I have a program that sends arp packets to all hosts in a network to figure out which ones are up, which works fine so far.
I just have some difficulties setting a proper timeout for the reply, so far I got this:
struct timeval tv;
tv.tv_sec = 0;
tv.tv_usec = 10000; //0.01sec
if (setsockopt(sock_fd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv)) < 0) {
...
}
...
if ((bytes = sendto(sock_fd, ether_frame, packet_length, 0, (struct sockaddr *) &device, sizeof (device))) <= 0) {
//error handle
} else {
if ((bytes = recv(sock_fd, packet, sizeof(packet), 0)) <= 0) {
...
} else {
...
When running the program with the above set value of 0.01sec, I sometimes get all replies and sometimes some replies are missing. When I increase the value to e.g. 1sec I get all values. But since there are a lot of requests to send, with 1sec it takes a huge amount of time till it finishes.
Is there a better way to calculate the timeout for the replies? Probably dynamically?
Related
A simple summary:
boost asio server, send a video frame 720x768x3 with simple compression
packet size is 186476, not really to much
nothing to complicated, anyway, if i test it in the hololens emulator or on the physical device
// uint32_t data_length == size of frame 'data_ptr'
enum max_length = sizeof(uint32_t);
memcpy(data_, &data_length, max_length);
auto length = boost::asio::write(*socket_, boost::asio::buffer(data_, max_length), e);
length = boost::asio::write(*socket_, boost::asio::buffer(data_ptr, data_length), e);
// receive
char data_[max_length] = { 0 };
fd_set readSet;
FD_ZERO(&readSet);
FD_SET(_socket, &readSet);
timeval timeout;
timeout.tv_sec = 0; // Zero timeout (poll)
timeout.tv_usec = 0;
auto result = select(_socket, &readSet, nullptr, nullptr, &timeout);
if (result == 0)
continue;
result = recv(_socket, data_, max_length, 0);
if (result == SOCKET_ERROR) {
closesocket(_socket);
_socket = INVALID_SOCKET;
break;
}
uint32_t msg_size(0);
memcpy(&msg_size, data_, max_length);
std::vector<char> vec(msg_size);
result = recv(_socket, &vec[0], msg_size, 0);
while (result < msg_size) {
result += recv(_socket, &vec[result], msg_size - result, 0);
}
but the hololens can't receive the full packet, i try it also with the .net streamsockets, same result. it tried a few times and then recv blocks in the while loop and doesn't receive anymore.
anyone, any idea? is it an uwp app problem, that i can't receive 'bigger' packets, or get it killed because it takes too long?
You have two main problems:
First, you need to check the return value of recv for errors. If it returns 0 or -1, you need to handle that.
Second, you ignore all the data you received from your first call to recv. You set msg_size to zero when it should be result minus however many bytes the length took.
I would suggest writing a function that reads exactly the specified number of bytes, checking for errors. Call it first to receive four bytes and check if it returned an error. Then call it to receive the number of bytes indicated by the length data you received.
Smaller problems include:
What if the first recv only returns one byte?
What if the way your platform stores 32-bit integers isn't the same as the way the emulator sends it?
I don't see these sort of question asked. Which is odd because of good benefits from single threaded server applications. But how would I be able to implement a timeout system in my code when the server is in nonblock state?
Currently I'm using this method.
while(true)
{
FD_ZERO(&readfds);
FD_SET(server_socket, &readfds);
for (std::size_t i = 0; i < cur_sockets.size(); i++)
{
uint32_t sd = cur_sockets.at(i).socket;
if(sd > 0)
FD_SET(sd, &readfds);
if(sd > max_sd){
max_sd = sd;
}
}
int activity = select( max_sd + 1 , &readfds, NULL , NULL, NULL);
if(activity < 0)
{
continue;
}
if (FD_ISSET(server_socket, &readfds))
{
struct sockaddr_in cli_addr;
uint32_t newsockfd = (uint_fast32_t)accept((int)server_socket,
(struct sockaddr *) &cli_addr,
&clientlength);
if(newsockfd < 1) {
continue;
}
//Ensure we can even accept the client...
