[asio-users] Question regarding asio::placeholders::bytes_transferred

[Jay A. P. <jay...@ui...>]

Hi,

Let us jump directly to code first. Here are the relevant chunks of code:

----chunk #1----

udp_server->async_receive_from(
   asio::buffer(_inbound_udp_data, MAX_STR_LEN),
   _incoming_udp_remote_endpoint,
   boost::bind(&Transport::handle_udp_read,
     this,
     asio::placeholders::error,
     asio::placeholders::bytes_transferred));

Note: _inbound_udp_data is char[MAX_STR_LEN], udp_server is an active 
server socket.

----chunk #2----

void Transport::handle_udp_read(const asio::error& error,
   size_t bytes_recvd) {

   if (!error) {

     printf("gotten msg:[[%s]]\n", _inbound_udp_data);
     printf("msg str_size: %u; bytes_recvd: %u\n",
       strlen(_inbound_udp_data), bytes_recvd);
   }
}

--------------

The code was compiled and successfully run between two different hosts 
on the Internet (multiple hops away). However, when some messages are 
received, bytes_recvd < strlen(_inbound_udp_data). Shouldn't they be 
equal? The value of _inbound_udp_data and that of 
strlen(_inbound_udp_data) is correct. In other words, bytes_recvd is 
much smaller than it should be.

A wild guess: Is this related to layer-2 fragmentation due to MTU? Does 
bytes_recvd get the value of the bytes read from the last network frame 
only? Note that the packet data is no longer than ~300 bytes.

I'm a bit confused. Any pointers will be greatly appreciated. Exposing 
stupidity (on my part) will be an added bonus.

Cheers,
Jay.

PS: Please CC me to reply. I do not monitor this mailing list yet.