+                if ($user instanceof User) {
+                        $profile = $user->getProfile();
+                        return false;
+                } else {
+                        $group = User_group::getKV ('uri', $uri);
+                        if ($group instanceof User_group) {
+                                $profile = $group->getProfile ();
+                                return false;
+                        }
+                }
+
+                // Now, check remotely
+                try {
+                        $aprofile = Activitypub_profile::get_from_uri ($uri);
+                        $profile = $aprofile->local_profile ();
+                        return false;
+                } catch (Exception $e) {
+                        return true; // It's not an ActivityPub profile as far as we know, continue event handling
+                }
+        }
+
             /********************************************************
              *                    Delivery Events                   *
              ********************************************************/
@@ -110,6 +405,7 @@ class ActivityPubPlugin extends Plugin
          * Having established a remote subscription, send a notification to the
          * remote ActivityPub profile's endpoint.
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Profile $profile  subscriber
          * @param Profile $other    subscribee
          * @return hook return value
@@ -137,6 +433,7 @@ class ActivityPubPlugin extends Plugin
         /**
          * Notify remote server on unsubscribe.
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Profile $profile
          * @param Profile $other
          * @return hook return value
@@ -163,6 +460,7 @@ class ActivityPubPlugin extends Plugin
         /**
          * Notify remote users when their notices get favorited.
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Profile $profile of local user doing the faving
          * @param Notice $notice Notice being favored
          * @return hook return value
@@ -221,6 +519,7 @@ class ActivityPubPlugin extends Plugin
         /**
          * Notify remote users when their notices get de-favorited.
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Profile $profile of local user doing the de-faving
          * @param Notice  $notice  Notice being favored
          * @return hook return value
@@ -279,6 +578,7 @@ class ActivityPubPlugin extends Plugin
         /**
          * Notify remote users when their notices get deleted
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @return boolean hook flag
          */
         public function onEndDeleteOwnNotice ($user, $notice)
@@ -331,6 +631,7 @@ class ActivityPubPlugin extends Plugin
         /**
          * Insert notifications for replies, mentions and repeats
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @return boolean hook flag
          */
         function onStartNoticeDistribute ($notice)
@@ -416,6 +717,7 @@ class ActivityPubPlugin extends Plugin
          * Override the "from ActivityPub" bit in notice lists to link to the
          * original post and show the domain it came from.
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Notice in $notice
          * @param string out &$name
          * @param string out &$url
@@ -451,23 +753,6 @@ class ActivityPubPlugin extends Plugin
                     return true;
             }
         }
-
-        /**
-         * Profile URI for remote profiles.
-         *
-         * @param Profile $profile
-         * @param string $uri in/out
-         * @return mixed hook return code
-         */
-        function onStartGetProfileUri ($profile, &$uri)
-        {
-                $aprofile = Activitypub_profile::getKV ('profile_id', $profile->id);
-                if ($aprofile instanceof Activitypub_profile) {
-                        $uri = $aprofile->uri;
-                        return false;
-                }
-                return true;
-        }
 }
 
 /**
@@ -504,6 +789,7 @@ class ActivityPubReturn
         /**
          * Return a valid answer
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param array $res
          * @return void
          */
@@ -517,6 +803,7 @@ class ActivityPubReturn
         /**
          * Return an error
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param string $m
          * @param int32 $code
          * @return void
diff --git a/actions/apactorfollowers.php b/actions/apactorfollowers.php
index 9205bd7..639cace 100644
--- a/actions/apactorfollowers.php
+++ b/actions/apactorfollowers.php
@@ -46,6 +46,7 @@ class apActorFollowersAction extends ManagedAction
         /**
          * Handle the Followers Collection request
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @return void
          */
         protected function handle ()
diff --git a/actions/apactorfollowing.php b/actions/apactorfollowing.php
index 4bb695e..86c895e 100644
--- a/actions/apactorfollowing.php
+++ b/actions/apactorfollowing.php
@@ -46,6 +46,7 @@ class apActorFollowingAction extends ManagedAction
         /**
