c - How to solve: sending UDP packet using Sendto() got "message too long"

Question

I want to use the sendto() API to send video and audio data through UDP packet. The sending buffer size I got using getsockopt() is 114688, however, sendto() returned -1 when the data packet less than 65536 not 114688. And the error message is Message too long.

When I used setsockopt() to adjust the sending buffer size as 200000, I used getsockopt() and found the sending buffer size was not 200000 but 262142. So I still got the same error when I sent data packet with a size bigger than 65536.

I am confused about this situation. I want to know what the reason is and how to solve this problem.

When I used FFMPEG library to send the video and audio packet, there is no error. So I am sure there is a solution for this problem and I missed something.

Is there anyone can help me about this problem? I really can not understand what the reason is.

The OS I used is ubuntu 11.04,I got the same results in ubuntu 11.10.

That is the code I used to create socket and configure the parameter：

unsigned char *output_buffer = (unsigned char*)av_malloc(IO_BUFFER_SIZE);
if (NULL == output_buffer) {
    printf("Couldn't allocate input buffer.
");
    return NULL;
}

output_context_data_t *context_data = (output_context_data_t *)malloc(sizeof(output_context_data_t));
if (NULL == context_data) {
    printf("Could not allocate output context data.
");
    av_free(output_buffer);
    return NULL;
}

context_data->socket = socket(AF_INET, SOCK_DGRAM, 0);
if(context_data->socket < 0) {
    printf("socket creating fail!
");
    return NULL;    
}

context_data->socket_addr->sin_family = AF_INET;
context_data->socket_addr->sin_port = htons(output_port);
ret = inet_pton(AF_INET, output_ip, &(context_data->socket_addr->sin_addr));
if(0 == ret) {
    printf("inet_pton fail!
");
    return NULL;
}

ret = setsockopt(context_data->socket, IPPROTO_IP, IP_MULTICAST_TTL,
                    &option_ttl, sizeof(int));
if(ret < 0) {
    printf("ttl configuration fail!
");
    return NULL;
}

ret = setsockopt(context_data->socket, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(int));
if(ret < 0) {
    printf("resue configuration fail!
");
    return NULL;
}   

That is the code to send UDP packet：

int send_size = sendto(context_data->socket, buf, buf_size, 0,
                      (struct sockaddr *)context_data->socket_addr, sizeof(*context_data->socket_addr)));
//the video or audio data is in buf and its size is buf_size.

That is the code I used to get the sending buffer size：

int bufsize; 
int size = sizeof(bufsize);
getsockopt(context_data->socket,SOL_SOCKET, SO_SNDBUF, &bufsize, &size);

That is the code I used to configure the sending buffer size：

tmp = 200000;
ret = setsockopt(context_data->socket, SOL_SOCKET, SO_SNDBUF, &tmp, sizeof(tmp));
if(ret < 0) {
    printf("sending buffer size configuration fail!
");
    return NULL;
}

Answer 1

You can not send messages (datagrams) larger than 2^16 65536 octets with UDP. The length field of a UDP packet is 16 bits. The buffer sizes you're requesting are not about the size for a packet, but how many octets the OS does buffer incoming and outgoing in total (spread over multiple packets). But a single packet can not get larger.