#include <stdio.h>
#include <sys/socket.h>
#include <netdb.h>
int main () {
char buf[4] = { 0xff, 0xff, 0xff, 0xff };
struct addrinfo adr, *res;
adr.ai_family = AF_INET;
adr.ai_socktype = SOCK_DGRAM;
getaddrinfo ("192.168.1.1", NULL, &adr, &res);
int sd = socket (res->ai_family, res->ai_socktype, res->ai_protocol);
if (sendto (sd, buf, sizeof (buf), MSG_OOB, res->ai_addr, res->ai_addrlen) < 0)
perror ("ERROR sendto"); //I have added an if tag and an error message posiblility
return 0;
}
ERROE sendto: Operation not supported
This is the all of message. The beej's guide network programming, i have read the getaddrinfo second parameter is NULL, and i had compiling it, it will be good, there was no problem this line. At now time the problem is Operation not supported error message.
There seem to be several mistakes.
First, I believe MSG_OOB is illegal for UDP. This is probably what the error message is trying to say. Try 0 instead.
Then, the getaddrinfo() call looks weird (at least I don't understand the point). You say "i had compiling it, it will be good, there was no problem this line" but then you don't have the error handling to prove it...
My hunch is that the address or port of the socket address you use in sendto() are incorrect and you will still get errors after fixing MSG_OOB. Is there a reason you aren't just setting them manually like here — Are you trying to make getaddrinfo() pick a suitable port for you? I don't think that works:
If service is NULL, then the port number of the returned socket
addresses will be left uninitialized.
Related
Before I get started. Yes, I could use leJOS, ev3dev, or some others, but I'd like to do it this way because that is how I learn.
I am using the CodeSourcery arm-2009q1 arm toolchain. I fetched the required libraries (bluetooth) from here: https://github.com/mindboards/ev3sources.
I am uploading the programs to the brick by using this tool: https://github.com/c4ev3/ev3duder
I have also fetched the brick's shared libraries, but I can not get them to work properly and there is 0 documentation on how to write a c program for the ev3 using the shared libraries. If I could get that working I might be able to use the c_com module to handle bluetooth, but right now bluez and rfcomm in conjunction with: https://github.com/c4ev3/EV3-API for motor and sensor control seems to be my best bet.
Now, with that out of the way:
I'd like to run the EV3 as a bluetooth "server" meaning that I start a program on it and the program opens a socket, binds it, listens for a connection, and then accepts a single connection.
I am able to do open a socket, bind it to anything but channel 1 (I believe this might be the crux of my issue), I am able to listen. These all return 0 (OK) and everything is fine.
Then I try to accept a connection. That instantly returns -1 and sets the remote to address 00:00:00:00:00:00.
My code is pretty much the same as can be found here: https://people.csail.mit.edu/albert/bluez-intro/x502.html
Here it is:
#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <bluetooth/bluetooth.h>
#include <bluetooth/rfcomm.h>
#include <ev3.h>
int main(int argc, char **argv)
{
InitEV3();
struct sockaddr_rc loc_addr = { 0 }, rem_addr = { 0 };
char buf[1024] = { 0 };
int sock, client, bytes_read;
socklen_t opt = sizeof(rem_addr);
sock = socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);
loc_addr.rc_family = AF_BLUETOOTH;
loc_addr.rc_bdaddr = *BDADDR_ANY;
loc_addr.rc_channel = 2; // <-- Anything but 1. 1 seems to be taken
bind(sock, (struct sockaddr *)&loc_addr, sizeof(loc_addr));
listen(sock, 1);
// accept one connection <-- PROGRAM FAILS HERE AS accept() returns -1
client = accept(sock, (struct sockaddr *)&rem_addr, &opt);
// ---- All following code is irrelevant because accept fails ----
ba2str( &rem_addr.rc_bdaddr, buf );
fprintf(stderr, "accepted connection from %s\n", buf);
memset(buf, 0, sizeof(buf));
bytes_read = read(client, buf, sizeof(buf));
if( bytes_read > 0 )
printf("received [%s]\n", buf);
close(client);
close(sock);
FreeEV3();
return 0;
}
I am able to get the same code working on my pi. Even communication back and forth when the ev3api-specific functions are commented out. I just can't fathom why it won't work on the EV3.
I figured it out.
On my raspberry PI, the accept call worked as expected with no quirks. On the EV3 however, the accept call is non-blocking even if it has not been told to act like so.
