I'm trying to write some code under Windows 7 to broadcast across my local network and can't get the following code to work. I come from a Linux background so apologies for style - the full code compiles etc and works and if I use an address of:
unsigned long broadcastAddr = inet_addr("192.168.10.0") | ~(inet_addr("255.255.240.0"));
Then that works fine, I just would really like to use the preferred INADDR_BROADCAST/255.255.255.255 method.
<snip>
SOCKET sockfd;
int broadcast = 1;
WSADATA wsaData; // Windows socket
// Initialize Winsock
if (WSAStartup(MAKEWORD(2,2), &wsaData) == SOCKET_ERROR) {
perror("WinSock Error");
getc(stdin);
exit(EXIT_FAILURE);
}
if ((sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1) {
perror("Socket Error");
getc(stdin);
exit(1);
}
if ((setsockopt(sockfd, SOL_SOCKET, SO_BROADCAST, (char *)&broadcast, sizeof(broadcast))) == SOCKET_ERROR) {
perror("Setsockopt - SOL_SOCKET");
getc(stdin);
exit(1);
}
struct sockaddr_in recvaddr;
recvaddr.sin_family = AF_INET;
recvaddr.sin_port = htons(PORT);
recvaddr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
memset(recvaddr.sin_zero,'\0', sizeof(recvaddr.sin_zero));
int numbytes = 0;
while ((numbytes = sendto(sockfd, greet, strlen(greet) , MSG_DONTROUTE, (struct sockaddr *)&recvaddr, sizeof(struct sockaddr_in))) != -1) {
printf("Sent a packet %d\n", numbytes);
Sleep(100);
}
There is a huge bug in Windows 7 for UDP broadcast which makes broadcasting on 255.255.255.255 not work on most windows 7 install: https://serverfault.com/questions/72112/how-to-alter-the-global-broadcast-address-255-255-255-255-behavior-on-windows
Basically it will send the broadcast only on a single network interface, which could be anything, even something like a VM network interface or bluetooth one, which can end up not broadcasting to any device.
Unless my bit maths is out, inet_addr("192.168.10.0") | ~(inet_addr("255.255.240.0")) is the same as inet_addr("192.168.15.255") which is the broadcast address for that subnet.
It looks to me like the most likely possibility is not that the sending code is wrong but that the receiving code is wrong. What address have you bound the receiving socket to? What subnet is it on?
Related
I have an application installed locally (not developed by me), which broadcasts UDP packets every second.
Reading the packets from my application (developed in C++ in Windows) which also is locally installed, works fine.
WSADATA data;
WORD version = MAKEWORD(2, 2);
int wsOK = WSAStartup(version, &data);
SOCKET serverIn = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
sockaddr_in serverHint;
serverHint.sin_addr.S_un.S_addr = INADDR_ANY;
serverHint.sin_family = AF_INET;
serverHint.sin_port = htons(UDP_RECEIVE_PORT);
bind(serverIn, (sockaddr*)&serverHint, sizeof(serverHint));
sockaddr_in client;
int clientSize = sizeof(client);
int RECIEVE_BUFFER_SIZE = 65507;
char* recieveBuffer = new char[RECIEVE_BUFFER_SIZE];
while(updating)
{
int bytesIn = recvfrom(serverIn, recieveBuffer, RECIEVE_BUFFER_SIZE, 0, (sockaddr*)&client, &clientSize);
}
closesocket(serverIn);
WSACleanup();
But I recently noticed while I was testing some code, while my app was running, that the bind(...)
function returned an error code of 10048 (WSAEADDRINUSE). Hence, it seems the first client bound to listen for the UDP packets is the only one who can listen, and the other clients is unable to read the broadcasted UDP packets.
So then I added the SO_REUSEADDR option before calling the bind(...) function to be able to bind successfully to the socket:
BOOL bOptVal = TRUE;
int bOptLen = sizeof(BOOL);
setsockopt((SOCKET)serverIn, SOL_SOCKET, SO_REUSEADDR, (char*)&bOptVal, bOptLen);
That works, but the recvfrom(...) function then does not recieve any data at all! I guess it waits for the other client to close its socket.
Next solution is to initialize the socket with SOCK_RAW instead.
The above option SO_REUSEADDR is now not needed, and remove it:
SOCKET serverIn = socket(AF_INET, SOCK_RAW, IPPROTO_UDP);
This works, I can read the data now! Though, Windows now requires the adminstrator rights for my application. Also I do recieve the UDP information in the data which I do not need.
Is there any better method to do this without requiring administrator rights, any possibility to discard the header information in the buffer?
Below is a little program I wrote to demonstrate that IPv4 UDP broadcast can and does work as expected under Windows (i.e. without requiring raw-sockets or Administrator privileges).
