I want to write a kernel thread for an application that will read all UDP packets. I am facing problem in binding as these packet can arrive in range of ports (say 5001 to 5005).
How to do this.
Any pointer/link will be helpful.
You can't bind a socket to more than one port, do as 0verbose suggested in a comment and use one socket per port
Besides opening multiple sockets, you need to use select()/poll() to listen to all sockets at once.
If you are programming in C/C++ under Linux, here is a pseudo-code in C:
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>
...
int main()
{
fd_set afds;
fd_set rfds;
int maxfd = -1;
int fd, ret;
/* initialize fdsets */
FD_ZERO(&afds);
/* create a socket per port */
foreach (port p) {
fd = create_udp_socket(p); /* also bind to port p */
if (fd < 0) error_exit("error: socket()\n");
FD_SET(fd, &afds);
if (fd > maxfd) maxfd = fd;
}
while (1) {
memcpy(&rfds, &afds, sizeof(rfds));
/* wait for a packet from any port */
ret = select(maxfd + 1, &rfds, NULL, NULL, NULL);
if (ret < 0) error_exit("error: select()\n");
/* which socket that i received the packet */
for (fd=0; fd<=maxfd; ++fd)
if (FD_ISSET(fd, &rfds))
process_packet(fd); /* read the packet from socket fd */
}
}
Hope this code will help you
Related
I'm trying to better understand how socket timeouts and keep-alive work in linux. This is the current snippet of code I'm using.
import socket
def set_keepalive_linux(sock, after_idle_sec=1, interval_sec=3, max_fails=5):
sock.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)
sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPIDLE, after_idle_sec)
sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPINTVL, interval_sec)
sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPCNT, max_fails)
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
set_keepalive_linux(s)
s.connect(("www.python.org" , 80))
s.recv(1024)
Now, running netstat I see the timer set for this connection which makes sense.
tcp 0 0 myhost:randomport 199.232.44.223:http ESTABLISHED 81658/python3 keepalive (0.88/0/0)
Now, if I replace this code with
import socket
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.settimeout(10)
s.connect(("www.python.org" , 80))
s.recv(1024)
I'm unable to see any timer set (I understand that the timer in netstat -o is specifically for keepalive/retransmission so off is the expected result on rerunning netstat but is it maintained elsewhere?). So my question would be, are socket timeouts expected to be implemented by the application and the kernel has nothing to do with it?
[[Edit 1]]
Seems like this is as expected for python. I've hacked together a C program from various parts of stackoverflow that does roughly the same. Would like to see if there's some way I can access the timeout information somewhere for this
#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>
int main(void)
{
int socket_desc;
struct sockaddr_in server_addr;
char server_message[2000], client_message[2000];
// Clean buffers:
memset(server_message,'\0',sizeof(server_message));
memset(client_message,'\0',sizeof(client_message));
// Create socket:
socket_desc = socket(AF_INET, SOCK_STREAM, 0);
if(socket_desc < 0){
printf("Unable to create socket\n");
return -1;
}
printf("Socket created successfully\n");
// Set port and IP the same as server-side:
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(80);
server_addr.sin_addr.s_addr = inet_addr("199.232.44.223");
struct timeval timeout;
timeout.tv_sec = 10;
timeout.tv_usec = 0;
if (setsockopt (socket_desc, SOL_SOCKET, SO_RCVTIMEO, &timeout,
sizeof timeout) < 0)
error("setsockopt failed\n");
if (setsockopt (socket_desc, SOL_SOCKET, SO_SNDTIMEO, &timeout,
sizeof timeout) < 0)
error("setsockopt failed\n");
// Send connection request to server:
if(connect(socket_desc, (struct sockaddr*)&server_addr, sizeof(server_addr)) < 0){
printf("Unable to connect\n");
return -1;
}
printf("Connected with server successfully\n");
// Receive the server's response:
if(recv(socket_desc, server_message, sizeof(server_message), 0) < 0){
printf("Error while receiving server's msg\n");
return -1;
}
printf("Server's response: %s\n",server_message);
// Close the socket:
close(socket_desc);
return 0;
}
From online resource, they said that if epoll listening on file descriptors using default mode(level trigger), when the fd(file descriptor) is ready to read and the buffer data associated with fd not fully consumed, epoll will continue to trigger until all data is consumed, however, when I test with epoll(LT mode) listening on udp socket, when multiple characters comes epoll only trigger once.
the process like below:
step 1: create epoll, udp socket fd, then make epoll listening on socket for write event.
step 2: send multiple characters("abc") to the udp socket
step 3: each time epoll triggered, then read 1 character from the udp socket.