if (num_clients >= op_max_clients) {
close(newsockfd);
continue;
}
fcntl(newsockfd, F_SETFL, O_NONBLOCK);
/* DISABLE TIMEOUT EXCEPTION FROM SIGPIPE */
#ifdef __APPLE__
int set = 1;
setsockopt(newsockfd, SOL_SOCKET, SO_NOSIGPIPE, (void *) &set, sizeof(int));
#elif __LINUX__
signal(SIGPIPE, SIG_IGN);
#endif
/* ONCE WE ACCEPTED THE CONNECTION ADD CLIENT TO */
num_clients++;
client_con newCon;
newCon.socket = newsockfd;
time_t ltime;
time(<ime);
newCon.last_message = (uint64_t) ltime;
cur_sockets.push_back(newCon);
}
handle_clients();
}
As you can tell, I've added a unix timestap to the client when they successfully connected. I was thinking of maybe adding another thread that sleeps every 1 second, and simply checks if any clients haven't made any sends for the max duration, but I'm afraid I'll run into bottlenecking because of the second thread locking up constantly when dealing with large amounts of connections.
Thank you,
Ajm.
The last argument for select is the timeout for the select call and the return code of select tells you, if it returned because a socket was ready or because of a timeout.
In order to implement your own timeout handling for all sockets you could have a time stamp for each socket and update it on any socket operation. Then before calling select compute the timeout for each socket and use the minimal value for the timeout of the select call. This is just the basic idea and one can implement it more efficient so that you don't need to recompute all timeouts before calling select. But I consider a separate thread overkill.
I am trying to set a 100ms timeout on a UDP Socket. I am using C. I have posted relavent pieces of my code below. I am not sure why this is not timing out, but just hangs when it doesn't receive a segment. Does this only work on sockets that are not bound using the bind() method?
#define TIMEOUT_MS 100 /* Seconds between retransmits */
if ((rcv_sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0)
DieWithError("socket() failed");
if ((rcv_sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0)
DieWithError("socket() failed");
//set timer for recv_socket
static int timeout = TIMEOUT_MS;
setsockopt(rcv_sock, SOL_SOCKET, SO_RCVTIMEO,(char*)&timeout,sizeof(timeout));
if(recvfrom(rcv_sock, ackBuffer,sizeof(ackBuffer), 0,
(struct sockaddr *) &servAddr2, &fromSize) < 0){
//timeout reached
printf("Timout reached. Resending segment %d\n", seq_num);
num_timeouts++;
}
The SO_RCVTIMEO option expects a struct timeval defined in sys/time.h, not an integer like you're passing to it. The timeval struct has as field for seconds and a field for microseconds. To set the timeout to 100ms, the following should do the trick:
struct timeval tv;
tv.tv_sec = 0;
tv.tv_usec = 100000;
if (setsockopt(rcv_sock, SOL_SOCKET, SO_RCVTIMEO,&tv,sizeof(tv)) < 0) {
perror("Error");
}
I have the same problem. I tried to adopt the solution you suggested, using the timeval struct. But it did not seem to work.
I have read on the Microsoft documentation and the time should be a DWORD with the number of milliseconds, but there is also another thing to do, If the socket is created using the WSASocket function, then the dwFlags parameter must have the WSA_FLAG_OVERLAPPED attribute set for the timeout to function properly.
Otherwise the timeout never takes effect.
I seem to have an issue with increasing latency on my packet transmission with my TCP server. Now, this server has to be TCP, since UDP is blocked by firewalls (this is a client-server-client type of communication). I'm also aware that the sending of a struct with floating point integers as I am is extremely non-portable, however, this system will operate Windows client to Windows server to Windows client for the foreseeable future.
The issue is this: the client begins receiving the data properly from the other client, however, there is a delay which gets exponentially worse (where, by about 3 minutes in, the packets are nearly 30 seconds behind - but correct, when they DO arrive). I researched it and found an answer on a Microsoft page explaining it is due to full send buffers, however, their syntax for the setsockopt doesn't match the documented examples, so perhaps I'm wrong.
