recvfrom in UDP not getting anything

Question

i'm trying to receive data on a UDP socket, but I cant find a way to receive anything.

I can see with wireshark that the data is actually coming to the computer, but recvfrom always timeout.

The involved code is pretty simple :

mUDPSocket = socket( AF_INET, SOCK_DGRAM, IPPROTO_UDP );
if( mUDPSocket == INVALID_SOCKET )
    return 1;

uint32_t aTimeout = 5000;
const int lResult = setsockopt( mUDPSocket, SOL_SOCKET, SO_RCVTIMEO, ( char * )&aTimeout, sizeof( aTimeout ) );

if( SOCKET_ERROR == lResult )
    return 1;

struct sockaddr_in addr = {};
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = htonl( INADDR_ANY ); //also tried with my local ip
addr.sin_port = htons( 48640 );

if( bind( mUDPSocket, ( const sockaddr * )&addr, sizeof( addr ) ) < 0 )
    return 1;

And later when trying to receive data

if(recvfrom( mUDPSocket, ( char * )aData, aSize, 0, NULL, 0 )<0) //function return -1
    std::cout << WSAGetLastError() << std::endl; //10060

Im trying to do something basic, so I guess im missing something simple.

Edit : the packet is sent several time by second and the timeout is 5second, so I should receive it before the real timeout

I've attached a screen of the wireshark capture

you got WSAETIMEDOUT. you yourself set some timeout aTimeout on socket and it expired before you got any datagram — RbMm
What is the actual value of lResult when recvfrom() exits? How is LAST_ERROR being set? Please provide a minimal reproducible example, and the actual Wireshark capture (or a screenshot of it) showing the details of the datagram that recvfrom() is not receiving. Just because a packet arrives on the machine does not guarantee it gets routed to an active socket. — Remy Lebeau
It isn't valid to call WSALastError() unless there was am error. Was there? — user207421

Remy Lebeau Remy Lebeau · Accepted Answer · 2017-10-25T21:33:04

The only way I can see the code as shown timing out is if either:

the datagram is not arriving before aTimeout elapses (what is the actual value of aTimeout?)
the datagram is not using IPv4
the datagram is not being sent to an IP on the machine, or is not being sent to port 48640
the datagram is being blocked, such as by a firewall.

recvfrom in UDP not getting anything

1 Answers