I am expecting that epoll trigger three times as udp socket receive 3 characters, but the result is epoll only trigger once.
here is my code:
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/epoll.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <sys/errno.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#define BUFFER_SIZE 512
#define log(fmt, arg...) printf(""fmt, ##arg)
void main(){
int fd1,efd, fds, i, fd;
int ret, addr_len;
struct epoll_event g_event;
struct epoll_event *epoll_events_ptr;
char buffer[BUFFER_SIZE] = {0};
struct sockaddr_in addr1;
fd1 = socket(AF_INET, SOCK_DGRAM, 0);
if (fd1 == -1) {
log("create socket fail \r\n");
return ;
}
addr1.sin_family = AF_INET;
addr1.sin_addr.s_addr = INADDR_ANY;
addr1.sin_port = htons(3500);
addr_len = sizeof(struct sockaddr_in);
if (0 != bind(fd1, (struct sockaddr *)&addr1, sizeof(struct sockaddr_in))) {
log("bind local listening addr fail，errno : %d \r\n", errno);
goto err;
}
efd = epoll_create1(0);
if (efd == -1) {
log("create epoll fail \r\n");
goto err;
}
log("create epoll instance success \r\n");
epoll_events_ptr = (struct epoll_event *)calloc(2, sizeof(struct epoll_event));
if (epoll_events_ptr == NULL) {
log("calloc fail \r\n");
goto err;
}
g_event.data.fd = fd1;
g_event.events = EPOLLIN;
epoll_ctl(efd, EPOLL_CTL_ADD, fd1, &g_event);
while(1) {
fds = epoll_wait(efd, epoll_events_ptr, 2, -1);
for (i = 0; i<fds; i++)
{
if (epoll_events_ptr[i].events & EPOLLIN)
{
ret = recv(fd1, buffer, 1, MSG_DONTWAIT);
if(ret != -1)
log("recv msg : %s \n", buffer);
}
memset(buffer, 0, BUFFER_SIZE);
}
}
err:
close(fd1);
if(epoll_events_ptr)
free(epoll_events_ptr);
return ;
}
enter image description here
You are treating UDP as though it was a streaming protocol, i.e. TCP. It isn't. It is a datagram protocol. If you read a UDP datagram into a buffer that is too small to receive it, the remainder of the datagram is discarded. Not left in the buffer for next time.
Reading one character at a time is therefore pointless in UDP, not to mention extremely inefficient in any protocol.
NB You don't need the memset(), and this:
log("recv msg : %s \n", buffer);
is invalid. It should be:
log("recv msg : %.*s \n", ret, buffer);
You can't assume the received data is null-terminated.
I like using systemd-activate(8) for testing socket-activated daemons during development,
however, it seems it only listens for TCP connections:
% /usr/lib/systemd/systemd-activate -l 5700 ./prog
Listening on [::]:5700 as 3.
% netstat -nl |grep 5700
tcp6 0 0 :::5700 :::* LISTEN
I am using a program that handles datagrams (UDP). How can I make systemd-activate listen on a UDP port? Or is there a
simple way to do this using other tools, without going to the trouble of crafting and installing a systemd unit file?
This was recently added to systemd-activate: https://github.com/systemd/systemd/pull/2411, and will be part of systemd-229 when it is released.
I'm not sure that there is a way to do it with systemd-activate.
You may want to employ some .service unit file and a .socket unit file with dependencies. In a .socket unit you will describe ListenDatagram= option. See here for more details.
I ended up writing a simple C program to do this; code below (public domain).
The usage is:
./a.out <port-number> <prog> [<arg1> ...]
The program opens a UDP socket on <port-number>, sets the environment variables that systemd socket-activated daemons expect, then executes <prog> with whatever arguments follow.
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <netinet/in.h>
int main(int argc, char **argv) {
if (argc < 2) {
printf("no port specified\n");
return -1;
}
if (argc < 3) {
printf("no program specified\n");
return -1;
}
uint16_t port = htons((uint16_t) strtoul(argv[1], NULL, 10));
if (port == 0 || errno) {
printf("failed to parse port: %s\n", argv[1]);
return -1;
}
/* create datagram socket */
int fd = socket(AF_INET, SOCK_DGRAM, 0);
if (fd < 0) {
printf("failed to open socket; errno: %d\n", errno);
return -1;
}
struct sockaddr_in sa;
sa.sin_family = AF_INET;
sa.sin_port = port;
sa.sin_addr.s_addr = INADDR_ANY;
/* bind socket to port */
int r = bind(fd, (struct sockaddr *) &sa, sizeof(struct sockaddr_in));
if (r < 0) {
printf("bind failed; errno: %d\n", errno);
return -1;
}
/* execute subprocess */
setenv("LISTEN_FDS", "1", 0);
execvp(argv[2], argv + 2);
}
I have application which uses sockets to transfer data between two clients. It uses a single socket to communicate control and data traffic (over UDP).
