Add rate limit support to API

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@xinu.at>
Signed-off-by: Lukas Fleischer <lfleischer@archlinux.org>

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

schema/aur-schema.sql

@@ -399,3 +399,13 @@ CREATE TABLE AcceptedTerms (
 	FOREIGN KEY (UsersID) REFERENCES Users(ID) ON DELETE CASCADE,
 	FOREIGN KEY (TermsID) REFERENCES Terms(ID) ON DELETE CASCADE
 ) ENGINE = InnoDB;
+
+-- Rate limits for API
+--
+CREATE TABLE `ApiRateLimit` (
+  IP VARCHAR(45) NOT NULL,
+  Requests INT(11) NOT NULL,
+  WindowStart BIGINT(20) NOT NULL,
+  PRIMARY KEY (`ip`)
+) ENGINE = InnoDB;
+CREATE INDEX ApiRateLimitWindowStart ON ApiRateLimit (WindowStart);

upgrading/4.7.0.txt

+1. Add ApiRateLimit table:
+
+---
+CREATE TABLE `ApiRateLimit` (
+  IP VARCHAR(45) NOT NULL,
+  Requests INT(11) NOT NULL,
+  WindowStart BIGINT(20) NOT NULL,
+  PRIMARY KEY (`ip`)
+) ENGINE = InnoDB;
+CREATE INDEX ApiRateLimitWindowStart ON ApiRateLimit (WindowStart);
+---

web/lib/aurjson.class.php

@@ -96,6 +96,11 @@ class AurJSON {
 
 		$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 +135,87 @@ class AurJSON {
 		}
 	}
 
+	/*
+	 * 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) {
+		$limit = config_get("ratelimit", "request_limit");
+		if ($limit == 0) {
+			return false;
+		}
+
+		$window_length = config_get("ratelimit", "window_length");
+		$this->update_ratelimit($ip);
+		$stmt = $this->dbh->prepare("
+			SELECT Requests FROM ApiRateLimit
+			WHERE IP = :ip");
+		$stmt->bindParam(":ip", $ip);
+		$result = $stmt->execute();
+
+		if (!$result) {
+			return false;
+		}
+
+		$row = $stmt->fetch(PDO::FETCH_ASSOC);
+		if ($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");
+		$db_backend = config_get("database", "backend");
+		$time = time();
+
+		// Clean up old windows
+		$deletion_time = $time - $window_length;
+		$stmt = $this->dbh->prepare("
+			DELETE FROM ApiRateLimit
+			WHERE WindowStart < :time");
+		$stmt->bindParam(":time", $deletion_time);
+		$stmt->execute();
+
+		if ($db_backend == "mysql") {
+			$stmt = $this->dbh->prepare("
+				INSERT INTO ApiRateLimit
+				(IP, Requests, WindowStart)
+				VALUES (:ip, 1, :window_start)
+				ON DUPLICATE KEY UPDATE Requests=Requests+1");
+			$stmt->bindParam(":ip", $ip);
+			$stmt->bindParam(":window_start", $time);
+			$stmt->execute();
+		} elseif ($db_backend == "sqlite") {
+			$stmt = $this->dbh->prepare("
+				INSERT OR IGNORE INTO ApiRateLimit
+				(IP, Requests, WindowStart)
+				VALUES (:ip, 0, :window_start);");
+			$stmt->bindParam(":ip", $ip);
+			$stmt->bindParam(":window_start", $time);
+			$stmt->execute();
+
+			$stmt = $this->dbh->prepare("
+				UPDATE ApiRateLimit
+				SET Requests = Requests + 1
+				WHERE IP = :ip");
+			$stmt->bindParam(":ip", $ip);
+			$stmt->execute();
+		} else {
+			throw new RuntimeException("Unknown database backend");
+		}
+	}
+
 	/*
 	 * Returns a JSON formatted error string.
 	 *