Run it with the command line argument "server" and it will send out one broadcast UDP packet per second.
Then also run several more instances of the same program, with no command line arguments, to receive the UDP packets and print a line of text to stdout whenever they do. The expected behavior should look like this:
As for why it's not working for you -- one possible guess is that your UDP-packet-sending program is actually sending out unicast UDP packets rather than broadcast. If that's the case, then I would expect that only one client program would receive packets (even if multiple clients are bound to the same port). A network trace tool like Wireshark might be able to help you determine if the UDP packets being sent are broadcast or unicast.
Anyway, here's the code:
#include <stdio.h>
#include <ws2tcpip.h>
#pragma comment(lib,"WS2_32")
static int BindUDPSocket(SOCKET sock, unsigned short port, bool allowPortSharing)
{
if (sock == INVALID_SOCKET) return -1;
if (allowPortSharing)
{
const BOOL trueValue = true;
if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (const char *) &trueValue, sizeof(trueValue)) < 0) return -1;
}
struct sockaddr_in bindAddr; memset(&bindAddr, 0, sizeof(bindAddr));
bindAddr.sin_family = AF_INET;
bindAddr.sin_addr.s_addr = INADDR_ANY; // aka 0.0.0.0
bindAddr.sin_port = htons(port);
return bind(sock, (struct sockaddr *) &bindAddr, sizeof(bindAddr));
}
int main(int argc, char ** argv)
{
WSADATA data;
WORD version = MAKEWORD(2, 2);
(void) WSAStartup(version, &data);
const unsigned short TEST_PORT = 12345;
SOCKET sock = socket(AF_INET, SOCK_DGRAM, 0);
if (sock<0) {printf("socket() failed\n"); exit(10);}
if ((argc > 1)&&(strcmp(argv[1], "server") == 0))
{
if (BindUDPSocket(sock, 0, false)<0) {printf("BindUDPSocket() failed for server\n"); exit(10);}
const BOOL allowBroadcast = true;
if (setsockopt(sock, SOL_SOCKET, SO_BROADCAST, (const char *) &allowBroadcast, sizeof(allowBroadcast)) < 0)
{
printf("setsockopt(SO_BROADCAST) failed\n");
exit(10);
}
const char buf[] = {0x01, 0x02, 0x03, 0x04}; // dummy data
struct sockaddr_in toAddr; memset(&toAddr, 0, sizeof(toAddr));
toAddr.sin_family = AF_INET;
toAddr.sin_addr.s_addr = INADDR_BROADCAST; // aka 255.255.255.255
toAddr.sin_port = htons(TEST_PORT);
printf("Sending outgoing broadcast UDP sockets on port %u, once per second\n", TEST_PORT);
while(true)
{
if (sendto(sock, buf, sizeof(buf), 0, (const sockaddr *) &toAddr, sizeof(toAddr)) == sizeof(buf))
{
printf("Sent %zu bytes of broadcast UDP data\n", sizeof(buf));
}
else printf("sendto() failed!\n");
Sleep(1000); // wait 1 second
}
}
else
{
if (BindUDPSocket(sock, TEST_PORT, true)<0) {printf("BindUDPSocket() failed for client\n"); exit(10);}
printf("Waiting to receive incoming broadcast UDP sockets on port %u\n", TEST_PORT);
while(true)
{
char buf[1024];
const int ret = recv(sock, buf, sizeof(buf), 0L);
printf("Received %i bytes of incoming UDP data\n", ret);
}
}
}
we have a requirement for UDP multicasting in our project using Linux 4.1 kernel
with static ip address.
basic UDP multicasting using sendto function to send data is working fine with device static ip 10.13.204.100, issue comes when i change ip of the device to 10.13.204.101 or any other ip in the same series, the udp multicasting is showing an error
sendto: network unreachable
im initializing the UDP as shown below
int udp_init()
{
char multicastTTL = 10;
// Create UDP socket:
memset(&socket_desc, 0, sizeof(socket_desc));
socket_desc = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (socket_desc < 0)
{
perror("socket");
return 1;
}
udp_socket_fd = socket_desc;
printf("udp_socket_fd=>%d\nsocket_desc==>%d\n", udp_socket_fd, socket_desc);
/* Set the TTL (time to live/hop count) for the send */
// if (setsockopt(socket_desc, IPPROTO_IP, IP_MULTICAST_TTL, &multicastTTL, sizeof(multicastTTL)) < 0)
if (setsockopt(socket_desc, SOL_SOCKET, SO_REUSEADDR, &multicastTTL, sizeof(multicastTTL)) < 0)
{
perror("setsockopt");
exit(1);
}
memset(&server_addr, 0, sizeof(server_addr)); /* Zero out structure */
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = inet_addr(EXAMPLE_GROUP); // INADDR_ANY;
server_addr.sin_port = htons(EXAMPLE_PORT); // htons(udp_port);
// bind to receive address
//
if (bind(socket_desc, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0)
{
perror("bind");
printf("line %s-->%s:%d\n", __FILE__, __FUNCTION__, __LINE__);
return 1;
}
}
once the ip is changed im closing the UDP socket using
close(socket_desc)
once again im using the udp_init function to initialize the UDP then im sending using sendto function to transmit the data but im get sendto:network unreachable
thanks in advance
"sendto: network unreachable" means you do not have a route to the new address, add it or change the mask for the .100 route
I am trying to bind a socket to a particular network interface on my computer. I have two network interfaces named interf0 and interf1. I want bind socket to a particular interface say interf0. My OS is vxWorks 6.2.