Qos and tos fields of IP header can be changed using
setsockopt(sockfd, IPPROTO_IP, IP_TOS, &tos, toslen);
setsockopt(sockfd, SOL_SOCKET, SO_PRIORITY, &cos, coslen);
But how many calls to setsockopt (to the same socket) is too many?
For example, lets assume it will be called every 1ms.
To narrow question scope, I am asking about modern linux system (generic explanation is more than welcomed).
Here is an example to demonstrate it (this is the sending-only part of the application):
#include <stdlib.h>
#include <memory.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#define NPACK 10000
#define PORT 44444
#define BUFLEN 128
void diep(char *s) {
perror(s);
exit(1);
}
#define SRV_IP "12.34.56.78"
int main(void) {
struct sockaddr_in si_other, si_me;
int s, i, slen = sizeof(si_other);
int toss[2] = { 56, 160 }, coss[] = { 1, 3 };
char buf[BUFLEN];
//Create UDP socket
if ((s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1)
diep("socket");
//Create remote socket
memset((char *) &si_other, 0, sizeof(si_other));
si_other.sin_family = AF_INET;
si_other.sin_port = htons(PORT);
if (inet_aton(SRV_IP, &si_other.sin_addr) == 0) {
fprintf(stderr, "inet_aton() failed\n");
exit(1);
}
//Create local socket and bind to it.
memset((char *) &si_me, 0, sizeof(si_me));
si_me.sin_family = AF_INET;
si_me.sin_port = htons(PORT);
si_me.sin_addr.s_addr = htonl(INADDR_ANY);
if (bind(s, &si_me, sizeof(si_me)) == -1)
diep("bind");
//Loop on number of packets
for (i = 0; i < NPACK; i++) {
sprintf(buf, "This is packet %d, %d\n", i, toss[i % 2]);
printf("Sending packet %d. %s", i, buf);
//Change tos and cos. odd packets high priority , even packets low priority.
setsockopt(s, IPPROTO_IP, IP_TOS, &toss[i % 2], sizeof(int));
setsockopt(s, SOL_SOCKET, SO_PRIORITY, &coss[i % 2], sizeof(int));
//Send!
if (sendto(s, buf, strlen(buf), 0, &si_other, slen) == -1)
diep("sendto()");
}
close(s);
return 0;
}
NOTES:
Both control and data should share the same socket (same UDP source port).
Multiple threads will use the same socket (so some locking mechanism needed between setsockopt and sendto; but this is outside the scope of the question).
SO_PRIORITY is linux only.
Okay, I've scoured the net (literally) for the last ten hours, but no one seems to have a tutorial explaining how to create a C++ Proxy server in Windows. Several times I've run into functions that work solely for UNIX, and it's been a frustrating experience. I am VERY new to socket programming, but I need to have this finished within 48 hours. It seems impossible right now.
Requirements for the program:
The daemon listens for TCP connections on a specified port number.
When a new client initiates a TCP connection request, the daemon accepts
the request and establishes a TCP connection with the new client.
The daemon forks a child process that is dedicated to handling the new
client.
The child process establishes a TCP connection to a pre-assigned port on the
actual targeted server.
The child process falls into a loop in which it acts as an intermediator
exchanging data (reading/writing or writing/reading) between the client and
the targeted server.
Once a child has been forked, the daemon process resumes listening for
additional TCP connections.
I've run a provided winsock client and program to get a better idea of how sockets work, but it's getting me nowhere fast. pid_t is unavailable for windows, so forking is out of the question (or so I've gathered from the 10 hours of net-scouring).
If you can point me in the right direction for being able to use Internet Explorer's proxy settings (the IP and Port number feature) in combination with the program to yield webpages that are redirected to another server, that would be great.
/* client.c - code for example client program that uses TCP */
#ifndef unix
#include<winsock2.h>
#include <windows.h>
#include <winsock.h>
#pragma comment(lib, "ws2_32.lib")
#else
#define closesocket close
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/param.h>
#endif
#include <stdio.h>
#include <string.h>
#include <iostream>
#define PROTOPORT 5193 /* default protocol port number */
extern "C";
char localhost[] = "localhost"; /* default host name */
#define QLEN 6 /* size of request queue */
int visits = 0; /* counts client connections */
/*------------------------------------------------------------------------
* Program: client
*
* Purpose: allocate a socket, connect to a server, and print all output
*
* Syntax: client [ host [port] ]
*
* host - name of a computer on which server is executing
* port - protocol port number server is using
*
* Note: Both arguments are optional. If no host name is specified,
* the client uses "localhost"; if no protocol port is
* specified, the client uses the default given by PROTOPORT.