          * Handle the Following Collection request
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @return void
          */
         protected function handle ()
diff --git a/actions/apactorinbox.php b/actions/apactorinbox.php
index 35bbb74..fbbe395 100644
--- a/actions/apactorinbox.php
+++ b/actions/apactorinbox.php
@@ -46,6 +46,7 @@ class apActorInboxAction extends ManagedAction
         /**
          * Handle the Actor Inbox request
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @return void
          */
         protected function handle ()
diff --git a/actions/apactorlikedcollection.php b/actions/apactorlikedcollection.php
index 3cc3cba..1f93a7d 100644
--- a/actions/apactorlikedcollection.php
+++ b/actions/apactorlikedcollection.php
@@ -46,6 +46,7 @@ class apActorLikedCollectionAction extends ManagedAction
         /**
          * Handle the Liked Collection request
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @return void
          */
         protected function handle ()
@@ -99,6 +100,7 @@ class apActorLikedCollectionAction extends ManagedAction
          * Take a fave object and turns it in a pretty array to be used
          * as a plugin answer
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Fave $fave_object
          * @return array pretty array representating a Fave
          */
@@ -114,6 +116,7 @@ class apActorLikedCollectionAction extends ManagedAction
         /**
          * Fetch faves
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param int32 $user_id
          * @param int32 $limit
          * @param int32 $since_id
diff --git a/actions/apactorprofile.php b/actions/apactorprofile.php
index b32d595..8ac1210 100644
--- a/actions/apactorprofile.php
+++ b/actions/apactorprofile.php
@@ -47,6 +47,7 @@ class apActorProfileAction extends ManagedAction
         /**
          * Handle the Actor Profile request
          *
+         * @author Daniel Supernault <danielsupernault@gmail.com>
          * @return void
          */
         protected function handle()
diff --git a/actions/apsharedinbox.php b/actions/apsharedinbox.php
index cec4e42..7c278b8 100644
--- a/actions/apsharedinbox.php
+++ b/actions/apsharedinbox.php
@@ -1,5 +1,4 @@
 <?php
-require_once dirname (__DIR__) . DIRECTORY_SEPARATOR . "utils" . DIRECTORY_SEPARATOR . "explorer.php";
 /**
  * GNU social - a federating social network
  *
@@ -47,6 +46,7 @@ class apSharedInboxAction extends ManagedAction
         /**
          * Handle the Shared Inbox request
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @return void
          */
         protected function handle ()
diff --git a/actions/inbox/Create.php b/actions/inbox/Create.php
index c12309a..d10409a 100644
--- a/actions/inbox/Create.php
+++ b/actions/inbox/Create.php
@@ -40,6 +40,8 @@ if (!isset ($data->object->content)) {
 }
 if (!isset ($data->object->url)) {
         ActivityPubReturn::error ("Object url was not specified.");
+} else if (!filter_var ($data->object->url, FILTER_VALIDATE_URL)) {
+        ActivityPubReturn::error ("Invalid Object Url.");
 }
 
 $content = $data->object->content;
diff --git a/classes/Activitypub_attachment.php b/classes/Activitypub_attachment.php
index e20a487..075015a 100644
--- a/classes/Activitypub_attachment.php
+++ b/classes/Activitypub_attachment.php
@@ -43,6 +43,7 @@ class Activitypub_attachment extends Managed_DataObject
         /**
          * Generates a pretty array from an Attachment object
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Attachment $attachment
          * @return pretty array to be used in a response
          */
diff --git a/classes/Activitypub_error.php b/classes/Activitypub_error.php
index e0637cd..35638b4 100644
--- a/classes/Activitypub_error.php
+++ b/classes/Activitypub_error.php
@@ -43,6 +43,7 @@ class Activitypub_error extends Managed_DataObject
         /**
          * Generates a pretty error from a string
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param string $m
          * @return pretty array to be used in a response
          */
diff --git a/classes/Activitypub_notice.php b/classes/Activitypub_notice.php
index 88f8f5c..954c1f6 100644
--- a/classes/Activitypub_notice.php
+++ b/classes/Activitypub_notice.php
@@ -44,6 +44,8 @@ class Activitypub_notice extends Managed_DataObject
         /**
          * Generates a pretty notice from a Notice object
          *
+         * @author Daniel Supernault <danielsupernault@gmail.com>
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Notice $notice
          * @return pretty array to be used in a response
          */
diff --git a/classes/Activitypub_profile.php b/classes/Activitypub_profile.php
index a1cb4da..701c762 100644
--- a/classes/Activitypub_profile.php
+++ b/classes/Activitypub_profile.php
@@ -1,5 +1,4 @@
 <?php
-require_once dirname (__DIR__) . DIRECTORY_SEPARATOR . "utils" . DIRECTORY_SEPARATOR . "explorer.php";
 /**
  * GNU social - a federating social network
  *
@@ -49,6 +48,7 @@ class Activitypub_profile extends Profile
         /**
          * Return table definition for Schema setup and DB_DataObject usage.