I am trying following code:
struct sockaddr_in fromAddr;
struct sockaddr_in sin;
int fromLen;
struct ip_mreq ipMreq;
int sockDesc;
STATUS temp;
if ((sockDesc = socket (AF_INET, SOCK_DGRAM, 0)) < 0)
{
printf (" cannot open recv socket\n");
return ERROR;
}
bzero ((char *)&sin, sizeof (sin));
bzero ((char *) &fromAddr, sizeof(fromAddr));
fromLen = sizeof(fromAddr);
#if 1
if ((temp = setsockopt(sockDesc, SOL_SOCKET, SO_BINDTODEVICE, "interf0", 7)) < 0)
{
perror("Server-setsockopt() error for SO_BINDTODEVICE");
printf("%s\n", strerror(errno));
close(sockDesc);
return ERROR;
}
#endif
sin.sin_len = (u_char) sizeof(sin);
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = INADDR_ANY;
//sin.sin_addr.s_addr = inet_addr(ifAddr);
/* UDP port number to match for the received packets */
sin.sin_port = htons (mcastPort);
/* bind a port number to the socket */
if (bind(sockDesc, (struct sockaddr *)&sin, sizeof(sin)) != 0)
{
perror("bind");
if (sockDesc != ERROR)
{
close (sockDesc);
}
return ERROR;
}
Here, it gives an error saying SO_BINDTODEVICE is not defined.
Is there any other way using which I can bind to a particular interface in vxWorks.
Other ref:
bind socket to network interface
Thank you.
It seems that SO_BINDTODEVICE is not part of POSIX, it's a Linux extension. So VxWorks won't necessarily implement interface binding the same way, if it does it at all. A quick look in the VxWorks manuals looks unpromising.
If you have VxWorks you likely also have access to WindRiver's support, assuming you've kept up with the support fees. If so, ask them too, that's what it's there for.
I would like to ask about the getpeername() function since it returns data as the title states. I tried to get value directly from accept() function, and the result also happens the same. Value of port seems to appear randomly even though value of address is correct(address is 127.0.0.1 since I run multi-processes on an only machine). The return code of getpeername() is 0 (status = 0). I'm using gcc version 4.8.1. I write a peer 2 peer chat application without server. The following is my code:
struct sockaddr_in addr;
socklen_t addr_len;
int tempPort, serverSockfd;
char test[100];
// Get serverSockfd successfully....
serverSockFd = initializeSock(PORT) // In this function I initialize socket(), bind() and listen(), serverSockFd is returned by the value of socket()
addr_len = sizeof addr;
newSock = accept(serverSockfd, (struct sockaddr *)&addr, &addr_len);
tempPort = ntohs(addr.sin_port);
inet_ntop(AF_INET, &(addr.sin_addr), test, sizeof test);
printf("tempPort\t%d\n", tempPort);
printf("test\t%s\n", test);
addr_len = sizeof addr;
if ((status = getpeername(newSock, (struct sockaddr *) &addr, &addr_len)) != 0){
printf("getpeername() error!\n");
}
tempPort = ntohs(addr.sin_port);
inet_ntop(AF_INET, &(addr.sin_addr), test, sizeof test);
printf("tempPort\t%d\n", tempPort);
printf("test\t%s\n", test);
Thanks very much for any your comment. Here is a partial code in initializeSock():
sd = socket(AF_INET, SOCK_STREAM, 0);
if(sd < 0)
{
perror("SocketInit(): socket() error!\n");
exit(1);
}
ret_val = setsockopt(sd, SOL_SOCKET, SO_REUSEADDR, (char*) &flag, sizeof(flag));
if(ret_val == -1)
{
perror("SocketInit(): setsockopt(SO_REUSEADDR) error!\n");
exit(1);
}
gethostname(hostname,100);
host_entry = gethostbyname(hostname);
addr.sin_family = AF_INET;
addr.sin_port = htons(port);
addr.sin_addr.s_addr = inet_addr(inet_ntoa(*(struct in_addr *)*host_entry->h_addr_list));
ret_val = bind(sd, (struct sockaddr*) &addr, sizeof(addr));
if(ret_val == -1)
{
perror("SocketInit(): bind() error!\n");
printf("For port:%d\n",port);
exit(1);
}
....