The solution was to place the accept call in a loop until an incoming connection was in the queue.
while (errno == EAGAIN && ButtonIsUp(BTNEXIT) && client < 0)
client = accept(sock, (struct sockaddr*)&rem_addr, sizeof(rem_addr));
I'll upload the code to github. Contact me if you'd like to do something similar with the EV3.
I'm learning socket programming in C. I have gotten my server to create a socket that was successful, but when I try to bind my socket to a port nothing happens. No error occurs and it is not successful. It's as if the bind() function is not even executing at all.
I've checked out the documentation on the bind() function here but there's no mention of why it won't execute at all. I've also tried searching through this site with no avail.
I also tried following this tutorial from start to finish but the error (or lack thereof) still occurs.
Here is my full code leading up to the problem:
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include "include.h"
int main() {
// Descriptors. Used to check the status of functions such as socket, listen, bind etc.
// If a descriptor is equal to 0, then everything is okay. Else, if they are equal to -1, something went wrong.
int socketDescriptor, newSocketDescriptor = 1;
// The process ID of a child process (the client) when a new one is spawned (the client connects).
pid_t childPID;
// A string to hold the commands being sent a received.
char* commandBuffer = calloc(BUFFER_SIZE, sizeof(char));
// A structure to hold information on the server address.
struct sockaddr_in serverAddress;
memset(&serverAddress, '\0', sizeof(serverAddress));
// Fill in the server address information.
// Set the address family to AF_INET, which specifies we will be using IPv4.
// htons() takes the given int and converts it to the appropriate format. Used for port numbers.
// inet_addr() takes the given string and converts it to the appropriate format. Used for IP addresses.
serverAddress.sin_family = AF_INET;
serverAddress.sin_port = htons(PORT);
serverAddress.sin_addr.s_addr = inet_addr("127.0.0.1");
// A structure to hold information a client when a new one connects to this server.
struct sockaddr_in clientAddress;
memset(&clientAddress, '\0', sizeof(clientAddress));
// socklen_t defines the length of a socket structure. Need this for the accept() function.
socklen_t addressSize;
// Creating the socket.
// AF_NET specifies that we will be using IPv4 addressing.
// SOCK_STREAM specifies that we will be using TCP to communicate.
socketDescriptor = socket(AF_INET, SOCK_STREAM, 0);
if (socketDescriptor < 0) {
perror("ERROR CREATING SOCKET");
exit(1);
}
else
printf("Socket created successfully.\n");
// Binding to the specified port. 0 if everything is fine, -1 if there was an error.
if (bind(socketDescriptor, (struct sockaddr*) & serverAddress, sizeof(struct sockaddr_in)) < 0) {
perror("ERROR BINDNING");
exit(1);
}
else
printf("Socket bound to %s:%s.\n", serverAddress.sin_addr.s_addr, serverAddress.sin_port);
The last if statement at the bottom is where the code fails. It should either print and error or print "Socket bound to 127.0.0.1:80" but neither happens. See an example here.
I'm lost for what to do.
A server socket won't show up in a netstat listing unless you call listen after binding the socket.
Also, you're using the %s format specifier in your printf after the bind call on serverAddress.sin_addr.s_addr and serverAddress.sin_port. These are not strings but integers. Using the wrong format specifier invokes undefined behavior and is likely causing your program to crash. Using the correct format specifier such as %d or %x will fix this.
if (bind(socketDescriptor, (struct sockaddr*)&serverAddress, sizeof(struct sockaddr_in)) < 0) {
perror("ERROR BINDNING");
exit(1);
}
else
// use %x to print instead
printf("Socket bound to %x:%x.\n", serverAddress.sin_addr.s_addr, serverAddress.sin_port);
if (listen(socketDescriptor, 3) < 0) {
perror("listen failed");
} else {
printf("socket is listening\n");
}
I'm writing a TCP server in C and find something unusual happens once the listening fd get "Too many open files" error. The accept call doesn't block anymore and returns -1 all the time.
I also tried closing the listening fd and re-opening, re-binding it, but didn't seem to work.
My questions are why accept keeps returning -1 in this situation, what am I supposed to do to stop it and make the server be able to accept new connections after any old clients closed? (the socket is of course able to accept correctly again when some connections closed)
====== UPDATE: clarification ======
The problem occurs just because the number of active clients is more than the limit of open fds, so I don't close any of the accepted fds in the sample code, just to make it reproduce more quickly.
I add the timestamp each time accept returns to the output and slow down connect frequency to once in 2 seconds, then I find that in fact the "Too many open files" error occurs immediately after the lastest success accept. So I think that is because when the maxium fds is reached, each call to accept will return immediately, and the return value is -1. (What I thought is that accept would still block, but returns -1 at the next incoming connect. The behavior of accept in this situation is my own theory, not from the man page. If it's wrong, please let me know).
