From 5376ed199622117403c51d1aef1733b1f3c5b7d8 Mon Sep 17 00:00:00 2001
From: Keith Winstein <keithw@mit.edu>
Date: Mon, 13 Aug 2012 16:48:25 +0300
Subject: [PATCH] Use end-to-end-to-end connectivity (in transport layer) to
 control port hop.

Avoid playing games with network-layer timestamps.
---
 src/network/network.cc          | 36 +++++++++++++++++++++++++--------
 src/network/network.h           | 11 +++++++++-
 src/network/networktransport.cc |  3 +++
 3 files changed, 41 insertions(+), 9 deletions(-)

diff --git a/src/network/network.cc b/src/network/network.cc
index 72af284..907b1d3 100644
--- a/src/network/network.cc
+++ b/src/network/network.cc
@@ -107,17 +107,15 @@ Packet Connection::new_packet( string &s_payload )
   return p;
 }
 
-void Connection::reset( void )
+void Connection::hop_port( void )
 {
-  if ( server ) {
-    has_remote_addr = false;
-  } else { /* client */
-    if ( close( sock ) < 0 ) {
-      throw NetworkException( "close", errno );
-    }
+  assert( !server );
 
-    setup();
+  if ( close( sock ) < 0 ) {
+    throw NetworkException( "close", errno );
   }
+
+  setup();
 }
 
 void Connection::setup( void )
@@ -128,6 +126,8 @@ void Connection::setup( void )
     throw NetworkException( "socket", errno );
   }
 
+  last_port_choice = timestamp();
+
   /* Disable path MTU discovery */
 #ifdef HAVE_IP_MTU_DISCOVER
   char flag = IP_PMTUDISC_DONT;
@@ -157,6 +157,9 @@ Connection::Connection( const char *desired_ip, const char *desired_port ) /* se
     saved_timestamp( -1 ),
     saved_timestamp_received_at( 0 ),
     expected_receiver_seq( 0 ),
+    last_heard( -1 ),
+    last_port_choice( -1 ),
+    last_roundtrip_success( -1 ),
     RTT_hit( false ),
     SRTT( 1000 ),
     RTTVAR( 500 ),
@@ -266,6 +269,9 @@ Connection::Connection( const char *key_str, const char *ip, int port ) /* clien
     saved_timestamp( -1 ),
     saved_timestamp_received_at( 0 ),
     expected_receiver_seq( 0 ),
+    last_heard( -1 ),
+    last_port_choice( -1 ),
+    last_roundtrip_success( -1 ),
     RTT_hit( false ),
     SRTT( 1000 ),
     RTTVAR( 500 ),
@@ -307,6 +313,19 @@ void Connection::send( string s )
     have_send_exception = true;
     send_exception = NetworkException( "sendto", errno );
   }
+
+  uint64_t now = timestamp();
+  if ( server ) {
+    if ( now - last_heard > SERVER_ASSOCIATION_TIMEOUT ) {
+      has_remote_addr = false;
+      fprintf( stderr, "Server now detached from client.\n" );
+    }
+  } else { /* client */
+    if ( ( now - last_port_choice > PORT_HOP_INTERVAL )
+	 && ( now - last_roundtrip_success > PORT_HOP_INTERVAL ) ) {
+      hop_port();
+    }
+  }
 }
 
 string Connection::recv( void )
@@ -364,6 +383,7 @@ string Connection::recv( void )
 
     /* auto-adjust to remote host */
     has_remote_addr = true;
+    last_heard = timestamp();
 
     if ( server ) { /* only client can roam */
       if ( (remote_addr.sin_addr.s_addr != packet_remote_addr.sin_addr.s_addr)
diff --git a/src/network/network.h b/src/network/network.h
index 4c42967..765990b 100644
--- a/src/network/network.h
+++ b/src/network/network.h
@@ -91,6 +91,9 @@ namespace Network {
     static const int PORT_RANGE_LOW  = 60001;
     static const int PORT_RANGE_HIGH = 60999;
 
+    static const unsigned int SERVER_ASSOCIATION_TIMEOUT = 20000;
+    static const unsigned int PORT_HOP_INTERVAL          = 20000;
+
     static bool try_bind( int socket, uint32_t addr, int port );
 
     int sock;
@@ -112,6 +115,10 @@ namespace Network {
     uint64_t saved_timestamp_received_at;
     uint64_t expected_receiver_seq;
 
+    uint64_t last_heard;
+    uint64_t last_port_choice;
+    uint64_t last_roundtrip_success; /* transport layer needs to tell us this */
+
     bool RTT_hit;
     double SRTT;
     double RTTVAR;
@@ -123,6 +130,8 @@ namespace Network {
 
     Packet new_packet( string &s_payload );
 
+    void hop_port( void );
+
   public:
     Connection( const char *desired_ip, const char *desired_port ); /* server */
     Connection( const char *key_str, const char *ip, int port ); /* client */
@@ -147,7 +156,7 @@ namespace Network {
       return have_send_exception ? &send_exception : NULL;
     }
 
-    void reset( void );
+    void set_last_roundtrip_success( uint64_t s_success ) { last_roundtrip_success = s_success; }
   };
 }
 
diff --git a/src/network/networktransport.cc b/src/network/networktransport.cc
index 7db4ef6..150f444 100644
--- a/src/network/networktransport.cc
+++ b/src/network/networktransport.cc
@@ -80,6 +80,9 @@ void Transport<MyState, RemoteState>::recv( void )
 
     sender.process_acknowledgment_through( inst.ack_num() );
 
+    /* inform network layer of roundtrip (end-to-end-to-end) connectivity */
+    connection.set_last_roundtrip_success( sender.get_sent_state_acked_timestamp() );
+
     /* first, make sure we don't already have the new state */
     for ( typename list< TimestampedState<RemoteState> >::iterator i = received_states.begin();
 	  i != received_states.end();