Simpler implementation of PMTU discovery (with 1400 cap)

network.cpp

@@ -82,6 +82,7 @@ Connection::Connection() /* server */
     remote_addr(),
     server( true ),
     attached( false ),
+    MTU( SEND_MTU ),
     key(),
     session( key ),
     direction( TO_CLIENT ),
@@ -111,6 +112,7 @@ Connection::Connection( const char *key_str, const char *ip, int port ) /* clien
     remote_addr(),
     server( false ),
     attached( false ),
+    MTU( SEND_MTU ),
     key( key_str ),
     session( key ),
     direction( TO_SERVER ),
@@ -134,12 +136,6 @@ Connection::Connection( const char *key_str, const char *ip, int port ) /* clien
     throw NetworkException( buffer, saved_errno );
   }
 
-  /*
-  if ( connect( sock, (sockaddr *)&remote_addr, sizeof( remote_addr ) ) < 0 ) {
-    throw NetworkException( "connect", errno );
-  }
-  */
-
   attached = true;
 }
 
@@ -154,7 +150,10 @@ void Connection::send( string s )
   ssize_t bytes_sent = sendto( sock, p.data(), p.size(), 0,
 			       (sockaddr *)&remote_addr, sizeof( remote_addr ) );
 
-  if ( bytes_sent == static_cast<int>( p.size() ) ) {
+  if ( (bytes_sent < 0) && (errno == EMSGSIZE) ) {
+    update_MTU();
+    throw NetworkException( "Path MTU Discovery", EMSGSIZE );
+  } else if ( bytes_sent == static_cast<int>( p.size() ) ) {
     return;
   } else {
     throw NetworkException( "sendto", errno );
@@ -289,3 +288,50 @@ uint64_t Connection::timeout( void ) const
   }
   return RTO;
 }
+
+class Socket {
+public:
+  int fd;
+
+  Socket( int domain, int type, int protocol )
+    : fd( socket( domain, type, protocol ) )
+  {
+    if ( fd < 0 ) {
+      throw NetworkException( "socket", errno );
+    }
+  }
+
+  ~Socket()
+  {
+    if ( close( fd ) < 0 ) {
+      throw NetworkException( "close", errno );
+    }
+  }
+};
+
+void Connection::update_MTU( void )
+{
+  if ( !attached ) {
+    return;
+  }
+
+  /* We don't want to use our main socket because we don't want to have to connect it */
+  Socket path_MTU_socket( AF_INET, SOCK_DGRAM, 0 );
+
+  /* Connect socket so we can retrieve path MTU */
+  if ( connect( path_MTU_socket.fd, (sockaddr *)&remote_addr, sizeof( remote_addr ) ) < 0 ) {
+    throw NetworkException( "connect", errno );
+  }
+
+  int PMTU;
+  socklen_t optlen = sizeof( PMTU );
+  if ( getsockopt( path_MTU_socket.fd, IPPROTO_IP, IP_MTU, &PMTU, &optlen ) < 0 ) {
+    throw NetworkException( "getsockopt", errno );
+  }
+
+  if ( optlen != sizeof( PMTU ) ) {
+    throw NetworkException( "Error getting path MTU", errno );
+  }
+
+  MTU = max( PMTU, SEND_MTU );
+}

network.hpp

@@ -63,6 +63,8 @@ namespace Network {
     bool server;
     bool attached;
 
+    int MTU;
+
     Base64Key key;
     Session session;
 
@@ -80,6 +82,8 @@ namespace Network {
 
     Packet new_packet( string &s_payload );
 
+    void update_MTU( void );
+
   public:
     Connection();
     Connection( const char *key_str, const char *ip, int port );
@@ -87,7 +91,7 @@ namespace Network {
     void send( string s );
     string recv( void );
     int fd( void ) const { return sock; }
-    int get_MTU( void ) const { return SEND_MTU; }
+    int get_MTU( void ) const { return MTU; }
 
     int port( void ) const;
     string get_key( void ) const { return key.printable_key(); }