So to my second question, to make it stop, I think it's a solution that stop to call accept before any connection is closed.
Also update the sample codes. Thanks for your help.
====== Sample codes ======
Here is how I test it. First set ulimit -n to a low value (like 16) and run the server program compiled from the following C source; then use the Python script to create several connections
/* TCP server; bind :5555 */
#include <stdio.h>
#include <unistd.h>
#include <time.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define BUFSIZE 1024
#define PORT 5555
void error(char const* msg)
{
perror(msg);
exit(1);
}
int listen_port(int port)
{
int parentfd; /* parent socket */
struct sockaddr_in serveraddr; /* server's addr */
int optval; /* flag value for setsockopt */
parentfd = socket(AF_INET, SOCK_STREAM, 0);
if (parentfd < 0) {
error("ERROR opening socket");
}
optval = 1;
setsockopt(parentfd, SOL_SOCKET, SO_REUSEADDR,
(const void *)&optval , sizeof(int));
bzero((char *) &serveraddr, sizeof(serveraddr));
serveraddr.sin_family = AF_INET;
serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);
serveraddr.sin_port = htons((unsigned short)port);
if (bind(parentfd, (struct sockaddr *) &serveraddr, sizeof(serveraddr)) < 0) {
error("ERROR on binding");
}
if (listen(parentfd, 5) < 0) {
error("ERROR on listen");
}
printf("Listen :%d\n", port);
return parentfd;
}
int main(int argc, char **argv)
{
int parentfd; /* parent socket */
int childfd; /* child socket */
int clientlen; /* byte size of client's address */
struct sockaddr_in clientaddr; /* client addr */
int accept_count; /* times of accept called */
accept_count = 0;
parentfd = listen_port(PORT);
clientlen = sizeof(clientaddr);
while (1) {
childfd = accept(parentfd, (struct sockaddr *) &clientaddr, (socklen_t*) &clientlen);
printf("accept returns ; count=%d ; time=%u ; fd=%d\n", accept_count++, (unsigned) time(NULL), childfd);
if (childfd < 0) {
perror("error on accept");
/* the following 2 lines try to close the listening fd and re-open it */
// close(parentfd);
// parentfd = listen_port(PORT);
// the following line let the program exit at the first error
error("--- error on accept");
}
}
}
The Python program to create connections
import time
import socket
def connect(host, port):
s = socket.socket()
s.connect((host, port))
return s
if __name__ == '__main__':
socks = []
try:
try:
for i in xrange(100):
socks.append(connect('127.0.0.1', 5555))
print ('connect count: ' + str(i))
time.sleep(2)
except IOError as e:
print ('error: ' + str(e))
print ('stop')
while True:
time.sleep(10)
except KeyboardInterrupt:
for s in socks:
s.close()
why accept keeps returning -1 in this situation
Because you've run out of file descriptors, just like the error message says.
what am I supposed to do to stop it and make the server be able to accept new connections after any old clients closed?
Close the clients. The problem is not accept() returning -1, it is that you aren't closing accepted sockets once you're finished with them.
Closing the listening socket isn't a solution. It's just another problem.
EDIT By 'finished with them' I mean one of several things:
They have finished with you, which is shown by recv() returning zero.
You have finished with them, e.g. after sending a final response.
When you've had an error sending or receiving to/from them other than EAGAIN/EWOULDBLOCK.
When you've had some other internal fatal error that prevents you dealing further with that client, for example receiving an unparseable request, or some other fatal application error that invalidates the connection or the session, or the entire client for that matter.
In all these cases you should close the accepted socket.
The answer of EJP is correct, but it does not tell you how to deal with the situation. What you have to do is actually do something with the sockets that you get as accept returns. Simple calling close on them you won't receive anything of course but it would deal with the resource depletion problem. What you have to do to have a correct implementation is start receiving on the accepted sockets and keep receiving until you receive 0 bytes. If you receive 0 bytes, that is an indication that the peer is done using his side of the socket. That is your trigger to call close on the socket as well and deal with the resource problem.
You don't have to stop listening. That would stop your server from being able to process new requests and that is not the problem here.
The solution I implemented here was to review the value of the new (accepted) fd and if that value was equal or higher then the allowed server capacity, then a "busy" message is sent and the new connection is closed.
This solution is quite effective and allows you to inform your clients about the server's status.
