[PATCH] Add rate limit support to API

[Florian Pritz]

This allows us to prevent users from hammering the API every few seconds
to check if any of their packages were updated. Real world users check
as often as every 5 or 10 seconds.

Signed-off-by: Florian Pritz <bluewind at xinu.at>
---

Basic idea for a rate limiting solution. Currently the cleanup of old
entries is done on each api request. That may be a bit excessive, but I
didn't find a cronjob to put it and given the table is indexed, the
query is probably fast enough. At least for a PoC this should be fine.
Tell me what you think.

 conf/config.proto         |  4 +++
 upgrading/4.7.0.txt       | 11 ++++++++
 web/lib/aurjson.class.php | 71 +++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 86 insertions(+)
 create mode 100644 upgrading/4.7.0.txt

diff --git a/conf/config.proto b/conf/config.proto
index 1750929..934d369 100644
--- a/conf/config.proto
+++ b/conf/config.proto
@@ -36,6 +36,10 @@ enable-maintenance = 1
 maintenance-exceptions = 127.0.0.1
 render-comment-cmd = /usr/local/bin/aurweb-rendercomment
 
+[ratelimit]
+request_limit = 4000
+window_length = 86400
+
 [notifications]
 notify-cmd = /usr/local/bin/aurweb-notify
 sendmail = /usr/bin/sendmail
diff --git a/upgrading/4.7.0.txt b/upgrading/4.7.0.txt
new file mode 100644
index 0000000..1b51cd2
--- /dev/null
+++ b/upgrading/4.7.0.txt
@@ -0,0 +1,11 @@
+1. Add ApiRateLimit table:
+
+---
+CREATE TABLE `ApiRateLimit` (
+  `ip` varchar(45) CHARACTER SET ascii COLLATE ascii_bin NOT NULL,
+  `requests` int(11) NOT NULL,
+  `window_start` bigint(20) NOT NULL,
+  PRIMARY KEY (`ip`),
+  KEY `window_start_idx` (`window_start`)
+) ENGINE=InnoDB;
+---
diff --git a/web/lib/aurjson.class.php b/web/lib/aurjson.class.php
index 9eeaafd..8a6dd7b 100644
--- a/web/lib/aurjson.class.php
+++ b/web/lib/aurjson.class.php
@@ -96,6 +96,11 @@ public function handle($http_data) {
 
 		$this->dbh = DB::connect();
 
+		if ($this->check_ratelimit($_SERVER['REMOTE_ADDR'])) {
+			header("HTTP/1.1 429 Too Many Requests");
+			return $this->json_error('Rate limit reached');
+		}
+
 		$type = str_replace('-', '_', $http_data['type']);
 		if ($type == 'info' && $this->version >= 5) {
 			$type = 'multiinfo';
@@ -130,6 +135,72 @@ public function handle($http_data) {
 		}
 	}
 
+	/*
+	 * Check if an IP needs to be  rate limited.
+	 *
+	 * @param $ip IP of the current request
+	 *
+	 * @return true if IP needs to be rate limited, false otherwise.
+	 */
+	private function check_ratelimit($ip) {
+		$limit = config_get("ratelimit", "request_limit");
+		$window_length = config_get("ratelimit", "window_length");
+		$this->update_ratelimit($ip);
+		$stmt = $this->dbh->prepare("
+			SELECT requests,window_start FROM ApiRateLimit
+			WHERE ip = :ip");
+		$stmt->bindParam(":ip", $ip);
+		$result = $stmt->execute();
+
+		if (!$result) {
+			return false;
+		}
+
+		$row = $stmt->fetch(PDO::FETCH_ASSOC);
+
+		if ($row['window_start'] < time() - $window_length) {
+			$stmt = $this->dbh->prepare("
+				DELETE FROM ApiRateLimit
+				WHERE ip = :ip");
+			$stmt->bindParam(":ip", $ip);
+			$stmt->execute();
+			return false;
+		}
+
+		if ($row['requests'] > $limit) {
+			return true;
+		}
+		return false;
+	}
+
+	/*
+	 * Update a rate limit for an IP by increasing it's requests value by one.
+	 *
+	 * @param $ip IP of the current request
+	 *
+	 * @return void
+	 */
+	private function update_ratelimit($ip) {
+		$window_length = config_get("ratelimit", "window_length");
+		$time = time();
+		$deletion_time = $time - $window_length;
+		$stmt = $this->dbh->prepare("
+			INSERT INTO ApiRateLimit
+			(ip, requests, window_start)
+			VALUES (:ip, 0, :window_start)
+			ON DUPLICATE KEY UPDATE requests=requests+1");
+		$stmt->bindParam(":ip", $ip);
+		$stmt->bindParam(":window_start", $time);
+		$stmt->execute();
+
+		// TODO: this should move into some cronjob
+		$stmt = $this->dbh->prepare("
+			DELETE FROM ApiRateLimit
+			WHERE window_start < :time");
+		$stmt->bindParam(":time", $deletion_time);
+		$stmt->execute();
+	}
+
 	/*
 	 * Returns a JSON formatted error string.
 	 *
-- 
2.15.1