Deliver sendto() exceptions without disturbing control flow

This prevents the client from waking up every 200 ms while the network is down.
Addresses #243.

src/frontend/stmclient.cc

@@ -415,6 +415,11 @@ void STMClient::main( void )
       }
 
       network->tick();
+
+      const Network::NetworkException *exn = network->get_send_exception();
+      if ( exn ) {
+        overlays.get_notification_engine().set_network_exception( *exn );
+      }
     } catch ( Network::NetworkException e ) {
       if ( !network->shutdown_in_progress() ) {
         overlays.get_notification_engine().set_network_exception( e );

src/network/network.cc

@@ -131,7 +131,9 @@ Connection::Connection( const char *desired_ip, const char *desired_port ) /* se
     expected_receiver_seq( 0 ),
     RTT_hit( false ),
     SRTT( 1000 ),
-    RTTVAR( 500 )
+    RTTVAR( 500 ),
+    have_send_exception( false ),
+    send_exception()
 {
   setup();
 
@@ -238,7 +240,9 @@ Connection::Connection( const char *key_str, const char *ip, int port ) /* clien
     expected_receiver_seq( 0 ),
     RTT_hit( false ),
     SRTT( 1000 ),
-    RTTVAR( 500 )
+    RTTVAR( 500 ),
+    have_send_exception( false ),
+    send_exception()
 {
   setup();
 
@@ -266,9 +270,14 @@ void Connection::send( string s )
   ssize_t bytes_sent = sendto( sock, p.data(), p.size(), 0,
 			       (sockaddr *)&remote_addr, sizeof( remote_addr ) );
 
-  if ( (!server) /* Server treats all sendto()s as successful. */
+  if ( bytes_sent == static_cast<ssize_t>( p.size() ) ) {
-       && (bytes_sent != static_cast<ssize_t>( p.size() )) ) {
+    have_send_exception = false;
-    throw NetworkException( "sendto", errno );
+  } else {
+    /* Notify the frontend on sendto() failure, but don't alter control flow.
+       sendto() success is not very meaningful because packets can be lost in
+       flight anyway. */
+    have_send_exception = true;
+    send_exception = NetworkException( "sendto", errno );
   }
 }
 

src/network/network.h

@@ -42,6 +42,7 @@ namespace Network {
     string function;
     int the_errno;
     NetworkException( string s_function, int s_errno ) : function( s_function ), the_errno( s_errno ) {}
+    NetworkException() : function( "<none>" ), the_errno( 0 ) {}
   };
 
   enum Direction {
@@ -101,6 +102,11 @@ namespace Network {
     double SRTT;
     double RTTVAR;
 
+    /* Exception from send(), to be delivered if the frontend asks for it,
+       without altering control flow. */
+    bool have_send_exception;
+    NetworkException send_exception;
+
     Packet new_packet( string &s_payload );
 
   public:
@@ -121,6 +127,11 @@ namespace Network {
     double get_SRTT( void ) const { return SRTT; }
 
     const struct in_addr & get_remote_ip( void ) const { return remote_addr.sin_addr; }
+
+    const NetworkException *get_send_exception( void ) const
+    {
+      return have_send_exception ? &send_exception : NULL;
+    }
   };
 }
 

src/network/networktransport.h

@@ -102,6 +102,8 @@ namespace Network {
     unsigned int send_interval( void ) const { return sender.send_interval(); }
 
     const struct in_addr & get_remote_ip( void ) const { return connection.get_remote_ip(); }
+
+    const NetworkException *get_send_exception( void ) const { return connection.get_send_exception(); }
   };
 }