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @return array array of column definitions
          */
         static function schemaDef ()
@@ -76,6 +76,7 @@ class Activitypub_profile extends Profile
         /**
          * Generates a pretty profile from a Profile object
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Profile $profile
          * @return pretty array to be used in a response
          */
@@ -118,6 +119,7 @@ class Activitypub_profile extends Profile
         /**
          * Insert the current objects variables into the database
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @access public
          * @throws ServerException
          */
@@ -154,6 +156,8 @@ class Activitypub_profile extends Profile
 
         /**
          * Fetch the locally stored profile for this Activitypub_profile
+         *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @return Profile
          * @throws NoProfileException if it was not found
          */
@@ -169,6 +173,7 @@ class Activitypub_profile extends Profile
         /**
          * Generates an Activitypub_profile from a Profile
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Profile $profile
          * @return Activitypub_profile
          * @throws Exception if no Activitypub_profile exists for given Profile
@@ -177,14 +182,14 @@ class Activitypub_profile extends Profile
         {
                 $profile_id = $profile->getID ();
 
-                $aprofile = Activitypub_profile::getKV ('profile_id', $profile_id);
+                $aprofile = self::getKV ('profile_id', $profile_id);
                 if (!$aprofile instanceof Activitypub_profile) {
                         // No Activitypub_profile for this profile_id,
                         if (!$profile->isLocal ()) {
                                 // create one!
                                 $aprofile = self::create_from_local_profile ($profile);
                         } else {
-                                throw new Exception ('No Activitypub_profile for Profile ID: '.$profile_id. ', this probably is a local profile.');
+                                throw new Exception ('No Activitypub_profile for Profile ID: '.$profile_id. ', this is a local user.');
                         }
                 }
 
@@ -200,6 +205,7 @@ class Activitypub_profile extends Profile
          * One must be careful not to give a user profile to this function
          * as only remote users have ActivityPub_profiles on local instance
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Profile $profile
          * @return Activitypub_profile
          */
@@ -227,6 +233,7 @@ class Activitypub_profile extends Profile
         /**
          * Returns sharedInbox if possible, inbox otherwise
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @return string Inbox URL
          */
         public function get_inbox ()
@@ -237,4 +244,122 @@ class Activitypub_profile extends Profile
 
                 return $this->sharedInboxuri;
         }
+
+        /**
+         * Getter for uri property
+         *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
+         * @return string URI
+         */
+        public function get_uri ()
+        {
+                return $this->uri;
+        }
+
+        /**
+         * Ensures a valid Activitypub_profile when provided with a valid URI.
+         *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
+         * @param string $url
+         * @return Activitypub_profile
+         * @throws Exception if it isn't possible to return an Activitypub_profile
+         */
+        public static function get_from_uri ($url)
+        {
+                $explorer = new Activitypub_explorer ();
+                $profiles_found = $explorer->lookup ($url);
+                if (!empty ($profiles_found)) {
+                        return self::from_profile ($profiles_found[0]);
+                } else {
+                        throw new Exception ('No valid ActivityPub profile found for given URI');
+                }
+                // If it doesn't return a valid Activitypub_profile an exception will
+                // have been thrown before getting to this point.
+        }
+
+        /**
+         * Look up, and if necessary create, an Activitypub_profile for the remote
+         * entity with the given webfinger address.
+         * This should never return null -- you will either get an object or
+         * an exception will be thrown.