return sd;
This is the code to connect to server part of a peer. ConnectSock(portOfPeerA):
sd = socket(AF_INET, SOCK_STREAM, 0);
if(sd < 0)
{
perror("ConnectToServer(): socket() error!\n");
exit(1);
}
if (port != 0) {
addr.sin_family = AF_INET;
addr.sin_port = htons(portOfPeerA);
addr.sin_addr.s_addr = inet_addr(inet_ntoa(*(struct in_addr *)*host_entry->h_addr_list));
// Do I need to bind() the port of peer B when it would like to connect to peer A?
ret_val = connect(sd, (struct sockaddr*)&addr, sizeof(addr));
if(ret_val == -1)
{
printf("Error connect());
exit(1);
}
...
I don't know which port you accept from the peer, but if the peer is connecting to your server (e.g. then one calling accept) it will connect from a (more or less) random port, that's how TCP works. It connects from a fixed port only if the peer explicitly binds to that port before connecting.
This means, that the peers originating port is not defined on the server side (where your code fragments are from) but on the client side (the side which calls connect and where you only do connect but no bind).
But, please note that it might give problems with repeated connections, if both client and server use fixed IP and ports, because then you will get the same 4-tupel in TCP which defines the connections for repeated connections and thus go into all this trouble with the various TIME_WAIT states. So it is better to let the client just pick an available port and not force it to use a specific one.
getpeername() (and accept()) reports the IP and port that the remote party is locally bound to on its end. If the remote party is a client that did not call bind() before calling connect() then connect() performs an implicit bind to a random available port. That is what you are seeing, and that it typical usage. Most clients do not need to call bind() before connect(), but there are use cases where doing so is necessary, so don't rule it out.
This is the main code of my server program in C:
int main(int argc, char** argv)
{
int sock, connected, bytes_received, true = 1;
struct sockaddr_in server_addr, client_addr;
int sin_size;
if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
perror("Socket");
exit(1);
}
if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &true, sizeof (int)) == -1) {
perror("Setsockopt");
exit(1);
}
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(atoi(argv[1]));
server_addr.sin_addr.s_addr = INADDR_ANY;
bzero(&(server_addr.sin_zero), 8);
if (bind(sock, (struct sockaddr *) &server_addr, sizeof (struct sockaddr))
== -1) {
perror("Unable to bind");
exit(1);
}
if (listen(sock, 5) == -1) {
perror("Listen");
exit(1);
}
printf("\nTCPServer Waiting for client on port 5000");
fflush(stdout);
while (1)
{
pthread_t child;
sin_size = sizeof (struct sockaddr_in);
connected = accept(sock, (struct sockaddr *) &client_addr, &sin_size);
printf("\n I got a connection from (%s , %d)\n", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));
threadInfo info;
info.argumentsPassedToCode = argv;
info.connected = connected;
pthread_create(&child, NULL, interpretMessage, &info);
}
close(sock);
return 0;
}
My server always prints out the IP of the incoming connection, and the port that it is coming in from. I noticed that the ports are always increasing.
Is this normal? If not, what am I doing wrong?
If my server runs for a long time, will it run out of ports? If so, what will happen?
If your server is working, you're not doing anything wrong. Source ports aren't guaranteed to follow a pattern, they just exist to complete the connection tuple, (source port, source address, dest port, dest address).
Ports are reused once connections close, so you should be okay.
TCP has a state called TIME_WAIT which is used to make sure that everything have been sent and received properly before cleaning up the socket. This happens after you have closed the socket in you code. The time that a socket is in the TIME_WAIT state depends on the OS.
That's why you don't get the same port again for client connections.
You can read more about the state here: https://stackoverflow.com/questions/41602/how-to-forcibly-close-a-socket-in-time-wait
1) Yes; the next available port is selected. It can be the same port (if the prev socket was freed already by kernel), it can be the next free one or any other port which is free, from 1024 to 65535 (first 1024 are reserved as you know); In your case you are seeing a different client port number because either you are not properly closing the client socket or the previous socket is still lingering when you are making the next connection or you are just making multiple parallel connections
2) If you are not properly shutting down the sockets, you will (probably first run out of file descriptor if you have lower default per-process limits which is ... 1024 fds per proc?) ; If you do tear them down correctly then you'll be fine