don't allow duplicate feeds for user

backend.php

@@ -951,15 +951,29 @@
 				$feed_link = db_escape_string($_GET["link"]);
 
 				$result = db_query($link,
-					"INSERT INTO ttrss_feeds (owner_uid,feed_url,title) VALUES ('".$_SESSION["uid"]."', '$feed_link', '')");
+					"SELECT id FROM ttrss_feeds 
+					WHERE feed_url = '$feed_link' AND owner_uid = ".$_SESSION["uid"]);
 
-				$result = db_query($link,
-					"SELECT id FROM ttrss_feeds WHERE feed_url = '$feed_link' AND owner_uid = " . $_SESSION["uid"]);
+				if (db_num_rows($result) == 0) {
+					
+					$result = db_query($link,
+						"INSERT INTO ttrss_feeds (owner_uid,feed_url,title) 
+						VALUES ('".$_SESSION["uid"]."', '$feed_link', '')");
+
+					$result = db_query($link,
+					"SELECT id FROM ttrss_feeds WHERE feed_url = '$feed_link' 
+						AND owner_uid = " . $_SESSION["uid"]);
 
-				$feed_id = db_fetch_result($result, 0, "id");
+					$feed_id = db_fetch_result($result, 0, "id");
+
+					if ($feed_id) {
+						update_rss_feed($link, $feed_link, $feed_id);
+					}
+				} else {
 
-				if ($feed_id) {
-					update_rss_feed($link, $feed_link, $feed_id);
+					print "<div class=\"warning\">
+						Feed <b>$feed_link</b> already exists in the database.
+					</div>";
 				}
 			}
 		}