+         *
+         * @author GNU Social
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
+         * @param string $addr webfinger address
+         * @return Activitypub_profile
+         * @throws Exception on error conditions
+         */
+        public static function ensure_web_finger ($addr)
+        {
+                // Normalize $addr, i.e. add 'acct:' if missing
+                $addr = Discovery::normalize ($addr);
+
+                // Try the cache
+                $uri = self::cacheGet (sprintf ('activitypub_profile:webfinger:%s', $addr));
+
+                if ($uri !== false) {
+                        if (is_null ($uri)) {
+                                // Negative cache entry
+                                // TRANS: Exception.
+                                throw new Exception (_m ('Not a valid webfinger address (via cache).'));
+                        }
+                        try {
+                                return self::get_from_uri ($uri);
+                        } catch (Exception $e) {
+                            common_log (LOG_ERR, sprintf (__METHOD__ . ': Webfinger address cache inconsistent with database, did not find Activitypub_profile uri==%s', $uri));
+                            self::cacheSet (sprintf ('activitypub_profile:webfinger:%s', $addr), false);
+                        }
+                }
+
+                // Now, try some discovery
+
+                $disco = new Discovery ();
+
+                try {
+                        $xrd = $disco->lookup ($addr);
+                } catch (Exception $e) {
+                        // Save negative cache entry so we don't waste time looking it up again.
+                        // @todo FIXME: Distinguish temporary failures?
+                        self::cacheSet (sprintf ('activitypub_profile:webfinger:%s', $addr), null);
+                        // TRANS: Exception.
+                        throw new Exception (_m ('Not a valid webfinger address.'));
+                }
+
+                $hints = array_merge (array ('webfinger' => $addr),
+                DiscoveryHints::fromXRD ($xrd));
+
+                // If there's an Hcard, let's grab its info
+                if (array_key_exists ('hcard', $hints)) {
+                        if (!array_key_exists ('profileurl', $hints) ||
+                        $hints['hcard'] != $hints['profileurl']) {
+                                $hcardHints = DiscoveryHints::fromHcardUrl ($hints['hcard']);
+                                $hints = array_merge ($hcardHints, $hints);
+                        }
+                }
+
+                // If we got a profile page, try that!
+                $profileUrl = null;
+                if (array_key_exists ('profileurl', $hints)) {
+                        $profileUrl = $hints['profileurl'];
+                        try {
+                                common_log (LOG_INFO, "Discovery on acct:$addr with profile URL $profileUrl");
+                                $aprofile = self::get_from_uri ($hints['profileurl']);
+                                self::cacheSet (sprintf ('activitypub_profile:webfinger:%s', $addr), $aprofile->get_uri ());
+                                return $aprofile;
+                        } catch (Exception $e) {
+                                common_log (LOG_WARNING, "Failed creating profile from profile URL '$profileUrl': " . $e->getMessage ());
+                                // keep looking
+                                //
+                                // @todo FIXME: This means an error discovering from profile page
+                                // may give us a corrupt entry using the webfinger URI, which
+                                // will obscure the correct page-keyed profile later on.
+                        }
+                }
+
+                // XXX: try hcard
+                // XXX: try FOAF
+
+                // TRANS: Exception. %s is a webfinger address.
