From 19b0dabe11cfbe87934e0f790607e282a09a695b Mon Sep 17 00:00:00 2001
From: Mikunj <mikunj@live.com.au>
Date: Fri, 13 Sep 2019 15:48:57 +1000
Subject: [PATCH 1/3] Keep a cache of the last 5 fetched messages for public
 chat so we can use it to detect duplicate messages.

---
 js/modules/loki_public_chat_api.js | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/js/modules/loki_public_chat_api.js b/js/modules/loki_public_chat_api.js
index 4823b0c1d..30a9758dc 100644
--- a/js/modules/loki_public_chat_api.js
+++ b/js/modules/loki_public_chat_api.js
@@ -213,6 +213,10 @@ class LokiPublicChannelAPI {
     this.deleteLastId = 1;
     this.timers = {};
     this.running = true;
+
+    // Cache for duplicate checking
+    this.lastMessagesCache = [];
+
     // end properties
 
     log.info(`registered LokiPublicChannel ${channelId}`);
@@ -574,6 +578,32 @@ class LokiPublicChannelAPI {
           return; // Invalid message
         }
 
+        // Duplicate check
+        const isDuplicate = message => {
+          const sameUsername = message.username === adnMessage.user.username;
+          const sameText = message.text === adnMessage.text;
+          // Don't filter out messages that are too far apart from each other
+          const timestampsSimilar =
+            Math.abs(message.timestamp - timestamp) <= 10000;
+
+          return sameUsername && sameText && timestampsSimilar;
+        };
+
+        // Filter out any messages that we got previously
+        if (this.lastMessagesCache.some(isDuplicate)) {
+          return; // Duplicate message
+        }
+
+        // Add the message to the lastMessage cache and keep the last 5 recent messages
+        this.lastMessagesCache = [
+          ...this.lastMessagesCache,
+          {
+            username: adnMessage.user.username,
+            text: adnMessage.text,
+            timestamp,
+          },
+        ].splice(-5);
+
         const messageData = {
           serverId: adnMessage.id,
           friendRequest: false,

From 001d8822738ae5e3586b8a84dd6e9256baf6f47d Mon Sep 17 00:00:00 2001
From: Mikunj <mikunj@live.com.au>
Date: Mon, 16 Sep 2019 10:10:05 +1000
Subject: [PATCH 2/3] Add comment to fix up confusion.

---
 js/modules/loki_public_chat_api.js | 1 +
 1 file changed, 1 insertion(+)

diff --git a/js/modules/loki_public_chat_api.js b/js/modules/loki_public_chat_api.js
index 30a9758dc..5bd563537 100644
--- a/js/modules/loki_public_chat_api.js
+++ b/js/modules/loki_public_chat_api.js
@@ -580,6 +580,7 @@ class LokiPublicChannelAPI {
 
         // Duplicate check
         const isDuplicate = message => {
+          // The username in this case is the users pubKey
           const sameUsername = message.username === adnMessage.user.username;
           const sameText = message.text === adnMessage.text;
           // Don't filter out messages that are too far apart from each other

From 75a527e82801513e6c09f44c61b9c5654801de10 Mon Sep 17 00:00:00 2001
From: Mikunj <mikunj@live.com.au>
Date: Mon, 16 Sep 2019 10:18:46 +1000
Subject: [PATCH 3/3] Replaced value with a descriptive constant.

---
 js/modules/loki_public_chat_api.js | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/js/modules/loki_public_chat_api.js b/js/modules/loki_public_chat_api.js
index 5bd563537..250baf1a3 100644
--- a/js/modules/loki_public_chat_api.js
+++ b/js/modules/loki_public_chat_api.js
@@ -9,6 +9,7 @@ const PUBLICCHAT_MSG_POLL_EVERY = 1.5 * 1000; // 1.5s
 const PUBLICCHAT_CHAN_POLL_EVERY = 20 * 1000; // 20s
 const PUBLICCHAT_DELETION_POLL_EVERY = 5 * 1000; // 5s
 const PUBLICCHAT_MOD_POLL_EVERY = 30 * 1000; // 30s
+const PUBLICCHAT_MIN_TIME_BETWEEN_DUPLICATE_MESSAGES = 10 * 1000; // 10s
 
 // singleton to relay events to libtextsecure/message_receiver
 class LokiPublicChatAPI extends EventEmitter {
@@ -585,7 +586,8 @@ class LokiPublicChannelAPI {
           const sameText = message.text === adnMessage.text;
           // Don't filter out messages that are too far apart from each other
           const timestampsSimilar =
-            Math.abs(message.timestamp - timestamp) <= 10000;
+            Math.abs(message.timestamp - timestamp) <=
+            PUBLICCHAT_MIN_TIME_BETWEEN_DUPLICATE_MESSAGES;
 
           return sameUsername && sameText && timestampsSimilar;
         };