Anyway, any advice would be appreciated:
The relevant part of the server:
(When accept() is called:)
int buff_size = 2048000;
int nodel = 1;
setsockopt(sock, SOL_SOCKET, SO_SNDBUF, (char*)&buff_size, sizeof(int));
setsockopt(sock, SOL_SOCKET, SO_RCVBUF, (char*)&buff_size, sizeof(int));
setsockopt(sock, IPPROTO_TCP, TCP_NODELAY, (char*)&nodel, sizeof(nodel));
The message redirect loop:
if (gp->curr_pilot < sz && gp->users[gp->curr_pilot].pilot == TRUE) {
char* pbuf = new char[1024];
int recvd = recv(gp->users[gp->curr_pilot].sockfd_data, pbuf, 1024, NULL);
if (recvd > 0) {
for (int i = 0; i < sz; i++) {
if (i != gp->curr_pilot && gp->users[i].unioned == TRUE)
send(gp->users[i].sockfd_data, pbuf, recvd, NULL);
}
}
delete[] pbuf;
}
The client (master is set when it's sending, and it does get set properly by my code):
(data is my struct of doubles that gets written by the client, cdata is a copy of it that gets written into the client).
while (kill_dataproc == FALSE) {
if (master == TRUE) {
char* buff = new char[1024];
int packet_signer = 1192;
memcpy_s(buff, intsz, &packet_signer, intsz);
memcpy_s((void*)(buff + intsz), sz, data, sz);
send(server_sock, buff, buffsize, NULL);
delete[] buff;
}
else {
char* buffer = new char[1024];
int recvd = recv(server_sock, buffer, 1024, MSG_PEEK);
if (recvd > 0) {
int newpacketsigner = 0;
memcpy_s(&newpacketsigner, intsz, buffer, intsz);
if (newpacketsigner == 1192) {
if (recvd >= buffsize) {
char* nbuf = new char[buffsize];
int recvd2 = recv(server_sock, nbuf, buffsize, NULL);
int err = WSAGetLastError();
memcpy_s(&newpacketsigner, intsz, nbuf, intsz);
memcpy_s(cdata, sz, (void*)(nbuf + intsz), sz);
//do things w/ the struct
delete[] nbuf;
}
}
else
recv(server_sock, buffer, 1024, NULL);
}
delete[] buffer;
}
Sleep(10);
}
As well, identical calls to setsockopt and are called for the client's sockets, and all of the sockets, server and client, are nonblocking.
You're assuming that your reads are filling the buffer. They are only obliged to transfer at least one byte. You you need to loop.
So, you have unread data backing up and stalling the sender.
NB Those receive buffers are greater than 64k and so may be inoperative unless they are set before the socket is connected. In the case of the server you need to set the receive buffer size on the listening socket. Accepted sockets will inherit it. If you don't to it his way, window scaling won't be in effect so a window > 64k cannot be advertised (unless the platform has window scaling on by default).
I have written simple C/S applications to test the characteristics of non-blocking sockets, here is some brief information about the server and client:
//On linux The server thread will send
//a file to the client using non-blocking socket
void *SendFileThread(void *param){
CFile* theFile = (CFile*) param;
int sockfd = theFile->GetSocket();
set_non_blocking(sockfd);
set_sock_sndbuf(sockfd, 1024 * 64); //set the send buffer to 64K
//get the total packets count of target file
int PacketCOunt = theFile->GetFilePacketsCount();
int CurrPacket = 0;
while (CurrPacket < PacketCount){
char buffer[512];
int len = 0;
//get packet data by packet no.
GetPacketData(currPacket, buffer, len);
//send_non_blocking_sock_data will loop and send
//data into buffer of sockfd until there is error
int ret = send_non_blocking_sock_data(sockfd, buffer, len);
if (ret < 0 && errno == EAGAIN){
continue；
} else if (ret < 0 || ret == 0 ){
break;
} else {
currPacket++;
}
......