+                throw new Exception (sprintf (_m ('Could not find a valid profile for "%s".'), $addr));
+        }
 }
diff --git a/classes/Activitypub_tag.php b/classes/Activitypub_tag.php
index 1e94862..7c1a838 100644
--- a/classes/Activitypub_tag.php
+++ b/classes/Activitypub_tag.php
@@ -43,6 +43,7 @@ class Activitypub_tag extends Managed_DataObject
         /**
          * Generates a pretty tag from a Tag object
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Tag $tag
          * @return pretty array to be used in a response
          */
diff --git a/utils/discoveryhints.php b/utils/discoveryhints.php
new file mode 100644
index 0000000..b14a174
--- /dev/null
+++ b/utils/discoveryhints.php
@@ -0,0 +1,154 @@
+<?php
+/**
+ * GNU social - a federating social network
+ *
+ * Some utilities for generating hint data
+ *
+ * LICENCE: This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * @category  Plugin
+ * @package   GNUsocial
+ * @author    GNUsocial
+ * @copyright 2010 Free Software Foundation http://fsf.org
+ * @license   http://www.fsf.org/licensing/licenses/agpl-3.0.html GNU Affero General Public License version 3.0
+ * @link      https://www.gnu.org/software/social/
+ */
+if (!defined ('GNUSOCIAL')) {
+        exit (1);
+}
+
+class DiscoveryHints {
+    static function fromXRD(XML_XRD $xrd)
+    {
+        $hints = array();
+
+        if (Event::handle('StartDiscoveryHintsFromXRD', array($xrd, &$hints))) {
+            foreach ($xrd->links as $link) {
+                switch ($link->rel) {
+                case WebFingerResource_Profile::PROFILEPAGE:
+                    $hints['profileurl'] = $link->href;
+                    break;
+                    $hints['salmon'] = $link->href;
+                    break;
+                case Discovery::UPDATESFROM:
+                    if (empty($link->type) || $link->type == 'application/atom+xml') {
+                        $hints['feedurl'] = $link->href;
+                    }
+                    break;
+                case Discovery::HCARD:
+                case Discovery::MF2_HCARD:
+                    $hints['hcard'] = $link->href;
+                    break;
+                default:
+                    break;
+                }
+            }
+            Event::handle('EndDiscoveryHintsFromXRD', array($xrd, &$hints));
+        }
+
+        return $hints;
+    }
+
+    static function fromHcardUrl($url)
+    {
+        $client = new HTTPClient();
+        $client->setHeader('Accept', 'text/html,application/xhtml+xml');
+        try {
+            $response = $client->get($url);
+
+            if (!$response->isOk()) {
+                return null;
+            }
+        } catch (HTTP_Request2_Exception $e) {
+            // Any HTTPClient error that might've been thrown
+            common_log(LOG_ERR, __METHOD__ . ':'.$e->getMessage());
+            return null;
+        }
+
+        return self::hcardHints($response->getBody(),
+                                $response->getEffectiveUrl());
+    }
+
+    static function hcardHints($body, $url)
+    {
+        $hcard = self::_hcard($body, $url);
+
+        if (empty($hcard)) {
+            return array();
+        }
+
+        $hints = array();
+
+        // XXX: don't copy stuff into an array and then copy it again
+
+        if (array_key_exists('nickname', $hcard) && !empty($hcard['nickname'][0])) {
+            $hints['nickname'] = $hcard['nickname'][0];
+        }
+
+        if (array_key_exists('name', $hcard) && !empty($hcard['name'][0])) {
+            $hints['fullname'] = $hcard['name'][0];
+        }
+
+        if (array_key_exists('photo', $hcard) && count($hcard['photo'])) {
+            $hints['avatar'] = $hcard['photo'][0];
+        }
+
+        if (array_key_exists('note', $hcard) && !empty($hcard['note'][0])) {
+            $hints['bio'] = $hcard['note'][0];
+        }
+
+        if (array_key_exists('adr', $hcard) && !empty($hcard['adr'][0])) {
+            $hints['location'] = $hcard['adr'][0]['value'];
+        }
+
+        if (array_key_exists('url', $hcard) && !empty($hcard['url'][0])) {
+            $hints['homepage'] = $hcard['url'][0];
+        }
+
+        return $hints;
+    }
+
+    static function _hcard($body, $url)
+    {
+        $mf2 = new Mf2\Parser($body, $url);
+        $mf2 = $mf2->parse();
+
+        if (empty($mf2['items'])) {
+            return null;
+        }
+
+        $hcards = array();
+
+        foreach ($mf2['items'] as $item) {
+            if (!in_array('h-card', $item['type'])) {
+                continue;
+            }
+
+            // We found a match, return it immediately
+            if (isset($item['properties']['url']) && in_array($url, $item['properties']['url'])) {
+                return $item['properties'];
+            }
+
+            // Let's keep all the hcards for later, to return one of them at least
+            $hcards[] = $item['properties'];
+        }
+
+        // No match immediately for the url we expected, but there were h-cards found
+        if (count($hcards) > 0) {
+            return $hcards[0];
+        }
+
+        return null;
+    }
+}
diff --git a/utils/explorer.php b/utils/explorer.php
index 8a70c5e..51ebd97 100644
--- a/utils/explorer.php
+++ b/utils/explorer.php
@@ -49,6 +49,7 @@ class Activitypub_explorer
          * This function cleans the $this->discovered_actor_profiles array