I am just learning socket programming on Linux by some websites and here are some parts of my code on server side by using TCP:
#define BufferLength 100
#define SERVPORT 3111
int main()
{
/* Variable and structure definitions. */
int sd, sd2, rc, length = sizeof(int);
int totalcnt = 0, on = 1;
char temp;
char buffer[BufferLength];
struct sockaddr_in serveraddr;
struct sockaddr_in their_addr;
fd_set read_fd;
/* Get a socket descriptor */
if((sd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
{
perror("Server-socket() error");
exit (-1);
}
else
printf("Server-socket() is OK\n");
/* Allow socket descriptor to be reusable */
if((rc = setsockopt(sd, SOL_SOCKET, SO_REUSEADDR, (char *)&on, sizeof(on))) < 0)
{
perror("Server-setsockopt() error");
close(sd);
exit (-1);
}
else
printf("Server-setsockopt() is OK\n");
/* bind to an address */
memset(&serveraddr, 0x00, sizeof(struct sockaddr_in));
serveraddr.sin_family = AF_INET;
serveraddr.sin_port = htons(SERVPORT);
serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);
printf("Using %s, listening at %d\n", inet_ntoa(serveraddr.sin_addr), SERVPORT);
/* continue */
}
When I did the last line (printf("using......")), I got a segmentation fault, why? Thanks.
The code as shown misses to #include any headers, so as it stands won't compile due to some undefined symbols.
It would compile however if you missed to just prototype any library functions referenced by the code, which would lead to any function being assumed to return int.
The latter fact might be fatal or not.
On a 64bit system at least it is fatal in the case of inet_ntoa() used as a parameter to printf(), as on a 64bit system it most likely is expected to return a 64bit (char-pointer) value (but a 32bit int). So (assuming the prototype misses) when generating the code the compilers assumes inet_ntoa() to return a 32bit int which would lead to "chopping-off" the most significant 32bits of the address returned. Trying to printf() from such a "crippled" and therefore (most likely) invalid address provokes undefined behaviour and in your case leads to the segmentation violation observed.
To fix this, add the relevant prototype (for inet_ntoa()) by adding:
#include <arpa/inet.h>
The compiler should have warned you about this. To enable all compiler's warnings for gcc use the options -Wall -Wextra -pedantic. Take such warnings serious.
It seems likely that inet_ntoa() is somehow returning NULL, leading to the segfault when it is dereferenced in the printf(). I can't find a direct reference plainly stating that this is possible with the Linux version of inet_ntoa, but I found several people who made that claim, and it is the only point in that code where a pointer is being dereferenced.
The answer at the bottom of this question: segmentation fault for inet_ntoa makes the claim that inet_ntoa can return NULL. However, following his reference links, I couldn't find an actual statement of that fact.
There is an MSDN article (which is suggestive, but of course doesn't apply directly to Linux code) that does state plainly that inet_ntoa() can return NULL here: https://msdn.microsoft.com/en-us/library/windows/desktop/ms738564%28v=vs.85%29.aspx
I'm writing a very small C UDP client. I know that a random port is chosen as source port when you send data to the server. I also know that you can use bind to specify yourself the port you want a response.
However, I don't know when is the port randomly chosen? For example, I would like to rely on the sender address to keep track of users. It currently works only if the client does not shutdown, the port is still the same then a simple memcmp is enough to detect the same client.
This small code will use the same source port until it exits:
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <err.h>
int main(void)
{
int s, error, ch;
struct addrinfo hints, *res;
memset(&hints, 0, sizeof (struct addrinfo));
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_DGRAM;
if ((error = getaddrinfo("localhost", "9988", &hints, &res)))
errx(1, "%s", gai_strerror(error));
if ((s = socket(res->ai_family, res->ai_socktype, 0)) < 0)
err(1, "socket");
while ((ch = fgetc(stdin)) != EOF)
sendto(s, &ch, 1, 0, res->ai_addr, res->ai_addrlen);
}
And running something like : dmesg | ./client will use the same address until the program exits. However, when you run it again, the port is different.
So is it the socket function that choose a port? Or the system? Is it sure that the port will still be the same during the client lifetime?
If the socket is not explicitly bound, then the OS will bind it (with a random port) when you send the first packet. This binding will be active as long as the socket is open, once it's closed the socket is (of course) unbound.
And due to the connectionless nature of UDP sockets, the "server" (if done correctly) should not keep the address of all "clients" that send to it indefinitely. Instead it should use the source address as received in the recvfrom call, and use that for a reply. The only reason to store the source address for more than just a simple request/response, is if you have a more advanced protocol on top of UDP with your own "connection" handling.