fix bandwith rate limit calculation (#2134)

back-port of fc0cbfb789

include/libtorrent/bandwidth_limit.hpp

@@ -47,7 +47,7 @@ namespace libtorrent {
 // member of peer_connection
 struct TORRENT_EXTRA_EXPORT bandwidth_channel
 {
-	static const int inf = boost::integer_traits<int>::const_max;
+	static boost::int32_t const inf = boost::integer_traits<boost::int32_t>::const_max;
 
 	bandwidth_channel();
 
@@ -55,8 +55,9 @@ struct TORRENT_EXTRA_EXPORT bandwidth_channel
 	void throttle(int limit);
 	int throttle() const
 	{
-		TORRENT_ASSERT_VAL(m_limit < INT_MAX, m_limit);
-		return int(m_limit);
+		TORRENT_ASSERT_VAL(m_limit >= 0, m_limit);
+		TORRENT_ASSERT_VAL(m_limit < inf, m_limit);
+		return m_limit;
 	}
 
 	int quota_left() const;
@@ -96,10 +97,9 @@ private:
 
 	// the limit is the number of bytes
 	// per second we are allowed to use.
-	boost::int64_t m_limit;
+	boost::int32_t m_limit;
 };
 
 }
 
 #endif
-

src/bandwidth_limit.cpp

@@ -33,8 +33,8 @@ POSSIBILITY OF SUCH DAMAGE.
 #include "libtorrent/bandwidth_limit.hpp"
 #include <algorithm>
 
-namespace libtorrent
-{
+namespace libtorrent {
+
 	bandwidth_channel::bandwidth_channel()
 		: tmp(0)
 		, distribute_quota(0)
@@ -45,9 +45,9 @@ namespace libtorrent
 	// 0 means infinite
 	void bandwidth_channel::throttle(int limit)
 	{
-		TORRENT_ASSERT(limit >= 0);
+		TORRENT_ASSERT_VAL(limit >= 0, limit);
 		// if the throttle is more than this, we might overflow
-		TORRENT_ASSERT(limit < INT_MAX);
+		TORRENT_ASSERT_VAL(limit < inf, limit);
 		m_limit = limit;
 	}
 
@@ -59,19 +59,27 @@ namespace libtorrent
 
 	void bandwidth_channel::update_quota(int dt_milliseconds)
 	{
+		TORRENT_ASSERT_VAL(m_limit >= 0, m_limit);
+		TORRENT_ASSERT_VAL(m_limit < inf, m_limit);
+
 		if (m_limit == 0) return;
 
-		// avoid integer overflow
-		if (m_limit >= std::numeric_limits<int>::max() / dt_milliseconds)
+		// "to_add" should never have int64 overflow: "m_limit" contains < "<int>::max"
+		boost::int64_t to_add = (boost::int64_t(m_limit) * dt_milliseconds + 500) / 1000;
+
+		if (to_add > inf - m_quota_left)
 		{
-			m_quota_left = std::numeric_limits<int>::max();
+			m_quota_left = inf;
 		}
 		else
 		{
-			m_quota_left += (m_limit * dt_milliseconds + 500) / 1000;
-			if (m_quota_left / 3 > m_limit) m_quota_left = m_limit * 3;
+			m_quota_left += to_add;
+			if (m_quota_left / 3 > m_limit) m_quota_left = boost::int64_t(m_limit) * 3;
+			// "m_quota_left" will never have int64 overflow but may exceed "<int>::max"
+			m_quota_left = std::min(m_quota_left, boost::int64_t(inf));
 		}
-		distribute_quota = int((std::max)(m_quota_left, boost::int64_t(0)));
+
+		distribute_quota = int(std::max(m_quota_left, boost::int64_t(0)));
 	}
 
 	// this is used when connections disconnect with

test/test_bandwidth_limiter.cpp

@@ -467,6 +467,7 @@ TORRENT_TEST(equal_connection)
 	test_equal_connections(33,   60000);
 	test_equal_connections(33,  500000);
 	test_equal_connections( 1, 1000000);
+	test_equal_connections( 1, 6000000);
 }
 
 TORRENT_TEST(conn_var_rate)