          * so that there is no erroneous data
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param string $url User's url
          * @return array of Profile objects
          */
@@ -64,6 +65,7 @@ class Activitypub_explorer
          * This is a recursive function that will accumulate the results on
          * $discovered_actor_profiles array
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param string $url User's url
          * @return array of Profile objects
          */
@@ -83,6 +85,7 @@ class Activitypub_explorer
          * Get a local user profiles from its URL and joins it on
          * $this->discovered_actor_profiles
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param string $url User's url
          * @return boolean success state
          */
@@ -116,6 +119,7 @@ class Activitypub_explorer
          * Get a remote user(s) profile(s) from its URL and joins it on
          * $this->discovered_actor_profiles
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param string $url User's url
          * @return boolean success state
          */
@@ -152,6 +156,7 @@ class Activitypub_explorer
         /**
          * Save remote user profile in local instance
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param array $res remote response
          * @return Profile remote Profile object
          */
@@ -174,6 +179,7 @@ class Activitypub_explorer
          * Validates a remote response in order to determine whether this
          * response is a valid profile or not
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param array $res remote response
          * @return boolean success state
          */
@@ -192,12 +198,13 @@ class Activitypub_explorer
          * potential ActivityPub remote profiles, as so it is important to use
          * this hacky workaround (at least for now)
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param string $v URL
          * @return boolean|Profile false if fails | Profile object if successful
          */
-        static function get_profile_by_url ($v)
+        public static function get_profile_by_url ($v)
         {
-                $i = Managed_DataObject::getcached(Profile, "profileurl", $v);
+                $i = Managed_DataObject::getcached("Profile", "profileurl", $v);
                 if (empty ($i)) { // false = cache miss
                         $i = new Profile;
                         $result = $i->get ("profileurl", $v);
@@ -214,10 +221,11 @@ class Activitypub_explorer
         /**
          * Given a valid actor profile url returns its inboxes
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param string $url of Actor profile
          * @return boolean|array false if fails | array with inbox and shared inbox if successful
          */
-        static function get_actor_inboxes_uri ($url)
+        public static function get_actor_inboxes_uri ($url)
         {
                 $client    = new HTTPClient ();
                 $headers   = array();
diff --git a/utils/postman.php b/utils/postman.php
index d7ae125..15dffa3 100644
--- a/utils/postman.php
+++ b/utils/postman.php
@@ -51,6 +51,7 @@ class Activitypub_postman
         /**
          * Create a postman to deliver something to someone
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Profile of sender
          * @param Activitypub_profile $to array of destinataries
          */
@@ -66,6 +67,8 @@ class Activitypub_postman
 
         /**
          * Send a follow notification to remote instance
+         *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          */
         public function follow ()
         {
@@ -79,6 +82,8 @@ class Activitypub_postman
 
         /**
          * Send a Undo Follow notification to remote instance
+         *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          */
         public function undo_follow ()
         {
@@ -97,6 +102,7 @@ class Activitypub_postman
         /**
          * Send a Like notification to remote instances holding the notice
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Notice $notice
          */
         public function like ($notice)
@@ -114,6 +120,7 @@ class Activitypub_postman
         /**
          * Send a Undo Like notification to remote instances holding the notice
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Notice $notice
          */
         public function undo_like ($notice)
@@ -135,6 +142,7 @@ class Activitypub_postman
         /**
          * Send a Announce notification to remote instances
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Notice $notice
          */
         public function announce ($notice)
@@ -156,6 +164,7 @@ class Activitypub_postman
         /**
          * Send a Create notification to remote instances
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Notice $notice
          */
         public function create ($notice)
@@ -183,6 +192,7 @@ class Activitypub_postman
         /**
          * Send a Delete notification to remote instances holding the notice
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @param Notice $notice
          */
         public function delete ($notice)
@@ -201,6 +211,7 @@ class Activitypub_postman
         /**
          * Clean list of inboxes to deliver messages
          *
+         * @author Diogo Cordeiro <diogo@fc.up.pt>
          * @return array To Inbox URLs
          */
         private function to_inbox ()