From 84be602aa503f2bc7f221337d66597368ccb4f2e Mon Sep 17 00:00:00 2001
From: Riccardo Binetti <rbino@gmx.com>
Date: Mon, 4 May 2020 19:00:42 +0200
Subject: [PATCH] vernemq_dev_api: add has_session/1 function

Allow checking if a given SubscriberID has an existing session
---
 doc/vernemq_dev_api.html | 10 ++++++++++
 src/vernemq_dev_api.erl  | 15 +++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/doc/vernemq_dev_api.html b/doc/vernemq_dev_api.html
index 7131dc7..8467599 100644
--- a/doc/vernemq_dev_api.html
+++ b/doc/vernemq_dev_api.html
@@ -37,6 +37,7 @@ <h3 class="typedecl"><a name="type-topic">topic()</a></h3>
 
 <h2><a name="index">Function Index</a></h2>
 <table width="100%" border="1" cellspacing="0" cellpadding="2" summary="function index"><tr><td valign="top"><a href="#disconnect_by_subscriber_id-2">disconnect_by_subscriber_id/2</a></td><td>Disconnect a client by <a href="#type-subscriber_id"><code>subscriber_id()</code></a></td></tr>
+<tr><td valign="top"><a href="#has_session-1">has_session/1</a></td><td>Check if a <a href="#type-subscriber_id"><code>subscriber_id()</code></a> has an existing session.</td></tr>
 <tr><td valign="top"><a href="#unword_topic-1">unword_topic/1</a></td><td>Convert a <a href="#type-topic"><code>topic()</code></a> list into an <a href="#type-iolist"><code>iolist()</code></a>  
 which can be flattened into a binary.</td></tr>
 </table>
@@ -52,6 +53,15 @@ <h3 class="function"><a name="disconnect_by_subscriber_id-2">disconnect_by_subsc
   Given a subscriber_id the client is looked up in the cluster and
   disconnected.</p>
 
+<h3 class="function"><a name="has_session-1">has_session/1</a></h3>
+<div class="spec">
+  <p><tt>has_session(SId) -&gt; true | false</tt>
+    <ul class="definitions"><li><tt>SId = <a href="#type-subscriber_id">subscriber_id()</a></tt></li>></ul></p>
+</div><p><p>Check if a <a href="#type-subscriber_id"><code>subscriber_id()</code> has an existing session</a></p>
+ 
+  Given a subscriber_id, this function checks if it has an existing
+  session.</p>
+
 <h3 class="function"><a name="unword_topic-1">unword_topic/1</a></h3>
 <div class="spec">
 <p><tt>unword_topic(Topic) -&gt; iolist()</tt>
diff --git a/src/vernemq_dev_api.erl b/src/vernemq_dev_api.erl
index 222408f..9063f4e 100644
--- a/src/vernemq_dev_api.erl
+++ b/src/vernemq_dev_api.erl
@@ -17,6 +17,7 @@
 
 -export([unword_topic/1,
          disconnect_by_subscriber_id/2,
+         has_session/1,
          reauthorize_subscriptions/3]).
 
 -type disconnect_flag() :: do_cleanup.
@@ -36,6 +37,20 @@ disconnect_by_subscriber_id(SubscriberId, Opts) ->
             vmq_queue:force_disconnect(QueuePid, normal, proplists:get_bool(do_cleanup, Opts))
     end.
 
+%% @doc Check if a {@link subscriber_id().} has an existing session
+%%
+%% Given a subscriber_id, this function checks if it has an existing
+%% session.
+-spec has_session(SId) -> true | false when
+      SId  :: subscriber_id().
+has_session(SubscriberId) ->
+    case vmq_subscriber_db:read(SubscriberId) of
+        undefined ->
+            false;
+        _Subs ->
+            true
+    end.
+
 %% @doc Reauthorize subscriptions by username and subscriber_id
 %%
 %% Given a username and subscriber_id all subscriptions