*
*------------------------------------------------------------------------
*/
int main(int argc, char *argv[])
{
struct hostent *ptrh; /* pointer to a host table entry */
struct protoent *ptrp; /* pointer to a protocol table entry */
struct sockaddr_in sad; /* structure to hold an IP address */
int port; /* protocol port number */
char *host; /* pointer to host name */
int n; /* number of characters read */
char buf[1000]; /* buffer for data from the server */
struct sockaddr_in cad; /* structure to hold client's address */
int sd, sd2; /* socket descriptors */
int alen; /* length of address */
#ifdef WIN32
WSADATA wsaData;
WSAStartup(0x0101, &wsaData);
#endif
memset((char *)&sad,0,sizeof(sad)); /* clear sockaddr structure */
sad.sin_family = AF_INET; /* set family to Internet */
sad.sin_addr.s_addr = INADDR_ANY; /* set the local IP address */
/* Check command-line argument for protocol port and extract */
/* port number if one is specified. Otherwise, use the default */
/* port value given by constant PROTOPORT */
if (argc > 2) { /* if protocol port specified */
port = atoi(argv[2]); /* convert to binary */
} else {
port = PROTOPORT; /* use default port number */
}
if (port > 0) /* test for legal value */
sad.sin_port = htons((u_short)port);
else { /* print error message and exit */
fprintf(stderr,"bad port number %s\n",argv[2]);
exit(1);
if (argc > 1) { /* if argument specified */
port = atoi(argv[1]); /* convert argument to binary */
} else {
port = PROTOPORT; /* use default port number */
}
if (port > 0) /* test for illegal value */
sad.sin_port = htons((u_short)port);
else { /* print error message and exit */
fprintf(stderr,"bad port number %s\n",argv[1]);
exit(1);
}
/* Map TCP transport protocol name to protocol number */
(int)(ptrp = getprotobyname("tcp"));
if ( ((int)(ptrp = getprotobyname("tcp"))) == 0) {
fprintf(stderr, "cannot map \"tcp\" to protocol number");
exit(1);
}
/* Check host argument and assign host name. */
if (argc > 1) {
host = argv[1]; /* if host argument specified */
} else {
host = localhost;
}
/* Convert host name to equivalent IP address and copy to sad. */
ptrh = gethostbyname(host);
if ( ((char *)ptrh) == NULL ) {
fprintf(stderr,"invalid host: %s\n", host);
exit(1);
}
memcpy(&sad.sin_addr, ptrh->h_addr, ptrh->h_length);
/* Map TCP transport protocol name to protocol number. */
(int)(ptrp = getprotobyname("tcp"));
if ( ((int)(ptrp = getprotobyname("tcp"))) == 0) {
fprintf(stderr, "cannot map \"tcp\" to protocol number");
exit(1);
}
/* Create a socket. */
sd = socket(PF_INET, SOCK_STREAM, ptrp->p_proto);
if (sd < 0) {
fprintf(stderr, "socket creation failed\n");
exit(1);
}
/* Connect the socket to the specified server. */
connect(sd, (struct sockaddr *)&sad, sizeof(sad));
if (connect(sd, (struct sockaddr *)&sad, sizeof(sad)) < 0) {
fprintf(stderr,"connect failed\n");
exit(1);
}
/* Bind a local address to the socket */
bind(sd, (struct sockaddr *)&sad, sizeof(sad));
if (bind(sd, (struct sockaddr *)&sad, sizeof(sad)) < 0) {
fprintf(stderr,"bind failed\n");
exit(1);
}
/* Specify size of request queue */
listen(sd, QLEN);
if (listen(sd, QLEN) < 0) {
fprintf(stderr,"listen failed\n");
exit(1);
}
/* Repeatedly read data from socket and write to user's screen. */
n = recv(sd, buf, sizeof(buf), 0);
while (n > 0) {
int _write(int fd, const void *buffer, unsigned int count);
n = recv(sd, buf, sizeof(buf), 0);
}
/* Main server loop - accept and handle requests */
while (1) {
alen = sizeof(cad);
printf("\nI'm waiting for connections ...");
fflush(stdout);
if ( (sd2=accept(sd, (struct sockaddr *)&cad, &alen)) < 0) {
fprintf(stderr, "accept failed\n");
exit(1);
}
printf("\nI received one connection.\n");
fflush(stdout);
visits++;
sprintf_s(buf,"This server has been contacted %d time%s\n",
visits,visits==1?".":"s.");
send(sd2,buf,strlen(buf),0);
printf("\nI sent the client a string.\n");
fflush(stdout);
closesocket(sd2);
}
/* Close the socket. */
closesocket(sd);
/* Terminate the client program gracefully. */
exit(0);
}
}
If you've made it this far, I thank you for your vigilance. Wish me luck...