sendto: invalid argument

Yury · 11-01-2006, 01:31 PM

I know this is very basic question, but i really need a little help here :\
In my program i have function mysend(), which is a wrapper to sendto() call:

Code:

void mysend(const char *sendstring, const struct sockaddr_in *addr){
  int sendstringlen = strlen(sendstring);
  if(sendto(main_socket, sendstring, sendstringlen, 0, addr, sizeof(struct sockaddr_in)) == -1){
    perror("sendto");
  }
  
}

The main_socket is UDP socket.
I also have a global struct sockaddr_in current, which represents address of the machine i currently communicate with. This stucture is already filled by the recvfrom(...) call.
But when i call mysend("hello",&current); it prints error: sendto: invalid argument.
I just can't find where the mistake is... :\
P.S. my platform is Gnu/Linux

nadroj · 11-01-2006, 01:44 PM

do all your parameters' type match the required:

Code:

int sendto(int, const char *, size_t, int, struct sockaddr *, size_t);

Mara · 11-01-2006, 01:59 PM

Code:

  if(sendto(main_socket, sendstring, sendstringlen, 0, (struct sockaddr *)addr, sizeof(struct

struct sockaddr and struct sockaddr_in are compatibile, so you can cast one to another, but they're still different types, that's why casting is required.

Yury · 11-01-2006, 05:31 PM

Hmm, added (struct sockaddr *), but it still returns an error

Strange behavior, isn't it?
Anyway, thanks for help

nadroj · 11-01-2006, 05:34 PM

then one of the other parameters is wrong. the first parameter says its supposed to be 'int', is main_socket of type 'int'??

Yury · 11-01-2006, 05:43 PM

Unfortunately it is int

nadroj · 11-01-2006, 08:23 PM

can you change sendstring to &sendstring does that help? (?)

orgcandman · 11-01-2006, 08:24 PM

can you post how you're filling up the sockaddr_in struct?

Mara · 11-02-2006, 04:34 PM

I have made a short test. The code below compiles fine:

Code:

#include <string.h>
#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>

int main_socket = -1;

void mysend(const char *sendstring, const struct sockaddr_in *addr){
  int sendstringlen = strlen(sendstring);
  if(sendto(main_socket, sendstring, sendstringlen, 0, (struct sockaddr *)add
    perror("sendto");
  }
}

int main(int argc, char **argv)
{
  struct sockaddr_in sock;
  mysend("blah", &sock);
  return 0;
}

Yury · 11-02-2006, 05:47 PM

Ok, i'll go little deeper.
Let's take the main_socket first.
Here is how it was declared:

Code:

int main_socket;

Later it has been manipulated by this function:

Code:

int create_socket(uint16_t port){
  /* Create a new socket unit */
  int sock = socket(AF_INET, SOCK_DGRAM, 0);
  struct sockaddr_in main_socket_name;
  main_socket_name.sin_family = AF_INET;
  main_socket_name.sin_port = htons(port);
  main_socket_name.sin_addr.s_addr = htonl(INADDR_ANY);
  
  /* Bind it to port */
  if(bind(sock, (struct sockaddr *) &main_socket_name, sizeof(main_socket_name)) < 0){
    perror("bind");
    exit(EXIT_FAILURE);
  }

  
  return sock;
}

And assigned:

Code:

...
  main_socket = create_socket(port); // port - global variable, == 4242 if user did not change it.
  ...

Now let's see what we have about sendstring.
It is assigned when i call the function mysend():

Code:

...
  mysend("hello",&currend);
  ...

Tried to change sendstring to &sendstring but it did not help

The int sendstringlen is strlen(sendstring).
And the most interesting and important part - struct sockaddr_in current.
Declaration:

Code:

struct sockaddr_in current;

It was initially filled in this way:

Code:

void myrecv(const struct sockaddr_in *addr){
  int addrlen = sizeof(struct sockaddr_in);
  buflen = recvfrom(main_socket, buffer, BUFSIZE, 0, (struct sockaddr *)addr, &addrlen);
  if(buflen == -1){
    perror("recvfrom");
  }
}

Code:

...
  myrecv(&current);
  ...

When someone connects, it sends the following: NEW myname, where myname is his id.
I successully receive this message, and call the client_new(char * login) function, which allocates memory for this guy and saves his id in that memory. When it is done, i should send him "hello" message:

Code:

mysend("hello",&current);

What happens later we already know

That stupid bug seems to be somewhere deeper. But where?????
I test this server with simple client written in python, here is the code:

Code:

#!/usr/bin/python

import socket
import sys

# Collect info
username = raw_input("Your login plz: ")
servername = raw_input("Server hostname: ")
serverport = raw_input("And port plz (default: 4242) : ")
if serverport == "":
	serverport = 4242
else: serverport = int(serverport)

serveraddr = ((servername, serverport))

# Have info, connect to the server
print "Connecting..."

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

# Send login info
sock.sendto("NEW %s" % username, serveraddr)
helloconfirm = sock.recv(256) # Here the server should send me "hello" message.
# Bug in the server! All i can do now is to kill this program.

# Send all what user types in, print all that server sends in
io = select((sys.stdin, sock), Null, Null, Null)
while(1):
	if io[0] == sys.stdin:
		# User typed something in termintal. Send it to the server
		str = raw_input()
		if str == "quit":
			sock.close()
			exit(0)

		sock.sendto(str, serveraddr)
	else:
		# Server sent something in. Print it
		str = sock.recv(256)
		print str

It seems to be all.

Yury · 11-03-2006, 01:00 PM

Added the following to the mysend function:

Code:

  if(debug){ // debug == 1
    printf("main_socket == %d\n", main_socket);
    printf("addr->sin_addr.s_addr == %d\n", addr->sin_addr.s_addr);
    /* Tried also to use the inet_ntoa() function here but it causes a segfault. */
  }

Here is what it prints when run:

Code:

main_socket == 4
addr->sin_addr.s_addr == 0 //??????
sendto: Invalid argument

Also tested this trough eth0 interface (i used loopback before) and this does not changed anything.

orgcandman · 11-03-2006, 02:44 PM

The answer is simple enough, I think.

Basically, you're assuming that the sockaddr_in is being correct assigned, but there is where you're incorrect.

On the stack, in myrecv(const struct sockaddr_in *addr), you are only modifying the local copy of addr. Try this, make it a **, use a local temporary copy (struct sockaddr *pSA = (sockaddr*)(*addr)

that you pass to the function, and then memcpy it back (if(*addr != pSA)memcpy(*addr, pSA, sizeof(struct sockaddr))

and see if that works. My guess is that it will.

If that doesn't work, please post a full transcript of the program so that I can see exactly what happens.

-Aaron

Yury · 11-04-2006, 07:06 AM

It works!
I did not add the struct *pSA because the ** is too complicated for me(newbie in programming

), thanx anyway for pointing where the problem is.
Here's what i did:
1. changed struct sockaddr_in current to struct sockaddr_in *current.
2. used malloc(sizeof(struct sockaddr_in)) to allocate memory for it.
3. current is now address of struct sockaddr_in in memory, so i don't need to do &current anymore:

Code:

myrecv(current);

Code:

mysend("hello",current);

And i was surprised when it started to work

Thank You guys for support, see ya.