}
}
//On windows, the client thread will do something like below
//to receive the file data sent by the server via block socket
void *RecvFileThread(void *param){
int sockfd = (int) param; //blocking socket
set_sock_rcvbuf(sockfd, 1024 * 256); //set the send buffer to 256
while (1){
struct timeval timeout;
timeout.tv_sec = 1;
timeout.tv_usec = 0;
fd_set rds;
FD_ZERO(&rds);
FD_SET(sockfd, &rds)'
//actually, the first parameter of select() is
//ignored on windows, though on linux this parameter
//should be (maximum socket value + 1)
int ret = select(sockfd + 1, &rds, NULL, NULL, &timeout );
if (ret == 0){
// log that timer expires
CLogger::log("RecvFileThread---Calling select() timeouts\n");
} else if (ret) {
//log the number of data it received
int ret = 0;
char buffer[1024 * 256];
int len = recv(sockfd, buffer, sizeof(buffer), 0);
// handle error
process_tcp_data(buffer, len);
} else {
//handle and break;
break;
}
}
}
What surprised me is that the server thread fails frequently because of socket buffer full, e.g. to send a file of 14M size it reports 50000 failures with errno = EAGAIN. However, via logging I observed there are tens of timeouts during the transfer, the flow is like below:
on the Nth loop, select() succeeds and read 256K's data successfully.
on the (N+1)th loop, select() failed with timeout.
on the (N+2)th loop, select() succeeds and read 256K's data successfully.
Why there would be timeouts interleaved during the receving? Can anyone explain this phenomenon?
[UPDATE]
1. Uploading a file of 14M to the server only takes 8 seconds
2. Using the same file with 1), the server takes nearly 30 seconds to send all data to the client.
3. All sockets used by the client are blocking. All sockets used by the server are non-blocking.
Regarding #2, I think timeouts are the reason why #2 takes much more time then #1, and I wonder why there would be so many timeouts when the client is busy in receiving data.
[UPDATE2]
Thanks for comments from #Duck, #ebrob, #EJP, #ja_mesa , I will do more investigation today
then update this post.
Regarding why I send 512 bytes per loop in the server thread, it is because I found the server thread sends data much faster than the client thread receiving them. I am very confused that why timeout happened to the client thread.
Consider this more of a long comment than an answer but as several people have noted the network is orders of magnitude slower than your processor. The point of non-blocking i/o is that the difference is so great that you can actually use it to do real work rather than blocking. Here you are just pounding on the elevator button hoping that makes a difference.
I'm not sure how much of your code is real and how much is chopped up for posting but in the server you don't account for (ret == 0) i.e. normal shutdown by the peer.
The select in the client is wrong. Again, not sure if that was sloppy editing or not but if not then the number of parameters are wrong but, more concerning, the first parameter - i.e. should be the highest file descriptor for select to look at plus one - is zero. Depending on the implementation of select I wonder if that is in fact just turning select into a fancy sleep statement.
You should be calling recv() first and then call select() only if recv() tells you to do so. Don't call select() first, that is a waste of processing. recv() knows if data is immediately available or if it has to wait for data to arrive:
void *RecvFileThread(void *param){
int sockfd = (int) param; //blocking socket
set_sock_rcvbuf(sockfd, 1024 * 256); //set the send buffer to 256
char buffer[1024 * 256];
while (1){
int ret = 0;
int len = recv(sockfd, buffer, sizeof(buffer), 0);
if (len == -1) {
if (WSAGetLastError() != WSAEWOULDBLOCK) {
//handle error
break;
}
struct timeval timeout;
timeout.tv_sec = 1;
timeout.tv_usec = 0;
fd_set rds;
FD_ZERO(&rds);
FD_SET(sockfd, &rds)'
//actually, the first parameter of select() is
//ignored on windows, though on linux this parameter
//should be (maximum socket value + 1)
int ret = select(sockfd + 1, &rds, NULL, &timeout );
if (ret == -1) {
// handle error
break;
}
if (ret == 0) {
// log that timer expires
break;
}
// socket is readable so try read again
continue;
}
if (len == 0) {
// handle graceful disconnect
break;
}
//log the number of data it received
process_tcp_data(buffer, len);
}
}
Do something similar on the sending side as well. Call send() first, and then call select() waiting for writability only if send() tells you to do so.